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' ELECTRICAL lNS'iALLATlO-Nb

HAZARDOUS LOCATsONm
‘6.“HESIS FOR THE DEGREE 0F :5 ' :~
, ;.;..4rs'mo WALTER cusmmtsa

19-32

'f H 5315

 

 

ELECTRICAL INSTALLATIONS
IN
HAZARDOUS LOCATIONS '

A Thesis Submitted to
the Faculty of
Michigan State College
of
Agriculture and Applied Science
by
Clifford Walter gustafson

Candidate for the Professional Degree of
Electrical Engineer
June 1932

TH EME

Pd
h»
”D
he
"4

INTRODUCTORY AND HISTORICAL

 

Containing a short history

of the development of rules
for the installation of
electrical apparatus and
wiring in.hazardous locations,
with special reference to the
rules of Article 32 of the
National Electrical Code.

Included also is a brief
description of the nature of
the problem which this Thesis
discusses.

INTRODUCTORY AND HISTORICAL

 

During the past four or five years fire prevention
engineers have given increased attention to the design and
installation of electrical apparatus and wiring in what are
termed ”Hazardous Locations.’ It was found that electrical
apparatus which was ordinarily considered safe for relatively
non-hazardous occupancies such as dwellings, mercantile build-
ings and those of similar nature, introduced definite and
serious fire and accident hazards into establishments where
processes involved the use or production of inflammable volatile
liquids, explosive gases, combustible dusts or easily ignitable
fibers 0

With the marked increase in efficiency in manufacturing
methods during the past decade or two, we have seen an increas-
ing use of materials known to be hazardous. Industry sought and
found materials and methods for the more rapid application of
finishes to automobile bodies, furniture and other manufactured
goods. The use of gasoline and other petroleum products has
increased many fold. Pyroxylin has come to be employed for
ever multiplying purposes. Such increased use of flammable
volatile liquids and substances which might be classed as
explosive has been attended by numerous fires and explosions
involving the loss of many lives and much prOperty.

During this same period we have witnessed the almost
universal adoption of electricity for power and lighting
purposes. Whereas a comparatively few years ago steam engine
power was used to a large extent, electric motor power now
prevails. Where formerly the steam power plant was isolated
from a hazardous area, we now find the demands of industry
specifying individual motor drives which very often place the
motors and their controllers directly in the hazardous area
despite the attempts of fire protection engineers to isolate
them. Fires and explosions caused by the ignition of hazardous
matter from electrical arcs and sparks have become frequent
and the need for adequate specifications and rules for the
design and installation of electrical apparatus and wiring
in hazardous locations asserts itself very forcibly. »

Attempts to guard against the ignition of these highly
flammable substances began with the first attempts of fire
underwriters to produce rules providing for the installation
of eleCtrical wiring. In fact, the "Underwriters'" Electrical
Codes of the early 1890's provided for the use of vapor
tight globes for enclosing incandescent lights and their
sockets when in rooms where flammable gases may exist. In
the National Electrical Code of 1901 we find the subject more

thoroughly covered in Rule 17b which stated: "Switches, cutouts,
circuit breakers, etc., must not be placed in the vicinity of
easily ignitable stuff or where exposed to inflammable gases,

, dust or to flyings of combustible material.” Following this rule
was this fine print note: ”In buildings used for starch or candy
factories, woodworkers, grain elevators or flouring mills, or
other purposes,where fittings are exposed to dust and flyings

of inflammable material, cutouts and switches should be placed
in an approved cabinet outside of the dust rooms, or if necessary
to locate same in the dust room, cabinet must be dust proof and
arranged with self closing door.”

In subsequent editions of the Code we find similar rules
continued and additional regulations included to provide necessary
protection for motors located in dusty places. In the 1909
edition for instance, this rule is found in section 8 -"Motors:
must be covered with a waterproof when not in use and, if deemed
necessary by the Inspection Department having Jurisdiction, must
be enclosed in an approved case. Such enclosures must be readily
accessible, dustproof and sufficiently ventilated to prevent
an excessiverise of temperature. Where practical, the sides
should.be made largely of glass so that the motor may always be
plainly visible. The use of enclosed type motor is recommended
in dusty places, being preferable to wooden boxing."

This same edition of the Code provides that: "When
switches are used in rooms where combustible flyings would be
likely to accumulate around them, they must be enclosed in
dust tight cabinets. "

Thus we see that many of the National Code rules for
hazardous locations were formulated, in intent at least, during
the early days of electrical development. Efforts were made in
succeeding issues of the Code to clarfiyPand extend the rules
for these so-called hazardous locations in order to make their
application.better understood. It was left entirely to the
Judgment of the inspection authority, without guidance, as to
whether or not the locations involved should be considered as
hazardous.

With the 1925 edition of the Code came an entire re-
arrangement of subject matter by which the Code was divided
into a number of Articles, each of which treated a separate
division of electrical wiring or apparatus. In this issue we
find the formation of Article 32 carrying the title ”Extra
Hazardous Locations," a single page outline of the precautions
necessary when electrical equipment was installed in locations
“where highly flammable gases, liquids, mixtures or other sub-
stances are manufactured, used or stored, in other than original
containers.” However, there were still retained in the respective
general lrticles of the Code the rules requiring the protection .
of lamps, switches, motors and other apparatus exposed to flammable

«of. PC mP. elm-‘2. W30“ II FM haw «HR 0 at“ it Iii ‘ujcnulalll 1-1 1!..4 cl]

dust or flyings. Although this rearrangement of the Code was a
step in the right direction, the desired results were not
entirely accomplished as the rules were distributed throughout
the Code in.such a manner that a person desiring complete
information on the Code requirements for hazardous lecations was
put to considerable trouble in attempting to select the rules
applying out of a great deal of matter.not directly concerned
with the problem at hand. . .

In 1911 the work of preparing the National Electrical
Code was passed from the Underwriters' National Electric Asso-
ciation to the National Fire Protection Association (N.F.P.A.)
under whose auspices it is still prepared. In addition to the
National Electrical Code, the N.F.P.A. sponsors a number of
other Codes on fire prevention and protection subjects. A survey
of these Codes made by the writer in 1927 revealed that many of
them contained specific rules for the installation of electric
wiring and apparatus in certain occupancies generally considered
hazardous by inspection authorities. Many of these electrical
rules differed widely both in wording and intent from the rules
in the Electrical Code in spite of the fact that these rules
were intended to protect against exactly the same hazards. For
instance, it was found that the N.F.P.A. regulations for Dry
Cleaning Plants, edition of 1925, provided that all wires for
lighting circuits be placed in conduit while the Electrical Code
permitted either armored cable or conduit wiring in locations
where highly flammable liquids were used. Such differences in
rules were found to be quite extensive throughout, and as a
result, there was considerable confusion in their application.
This may have introduced serious conflicts where municipalities
or states had adopted both sets of regulations as parts of their
fire prevention ordinances. - ~

Many inspection authorities considered the National
Electrical Code, in itself, an insufficient guide for obtaining
the proper type of electrical installations in certain hazardous
occupancies. The natural result of this opinion was the develop-
ment of individual special rules and even special codes by
municipalities and insurance underwriters specializing in certain
hazardous classes of plants. This trend presented a definite
obstacle to the adoption of the National Electrical Code as the
single American Standard, at least in point of usage. Special
rules and special codes work directly against the interests of
the much desired uniformity and, hence, it was felt that con-
siderable could be accomplished in the direction of general
acceptance by rewriting Article 32 of the Code to include complete
rules for all hazardous locations in the one Article. It was
also felt desirable to attempt to coordinate the many special
rules in other N.F.P.A. Codes in such a way as to make necessary
in them only a simple reference to the proper classification in
Article 32 of the National Electrical Code.

In 1927, at the suggestion of Mr. A. R. Small, Chairman
of the Electrical Committee of the N.F.P.A., the writer who had
been appointed Chairman of Article 52 Sub-Committee proceeded,
with the help of the members of his Sub-Committee, to make a
study of industry in general to ascertain in what industries
and to what extent there existed hazardous processes involving
or producing liquids, vapors, gases, dusts, fibers or other
hazardous substances of a highly flammable, explosive or easily
ignitable nature. This study was made through actual inspections
of representative plants and by reading available literature on
the subject. The published N.F.P.A. Codes treating the various
hazardous industries or processes were consulted, for it was
felt very desirable to include in the proposed Article 52 the
ideas of the writers of those Codes so far as it could be done
consistently. All available reports of fires and accidents '
involving the hazardous conditions under consideration were
studied, for from.such reports was obtainable the most accurate
information on the actual conditions existing in the field.

The report of Article 32 Committee which resulted from
this preparatory study was unanimously approved at the February
1928 meeting of the National Code Committee and subsequently
adopted by the N.F.P.A. at its annual convention as an.amendment
to the National Electrical Code. As presented at that time,
Article 32 consisted of three classifications, viz: Class I,
those locations dealing with flammable vapors, gases and liquids;
Class II, those dealing with.flammable dusts; and Class III,
those dealing with combustible fibers and lint. The latter class
was subsequently divided so as to make a fourth - Class IV,
‘which deals with the storage of cotton and other combustible '
fibers. Except for this latter and a few other minor changes,
Article 32 remains as adopted originally and so appears in the
latest (1951) edition of the National Electrical Code which has
been adopted as an American Standard by the American Standards
Association.

From.the many favorable remarks which has been heard,
the writer is led to believe that the new Article 32 has filled
a very definite need on the part of inspection authorities.
Considering the relative newness of the rules, their application
has been quite general and as a result, it is the opinion that
a marked improvement has been made in electrical installation in
hazardous locations. Some questions of interpretation have been
raised, however, on some parts of Article 52. This is especially
true of those parts in which the attempt is made to define the
conditions and processes which warrant the particular location
involved being classed as hazardous.

Interpretations have also been requested at various
times on the meaning or application of certain rules. It is
the purpose of this paper to attempt to answer these questions;
first, by discussing a number of typical materials and industries
for the purpose of determining where and to what extent hazardous

,‘

 

 

5

conditions obtain; and second, by going into detailed explanation
of each rule, illustrating its application with drawings or
photographs of available apparatus or actual installations in

the field. Included also are a number of typical fire and
accident reports involving hazardous locations which serve to
emphasize the importance of the subject.

It should be pointed out that the procedure in the
development of Article 52 is reversed from.that usually followed.
That is, the rules were develOped before the electrical manufac-
turers had suitable apparatus available to comply with them.
However, considering the short space of time which has elapsed
since the Article was formulated, surprising progress has been
made and we now find complete lines of motors and control
apparatus of specially approved types readily available on the
market. Rapid headway is also being made in the design of suit-
able lighting fixtures, fittings and other devices specially for
hazardous locations.

Standards for the performance of motors,controllers,
fittings and lighting fixtures have been developed by the Under-
writers' Laboratories as have suitable apparatus and methods for
their testing. The manufacturers are making full use of these
facilities.

It is gratifying indeed to witness such a complete
alignment of interests in this comparatively short space of time
in the effort to obtain safer electrical installations in the
hazardous industries. A marked tendency toward the reduction
of loss of life and property must surely follow.

£55! I

CLASSIFICATION

Containing a discussion of
(1) types and characteristics
of hazardous materials and,
(2) industries and processes
using or producing these
hazardous materials, as per-
taining to their classifi-
cation under the rules of
Article 32 of the National
Electric al Code .

CLASSIFICATION
EXPLANATORY

In the formation of the present Article 52 of the
National Electrical Code, it became apparent to those responsible
for its development that it was necessary to provide the proper
forms of apparatus and wiring to suit the particular type of
hazardous condition to which they would be exposed. For instance,
a motor which could be operated with perfect safety in an atmos-
phere of combustible dust might not be safe for Operation in a
location where an explosive mixture of a flammable gas or vapor
and air was present. Conversely, while it might happen that a
motor suitable for use in an explosive vapor and air atmosphere
would be safe for use in a dusty atmosphere, it seemed unfair to
require the installation of a motor designed to a more rigid
standard than the actual requirements demanded. Therefore, a
close study of the nature of each type of hazardous material was
necessary to make certain that the type of electrical installation
for locations where such material was used, stored or handled
was suitable and safe.

While the term "hazardous material" in the larger sense
may mean a material which is a hazard to life and property
because of its ease of ignition, toxicity, combustibility or
susceptibility to spontaneous ignition, we are immediately con-
cerned only with its hazard from the standpoint of the possible
effects of ignition of the material (or its vapors mixed with
air) by arcs, sparks or high temperatures resulting from.the
normal or abnormal operation of electrical apparatus and wiring.

Closely associated with the hazard of the material
itself is the process or manner in which it is used. To illus-
trate, let us assume a typical case of varnish or lacquer in
which a highly flammable volatile liquid,such as naphtha,is used
as the thinner. While such a preparation.might be stored with
comparative safety in tightly closed containers on the shelves
of paint stores or in warehouses, a considerable hazard is
introduced when this same varnish or lacquer is used in connec-
tion with the spray finishing of furniture or similar goods.
Thus, a study of the processes involving the various hazardous
materials and the methods by which they are manufactured and
used was an important step in the formation of Article 32.

We shall, therefore, proceed to discuss,first the types
of hazardous materials, their properties and hazards, and
second, the processes, both specific and general, involving
their use and handling.

CLASSIFICATION
AS TO
TYPES OF HAZARDOUS MATERIALS

A survey of the field of commerce and manufacture
revealed that the various forms of hazardous matter could be
grouped into the following general types:

1.

2.

3.

4.

5.

6.

7.

Flammable liquids, which.may'be divided into two
classes, viz: ‘

(a) Volatile flammable liquids, those giving off
flammable vapors at ordinary temperatures.

(b) Relatively non-volatile flammable liquids,
those giving off flammable vapors at tempera-
tures not reached in their ordinary use.

Flammable gases, those gases which form flammable

or explosive mixtures with.air as contrasted with
inert gases such.as nitrogen, or gases which support
combustion such as oxygen.

Highly flammable solids, which.might‘more fairly be
classed as explosives. '

Highly flammable mixtures, which in reality are
combinations either of a material in one of the
foregoing classes with a nonphazardous substance

as in the case of rubber cement, or a combination

of two or more materials of the same or separate
foregoing classes as in the case of pyroxylin lacquer.

Combustible dusts, which may be either carbonaceous
or metallic in nature, either in themselves easily

ignitable or capable of forming explosive mixtures

With air e

Easily ignitable combustible lints, fibers or
"flyings e "

Combustible light material such as wood shavings or
paper trimmings.

It was found convenient to arrange these types of
,hazardous materials into four groups and treat each as a separate
class insofar as electrical rules are concerned. In Section 3201
of the 1931 edition of the National Electrical Code, we find
these four classes defined as follows:

Class I locations are those in which flammable volatile liquids,
highly flammable gases, mixtures or other highly

flammable substances are manufactured, used, handled
or stored in other than their original containers.

Class II locations are those in which (1) combustible dust is
thrown or is likely to be thrown, into suspension in the
air in sufficient quantities to produce explosive
mixtures or (2) those where it is impracticable to prevent
such combustible dust from collecting in such quantities
on or in motors, lamps or other electrical devices that
they are likely to become overheated because normal
radiation is prevented.

Class III locations are those in which easily ignitable fibers
or materials producing combustible flyings are handled,
manufactured Or used and which are hazardous through
such fibers or flyings collecting on or being ignited
by arcing contacts, resistors, lamps or similar apparatus.
For combustible fiber warehouses see paragraph e of this
section and section 3206 of this article.

Class IV locations are those in which easily ignitable combustible
fibers are stored or handled (except in rooms wherein
process of manufacture) and which are hazardous through
such fibers being ignited by arcing contacts, resistors,
lamps or similar apparatus.

It will be noted from these definitions that all of the
various types of hazardous materials previously listed are
included in what appears to be an entirely logical arrangement.
It was possible through this method of classification to draw
individual sets of rules for each class in such a manner that
all rules of each set apply with few exceptions to-all conditions
met in the respective class. Such treatment is much to be
preferred to one in which an attempt is made to have one set of
rules apply to all conditions of use of all types of hazardous
materials.-

The conditions represented by Class III and Class IV are
somewhat alike inasmuch as both treat with readily ignitable
materials of the lint type. However, Class IV locations repre-
sent those where easily ignitable fibers are stored. The rules
under it will be applied chiefly to the large cotton warehouses
common in the Southern States at terminal points and the majority
of these rules formerly appeared in the N.F.P.A. regulations on
"The Storage and Handling of Combustible Fibers." The rules in
Class IV are somewhat more rigid than those in Class III for it
was felt necessary to take every precaution to prevent ignition
of stored fibers in large storages because of the high values of
property involved. The N.F.P.A. Committee on "The Storage and
Handling of Combustible Fibers" has amended their regulations to
include only a simple reference to the rules of Class IV,
deleting its own detailed electrical rules.

HAZARDOUS MATERIALS
AND
THEIR CHARACTERISTICS

In order that the engineer may have a more complete
knowledge of the characteristics of the various hazardous
materials under consideration, it seems advisable to discuss
in some detail some of these characteristics. Matters such as
flashpoints, ignition temperatures and flammable limits of
vapors have an important bearing on the selection of electrical
equipment for locations where flammable liquids will be used.
Likewise, ease of ignition is of great importance in the choice
of electrical equipment for dusty or linty locations.

It is not intended that the following discussion be
considered a complete treatise on the subject. There are many
excellent publications available, as will be seen by referring
to the bibliography, which cover the subject very completely.

The examples of the hazardous materials given.under each
type are partial lists only. Space would not permit listing
every known hazardous material and its characteristics. However,
should the engineer encounter any material of the hazards of
which.he is in doubt, he should submit the problem.to the
Underwriters' Laboratories, the National Fire Protection Asso-
ciation or other acknowledged and competent organization for
analysis. In the case of hazardous chemicals and flammable
liquids, the N.F.P.A. Committee reports and regulations will be
found very useful.

Flammable Volatile Liggids

The hazard incidental to the storage, handling and use
of flammable volatile liquids is an important and serious matter
in many industries. In some instances, such as in dry cleaning
operations, these liquids are used in an unmixed state, but the
important uses of flammable liquids in industry are represented
by their employment as vehicles or solvents for finishes, as
constituents of manufactured materials and as solvents for rubber
or similar substances for the purpose of reducing them.to a
plastic state.

The handling of flammable volatile liquids in large
quantities has also become a serious problem for the fire
prevention engineer. Such handling involves the use of pumps,
piping and tanks, which, while introducing relatively little
hazard when in proper operation, become major hazards when
irregularities such as leakage or rupture of such equipment
occurs. Unfortunately, accidents of this type are not uncommon
and therefore, electrical apparatus and wiring must be designed
with.full consideration given to such possibilities.

10

In order that a clear understanding of the hazards of
flammable volatile liquids might be had, it is necessary that
one be somewhat familiar with their characteristics. To this
end let us first discuss the various terms associated with them.
This involves mention of volatility, flash point, ignition
temperature, flammable or explosive limits, vapor density, and
their definitions. :

Volatility is the tendency of a liquid to assume the
vapor state, that is, to evaporate. This tendency varies quite
widely for the various liquids. For instance, gasoline evaporates
:much more rapidly than kerosene, while paraffin oil evaporates
very slowly. For all liquids the volatility increases with rise
of temperature, and for any liquid there corresponds a temperature
below ihich it will not assume the vapor state in dangerous
quantity. This temperature then becomes a dividing line above
which a flammable or explosive mixture may be formed with the
surrounding air by the vapor from the liquid. The determination
of this temperature is of great importance in classifying the
hazards of a liquid. The flash point test is used when possible
in the case of liquids of both high and low volatility, to
determine the temperature at which liquid gives off vapors in
sufficient quantities to form a flammable or explosive mixture
with the surrounding air. This temperature is usually referred
to as the flashpoint of the liquid and has long been.used by
fire prevefition engineers as an approximate measure of the fire
hazard of the liquid. In cases where a liquid is composed of a
mixture of volatile ingredients, the flash point tests made by
the conventional closed or Open cup methods are not a truly
reliable measure of the hazard of a liquid and therefore, the
tests:must be supplemented by further tests, but discussion of
these tests is not within the scope of this work.

A arent I ition Tem erature, as applied to the vapors
given off Hy fIammagIe IIquIds, Is the designation given to the
lowest temperature to which any part of a vapor air mixture must
be raised by the application of heat, whether in the form of a
flame, spark or a hot surface, to produce combustion that will
propagate itself. The ”apparent ignition temperature" is of
great value for comparative purposes, and in indicating dangerous
temperature limits of exposure particularly in industrial
operations.

 

 

Flammable or Explosive Limits. In the case of most
flammable liquids,_?here is a mInImum as well as maximum concen-
tration of vapor in air below and above which, respectively,
propagation of flame does not occur on contact with a source of
ignition. These are known as the lower and higher flammable or
explosive limits and are usually expressed in terms of percentage
of vapor in air by volume. Between the lower and higher limits,
there is a certain concentration that will produce the most
intense combustion or explosion of which the vapor is capable.

It is this concentration that we attempt to secure, for instance,

 

 

Quiet 10;.-

all

‘0

10

In order that a clear understanding of the hazards of
flammable volatile liquids might be had, it is necessary that
one be somewhat familiar with their characteristics. To this
and let us first discuss the various terms associated with them,
This involves mention of volatility, flash point, ignition
temperature, flammable or explosive limits, vapor density, and
their definitions. :

Volatility is the tendency of a liquid to assume the
vapor staté, that—is, to evaporate. This tendency varies quite
widely for the various liquids. For instance, gasoline evaporates
mmch.more rapidly than.kerosene, while paraffin oil evaporates
very slowly. For all liquids the volatility increases with rise
of temperature, and for any liquid there corresponds a temperature
below which it will not assume the vapor state in dangerous
quantity. This temperature then becomes a dividing line above
which a flammable or explosive mixture may be formed with the
surrounding air by the vapor from the liquid. The determination
of this temperature is of great importance in classifying the
hazards of a liquid. The flash point test is used when possible
in the case of liquids of both high and low volatility, to
determine the temperature at which liquid gives off vapors in
sufficient quantities to form a flammable or explosive mixture
with the surrounding air. This temperature is usually referred
to as the flashpoint of the liquid and has long been used by
fire prevention engineers as an approximate measure of the fire
hazard of the liquid. In cases where a liquid is composed of a
mixture of volatile ingredients, the flash point tests made by
- the conventional closed or cpen.cup methods are not a truly
reliable measure of the hazard of a liquid and therefore, the
tests must be supplemented by further tests, but discussion of
these tests is not within the scope of this work.

 

 

A arent I ition Tempgrature, as applied to the vapors
given off Hy fIamma e quids, is the designation given to the

lowest temperature to which any part of a vapor air mixture must
be raised by the application of heat, whether in the form of a
flame, spark or a hot surface, to produce combustion that will
propagate itself. The "apparent ignition temperature" is of
great value for comparative purposes, and in indicating dangerous
temperature limits of exposure particularly in industrial
operations.

Flammable or Explosive Limits. In the case of most
flammable liquids,-there is a minimum as well as maximum concen-
tration of vapor in air below and above which, respectively,
propagation of flame does not occur on contact with a source of
ignition. These are known as the lower and higher flammable or
explosive limits and are usually expressed in terms of percentage
of vapor in air by volume. Between the lower and higher limits,
there is a certain concentration that will produce the most
intense combustion or explosion of which the vapor is capable.

It is this concentration that we attempt to secure, for instance,

 

11

when we adjust the carburetors of automobile engines. The
difference between the two limits is known as the flammable or
explosive range. For gasoline, as an example, the lower limit
has been found to be approximately 1.4% while the upper limit
is approximately 6%, giving a range of 4.6%.

Vagor Densit is the weight of a given volume of vapor
as compare wi e weight of an equal volume of air taken as

a standard under similar conditions as to temperature and
pressure. Consideration of vapor density is important as it is
an accurate indication of the behavior of vapors with respect

to their movement when released from containers such as tanks or
piping. For instance, we have found that gasoline vapor, which
is known to be heavier than air, has a tendency to cellect in the
basements or pits of gasoline filling establishments. Many
serious explosions have occurred in such locations because of
this tendency and as a result, the rules governing electrical
installations in such locations give full recognition to the
behavior of gasoline vapor and similarly with other flammable
volatiles. The following table gives the relative densities of
the vapors of several common volatile liquids:

Table No. _1_,_

 

 

.Gasoline (Mean value)
Kerosene (Mean value)

Vapor Approximate Vapor Density
Air equaIé 1
Alcohol Methyl 1.1
Alcohol Ethyl 1.6
Acetone 2.0
Ether Ethyl 2.6
Benzene 2.7
5 5
4 5

It is well known that when a gas or vapor has a density less

than that of air, it will ascend and tend to mix comparatively
rapidly with air. 0n the other hand, relatively heavy vapors
will tend to descend and to diffuse or mix with air very slowly.‘
In fact, the velocity of diffusion of a gas or vapor varies
inversely with the square root of its density, so the lighter
heavier-than-air vapors mix.more rapidly than the heavier vapors.

As an aid to fire prevention engineers, the Underwriters'
Laboratories have adopted a method of testing and listing
flammable liquids which.has been widely applied. A complete
explanation of this method is contained in a most excellent
brochure written by Mr. A. H. Nuckolls, Chemical Engineer of the
Laboratories, entitled "Underwriters' Laboratories' Method for
the Classification of the Hazards of Liquids." The method, too
lengthy to be explained here, involves a general classification

 

,'

12

of liquids and embraces the assignment of the various flammable
liquids to positions on a numerical scale of hazard ranging from
0 to 110 as follows:

Table 313. _2_.

 

 

General Classification Numerical Hazard Rating Scale
Ether Class ' ' 100 - llO
Gasoline Class 90 - 100
Alcohol (Ethyl) Class 60 - 70
Kerosene Class 30 - 40
Paraffin Oil Class 10 - 20

In explanation of the foregoing table, it should be pointed
out that pure other is given a ratin of 100; a standard kerosene
with a flashpoint of 100 degrees F. %closed cup tester) a rating
of 40; and paraffin oil with a flash of 440 degrees F. a rating
of 100

The general practice of fire prevention engineers has been
to regard a flash point of 100 degrees Fahrenheit as the dividing
line on which to differentiate the volatility hazards of common
liquids, in other words, to regard liquids of the kerosene class,
or higher in flash point temperature, as relatively non-hazardous.
For general practice, when such relatively low hazard liquids are
not heated, but are used at ordinary room temperatures, this is
probably a safe guide, but a careful investigation should first
be made of the uses and processes involving the liquid before
definite conclusions are reached.

In arriving at the numerical hazard classification, full
consideration has been given to vapor ignition temperatures. The
ignition temperatures of the vapors of most common liquids, par-
ticularly those of petroleum products, are considerably above
ordinary tenperatures and usually high temperature sources of
ignition such as arcs, sparks, or flames are necessary to cause
fire. There are some vapors such as those of carbon disulphide
which have ignition points as low as 212 degrees Fahrenheit

Since the Underwriters' Laboratories originated this
method of hazard classification of liquids, many commercial liquid
products such as solvents, thinners for paints and varnishes, floor
oils and many other have been tested and the results published
in the Underwriters' Laboratories' lists. Reference to these
lists will inform the engineer regarding the hazard of these
products.

In the following table will be found the hazard classification
of a number of common flammable liquids, together with their flash
oints, apparent ignition.temperatures and hazard classifications.
is table is based on the table appearing in the brochure by Mr.
Nuckolls whhh was previously mentioned.

13

Table Nb. 5;

 

 

 

Liguid Flash Point A arent Hazard
(Closed Cup) I Ition Classi-
eg. a . Temperafure fIcatIon
eg.‘Fahr.
Acetone (C.P.) 5 1000-1050 90
Acetate, Amyl (Pure) 77 ‘ 750-800 55-60
Acetate, Butyl, Normal (C.P.) 84 700-825 55-60
Acetate, Ethyl (C.P.) — 23 800-925 90
Acetate, Methyl (Anhydrous) 14 850-925 90-100>
Acetic ACid, Glacial (99.5) 107 800-925
Acetic Anhydride (C.P.) 127 600-675
Alcohol, Amyl (Fusel Oil) 100 700-725 40
Alcohol, Amyl Sec. (Technical) 94 650-725 40
Alcohol, Amyl Iso ' 114 650-725 55-40
Alcohol, Butyl Iso (106-108°B.P.) 86 700-800 40
Alcohol, Butyl Normal (116-1180B.P.) 100 650-725 40
Alcohol, Denatured (Formula No. 5) 61 750-810 70
Alcohol, Ethyl (Absolute) 54 700-800 70
Alcohol, Methyl (C.P.) 52 800-900
Alcohol, Propyl Iso (81.5-82.1°B.P.) 61 750-850 70
Alcohol, Prop 1 NOrmal (96-98 B.P.) 77 700-800 55-60
Aniline, Dimethyl (C.P.) 165 700-750
Benzol (C.P.) -4 1000-1060 95-100
Benzaldehyde (C.P.) 147 - 577
Carbon Disulphide (C.P.) , -22 212-225 110 Plus
Ether, Ethyl (C.P.) -49 356 100
Furfural 54-55°B.P./17mm.) 145 600-675
Gasoline 74-76 A.P.I.) -45 556 90-100
Hexane (From Petroleum) -15 500-565 90-95
Nitro Benzene (C.P.) 198 900-950
Petroleum.Ether (40-60°B.P.) -69 624 95-100
Pyridine (C.P.) 74 900-1100 55-60
Toluene (C.P.) 48 1050-1125 75-80
O-Toluidine (85-85°B.P./15mm.) 202 900-1000
Xylene (158-1590B.P.) 86 900-1150

 

Several additional flammable liquids were included in
the original list some of which are ordinarily considered
hazardous only from the standpoint of contributing to the
spontaneous ignition hazard, a subject with which we are not

immediately concerned.

This table is not intended to include all flammable
volatile liquids encountered in industry, but does probably
contain those most commonly found. Two widely used flammable
volatile liquids are the so-called naphtha and benzine neither

of which will be found in Table No. 5. In the petroleum

refinery industry, benzine is that fraction of the oil which

K

7-1

 

 

O
\

 

 

 

l4

boils between 158 and 248 degrees Fahrenheit. Its hazard rating
is slightly higher than that of gasoline, namely, 100. Naphtha is
a term formerly applied to a petroleum.distillate of a definite
specific gravity, but is now generally used to include any
petroleum distillate with a f1ash.point less than 280 degrees
Fahrenheit. It also has been given a hazard rating of 100.

The use of the information given ianable No. 5 is best
illustrated by assuming a typical case where gasoline is being
used as a solvent in an open tank within.a building. We find by
referring to the table (Table No. 5) that gasoline gives off
flammable vapors at a.temperature as low as minus 45 degrees
Fahrenheit, that is, at much below ordinary room.temperatures.

‘We can then expect that a considerable amount of gasoline vapor
will be present in the vicinity of the tank, and, unless con-
tinually effective means are provided for the removal of these
vapors they will diffuse quite rapidly, mixing with the air
probably in explosive proportions. All that is needed then, is

a source of ignition having a temperature equal to or higher
than the apparent ignitidn temperature of gasoline vapor Which,
from the table (Table No. 5), we find to be 556 degrees Fahrenheit.
An electric spark or arc occurring in the open.in this atmosphere
would be sufficient to cause ignition as would the tempenture
reached by the frame of an open motor in event of burnout. Con-
sequently, these factors must receive full consideration in
deciding what types of electrical equipment are safe in such
atmospheres.

Flammable Gases

Flammable gases form explosive mixtures with air in.the
same manner as do the vapors of flammable liquids which we have
previously discussed. The hazards of the two classes of matter are,
therefore, quite similar from the viewpoint of the fire prevention
engineer. The same problems of storage, handling and.use are
present, and as in the case of flammable volatile-liquids, it is
true that if it were possible to positively confine flammable gases
within.tanks and piping or within the stoves, heaters, ovens or
other devices specially designed to consume the gas, the hazard
involved in connection with flammable gases would be slight. However,
experience has shown.that leaks develop in tanks and piping, that
pumps or compressors become defective from wear and rupture, and
that very often in the process of manufacture of gas the retorts
and other appaatus burst. Naturally, when such an accident occurs
within a building, the room or often the entire structure is
filled with a highly explosive mixture of gas and air, lacking
only a source of ignition to cause havoc. Such occurrences have
been only too frequent and electrical hazards have been con-
tributing factors in many of them.

15

Within recent years we have witnessed the introduction of
various hydrocarbon gases in liquified form for use in communities
where natural or manufactured illuminating gas was not available.
We have also seen marked extension in the practice of piping
natural gas to points far remote from the gas fields. These
developments have had the effect of introdu_cing explosion hazards,
especially in punping or compressing stations.

In the following table will be found listed a number of
flammable gases with their commonly accepted explosive limits,
densities and ignition temperatures:

Table 312. _4_.

 

Explosive Limits Relative Apparent
IfimPercentage by Weight Ignition
0 Air.

 

 

 

Volume . Tannersiszs

Deg, Fahr.
Illuminating Gas 7 - 21' ‘.65 1094
Hydrogen 9.5 - 66. 5 .069 ‘ 1051
' Acetylene 5.2 - 52.2 .898 948 - 959‘
Ethylene 4.2 - 14. 5 .967 1071 - 1110
Ethane 303 - 1006 1.0494 950 - 1152
Propylene ' 1.451 927 - 952
Propane 2.5 - 7.5 1.505 870.8
Carbon Monoxide 16.6 - 74.8 .967 1177 - 1497
Butane 1.6 - 6.5 2.01 806
Methane 5.6 - 15.5 .5576 998.6
Hydrocyanic Acid Gas 5.6 - 59.8 725

Of the liquified hydrocarbon gases used for heating and
lighting purposes, butane and propane are very common. These
are often sold under trade names as in the case of Blau Gas, named
after its inventor. Pintsch Gas is a product made in much the same
manner as ordinary coal gas except that petroleum is decomposed
rather than coal.

Highly Flammable Solids

In this class we may place many commercial solid sub-
stances which might well be called explosives, for in the final
analysis, the only distinction between ordinary combustion or'
bgrning and explosion is the rate at which the action takes
p ace.

16

Gunpowder, dry picric acid, nitrocellulose, nitrosophenol,
naphthalene and pyroxlyn plastic are prominent examples of highly
flammable solids which may be encountered.

In the more usual manufacturing operations, pyroxylin
plastic, nbetter known as"ce11uloid", probably represents the most
hazardous material found. It is a material which is used to a great
extent for the manufacture of many types of goods, including .
toilet articles, photographic film, artificial leather, billiard
balls, piano keys, and a host of others. Its manufacture and use
involves great hazard for its ignition point is extremely low,'
probably in the neighborhood of 500 degrees Fahrenheit and may,
therefore, be ignited by any slight spark or arc, or even by the
heat of an incandescent lamp. It burns very rapidly and com-
bustion is attended by the rapid evolution of explosive and
poisonous fumes or vapors. It is stated that 1000 pounds of
pyroxylin plastic will form from 5000 to 85000 cubic feet of
vapor. This decomposition may begin at a temperature much lower
than that of actual ignition and with it occurs a gradual rise
in temperature which in itself may be sufficient to cause fire.
Considerably more will be said on this subject in discussion to
follow.

Highly Flammable Mixtures

Many substances, in themselves non-hazardous from the
standpoint of ignition points and combustibility, are formed
into hazardous materials or mixtures when low flashpoint solvents
are used to place them.in solution or to form a paste. When the
process or use involves the solution of a hazardous material in
an equally hazardous solvent, the resultant hazard is usually
greatly multiplied.

As a representative mixture of the class first mentioned,
we have rubber cement which is usually dissolved in gasoline or
naphtha. This type of cement is used in many processes in the
rubber industry, often in such a manner that the rooms in which
operations take place have a very appreciable amount of gasoline
or naphtha vapor present, necessitating adequate artificial
ventilation and rigid precautions to remove sources of ignition.
0f the second class, where a hazardous solid is dissolved in a
flammable volatile liquid, a good example" is afforded by pyroxylin
spray finishes or lacquers of Which. "Duco" is a p0pular trade
brand. These finishes or lacquers consist of pyroxylin or nitrated
cotton, in themselves hazardous, blended with the desired oil and
pigments and mixed with very flammable volatile solvents and
thinners such as, ethyl acetate, butyl alcohol, acetone, amyl
acetate, benzol and high test benzine. We have already discussed
the component parts of such mixtures and the hazards associated
with them. More will be said about the general process of spray
finishing in another chapter.

17

Following are a few commonly found mixtures which are classed
as hazardous:

Paints lacquers Japans and varnishes which employ flammable
volatile solven s or inners as vehicles or drying agents.

Rubber cements consisting of gum rubber dissolved in
various soIvenEs such as gasoline, naphtha or benzine.‘

PEroxylin lac uers or varnishes consisting of pyroxylin.
or nitra e co on sso ved in a solvent such as amyl acetate

and frequently diluted or thinned with benzol or an alcohol.

Collodion made up of a solution of nitrated cellulose in
ether and alcohol or in some other solvent.

 

Cleaning fluids which are often undiluted benzine or
naphtha, a1though.there are some fluids which are non-hazardous,
and others which are only hazardous in the same degree as
kerosene, such as Stoddard's solvent.

Combustible and Explosive Qgsts

"Combustible dusts, whether of a carbonaceous or metallic
nature, form.very explosive mixtures when mixed with air in prOper
proportions. The theory of dust explosions is very similar to that
of flammable vapors or gases. Various dusts have definite flammable
or explosive limits as do vapors, and there must be present a
source of ignition of sufficient intensity to ignite the dust and
air mixtures. ‘

Considerable research and experimental work has been done
in an attempt to determine the characteristics of various dusts.
As a general thing, it has been.dbtermined that any dust from a
highly carbonaceous material, or from any material which will burn,
will explode under prOper conditions. In the carbonaceous dust class
will fall dusts such as coal dust, flour dust, starch dust, grain
dust and wood dust. While metallic dusts such as of a1uminum.and
bronze are not generally said to be combustible, it is a proven
fact that they are explosive under proper conditions.

When a finely divided combustible dust is in suspension
in air so as to give access to an abundant supply of oxygen,
combustion once started, usually proceeds with explosive rapidity.',
The force of a dust explosion cannot be appreciated until one
has had the opportunity of viewing its effects. The writer has
seen reinforced concrete walls seven inches or more in thickness
shattered into bits by a grain dust explosion. In a cereal mill
explosion, it was reported that debris was found at a distance
of more than two and one half miles from the plant.

18

Dust explosions, especially those which involve grain
elevators and flour mills, occur in a series of two or more
explosions of increasing intensity. The primary explosion is
usually of a minor intensity, but the forces set up are of
such a nature as to dislodge other dust Which is in turn ignited,
producing an explosion of magnified volume and destructiveness.

It is not the intent to discuss at great length the
theory of dust explosions. For those who wish to study the problem
further, they areleferred-to an outstanding work on the subject,
”Dust Explosions" by Drs. Price and Brown of the U. S. Department
of Agriculture.

Statistics show that common sources of ignition of dust
and air mixtures have'been electric arcs, sparks and overheated
electrical machinery or devices. Hence, the need for special
consideration of the type of electrical installation which should
be permitted in dusty locations.

There are two angles of the case which require treatment
as has previously been pointed out; first, those where combustible
dust is thrown or likely to be thrown into suspension in the air
in sufficient quantities to produce explosive mixtures; and,
second, those where it is important to prevent such combustible
dust from collecting in.such quantities on or in motors, lamps,
or other electrical devices, that they are likely to become over-
heated because normal radiation isprevented. In the first, the
rules in the body of Article 52, Class II are designed to prevent
ignition of suspended dust by electrical arcs or sparks originating
from the Operation of switches, ques and the brushes of motors
or the breakage of electric lamps. In the second case we consider
the ignition of dust through overheating of motors because normal
radiation of heat is prevented by accumulations of dust on the
windings of the motors and in their ventilating slots, or the
ignition of dust by heat from electric lamps or resistors.

To illustrate, consider a modern flour mill with an up-
to-date dust colbcting system and adequate housekeeping. It is
probable that dust would not accumulate in cpen type motors to
such a degree that overheating would result, yet it would be
extremely important to remove to a non-haZardous location motors
of the brush type unless the brushes and slip rings were enclosed
in dust tight housings or the entire motor enclosed. In this
there is present a'problem of mathematical probability of an
electrical fault occurring at the-same moment when dust is in
suspension in the air in explosive proportions. More will be said
of this later, but for the time, suffice it to offer the suggestion
that only the most rigid precautions be enforced to eliminate
sources of ignition in view of the human lives and property values
which.might be sacrificed in event of an explosion coming as the
result of too great a dependence on the result of applying the
principles of probability.

19

Following are typical examples of dusts which have been
definitely classed as explosives:

Grain Dusts Spice Dust

Rice Dust Cocoa Dust
Starch Dust Sulphur Dust
Flour Dust Hard Rubber Dust
Wood Dust Dextrine Dust
Coal Dust Sugar Dust

Cork Du st

Easily Ignitable Combustible Fibers

Easily ignitable combustible fibers have proven to be
decidedly hazardous materials due to the ease of ignition and the
speed at Which flames spread through them when once ignited. When
a fibrous material such as cotton is distributed in the form of
lint or "flyings” in a thin film over machinery and building
members, a fire travels with almost explosive speed through the
entire room. Such fires are usually called "flash fires.

When fibers are compressed into bales and wrapped with
buflap, the apparent hazard would seem.to be reduced. However, in
baled storage there is usually sufficient loose lint protruding
from the bales to permit travel of fire over the surface with
amazing speed. Very often smouldering fires are left in individual
bales after the primary flash fire, and these are very difficult
to extinguish.

Many vicious fires have occurred in the large terminal
cotton warehouses, especially in those of the less modern t e
where the warehouses are of several acres in area without f re
'cut-off partitions. Large property values are usually present.

In manufacturing operations involving combustible ’
fibers such as in the picking department of cotton mills, in
mattress factories and in.upholstery works, the primary hazard is
somewhat increased due to the factthat the materials are handled
in light, loose form.offering ample surface for ignition and
combustion. However, the amount of material present is considerably
less than in the terminal warehouses and, therefore, the actual
property loss may be somewhat smaller.

In cotton ginning plants we find cotton in a very loose
form and in the gin building it is not usual to find much lint
clinging to machinery, building members and lamp cords. The amount
of cotton in the gin house at any one time is usually small, but
a fire once out of control is difficult to extinguish. The bad
fire record of cotton gins attests to the hazards involved.

20

Electrical hazards occupy a prominent position in the
list of causes of fires in the combustible fiber industry. The
breakage of electric lamps, overheated motors, sparks from
motors and short circuits have all been prominent figures in
disastrous fires. The need for a superior type of electrical
installation for such industries has been clearly shown.

While cotton is probably the most common of the combust-
ible fibers, others are of importance. The following list in—
cludes most of those commonly found: , .

Cotton Tow

Sisal or Henequen Cocoa Fiber
Ixtle -0akum

Jute Baled Waste
Hemp Kapok
Spanish loss Excelsior

Combustible Light Iaterial

 

In this class are included paper, wood shavings, wax-
coated papers and similar materials which, while comparatively
easily ignitable, are not to be considered as hazardous as the
others previously discussed. In some types of industries, how-
ever, the amount of material present renders the hazard a real
One, as a fire once started in transmitted with considerable
speed, especially when the material is in loose form.

In the case of paper, we do not have the hazard of
collection of the material in the windings of motors,cn lamps,
or within switch boxes as might be the ease with wood shavings
or sawdust. Therefore, the classification of the hazards of
this type of material, from our viewpoint, is not as definite
as in the case of other types of hazardous materials.

The engineer is required to make a complete study of
possible conditions in each instance in order to determine
what precautions should be taken in the choice and installation
of electrical equipment. Ordinarily, only reasonable enclosing
of sparking apparatus is necessary to provide the needed safe-
guards.

21

CLASSIFICATION
AS TO
INDUSTRIES AND PROCESSES

 

General Procedure

Having discussed the characteristics of the various
hazardous materials we shall now consider the industries and
processes which produce, use, or otherwise handle these materials,
in an attempt to determine where and to what extent special con-
sideration must be given to the selection and installation of
electrical equipment.

In the fine print notes following the definitions in
Section 3201 of the 1931 edition of the National Electrical Code,
some guidance is given to the engineer to assist him in deter-
mining in what industries or processes the hazards specified in
the bodies of the definition were likely to occur. These fine
print notes suggested the following for the respective classes.

Glass 1. This class may include such locations as some
parts of dry cleaning and dry dyeing plants,
pyroxylin plastic manufacturing plants, spray
painting establishments, gas plants, varnish
manufacturing plants, and establishments or
industries involving similar hazardous pro-
cesses or conditions.

Class 2. This class may include such locations as some
parts of flour mills, feed mills, grain
elevators, starch plants, sugar, cocoa and
coal pulverizing plants, and establishments or
industries involving similar hazardous pro-
cesses or conditions.

Class 3. This class may include locations sudh as some
parts of cotton and other textile mills, com-
bustible fiber manufacturing plants, cotton
gins, clothing manufacturing plants, cotton
seed mills, woodworking plants and establish-
ments or industries involving similar hazard-
ous processes or conditions.

Class 4. This class may include locations such as ware-
houses in which are stored or handled combust-
ible fibers, such as cotton (including cotton
linters and cotton waste), sisal or henequen,
ixtle, jute, hemp, tow, cocoa fiber, oakum,
baled waste, kapok, Spanish moss, excelsior
and other similarly readily ignitable fibers.

It is obvious that it would be impractical to attempt
to list all hazardous industries or processes in these fine
print notes and endeavor to point out with any degree of exact-
ness the extent of the hazardous area. Some of the more prom-
inent examples of industries and processes are included, how-

22

ever, which were for the purpose of giving the engineer some
idea as to what type of hazards were intended to be covered by
each respective class.

As the introductory rule of Article 32, (Rule 3201a),
there appears the following: ”The provisions of this article
are intended to apply to locations in which the authority en-
forcing this Code judges the apparatus and wiring to be subject
to the conditions indicated by the following classifications.
Where the apparatus and wiring are installed in rooms or
sections in which the particular hazardous conditions do not
prevail, such wiring and apparatus may be of the type approved
for such locations. For garages see Article 33." From this
rule it is seen that the authority enforcing the Code is
charged with the responsibility of determining where and to
what extent the apparatus and wiring are subject to the hazard-
ous conditions. Without some knowledge of the hazards of
materials and the processes involving their use, the engineer
or inspector enforcing the rules will encounter considerable
difficulty. The second sentence of this rule suggests the
possibility of so isolating electrical apparatus from the
hazardous area that it will not be subject to the hazardous
conditions. Considerable use is made of this alternative where
all machines are required to operate coincidentally in which
the motors and controllers, for instance, can be located in a
separate power room cut off from the hazardous area. However,
in instances where machines are not required to operate at the
same time, such isolation of motors may cause serious hazards
to be introduced by the many additional bearings, belts and
possibly clutches that would be required. In other words, the
result of removing one form of hazard from a hazardous area
may cause the introduction of additional hazards of a more
severe nature. Overheated bearings, static electricity
generated by moving belts and friction sparks in clutches have
proved to be frequent causes of fires and explosions. The con-
struction of motor rooms or other enclosures may entail con-
siderable expense and so the advantage, from an economic stand-
point, may often favor individual motor drives using motors
approved for use in hazardous locations. As applied to motor
controllers these might also more economically be of the type
approved for hazardous locations and placed in the hazardous
area, when controllers are few in number or are so widely dis-
tributed that grouping in a specially built control room is
impracticable.

The power losses occasioned by the additional bearings,
belts and clutches and the convenience attached to individual
motor drives are also an important consideration in determin-
ing whether or not motors should be isolated from the hazard-
one area.

In the fine print notes quoted above it should be noted
that use is made of the words: "lay include such locations as
some parts of," and a word or two in explanation of this phrase
may be valuable. Probably the best illustration is afforded
by considering a dry cleaning establishment. In the first
place, if such an establishment employed none but a non-
flammable solvent or cleaning fluid such as carbon tetra-

chloride, it would not be considered a hazardous location and,

25

therefore, would not be subject to the rules of Article 32.
However, if a flammable volatile solvent such as naphtha were
used and the establishment were divided by standard fire out-
Offs into several departments, only those departments where the
naphtha vapors were present in the atmosphere would be con-
sidered as hazardous locations.

This would usually eliminate, if cutoff as mentioned,
the receiving department, the dusting room, the boiler room and
the shipping department, but there would remain in the hazardous
classification the dry cleaning room, drying room, spotting room
and the solvent storage and recovery departments,.all subject
to the rules of Article 52, Class I locations.

From the above analysis it is clear that considerable
study must be given individual cases because of the many factors
which have bearing on the matter of classification. It is
admittedly a difficult task to arrive at definite conclusions
if the plant has not been placed in operation. However, there
are several general suggestions which may serve as aids. These
include:

1. A thorough study of the processes involved including
an investigation of the liquids, gases or solid sub-
stances which are to be used, scrutinizing these
materials from the standpoint of ease of ignition,
volatility, explosibility and general hazard rating.

2. A careful checking of the machines or devices which
are to be used. This to determine whether or not the
hazardous materials will be confined within tanks,
drums or piping, or whether or not there will be a
possibility of leakage into the open room, either
during normal operation or through accidents.

3. An inspection of the layout of buildings, either from
building plans or by actual visual inspection. This
to determine whether one small section of the plant
should be thrown into the hazardous classification
or whether or not the hazardous conditions extend
to all parts.

4. Consulting and co-operating with other inspection
authorities, particularly Uhderwriters' special
hazards inspectors and engineers who are familar with
conditions in establishments of a nature similar to
those under consideration.

5. Frequent reinspections of plants involving hazardous
processes or conditions to determine what conditions
prevail during actual operation.

6. A study of statistics and reports on fires and
accidents suffered in properties where hazardous
processes are involved.

Matters such as ventilation, mathematical probability,
housekeeping, confinement of hazardous materials and cutoffs
also have important bearings on classification and extent of
the hazardous area. Possibly a few remarks on these factors

as affecting classification, will not be amiss.

24

Special Considerations

Ventilation: In previous discussion it has been pointed
out that"vapors,*gases and dusts have definite explosive or
flammable limits. Obviously then, it would be practical to
arrange a natural or artificial ventilation system.which would
reduce the amount of the vapor, gas or dust in a room or building
so that the resulting mixture would be below the lower flammable
limit of the vapor, gas or dust involved. The N. F. P. A. regulations
on ”Blower and Exhaust Systems" provide the necessary instructions
for the installation of suitable artificial ventilation systems,
which regulations have been adopted by the various N.F.P.A.
Committees dealing with hazardous processes or industries. These
are generally applied to new construction and probably deal with
the situationquite satisfaCtorily.

 

In actual practice, however, it would.be folly indeed to
place full confidence in such a ventilating system.to remove enough
of the vapors, gases or dusts to render the remaining mdxture below
the lower flammable limit under all conditions. Unusual weather
conditions, the failure of the ventilating system, and the
probability of insufficient capacity of the ventilating system
under adverse conditions, are factors which might be the indirect
cause of a serious explosion if complete faith were placed in the
ventilating system.

Natural ventilating systems, consisting of vent pipes
directed to the out of doors from the hazardous areas are even
more unreliable. Conditions of humidity, direction of wind, and
‘wind velocity greatly affect the value of natural ventilation and,
therefore, it cannot be depended upon to consistently do the
work for which it was designed.

In practically all instances, the engineer is forced to
eliminate from consideration entirely, the possible value of
ventilating systems in his attempts to determine the extent .of
a hazardous area.

Mathematical Probability: It is obvious that in order to
obtain an eprosion a number 0 conditions must prevail coincidentally.
First, there must be an available supply or flammable vapor, gas or
dust; second, a supply of oxygen; third, the vapor, gas or dust
must be in admixture with oxygen (or air) in proportions within
the flammable or explosive limits; and fourth, there must be present
at the moment the mixture is within the flammable or explosive
limits a source of ignition of sufficient intensity to ignite
the mixture.

What then is the mathematical probability that all of
these conditions might obtain at the same moment? In extreme cases

25

it is probable that this would not occur 99 times out of 100, yet
at the 100th time, conditions might be just right for a disastrous
explosion or fire which might destroy many human lives and
thousands of dollars in prOperty value.

The writer has knowledge of many instances where motors
burned out or electric lamps were broken in extremely dusty
atmospheres in grain elevators without an explosion, due, probably,
to an "over rich" mixture of dust and air, that is, one above
the explosive limit. Had the mixture been less "rich", undoubtedly
an explosion would have occurred. It is probably due to this
condition of widely varying mixtures that explosions in grain
elevators are not even more frequent than records indicate.

No one can presume to estimate the mathematical probability
of coincidence of conditions necessary to an explosion of vapor,
gas or dust mixtures and, therefore, the engineer should not
consider this factor in selecting apparatus or making installations
where the conditions mgy'be present at any time. It is far better
to err on the side of safety than to gamble against the probability
of conditions being such as to produce an explosion.

Housekeepingj The standard of cleanliness maintained in a
plant has an important bearing on the fire hazard. This applies
to the electrical fire hazard as well. It is a foregone con-
clusion that Opportunity for ignition by an electrical arc in a
factory manufacturing articles from pyroxylin plastic where waste
material is permitted to accumulate on floors and work benches,
is much greater than in a similar factory where waste is promptly
deposited in covered metal receptacles.

 

‘Similarly, in a flour mill of modern design, with an
adequate dust collection system and with a high standard of
housekeeping, one could probably'install an open squirrel cage
motor with perfect safety on some floors of the mill building, as
excessive accumulations of dust in the motor windings would not
occur. Yet in a flour mill of less modern design, with an
inadequate dust collection system and under poor supervision, one
should expect even an Open squirrel cage motor to be a serious
electrical fire hazard.

Thus, on this basis, the engineer would feel justified
in discriminating between two factories involving identical
fundamental manufacturing hazards so far as a prOposed electrical
installation is concerned. On the other hand, he has no assurance
that the favorable conditions of housekeeping, supervision and
general arrangement will be continued indefinitely, and were he
to approve a type of installation based on a high standard of
maintenance, a change in management might cause conditions to
decline to such a degree that the most rigid standard of elec-
trical construction would not be sufficient.

26

Faced with such considerations, the engineer must, to a
large extent, disregard housekeeping, maintenance, and general
supervision in determining the type of apparatus and wiring to be
installed. The only possible exception is to permit Open squirrel
cage motors in certain parts of flour mills and feed mills as
will be discussed later.

Confinement 2f Hazardous Materials: In many types of
processes hazardous materials are handled in what are designed
to be entirely closed continuous systems. These may be so de-
signed primarily in the interests of economy as in the case of
volatile liquids where a closed system is necessary to avoid loss
'by evaporation. In other instances the materials are so handled
in order that working conditions for employees might be improved
and in others to reduce fire hazards. Usually an effort is made
to keep such systems in good order and free from leaks. Yet,
with even the best of maintenance, leaks develop, containers are
ruptured or piping bursts because of mechanical disturbances.
Should such accidents happen in a room or section of a building,
which might not otherwise be classed as hazardous, such a location
would immediately be subject to classification as a hazardous area.

 

As an eXample, let us consider a bulk gasoline unloading
station where gasoline is pumped from tank cars to storage tanks.
The pumps, usually electric driven, are generally located in a
small pump house. In normal Operation there is little gasoline
vapor present in the pump house, but should a pipe connection
develop a leak or the pump packing "blow", the pump house would
immediately be filled with explosive vapor. Should an Open arc
from a switch or a motor occur at that moment, an eXplosion would
surely result.

Thorough study must be given individual cases to determine
just how much special dispensation should be given processes where
the hazardous materials are handled in closed continuous systems.
Here again the best guide is to err on the side of safety in case
of any doubt.

Fire Cut-Offs: The modern manufacturing plant does not
usually consist of a single area as in the older types of plants.
Due to efforts of fire prevention engineers, factories are now
built so as to distribute the various processes or facilities into
several separated buildings, or into several rooms or departments
in the same building, each cut off from the next by standard fire
walls. The first thought in this action was to separate the raw
and finished products from the hazardous manufacturing Operations.
With the introduction of unusually hazardous finishing processes,
such as spraying and dipping, we find a trend toward further
division by confining these hazardous finishing operations to
separate rooms or sections cut off from theremainderof the actual
manufacturing section. Thus, rather than grading the entire
factory on the basis of the most serious hazard, namely that
associated with spray or dip finishing processes, it is possible

27

to grade the factory as a whole on the basis of a portion being
high hazard (the finishing processes), a portion medium hazard
(the assembling and forming processes), and a portion low hazard
(the storage of non-hazardous raw and finished products.)

The benefits of such sub-division extend to the electrical
installation also, as under the conditions stated in the pre-
ceding paragraph it would be necessary to follow Class I rules,
probably only in the room or section containing the finishing
processes, while in the actual manufacturing section it is
probable that only the rules of Class 3 or even of only the
general Articles of the Code need be applied, and in the case of
the storage sections only the latter.

Therefore, the arrangement of the factory, refinery, mill
or whatever the plant may be has much to do with the extent of
the hazardous area.

In the less modern plants, it is not uncommon to find
a hazardous process in the midst of other operations with no
attempt at isolation. In such cases the engineer is justified
in considering a large portion of the plant as being in the
hazardous area depending on the nature of the hazardous process.
As an example, let us consider an old style mattress factory.
In such a plant the fiber and tick stock is probably stored in
one end of the room from which the fibers are fed into pickers
by hand and then blown into the ticking until the desired quantity
has been inserted. The sewing is then completed and the mattress
carried to the storage and shipping department. It is difficult
to imagine any part of such a factory which would not have a
liberal quantity of fiber lint clinging to woodwork, machines
and other objects and for that reason the engineer would probably
specify compliance with Class 3 rules.

As has been stated previously, it is difficult to fore-
cast the extent of the hazardous area, but in the following the
writer will review some of the prominent industries and processes
and attempt to advise regarding classification and extent of the
hazardous area.

[a

27

to grade the factory as a whole on the basis of a portion being
high hazard (the finishing processes), a portion medium hazard
(the assembling and forming processes), and a portion low hazard
(the storage of non-hazardous raw and finished products.)

The benefits of such sub-division extend to the electrical
installation also, as under the conditions stated in the pre-
ceding paragraph it would be necessary to follow Class I rules,
probably only in the room or section containing the finishing
processes, while in the actual manufacturing section it is
probable that only the rudes of Class 3 or even of only the
general Articles of the Code need be applied, and in the case of
the storage sections only the latter.

Therefore, the arrangement of the factory, refinery, mill
or whatever the plant may be has much to do with the extent of
the hazardous area.

In the less modern plants, it is not uncommon to find
a hazardous process in the midst of other operations with no
attempt at isolation. In such cases the engineer is justified
in considering a large portion of the plant as being in the
hazardous area depending on the nature of the hazardous process.
As an example, let us consider an old style mattress factory.
In such a plant the fiber and tick stock is probably stored in
one end of the room from which the fibers are fed into pickers
by hand and then blown into the ticking until the desired quantity
has been inserted. The sewing is then completed and the mattress
carried to the storage and shipping department. It is difficult
to imagine any part of such a factory which would not have a
liberal quantity of fiber lint clinging to woodwork, machines
and other objects and for that reason the engineer would probably
specify compliance with Class 3 rules.

As has been stated previously, it is difficult to fore-
cast the extent of the hazardous area, but in the following the
writer will review some of the prominent industries and processes
and attempt to advise regarding classification and extent of the

hazardous area.

28

 

INDUSTRIES AND PROCESSES
“—IND THEIR
CLIESIFI'CITION

FINISHING PROCESSES

In our consideration, finishing processes include the
application of protective and decorative coatings to metal or
. wooden manufactured articles. Such coatings may be of paint,
varnish, japan, lacquer or enamel and may be applied by brush,
by dipping or by spraying. In general, and except for pyroxylin
lacquers, the hazards of these finishing materials are those
associated with the use of highly flammable volatile solvents
‘and thinners such as benzine, alcdhol, substitute turpentine,
benzol, amyl, acetate and others.

In the case of pyroxylin lacquers employing a base of
cellulose nitrate either gun cotton or pyroxylin, the hazard is
multiplied due to the fact that not only are the vapors of the
solvents and thinners almost always highly flammable, but the
bases themselves are of what might be termed an explosive nature.

In large scale manufacturing operations, it is practically
imperative that these highly volatile thinners and solvents be
used, for modern efficiency would not permit the use of the slow
drying oils such as linseed or similar oils alone, and depend
entirely on absorption of oxygen from the air for drying or
hardening of the finish. ’

Very often specially built ovens or closets are provided
for the drying or baking processes and these are frequently
heated to hasten evaporation of the solvent and thinner.

In most of these finishing operations there are present,
therefore, definite hazards in the form of highly flammable
vapors in the atmosphere in and surrounding the application and
drying departments, its extent depending upon the effectivenes
of the ventilation system. .

Not all finishing materials should be classed as highly
hazardous from our viewpoint. For instance, some enamels
consist of drying oil varnishes containing finely ground pigments
without highly flammable thinners or solvents and are not classed
as hazardous from the standpoint of easy ignition. Others of
the non-hazardous class are water-japans and paints containing
only drying oils and pigments. But it should be emphasized that
the addition of hazardous thinners to any of these materials,
such as is necessary to promote quick drying, immediately
transfers them to the hazardous class. The engineer should
make careful investigations as to the type of material which
is to be employed.

29

In the application of the coatings, the following
methods are used:

The Brush Process is used more commonly in small scale
operations and the work usually dried in the air without special
heat. Therefore, it is common to find benzine, substitute
turpentine or other volatile thinners freely used.

The Dippigg Process used in both small and large scale
operations cons s s of suBmerging the articles in an open tank
of the coating material. The degree of hazard as before is
dependent on the type of thinner used, naphtha, benzine and
alcohol being the most common. When higher flash point thinners,
such as kerosene or turpentine are employed, the hazard is
materially lessened, but the vapors of all are flammable to a
greater or lesser degree. After the articles have been dipped,
they are usually placed or hung on continuous conveyors which
travel through a heated drying oven to hasten evaporation of
the thinner. In smaller plants the articles may be dried by
the "batch" method in which the articles are simply hung on
racks in drying ovens or cabinets and removed when dry. In
either case, a considerable amount of flammable vapor is present
within the oven or dryer. While some dependence is placed on
artificial or natural ventilation for the removal of the vapors,
it is imperative that all sources of ignition be removed or
guarded.

The Spray gpplication of coating materials has come into
very wide use and its growth has been attended by numerous fires
and accidents. Spraying is usually done in booths or under
hoods, all ordinarily equipped with positive artificial means
of ventilation. The booths vary in size from that required to
accomodate small articles of furniture to the mammoth tunnel
type booths required for railroad coaches and automobile bus
bodies. Air brushes are used to secure an even and smooth
finish. The coating material may be paint, varnish, japan or
enamel consisting of a mineral, resinous or oil varnish usually
thinned with a flammable volatile liquid such as alcohol, naphtha,
benzine, or substitute turpentine to permit of ready flow. But
more hazardous from our standpoint are the pyroxylin varnishes
or "lacquers” which have already been mentioned. When such
materials are used in spray finishing, we not only have the
atmosphere charged with the vapors of a highly flammable solvent
or thinner, but also with a fine dust or residue which is in
itself an explosive. This dust or residue is highly combustible
and very easily ignitable, decomposing at low temperatures,
often spontaneously. It is found that the dust forms a coating
on the interior of the spray booth or hood and in the vent pipes
connected to it, necessitating extreme caution to prevent
ignition. The hazard of this type of lacquer is considerably
reduced when a base of cellulose acetate is used rather than
cellulose nitrate, but we still have the hazard of the thinner
to contend with. Much could be written regarding the hazard of
pyroxylin spraying operations, but space does not permit.

 

 

50

All rooms or departments containing finishing processes,
including the drying or baking ovens, should be considered as
candidates for classification as Class I locations except those
where non-hazardous finishing materials are used. A possible
exception might also be made in the case of small scale operations
where only a quart or two of the finishing material is exposed
at a time and applied by the bruSh method.

In factories where the painting, dipping or spraying
Operations are of considerable volume, separate cut-off rooms are
provided for the storage and mixing of the paints, varnishes and
lacquers. Here we usually find open containers in which the
mixing is done and as a result, when flammable volatile thinners
are used, we can expect that considerable explosive vapor will be
present, the amount depending upon the efficiency of the ventilating
system. Where pyroxylin varnishes are used the hazard is, of
course, much greater. Often the stirring, mixing and clarifying of
these materials are done mechanically by motor driven agitators.

It is necessary that these rooms be considered as Class I locations
and all lighting and power apparatus and wiring installed
accordingly.

The flammable volatile liquids used as thinners and
solvents, and sometimes the varnishes also, when used in large
quantities are generally stored in underground tanks outside of
buildings. This necessitates the employment of pumping apparatus
to transfer the liquids from the tanks to the mixing room. The
hazard of this operation is similar to thatciescribed under "Paint
and Varnish Manufacturing" in this thesis to which section reference
should.be made.

The extent of the hazardous area is a matter for conjecture.
When spray booths or hoods, which effectively confine the vapors
and residue and which are adequately ventilated, are used, it
is prObable that the hazardous area may be considered to extend
to a distance of from ten feet to twenty five feet, depending
on arrangement, beyond the spraying operations. In the case of
dip tanks and drying ovens, it is necessary to consider the
entire room containing this equipment as a Class I location, for
with open dip tanks it is probable that the hazardous vapors will
diffuse quite thoroughly throughout the room, especially in event
of failure of the ventilating system.

51

THE PETROLEUM INDUSTRY

The petroleum.industry may be divided into several
divisions as follows:

1. Production in the oil fields.

2. Transportation by pipe lines, tank cars or ships.
3. Refining.

4e Storage.

5. Distribution.

In the first division we are dealing with crude petroleum
which should be considered a hazardous flammable liquid as the
lighter petroleum vapors are given off at ordinary temperatures.
Due consideration must therefore be given the proper installation
of electrical apparatus in or about places where these vapors are
likely to be present in explosive mixtures. In the oil fields
such locations are likely to be the enclosed pump houses at the
rigs or elsewhere where pumps are driven by electric motors and
in which electric lighting may be employed. Such pump houses and
any other similar buildings are to be designed as Class I locations.
Motor driven pumps located in the open without enclosure would
probably not be in a hazardous atmosphere due to the dilution of
the mixture by the free circulation of air. However, it is
possible that the burning out of an Open type motor would cause
sufficient heat to ignite the oil or its vapors and therefore,
the use of motors approved for Class I locations is to be recommended
even.when in the open.

In the second division, transportatiop, there is little
application of electrical safety rules except in the case of long
pipe lines where pumping or booster stations are located at
intervals along the course of the pipe line between the oil
fields and the refinery. The pumps of such stations are often
electric motor driven and this, with the fact that the stations
are usually electric lighted, warrants the room or compartment
in which the pumps are located being classed as Class 1 locations
and the electrical equipmentrnedstp‘hainstalled accordingly.

In the refiner , the third division of the industry, we
find first, the hazards of pumping the oil from the pipe lines to
storage tanks, and the precautions suggested in the preceding
paragraphs apply. From.these storage tanks the crude oil is pumped
to steam or fire heated stills where the oil is distilled fractionally,
producing the lighter liquids such as benzine and naphtha first,
then gasoline and on down to the residue of paraffin and tar. The
process of “cracking has come into considerable use. This process
is, in effect the destructive distillation of certain components
of petroleum to secure a preponderance of certain products, in
late years, notably motor gasoline. The hydrocarbon gases, ethane,
propane and butane are evolved When petroleum is heated and, when

32

these are collected from.the stills and compressed, they yield a
liquid usually called cymogene. The principal constituent is
butane, a gas at ordinary temperature and pressures, and this as
well as ethane and propane are readily flammable. These gases

are used for heating and lighting and as refrigerants. Attention
is called to the discussion under "Compressed Gas Systems." Re-
distillation apparatus is often provided to effect greater

purity and uniformity. To remove offensive sulphur odors often
present in the raw gasoline and kerosene and to improve color,
deodorizing and decolorizing facilities are provided, usually
consisting of large upright shells called"agitators" where the
liquids are treated with acid, meter and neutralizing wash. These
”agitators" are generally associated with other towers where
filtration, neutralizing and other treatment proceeds. After final
treatment, in accordance with the needs of the particular grades
of products, the liquids are pumped to the storage tanks.
From.these tanks the oils are withdrawn for distribution by tank cars
or trucks. With the exception of offices, shops, lubricating oil
warehouses and probably laboratories, there are few, if any,
buildings of an oil refinery which should escape classification

as Class I locations. There is much handling of oil by pumps and,
although internal combustion or steam engine power is used to a
considerable extent, electric power is gaining in use. Electrical
hazards have long been recognized in oil refineries and an attempt
has been.made to pretect against these hazards by isolating motors
and control apparatus so as to place them outside of the hazardous
area, but this is not always a convenient procedure.

In the fourth division, stora e, we find the various
petroleum oils stored in buried or anve ground tanks at the
refinery and at the bulk or wholesale distributing stations.
There are no electrical hazards conneted with such storage except
in the process of pumping oil from tank cars to the storage tank.
Centrifugal or rotary pumps are used for this duty and these are
usually motor driven. In some cases, these pumps and motors are .
placed in the open without enclosure, but more often are located
within pump houses or even in a warehouse used jointly as a
storehouse for lubricating oils, salesroom and as a shelter for
the punmsand.their driving motors. Attempts have been made to
divide the pump house into two compartments, one containing the
pump and the other its motor and control apparatus. Unless the
partition so dividing the pump house is practically vapor-tight,
it should not be depended upon to prevent the passage of vapors
from the pump compartment to the motor compartment. The proper
protection of the shaft opening alSo presents an obstacle which is
difficult to surmount. One method often used is to place the
motor and its control apparatus outside of the pump house in
the open air, but this is not convenient nor practicalin many
cases. It is certain that the room or compartment containing the
pump or pumps must be classed as a Class I location with regard

55

to both the lighting and power installations. Attention should be
called to the concluding section of thisnpaper on "Loss Record"

which lists several fires and explosions originating in oil pump

houses from electrical causes.

In the distribution of petroleum products, the fifth division
of the industry, we are concerned first, with the delivery of the
gasoline or kerosene or other liquid petroleum products to the
buried tanks at gasoline filling stations or industrti plants.
Such delivery is generally accomplished by tank trucks which are
filled by gravity or by pump from the bulk station tanks or tank
cars, and emptied into the buried tanks. The hazard of pumping
is similar to that discussed in the preceding paragraph and needs
no further comment. With the introduction of motor driven gasoline
discharge devices, (or meter pumps), into automobile filling
stations, a considerable hazard might have been introduced had
not fire prevention engineers been quick to sense the need for
compliance with rigid standards regarding the nature of the motor,
and its wiring and control apparatus with which the device is
equipped. The standards of the Underwriters' Laboratories specify
compliance with Class I rules before approval of discharge is given.
In the ordinary filling" station we usually find the discharge
devices or pumps on an "island" under or immediately beyond a
canOpy attached to the station shelter or office. The hazardous
area, coming under the rules of Class I locations may be assumed
to be confined to the discharge devices or pumps themselves and
does not extend to the interior ofthe shelter. The construction
of the discharge devices and their wiring will be considered
later in this paper. When discharge devices are installed within
garage buildings, the rules of Article 55 "Garages" , of the

ational Electrical Code apply and, therefore, this phase of the
problem will not be discussed here.

PAINT AND VARNISH MANUFACTURING

Paint consists principally of a pigment and a vehicle with
which are usually included "driers" and solvents. In the preparation
of the pigments there are no electrical hazards from the standpoht
of Article 32 except for possible minor dust explosion hazards in
the pulverizing of carbonaceous material in the preparation of
black pigments. The various drying oils used in the manufacture
of paints are of high flash pointtype and therefore do not easily
give off flammable vapors. However, to reduce the viscosity of
paint to permit of ready application, a volatile solvent is used,
commonly turpentine, but often more flammable volatiles such as
naphtha and benzine. In the manufacture of paints, special pre-
cautions need be taken so far as the electrical installation is
concerned, only in that section where the thinners are added and
in that where the finished paint is strained and placed in

55

to both the lighting and power installations. Attention should be
called to the concluding section of thisnpaper on "Loss Record"

which lists several fires and explosions originating in oil pump

houses from electrical causes.

In the distribution of petroleum products, the fifth division
of the industry, we are concerned first, with the delivery of the
gasoline or kerosene or other liquid petroleum products to the
buried tanks at gasoline filling stations or industrhd plants.
Such delivery is generally accomplished by tank trucks which are
filled by gravity or by pump from the bulk station tanks or tank
cars, and emptied into the buried tanks. The hazard of pumping
is similar to that discussed in the preceding paragraph and needs
no further comment. With the introduction of motor driven gasoline
discharge devices, (or meter pumps), into automobile filling
stations, a considerable hazard might have been introduced had
not fire prevention engineers been quick to sense the need for
compliance with rigid standards regarding the nature of the motor,
and its wiring and control apparatus with which the device is
equipped. The standards of the Underwriters' Laboratories specify
compliance with Class I rules before approval of discharge is given.
In the ordinary filling station we usually find the discharge
devices or pumps on an "island” under or immediately beyond a
canOpy attached to the station.shelter or office. The hazardous
area, coming under the rules of Class I locations may be assumed
to be confined to the discharge devices or pumps themselves and
does not extend to the interior ofthe shelter. The construction
of the discharge devices and their wiring will be considered

later in this paper. When discharge devices are installed within
garage buildings, the rules of Article 53 "Garages" , of the

ational Electrical Code apply and, therefore, this phase of the
problem will not be discussed here.

PAINT AND VARNISH MANUFACTURING

Paint consists principally of a pigment and a vehicle with
which are usually included "driers" and solvents. In the preparation
of the pigments there are no electrical hazards from the standpoht
of Article 32 except for possible minor dust explosion hazards in
the pulverizing of carbonaceous material in the preparation of
black pigments. The various drying oils used in the manufacture
of paints are of high flash pointtype and therefore do not easily
give off flammable vapors. However, to reduce the viscosity of
paint to permit of ready application, a volatile solvent is used,
commonly turpentine, but often more flammable volatiles such as
naphtha and benzine. In the manufacture of paints, special pre-
cautions need be taken so far as the electrical installation is
concerned, only in that section where the thinners are added and
in that where the finished paint is strained and placed in

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containers. The thinning is done in tanks equipped with
mechanical stirring apparatus, usually motor driven. The
presence of these flammable volatile thinners in more or less
Open containers and tanks results in the evolution of a con-
siderable amount of vapor in the room or section where these
materials are handled and, therefore, the application of the
rules of Class I is required. In small plants the thinners
may be received and dispensed out of drums. Reserve supplies
are usually stored in a detached building, and if the drums
are kept sealed no special precautions are needed with regard
to any electrical apparatus installed in the storage house.
If drums are Opened in this detached building, the lighting
installation and any other electrical wiring or apparatus in
it must comply with the rules for Class I locations. In large
paint factories, the thinners are handled in quantities large
enough to warrant their purchase in tank car quantities. This
involves storage in outside buried tanks and a pump installa-
tion to transfer the liquid into the main factory as needed.
The pump house or compartment, whether within or outside the
main building, becomes a Class I location and must be treated
accordingly.

Varnishes are of several types including natural var-
nish, oIl varnish (which dries by oxidation), spirit varnish
(which dries through evaporation of solvent), pyroxylin var-
nish, and water varnish, Some of these are often referred to
as enamels, japans and lacquers. Inasmuch as there are no
unusual electrical hazards associated with the preparation
or use of natural and water varnishes, we shall not discuss
them here. Oil varnish is produced by melting resin, boiling
with a drying oil, thinning with turpentine or other solvents,
cooling, filtering, ageing and finally packing in containers.
The process of adding the thinner is practically identical
with that discussed in the manufacture of paint. Obviously,
the hazards are identical to those of paint manufacture from
our viewpoint, and the rooms or sections from the point where
the thinners are introduced up to the point where the con-
tainers are sealed must be considered as Class I locations.

 

Spirit Varnishes are made by dissolving a resin such
as rosin or sheIIac in alcohol, acetone, benzine or turpentine.
The preparation is accomplished by placing the resins and sol-
vents in revolving wooden drums or in a wooden tank kept
agitated until the resins are thoroughly dissolved. The
usual straining and packing process follows. The use of large
quantities of flammable volatile solvents requires compliance
‘with the rules for Class I locations throughout, excepting
the warehouses where the resins and sealed containers of the
finished products are stored. The handling and storage of
the solvents are of a similar nature to that discussed under
paint manufacture and the hazards are identical.

 

55

gyroxylin Varnishes 23 Lacquers, as they are more fre-
quently called, are made by dissolving a cellulose nitrate,
either guncotton or pyroxylin in a solvent. Amyl acetate or
"banana oil" is the solvent most commonly used. To this solu-
tion, flammable volatile thinners such as benzol or alcohol,
are usually added to obtain free flow of the liquid, especially
when intended to be used in spray painting processes, The
process of manufacture is extremely hazardous and usually
more stringent requirements than those imposed by the rules
for Class I locations are observed. There are several types
of special japans, varnishes and enamels manufactured, includ-
ing clear pyroxylin lacquers for coating brass articles.
In some instances bronze or aluminum powders are combined with
clear pyroxylin lacquer to produce decorative effects. The
preparation of the lacquer is attended with the same hazards
as discussed under pyroxylin varnishes with the addition of
the dust enclosion hazard when the bronze or aluminum powders

are prepared.

56

DRY CLEANING AND DRY DYEING

The removal of dirt, grease and stains from clothing,
textiles, rugs and other similar articles by the use of a liquid
solvent is known as dry cleaning. While non-flammable solvents,
such.as carbon tetrachloride, are sometimes used for small scale
cleaning, the use of a flammable volatile solvent such as naphtha
is almost universal in dry cleaning operations due to its effective-
ness and quick drying qualities. Efforts have been made to develop
a high flash point cleaning solvent, and of these Stoddard's
solvent is an example. This material is used to some extent,
but because of its reported slow drying and clinging odor
it is not entirely satisfactory. Therefore, in the large majority
of dry cleaning plants, we can expect the use of a highly
flammable volatile solvent.

There are four common methods of dry cleaning as
follows:

l.”Scrubbing" by immersion and agitation in the solvent
in Open vessels.

2."Scouring" by brushing the article with the solvent
or solution.

3. "Spotting" by the local application of the solvent
or solution to remove spots or stains, usually to
supplement methods 1 or 4.

4. "Washing" by immersiOn and agitation in the solvent
in closed containers. l ~

Scrubbing is the method employed when the character of the
articles to Be cleaned, is such.as to prevent their being cleaned
‘by the more usual method of "washing”. Such.articles are placed
in a tub or other vessel containing the solvent where they are
scrubbed by hand. Various insurance regulations and governmental
ordinances have imposed severe regulations on the use of this
method, one of whfii1states that not more than a total of three
gallons of flammable volatile solvent shall be exposed in open
containers. Even with amount of solvent there is considerable
explosive vapor in the atmosphere of the room and necessarily
such a room comes definitely under the Class I classification.

The Securing method.entails hazards similar to thoseof
scrubbing. However, in this method the article to be cleaned
is laid on a table and secured or brushed with a hard brush
and the solvent, usually naphtha. As in the preceding method
the amount of flammable solvent permitted to be exposed is
limited to three gallons, and as before, this room.also should
be classed as a Class I location.

37

S ottin as before stated, is usually an adjunct to the
other meEHods of cfleaning to remove spots not removed by the
other methods. It consists of applying the solvent locally to
spots of grease, paint or dirt. Very often a mixture of solvents,
such as one of naphtha and carbon tetrachloride or alcohol and
carbon tetrachloride, is used to produce a solvent of high flash
point. However, there is no assurance as to the composition of
such mixtures and, therefore, to be safe, one should treat them
as hazardous liquids. After the articles are "spotted" they are
hung on racks to dry and are then pressed. Although fire preven-
tion regulations stipulate that the flammable solvents used shall
be limited in quantity to one quart, and this in safety cans, it
may be reasonably expected that there will be considerable ex-
plosive vapor in the spotting room, especially Where a consider-
able volume of cleaning is done and therefore, the spotting
room should be regarded as a Class I locaflon. The spotting
method is that commonly used in small pressing parlors and in small
hat cleaning establishments. It is not intended that such small
establishments be made subject to all of the rules for Class I
locations, but reasonable precautions should be taken to avoid
electrical arcs or sparks in the vicinity where the flammable
solvent is used. Numerous fires of electrical origin have
occurred in.suCh hat cleaning places.

The Washin method is the one most commonly employed and
is probably of most importance to us due to the involved nature
of the process. In this method the articles to be cleaned are
tagged, searched for foreign materials, and then placed in a
dusting machine where loose dirt is removed. The articles are then
placed in the washing machines. These are machines in the form
of cylinders arranged to revolve and having openings capable
of being tightly closed, for the insertion of the articles to
be cleaned. When the articles are in the machine the cylinder
is partially filled with the solvent, usually naphtha, and the
cylinder revolved for a certain time. The solvent is then drawn
off and the clothes removed and placed in an extractor. The
extractor consists of a basket arranged for rotation within a
metal shell, in effect, a centrifugal drier. This is the first
drying Operation, after which the articles are transferred to
drying tumblers where the drying is completed. The drying
tumbler consists of a cylinder of wire screening enclosed
within a tight metal housing. Heated air is circilated through
the housing while the cylinder is revdyed.by mechanical means,
causing the articles to be tumbled about while exposed to the
heated air. This air is exhausted to the outside. After drying
by this method is completed, the articles are removed, spot-
cleaned, if necessary, and then pressed. The regulations of
the N.F.P.A. provide that if the drying equipment is not in a
separate building, that it be in a room cut off from that con-
taining the washers by a standard fire wall.

An important part of dry cleaning operations is the re-
covery of the solvent and the facilities used in handling the
solvents. Regulations require that flammable Solvents be
stored in buried tanks. This requires pumps with a system of
piping leading from the tanks to the washers. After the
liquid has been drawn from the washers, it is necessary that
it be clarified to permit its being used again. The centri-'
fugal clarifier is used for this purpose, it being located near
the washer when the continuous system of clarification is used.
For further purification of solvents, stills, condensers and
settling tanks are used.

It is clear that in all of the locations of a dry
cleaning plant so far mentioned, there is present or likely
to be present, a considerable quantity of flammable vapors.
Necessarily then, they must be classed as Class I locations,
including the rooms containing the washers, extractors, tumblers,
clarifiers, stills, condensers and pumps. Ventilation is impor-
tant, and in the more modern plants considerable effort is made
to obtain proper ventilation. Motor driven fans are used, these
being either mounted in the wall or in the ventilating ducts.
Dry cleaning plants have long been recognized as a hazardous
class, for many state and municipal ordinances even yet prohibit
the installation of motors and controllers in dry cleaning and.
drying rooms. However, in many instances these ordinances are
being amended permitting the installation of electrical appar-
atus, provided the requirements of Class I are met. This will
permit the use of individual motor drives on the various machines,
eliminating what any have been more severe hazards introduced
when group drives were used, and the motor located outside of
the hazardous area. This latter practice usually involved
long line shafts with numerous bearings and considerable rapidly
moving belting, thus presenting the possibility of overheated
bearings and static discharges from belting, both of which have
been the cause of many fires and explosions in dry cleaning
plants. Of the areas or sections which might not be considered
subject to Class I rules are the delivery room the receiving
and dusting room and the boiler room, proVided these are so cut
off as to be free from flammable vapors.

Dr D~ein is the process of dyeing materials or articles
in a so ion of dye colors and flammable liquids This necess-
itates the use of drying equipment and the operations are attended
by the evolution of flammable vapOrs in the room or section in
which the dyeing operations are carried on. Such rooms or sec-

tions should be classed as Class 1 locations.

39

GAS WORKS

Illuminating gases used in this country are of two
varities, known as coal gas and water gas.

Water Gas is manufactured usually by the Lowe process
which depends-upon the decomposition of water in the form of
steam in contact with incandescent coal or coke contained in a
generator. The gases so produced are led into contact with a
spray of partially vaporized oil and the two are passed over
highly heated surfaces, first in a carburetor and finally in a
superheater, resulting in the gasification of the oil vapors
fixed in the presence of non-luminous water gas. This forms a
thoroughly fixed and permanent carbureted water gas. The
generator, carburetor and superheater are steel shells lined
with fire-brick with suitable Openings for charging and firing.
The gas is now ready for purification which is accomplished
by the washer, to remove tar; the washer, scrubber, to effect
further removal of tar; the condenser, to cool and purify the
gas; the shaving scrubber, to remove moisture from the gas and
take out what little tar remains. The gas at this point contains
carbon dioxide and sulphuretted hydrogen which are removed by
oxide purifiers sometimes located within a building, but in newer
installations in the yard partly buried. The gas now passes
through meters into the familar gas holders and thence into
the pipe distribution system. ..

Coal Gas is made by the destructive distillation of
coal in retorts-externally heated. The retorts are filled with
gas coal and allowed to heat for five or six hours. The heat
causes the evolution of the volatile gases leaving behind in-
candescent coke which is drawn off, cooled and finally dumped
in the yard. The gas, as it leaves the retort, passes into a
standpipe, the outlet of which dips below a water or weak
ammonia seal in what is termed the "hydraulic main." Thts causes
the gas to be cooled somewhat as well as causing the removal of
the bulk of the tar and ammonia liquor. A large drum is attached
below each hydraulic main in which the tar collects. An exhauster
fan now draws the gas through a condenser which further cools
the gas and removes more of the tar and ammonia._ The balance of
the tar is removed by the tar extractor through which the gas
now passes. The scrubbers come next in the process, these being
for the purpose of separating out the naphthalene and ammonia
that remains. As in the water gas process, the oxide purifiers
effect final purification in removing hydrogen, sulphide, carbon
disulphide and carbon dioxide and the gas is now passed through
meters and thence to the storage holders ready for distribution.
As byproducts in the manufacture of coal gas, coke, tar and
ammonia liquor are derived. The latter is sometimes reduced to
ammonium sulphate by distillation and surface contact with
sulphuric acid,and sold in the solid form. The tar is shipped
to chemical plants where it is used as the basis for the
production of a variety of dyes and other chemicals.

40

The possibility of leakage of gas is present continually
during the process of gas manufacture, especially in the con-
denser building, purifier room, meter room, valve and governor
rooms. Special precautions to remove all sources of ignition
are imperative. All parts of gas plants should be regarded as
Class I locations with the exception of the office building,
shops, change and locker building and similar buildings not
associated with the actual production Of gas. In some coal
gas plants, facilities are provided for the crushing of coal
and in both water and coal gas plants considerable quantities
of coal are handled. It is very probable that in some of the
less efficiently arranged plants the dust conditions incidental
to this handling of coal are such as to warrant classifying
the coal handling and coal crushing departments as Class II
locations.

41

CHEMICAL WORKS
General

Owing to the extremely large variety of chemicals being
manuafctured and the many and varied types of processes employed,
it is Obviously impractical to attempt to include herein a
discussion even approaching completeness. Chemical works, as such
should not all be thrown indiscriminately into the hazardous
classification. Many are concerned with the production of heavy
chemicals of a non-hazardous nature. Some may produce relatively
non hazardous products, but the processes or materials employed
in their making may be extremely hazardous. On the other hand,
the materials, and Often the methods, used .in the manufacture
of a distinctly hazardous product, may be of a relatively dafe
nature. Hence, the need for detailed study of each individual
case as it appears, to determine what the hazards are and
what precautions need be observed in the selection and in-
stallation of electrical equipment. There are some types of
processes which are sufficiently general and important to warrant
brief discussion.

The production of the acids, nitric, sulphuric and hydro-
chloric, as well as the less common boric, hydrofluoric and
phosphoric acids, is not usually attended by hazards of ready
flammability in materials or products and, therefore, little
if any, application of the rules of Article 32 is involved
in the works where they are made. This is also true of many
of the heavy chemicals and alkaline salts such as sodium
sulphate, sodium.bisulphate, alum, sodium carbonate (except
when made by the electrol tic process which may introduce the
hydrogen explosion hazard , and others.

Ammonia Manufacturing

Ammonia is manufactured by several processes including the
synthesis method which is dangerous because of the free hydrogen
evolved during one step Of the process and the production of coal
gas as the base from which the needed gases are obtained. The
sections where this work is carried on are clearly Class I
locations due to the extremely explosive nature of hydrogen and to
a lesser degree, coal gas. Thec anamid process is used to a con-
siderable extent and, briefly, consists first, of forming lime
'by the calcining of limestone in a kiln. The lime and coke is
then fed into electric furnaces thus forming calcium carbide
which is pulverized and brought tOgether with nitrogen in the
presence of electric heat to form.cyanamid. The nitrogen used
in this method is usually produced by partial distillation of

42

liquid air and therefore, a plant for the purpose of liquifying
and distilling air is an adjunct to the main process. Ammonia
gas is formed in the next step by introducing water and caustic
soda into a large steel cylinder called an autoclave which is
then charged with powdered cyanamid. The autoclave is then
sealed and the reaction started by means of steam and it

then continues by its own heat. The final step involves the
neutralization of nitric acid with ammonia and the evaporation
of the solution to secure the salt, ammonium.nitrate, which

is crystallized and dried. With the cyanamid process are
associated several forms of electrical hazards Which require
the application of the rules of Article 52. First, the handling
and pulverizing of coal Which may introduce dust explosion
hazards in the section of the plant where this is done, thus
requiring compliance with rules for Class II locations. The
production and handling of calcium carbide may entail the
evolution of acetylene should it come into contact with

water, hence, the need for application of the rules under

Class I to prevent ignition and subsequent explosion. The
danger point for ammonium nitrate is 350 degrees Fahrenheit
and should the material become tOo dry it can be easily ignited
by a spark, flame or overheating. Considerable electrical
apparatus is installed in plants producing ammonium nitrate

by the cyanamid process, due to the use of electric furnaces
and the rules for Class I locations should be followed as far
as they apply. '

Wood Distillation Products

The distillation of wood in closed retorts is an important
chemical process as there is produced, in addition to charcoal,
either by condensation or auxiliary chemical processes, a wide
variety of valuable materials. These include acetic acid, wood
alcohol, carbon monoxide, methane, acetone, metacetone, aldehyde,
acetylene, naphthalene and hydrogen. In strictly chemical
works, the gases, carbon monoxide, methane and hydrogen are
piped back and burned under the retorts. The liquid which
results from the condensation of the volatiles driven from the
wood by distillation is a complex material known as crude
pyroligneous liquor. This, in the form of the condensate,
separates into three layers, namely, tarry oils, pyroligneous
acid and tar, each of which may be drawn off at different
levels in the condensers. From the tarry oils and tar, creosote
and tar oils are obtained. The pyroligneous acid is commonly treated
with lime or sodium carbonate and distilled to give wood alcohol
and brown acetate of lime, or is distilled to give wood alcohol
first, following which the acid is nemralized with lime to form
gray acetate of lime. These acetates anscften involved in
further processes to form acetone, acetic acid and other
chemicals or solvents. Frequently the acetates are shipped
and further treated at a separate plant. '

43

The hazards, from our viewpoint, associated with wood ~
distillation plants are those represented by the presence of
the vapors of alcohol, acetone and naphthalene. The handling
and storage of liquid alcohol and acetone are also hazardous,
requiring electric motor driven pumps in many instances. All
sections of a wood distillation plant from the retorts to
storage and shipping department should be considered as Class
I locations. Shops, office buildings, laboratories and similar
buildings where the hazardous conditions are not present are
naturally eliminated.

Coal Tar and Its Products

As in the case of wood tar, a host of varied products
are obtained from the tar produced from the destructive distilla-
tion of coal. Coal tar is a by-product of coal gas plants and is
also secured from.by-product coke ovens. The industry may be
divided into four parts which we shall discuss individually.

Coal Tar Distilling Plants, the first division, are
generally in conjunction with gas or coke works and the chief
operation is that of distilling. By the first distillation‘
processes the coal tar is separated into several fractions,
namely; light oil, middle or carbolic oil, heavy or creosote
oil, anthracene oil and residual pitch. The light oil is re-
distilled, washed and purified and then fractionally re-
distilled, yielding benzol, toluol, xylol and solvent naphtha,
all flammable volatile liquids. Some of these such as benzol
or benzine are used as raw materials for intermediate dye-
stuffs and explosives. The middle oil is usually permitted tO'
settle in large pans, allowing crude naphtha to crystallize
out. These crystals are then washed, melted and purified
in agitators with sulphuric acid and neutralized with caustic
soda. It is finally redistilled and becomes the final white
product familiar to us in the form of moth balls. It is a
hazardous material as has been previously pointed out. After
the naphthalene has been taken out of the middle 011 there
remains phenol and cresol. This is treated with caustic soda,
causing the phenol to separate as an Oily layer which is drawn
off fractionally, distilled and redistilled. Neither phenol
nor cresol are particularly hazardous, but the former, more
commonly known as carbolic acid whenvin the refined ferm, is
used in the manufacture of high explosives and dye stuffs. The
heavy oil is generally used as a preservative for wood railroad
ties and piling without further treatment and is known to the
trade as creosohx The anthracene oil is permitted to settle
in pans and after artificial cooling yields anthracene, a
crystalline substance. This is washed in solvent naphtha and
purified by treatment with caustic, distillation and further
washing with naphtha. Anthracene is.the base for alizarine dyes,

44

a valuable group and is not in itself hazardous from our view-
point. The pitch, the residue of the coal tar, is cooled when
drawn from the still and solidifies in the barrels used for
its shipment. It is employed for roofing materials and.road
making.

It will be noted that practically throughout the process
of coal tar distillation, we are dealing with the distillation
and handling of flammable volatile liquids and in the case of
naphthalene,with sxhighly flammable solid. Special efforts are
made to divide the plant into a number of fire areas, either
by the coretruction of separate buildings or by fire walls.
Class I rules should prevail for the installation of electrical
equipment in all departments except those where the heavy oil
and pitch are handled, provided these are likely to be free
from.cxplosive vapors. The power house, offices, laboratories
are likeWise exempted as they are usually outside the hazardous
area. Some consideration may have to be given to the electrical
installation in the power house if pulverized fuel is used. In
this case, a portion of the power house may be classed as
a Class II location.

Coal Tar Intermediates, the production of which forms the
second diviETOnfEf thawindustry, involves processes which develop
raw materials or bases for the manufacture of explosives, dye-
stuffs and tanning materials from the coal tar distillates
which were disCussed in the preceding section. Hence, the term
”intermediates.” The manufacture of these intermediates is
carried on in plants or units moreor less separate and distinct
from others. The more important coal tar distillates used in
the manufacture of intermediates are benzol, toluol, naphthalene,
phenol, and anthracene. The operations and processes by which
intermediates are prepared are so great in number and nature
that volumes could be written on that subject alone. It should be
emphasized, however, that in most cases, flammable volatile
liqiids or highly flammable solids are involved, necessitating
extreme caution in the selection and installation of electrical
apparatus and requiring compliance with Class I rules in all
locations where these hazardous materials or their vapors are
hkely to be present. Careful study of specific processes and
plants is necessary to form an accurate opinion of the conditions
which may be expected. ‘

 

Coal Tar Eyg'manufacture is the third division of the

. coal tairiihfiitry and, as in the case of the intermediates, there
is a vast number of dyestuffs and a wide variation in the
processes by which they’are made. Without going into detail, it
should be mentioned that the manufacture of most dyes is attended
by hazards ranging from those involving the use of flammable

45

solvents to those where nitration processes are used Which result
in materials which are at times high explosives. As an example,
nitro dyes are made from the nitration products of phenol and
include the explosive picric acid. The grinding of dyes to

reduce them to powdered form may also introduce severe hazards
from our viewpoint, as thereamay be present in the room or
section where the grinding is done considerable finely divided
flammable dust. Here, as in the case of intermediates, the engineer
is forced to study each.oase individually. In some'instances,
more rigid precautions than those prescribed by the rules for
Class I locations may needs be applied, even to the extent of
excluding all electrical apparatus from certain locations.

Coal Tar Ex losives whose production represents the
fourth division 0 e n ustry, are made by the nitration Of
distillates or intermediates such as benzol, toluol or phenol
which yield mono-nitro benzol, tri-nitro-toluol (T.N.T) and
picric acid respectively. Necessarily, extreme care is taken
‘to remove all sources of ignition when these materials are
made and handled, and in this connection, due attention is given
to the installation of electrical apparatus. In some cases,
even electric lights are placed outside the hazardous area
with glass covered openings provided to permit the entrance of
light into the hazardous area. The manufacture of these ex-
plosives is usually in the hands of firms which are thoroughly
aware of the hayards involved and Who take upon themselves
full responsibility for the safety of employees and property.

General Organic Chemical Processes

In the production of organic chemicals generally, there
are several processes which might well be discussed briefly at
this point in an endeavor'to assist the engineer to determine
the treatment of prOposed electrical installations.

Sulponation is the process of treating a hydrocarbon
with sulphuric acid, sometimes encouraged by the application of
heat and pressure. Materials commonly sulphonated are benzol and
naphthalene, and irithe process one can expect the evolution
of flammable vapors. ‘

 

Chlorination is the process of treating a hydrocarbon
with hydrochIOric acid in kettles or closed retorts. Toluol and
benzol are frequently involved in chlorination processes, and
in many cases their vapors, which are explosive, escape into the
room.and may be ignited by flames and electrical sparks or arcs.

 

Nitration consists in treating an organic material with
mixed afiIpEfiiiE—and nitric acid. Here again we have a condition
where the flammable vapors of the material, such as benzol,
toluol or phenol may be liberated into the room.

45

solvents to those where nitration processes are used which result
in materials which are at times high explosives. As an example,
nitro dyes are made from the nitration products of phenol and
include the explosive picric acid. The grinding of dyes to

reduce them to powdered form may also introduce severe hazards
from our viewpoint, as thereamay be present in the room or
section where the grinding is done considerable finely divided
flammable dust. Here, as in the case of intermediates, the engineer
is forced to study each.case individually. In some'instances,
more rigid precautions than those prescribed by the rules for
Class I locations may needs be applied, even to the extent of
excluding all electrical apparatus from certain locations.

Coal Tar Ex losives whose production represents the
fourth division of the Industry, are made by the nitration of
distillates or intermediates such as benzol, toluol or phenol
which yield mono-nitro benzol, tri-nitrO-toluol (T.N.T) and
picric acid respectively. Necessarily, extreme care is taken
yc> remove all sources of ignition when these materials are
made and handled, and in this connection, due attention is given
to the installation of electrical apparatus. In some cases,
even electric lights are placed outside the hazardous area
with glass covered openings provided to permit the entrance of
light into the hazardous area. The manufacture of these ex-
plosives is usually in the hands of firms which are thoroughly
aware of the hayards involved and who take upon themselves
full responsibility for the safety of employees and property.

General Organic Chemical Processes

In the production of organic chemicals generally, there
are several processes which might well be discussed briefly at
this point in an endeavor'to assist the engineer to determine
the treatment of proposed electrical installations.

Sulponation is the process Of treating a hydrocarbon
with sulphuric acid, sometimes encouraged by the application of
heat and pressure. Materials commonly sulphonated are benzol and
naphthalene, and irithe process one can expect the evolution
of flarmable vapors.

 

Chlorination is the process of treating a hydrocarbon
with hydrochloric acid in kettles or closed retorts. Toluol and
benzOl are frequently involved in chlorination processes, and
in many cases their vapors, which are explosive, escape into the
room.and may be ignited by flames and electrical sparks or arcs.

 

Nitration consists in treating an organic material with
mixed sfiIpEEFIE'and nitric acid. Here again we have a condition
where the flammable vapors of the material, such as benzol,
toluol or phenol may be liberated into the room.

46

Reduction may be described as the removal of oxygen from
a compound and, in organic chemical processes, this is often
done by use of zinc dust. In the process, flammable liquids as
solvents may be used and, therefore, the poSsibility of
explosive vapors being liberated is present.

 

Distillation is perhaps the most common process found in
chemical—works. Stills are used in connection with the refining
and purifying of a large variety of materials. Ruptures of stills
through corrosion, weakness or excessive pressures are not un-
known and such accidents taken with breakage of piping liberates
in many cases, large quantities of explosive vapors.

 

Sublimation is the process of distilling a material in.which
the condensate is deposited in the form of solid particles.
The sublimation of naphthalene is a typical example. The solid
particles are often in the form of a finely divided dust and
when these escape from the subliming chambers or connections
the room.may be filled with the fine explosive dust or vapors.

 

Fusion is the melting together of substances in fire
heated pans or kettles. The fusion of sulphur and anthracene
is a typical process. The hazard of the fusion process is
probably not as great from.cur standpoint as some of those
previously described, but this depends on the materials used.

Grindin 'of dyes and other chemicals is a process
frequentIy useg. The grinding is done by ball mills, hammer
mills and, sometimes buhr mills. Where the materials ground
are of a metallic or flarmable nature, the dust explosion
hazard is active, especially in event of liberation of the
dust into the room. It is usually quite impossible to main-
tain the grinder and its connections perfectly tight so the
issue of dust in some quantity is common.

Dryers are used to a considerable extent in some types
of she ca plants. The hazard connected with their use is
dependent on the nature of the materials being dried. If
flarmable solvents or materials which give off flammable vapors
are used, dryer and rOom.in which it is located should be judged
as a Class I location.

5 and P1 1 represent equipment ver commonl found
in.most cHe m‘EEI pIanEs, due to the great amount of handling of
liquids and vapors which is necessary. Leaks and rupture of such
equipment are frequent and when the materials handled are of a
flammable nature, considerable hazard is introduced. The electri-
cal hazard is moreprmmmnced here than in the case of Some other
processes, due to the fact that the pumps are frequently motor
driven. Obviously, the places where pumps handling flammable
materials are installed, should be considered Class I locations.

47

Extraction Processes are used to some extent in the
separation of certain vegetable oils or extracts from the
crushed.meals, plants or fibers in which they are contained.
The process involves the use of flammable solvents such as
benzol or naphtha for placing these oils or extracts in
solution. The oils or extracts and solvents are then separated
by distillation. Naturally, processes of this kind are re-
garded as hazardous due to the liklihood that the explosive vapors
of the solvents will be present in the rooms or sections where
the process is carried on. The storage and handling of the
solvents are also to be considered. The rooms or sections con-
taining extraction processes should be regarded as Class I
locations.

 

Alcohol Production

Alcohols are manufactured commercially chiefly by the
fermentation of grains and vegetables and from petroleum by
various processes. Methyl or wood alcohol, which is obtained
from the destructive distillation of wood, as a byproduct
of the beet sugar industry, or by the synthesis of carbon
monoxide, is the exception. The list of alcohols contain~
sixteen different types, including one methyl, one ethyl, two
propyl, four butyl, and eight amyl alcohols. The characteristics
of most of these have already been discussed under "Flammable
Volatile Liquids” and their properties as regards flash points,
apparent ignition temperatures, and hazard grading will be found.
listed in Table Number 3.

It is not intended to discuss in detail the various
methods of manufacture, but it should be pointed out that the
production of many alcohols is attended by hazards which deserve
the consideration of fire prevention engineers. Some of the
alcohola,notably, methyl, ethyl, propyl, secondary butyl and
tertiary butyl, have flash points within range of ordinary
room temperatures or lower and therefore, their vapors may be
easily released into the rooms where they are handled to form
explosive mixtures. The amyl alcohols, with the exception of
the tertiary amyl,have flash points of 100 degrees Fahrenheit
or higher, and so in their unheated state are not as hazardous as
the other alcohols. However, in some processes, even the amyl
alcohols may produce hazardous conditions whbh.require special
attention.

Generally, the pnocess of alcohol production involves
the use of distilling and condensing apparatus, clarifiers and
a variety of pumps for handling the liquids at various stages.
In the manufacture of some of the amyl alcohols pentane is used
and, as this is an explosive gas considerable care is necessary
to remove possible sources of ignition in the rooms where it is
used. The engineer should be prepared to consider as Class I

48

locations practically all parts of most alcohol manufacturing
plants with the exception of the usual shops, offices, lab-
oratories and the warehouses used for the storage of non-
hazardous raw materials.

From the alcohols are manufactured a host of useful
materials includingnany of the commercial solvents, paint and
varnish.thinners, preservatives, pharmaceutical articles, soaps,
fruit essences and perfumes. From.some of the amyl alcohols,
various acetates, such.as amyl acetate, important in the
pyroxylin lacquer industry, are derived Fusel oil, a constituent
of thezresidue remaining after the ethyl alcohol is recovered in
fermentation alcohol production, Which is important in the
manufacture of amyl acetate and fruit essences. Essentially
then, factories employing quantities of the various types of
alcohol should be carefully analyzed to determine the extent of
the hazards and.where the rules for Class I locations should

apply. .

Production 2; Typical Organic Chemicals

Eth 1 Acetate is produced by the distillation of acetic
acid or so um acetate and ethyl alcohol in the presence of
sulphuric acid. The flash point of the product when pure
is 28 degrees Fahrenheit. It is used as a solvent in the '
preparation of fruit flavors and in perfumery manufacture.
Both the base (ethyl alcohol) and the finished products are
classed as hazardous. ‘

' Eth l Chloride is made from trimethyl aniline distilled
from.the:refuse of Beet sugar works, or may be produced by
distilling ethyl alcohol with sodium chloride and sulphuric
acid. The product is used as a refrigerant and as a local
anaesthetic and is a flammable volatile liquid flashing at
ordinary temperatures.

. Ether gr sulphuric Ether is manufactured by mixing
ethyl aIcoEol with’an equaI amount of concentrated sulphuric
acid, cooling and then heating to the boiling point. More
alcohol is then added and the resulting vapor condensed,

ether being separated from the condensate. Ether has many
uses; as an anaesthetic, as a solvent for nitro-cellulose
compounds, and for artificial silk manufacture. Its flash
point is very low and forms very explosive mixtures with air.
Both the raw material (ethyl alcohol) and the finished (ether)
are hazardous flammable liquids.

 

Eth%l Bromide is made by adding red phosphorous to
absolute e yI alcohol, then adding bromine and distilling.
It is used in medicines and as a refrigerant, and while

I.

49

usually considered as a flammable volatile liquid, it is difficult
to ignite its vapors because of the fact that they are very
heavy and do not diffuse readily. The manufacture of the

material is hazardous,however, due to the use of ethyl alcohol.

Miscellaneous Industrial Chemicals. There is on the
market a‘large number-3f liquids, pastes and solids which
are either hazardous in themselves or hazards are associated
with their preparation. These include shoe dressings, stove
polishes, varnish removers, clothes cleaning liquids, fumigants
and insecticides, deodorizers and many others. Very often
these contain solvents of a flammable volatile nature and,
hence, the prdnsses by which they are prepared are attended
by definite explosion hazards.

 

Pharmaceutical and Fine Chemicals

The manufacture of pharmaceutical and fine chemicals,
including patent medicines, drugs, perfumes, fruit essences
and similar materials may be hazardous, especially When solvents
such as alcohol or essential oils in solution with hazardous
liquids are employed in their preparation. Various alcohols
form the bases of many fruit essences and the process is usually
attended by the evolution of explosive vapors in the sections
where the alcohols are handled. In the preparation of some
drugs or medicines, the grinding of herbs, roots and chemicals
is a part of the process and where this is done on any
pretentious scale, the possibility of dust explosion.hazards
is introduced. Extraction by flammable solvents is also a
common process.

Each plant of this type using flammable volatiles should
be considered by itself to determine the extent of the hazardous
area and where the application of the rules for Class I
locations is needed. Where grinding is done to any extent, it is
probable that the engineer will be Justified in.applying the
rules for Class II locations to the grinding department to
protect against the dust explosion hazard.

In the larger pharmaceutiCal and fine chemical plants,
the variety of products manufactured is often very wide, and
in.many cases, the same apparatus is used for the production
of several materials. Therefore, in judging what hazards prevail
in a room or department, consideration should be given to every
probable process or material which will be used in that room
or section.

50

ARTIFICIAL SILK MANUFACTURE

Artificial silk, of which Rayon is a pOpular trade
brand, is made by several processes. In general, all of
these processes, however, adhere to the fundamental principle
of preparing a viscous solution of cellulose and forcing it
through minute orifices or dies to form filaments which are
then coagulated by a chemical solution. These filaments are
then "thrown" in much the same manner as natural silk is pro-
cessed and made ready for weaving by dyeing, weighting and
winding on bobbins or shuttles.

The raw material used for the manufacture of artifi-
cial silk is cellulose in the form of wood pulp or raw cotton,
the latter being usually in the form of linters obtained from
cotton seed Oil mills. When wood pulp is used, the wood stock
is received in the form of logs from which the bark is removed
and then cut up into fine chips. These chips are treated
with sulphite of lime under heat and pressure, then bleached
and washed much in the same manner as employed in the paper
‘manufacture.

The hazards of the processes thus far, from our view-
point, are represented by the storage, handling and cleaning
Of cotton linters requiring the application of Class III and
ClaEBIV rules. When the wood cellulose process is followed
there appears the probability of necessitating the classifi-
cation of the wood chipping or grinding department as a Class
III location, unless effective means are provided to remove
waste and dust so as to prevent their accumulation in the
motors and other electrical apparatus.

After the cotton or wood pulp is prepared, the process
proceeds by one of several general methods which we shall dis-
cuss separately.

The Viscose Process, generally speaking, consists of
treating-High grade Bleached wood pulp with a solution of
caustic soda. After a certain period of time the excess soda
is removed by passing the mass through rollers, following which
the pulp is placed in shredders. During this Operation the
temperature must be held down to less than 69 degrees Fahren-
heit. The ripening process follows in which the material is
kept for a period at a temperature of 70 degrees Fahrenheit.
The next step in the process is extremely hazardous as it in-
volves the treatment of the pulp by carbon bisulphide in churns
or mixers, resulting in its conversion to a substance known as
cellulose xanthate. This is further treated with water and
caustic soda, in the course of which it is kept cool, and after
thorough mixing and agitation it is in the form of a viscous
liquid. This is allowed to ripen and settle to remove all
traces of foreign materials or impurities. It is now ready

.1

51

for conversion into filaments or threads which is done by forcing
it through minute orifices into a hardening or coagulating bath
of diluted sulphuric acid. The threads are then wound on glass
spools ready for "throwing" and other finishing. The hazard
peculiar to the viscose process is the use of carbon bi-sulphide,
a liquid which is probably the most hazardous liquid used in
manufacturing processes. Its hazard rating is 110 plus and its
vapors form very explosive mixtures with air. In practically

all viscose factories in this country, the carbon bi-sulphide
treatment is carried on in separate buildings well detached from
the main plant. The supply of this liquid is stored in buried
tanks from which it is pumped into the treating plant as needed.
The buildings containing the carbon bi-sulphide, as well as any
containing pumps or other equipment handling the carbon bi-
sulphide, are subject to the strict application of the rules

for Class I locations.

Cellulose Acetate Silk is made by the treatment of
cleaned, bleached, cotton‘Iinters with a mixture of acetic
anhydride, acetic acid and sulphuric acid in churns kept
cool by refrigeration, where the mass is worked for several
hours. The material is then removed and permitted to ripen
for several hours, during which time the reaction takes place.
The cellulose acetate so made is precipitated out by placing
the mixture taken from the churns into tanks, adding water
and allowing it to stand quietly. The solid cellulose acetate
is separated from the liquid, which is acetic acid, by centri-
fuging and is then washed, centrifuged, granulated and dried.
In this condition the material will not burn. The next step
involves the solution of the acetate in acetone, following
which it is filtered through cotton batting. It is then ready
to be formed into filaments in the same manner as in the viscose
process, except that the hardening bath is not used. The threads
solidify as soon as they reach the air and are placed on reels
as they emerge from the dies. Outside of the hazards associated
with the storage, cleaning and handling of cotton linters which
we have previously discussed, the hazards of acetate silk
manufacture are those associated with the use and recovery Of
acetone in one step of the operation. Acetone is a hazardous
flammable volatile liquid, giving Off explosive vapors at
temperatures as low as three degrees Fahrenheit. Although the
acetone is usually stored in underground tanks and is handled
by pumps through closed systems of piping, the possibility
of rupture or leakage is present. Therefore, the rooms or
sections from the point where the acetone is introduced to
the point where the filaments are formed, and including the
pump houses containing the acetone handling pumps, should be
considered as Class I locations.

 

52

Nitro Silks are made by what is called the Chardonnet process
using cotton IInters as the basis. The cotton linters are cleaned
and bleached and then are nitrated by a mixture of sulphuric
and nitric acids. The nitrated cotton is throughly washed, de-
hydrated and then dissolved in a.mixture of ether and alcohol.
After settling and filtering, the solution is forced through
glass nozzles of minute diameter into a bath of weak sulphuric
acid from which it is reeled onto glass spools, removed to an
alkaline denitrating bath, washed, bleached and dried. The
hazards of the nitro process are threefold: First, the storage,
cleaning and handling of cotton linters, a matter which has
alread been discussed. Second, the nitration of cotton which
is to e regarded as a serious hazard, and the locations where
this process is carried on should be regarded as Class I
locations. In this connection, it should be noted that the
silk is not denitrated until after it has been formed into
threads. Third, the use of ether and alcohol for dehydrating
and dissolving the nitrated cotton which involves storage and
handling of these flammable volatile liquids with incidental
possibility Of liberation of their vapors. Recovery of the
solvents may also be a part of the process. Consequently the
departments where these liquids are used or handled should be
classed as Class I locations.

S inni and‘Weavipg of artificial silk are not attended
by any great fifizards. n self the silk is no more flammable
than cotton and probably produces little or no lint or "flyings"
in its use.

52

'Nitro Silks are made by what is called the Chardonnet process
using cotton IInters as the basis. The cotton linters are cleaned
and bleached and then are nitrated by a mixture of sulphuric
and nitric acids. The nitrated cotton is thmoughly washed, de-'
hydrated and then dissoived in a mixture of ether and alcohol.
After settling and filtering, the solution is forced through
glass nozzles of minute diameter into a bath of weak sulphuric
acid from which it is reeled onto glass spools, removed to an
alkaline denitrating bath, washed, bleached and dried. The
hazards of the nitro process are threefold: First, the storage,
cleaning and handling of cotton linters, a matter which has
alread been discussed. Second, the nitration of cotton which
is to e regarded as a serious hazard, and the locations where
this process is carried on should be regarded as Class I
locations. In this connection, it should be noted that the
silk is not denitrated until after it has been formed into
threads. Third, the use of ether and alcohol for dehydrating
and dissolving the nitrated cotton which involves storage and
handling of these flammable volatile liquids with incidental
possibility Of liberation of their vapors. Recovery Of the
solvents may also be a part of the process. Consequently the
departments where these liquids are used or handled should be
classed as Class I locations.

S inni and.Weavi of artificial silk are not attended
by any great fifizar Ts. self the silk is no more flammable
than cotton and probably produces little or no lint or "flyings"
in.its use.

,‘

 

 

53

PYROXYLIN PLASTIC INDUSTRY

Manufacture g; Proxylin Plastic

 

Pyroxylin Plastic or Celluloid, as it is more commonly
called, is a solid solution of pyroxylin. and another substance,
usuall camphor. Pyroxylin, the more active ingredient, is
classe in general with gun cottOn, and is probably a mixture
of cellulose of higher nitration.

The raw stock consists of pure cotton or what is more
commonly used, a special grade of tissue paper. If cotton is
used, the process involves its cleaning, bleaching and drying.
Hence, the hazard of combustible flyings is present where it is
stored and handled which makes it necessary to apply the rules
for Class III locations. When tissue paper is used, it is cut
and shredded into small pieces and blown to dry rooms or to
mechanical dryers where it is dried until the moisture content
is from 1 to 2%. Unless rigid precautions are taken to maintain
cleanliness, accumulations of the dry material can be easily
ignited by a spark. It is probable that in many cases the rules
for Class III locations should apply to the cutting and drying
departments.

The next step in the process is the nitrating operation
which may be done by any of several methods, but in general all
consist of treating the cotton or paper cellulose with a mixture
Of nitric and sulphuric acids, often helped by mechanical ’
agitation. The nitrated cellulose or pyroxylin, as it is termed,
is now washed, centrifuged and rewashed a number of times, then
bleached if an "Ivory" product is desired, and sometimes
reduced to a pulp in a beater mill. After leaving the wash
house the pyroxylin contains about 40% of moieture, and in this
state is non-hazardous. The next step is a drying process which
is done by, (1) pressing and blotting in hydraulic presses,

(2) by pressing and alcohol displacement, or (5) by pressing,
blotting and hot air drying, in which Operation camphor is
usually added and the mixture pressed between blotting paper
or cheesecloth. In the dry houses, the pyroxylin is in a state
in which it becomes very hazardous, more so than the finished -
product, and extreme care is needed to prevent ignition.
'Usually rules more rigid than those prescribed by Article 52
are adhered to even to the extent of requiring that electric
lights in vapor proof globes be placed outside windows to
provide artificial illumination. In the case of method (2)
above, the hazards are those involved in the presence Of the
flammable vapors of alcohol and usually include alcohol recovery
processes.

The next step is the removal of the cheesecloth, an
operation known as stripping. As the pyroxylin at this point is
extremew dry and dangerous, stripping is done in a separate
building containing no elemtzical equipment. In some plants the

54

pyroxylin may be dried before being mixed with camphor and it is
necessary to break up the pressed cake by use of a breaker, con-
sisting of two revolving rolls fitted with spikes or a ball mill.
Here again the pyroxylin is in a dangerous state on account of

its dryness and extreme precautions are necessary to prevent
ignition. All electrical eqiipment is usually placed outside of the
hazardous area.

The next step is the mixing process which is probably the
most hazardous of any. The mixing machines are similar in
appearance to bread mixers and into these the pyroxylin and
camphor are placed together with a solvent such as wood alcohol
or acetone and denatured alcohol, to effect a more intimate
contact or solution between the pyroxylin and camphor.
Stabilizers for neutralizing any acid which might remain are
added with the solvent. After the pyroxylin is thoroughly
dissolved the plastic mass is removed and placed in a warm
room to permit partial Conversion, and this is later completed
by rolling and pressing. In this mixing process we have the
hazards of flammable volatile solvents in addition to that of
dry pyroxylin, and more than usual precautions should be taken.
The mixture burns readily with a high degree of heat evolving
explosive flammable gases or vapors. The mixing houses are
definitely Class I locations, and the rules for this class should
be strictly followed for any electrical installations in
mixing houses. As a matter Of fact, motors and controllers,
switches and such equipment are usually located outside of the
mixing houses in a motor and control room, and even then.are
to be of the type approved for Class I locations.

After the mixing process, the plastic mass, sometimes
softened with a solvent, is worked in rolls and colors are added
when a colored product is desired, and then placed in hydraulic
presses. If rods or tubes are to be made, the stock from the
rolling mill is processed in an extruding machine, a steam
heated cylinder, operating by forcing the stock through a die
by hydraulic pressure. Where sheets are desired, a sheeting
machine, similar to a machine shop planer, is used which cuts
the blocks received from the presses down to required 3126.

The sheets, rods and tubes are then hung in dry houses to season
and are finally straightened and polished. All through these
latter processes we areciealing with pyroxylin plastic, a '
hazardous material with considerable alcohol vapors present.
Necessarily, the storage and handling of alcohol is involved

as is, in most cases, the recovery of alcohol from the various
processes where it is used. It is obvious that the roll and
press departments, the shaping department and the dry houses

are definitely Class I locations, as are the solvent handling
and solvent recovery buildings or sections. Portable lights
should not be permitted where pyroxylin plastic is manufactured
or stored, as the heat of the light, even though enclosed in a
vapor proof globe, is sufficient to cause decomposition and
posiibly ignition Of theplastic with which the light may come in
con ac .

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54

pyroxylin may be dried before being mixed with camphor and it is
necessary to break up the pressed cake by use of a breaker, con-
sisting of two revolving rolls fitted with Spikes or a ball mill.
Here again the pyroxylin is in a dangerous state on account of

its dryness and extreme precautions are necessary to prevent
ignition. All electrical eq11pment is usually placed outside of the
hazardous area.

The next step is the mixing process which is probably the
most hazardous of any. The mixing machines are similar in
appearance to bread mixers and into these the pyroxylin and
camphor are placed together with a solvent such as wood alcohol
or acetone and denatured alcohol, to effect a more intimate
contact or solution between the pyroxylin and camphor.
Stabilizers for neutralizing any acid which might remain are
added with the solvent. After the pyroxylin is thoroughly
dissolved the plastic mass is removed and placed in a warm
room to permit partial Conversion, and this is later completed
by rolling and pressing. In this mixing process we have the
hazards of flammable volatile solvents in addition to that of
dry pyroxylin, and more than usual precautions should be taken.
The mixture burns readily with a high degree of heat evolving
explosive flammable gases or vapors. The mixing houses are
definitely Class I locations, and the rules for this class should
be strictly followed for any electrical installations in
mixing houses. As a matter of fact, motors and controllers,
switches and such equipment are usually located outside of the
mixing houses in a motor and control room, and even then are
to be of the type approved for Class I locations.

After the mixing process, the plastic mass, sometimes
softened with a solvent, is worked in rolls and colors are added
when a Colored product is desired, and then placed in hydraulic
presses. If rods or tubes are to be made, the stock from the
rolling mill is processed in an extruding machine, a steam
heated cylinder, Operating by forcing the stock through a die
by hydraulic pressure. Where sheets are desired, a sheeting
machine, similar to a machine shop planer, is used which cuts
the blocks received from the presses down to required size.

The sheets, rods and tubes are then hung in dry houses to season
and are finally straightened and polished. All through these
latter processes we areciealing with pyroxylin plastic, a
hazardous material with considerable alcohol vapors present.
Necessarily, the storage and handling of alcohol is involved

as is, in most cases, the recovery of alcohol from the various
processes where it is used. It is obvious that the roll and
press departments, the shaping department and the dry houses

are definitely Class I locations, as are the solvent handling
and solvent recovery buildings or sections. Portable lights
should not be permitted where pyroxylin plastic is manufactured
or stored, as the heat of the light, even though enclosed in a
vapor proof globe, is sufficient to cause decomposition and
posiibéy ignition of theplastic with’which the light may come in
con EC 0

55

Manufacture 2; Articles From Pyroxylin Plastic

 

Many articles are manufactured from pyroxylin plastic or
celluloid, among which are photographic and motion picture films,
artificial leather, toilet goods, drafting tools, such as
triangles and tee square facings, box toes for shoes, eye
shades, eyeglass rims, advertising novelties, and many others.
The processes involve the use of sheet or formed pyroxylin
plastic and usually equipment for the utilization of scrap
pyroxylin plastic. Often these factories are Operated in
connection with the plants producing the plastics, but as
separate units. The storage of the pyroxylin plastic in large
quantities, together with the forming of articles and their
storage, renders the hazards of such factories of a serious
nature. Coupled with this are the hazards connected with the
storage, handling and use of solvents, and the reworking of
pyroxylin plastic scrap, all of Which are similar to those we
have previously discussed. Rigid requirements are imposed by
fire inspection authorities on the matter of storage of
pyroxylin plastic, and all precautions are taken to prevent
ignition. The rules for Class I locations apply in full to
factories Of this type, except in those sections where the
pyroxylin plastic or articles made from it are not stored
,Or‘used, which would probably exempt offices, power houses and

similar locations. Due to the low decomposition and ignition
temperatures Of the material, portable electric lights should
not be used, due to the posSibility of their being left lying
on the material and thus cause fire. In factories where only a
small part of the space is utilized by processes involving
pyroxylin plastics, the hazardous area is generally taken to
extend to a distance of twenty feet from the particular process.

Owing to the fact that Article 34 of the National
Electrical Code rules on electrical installationswhere
cellulose nitrate motion picture films are manufactured,
exposed, developed, printed, rewound, repaired, and stored, we
shall not discuss these requirements here. Under "Hospitals"'
in this thesis, the matter of electriCal installations in
X-Ray film storages will be discussed.

56

THE COTTON INDUSTRY

The cotton industry from the point where the cotton is
picked in the field to the point where it is woven into cloth,
is attended by the hazard represented by the production of
considerable easily ignitable lint or flyings." In loose
fluffy condition, the bulk cotton is also readily ignitable.
Necessarily then, every precaution must be taken through the
entire process to prevent the ignition of the loose cotton,
the lint, and even the thread and cloth while on the looms.

In the following the various divisions of the cotton
industry will be discussed briefly.

Cotton Gins

When the cotton is picked in the field, it is trans-
ported by wagons or trucks to the gin for cleaning, removal
of the seed or ginning, and packing in bales for shipment. The
small country gins are usually frame buildings Of highly com-‘
bustible nature and often without fire protection of any kind.
The country gin plant generally consists of three main buildings,
viz: the seed cotton storage building where loose cotton is
stored in open bins or compartments to await ginning; the gin
building where the ginning machines, cleaners, boll breakers
and presses or balers are located; the seedhouses into which
the cotton seed, which is taken out Of the diton, is stored,
awaiting shipment. In the larger gin plants, separate cleaning
buildings are provided and sometimes a boiler house is added.
In the larger and more modern gin plants the buildings are of
brick or steel construction, corsiderably feducing the fire
hazard. In the process of receiving and ginning of cotton, a
large amount Of loose, easily ignitable lint is exposed. In the
gin building proper, it is ccmmon to see lint clinging in fihms
to walls, timbers, maChines, electric light pendant cords,and
to other equipment. Inasmuch as such lint is easily ignited
by a static spark, the importance of removing electrical sources
of ignition should be clear. Cotton lint, When ignited, burns
rapidly, rather as a flash fire. Cotton ginning plants, including
all buildings other than the Office, boiler house and shop,‘
should be iconsidered as Class III locations. In some cases,
especially in.the so called one story gins, the motors are
so located tha; accumulations of lint in the windings results
in a severe hazard. In such cases, the motor should be of the
enclosed type or provided with an enclosure as specified in
rule 5205s. In most gins it is a practical procedure to
isolate the power equipment from the lint hazard by placing it
tn a separate power house. This is much to be recommended.

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57
Cotton Compresses

After the cotton leaves the gin plant in banded burlap
wrapped bales, it is shipped to compresses where the bales are
pressed into bales of smaller volume. These compresses are
sometimes separately owned units, but are often a part Of
a large terminal cotton warehouse. In any event, the hazard is
practically identical, for the usual compress plant includes
facilities for the storage of large quantities of baled cotton.
Cotton in bales, as was pointed out previously in this thesis,
while wrapped in burlap or similar material, has considerable
loose lint or fiber protruding from the bale covering. The lint
is easily ignited by any spark or heated metal, as from the
breaking Of electric light, and this fire flashes from one bale
to the next with great rapidity. In the neighborhood of the
compressing machine proper, there is often considerable loose
cotton and, therefore, the hazard is that vicinity is of a
greater degree. Compresses and their associated warehouses
should be treated as Class III locations, the rules of which
Class are intended to guard against ignition of this cotton
lint from electrical sources.

Cotton Warehouses

Warehouses used for the storage of cotton present hazards
identical with those described in the immediately preceding
section. In the case of warehouses at terminal points where the
cotton is stored, pending shipment by sea or rail, the buildings
are extremely large and are several acres in area. The hazard
is multiplied because of this, as a flash fire Once started, can
easily travel the entire length of the warehouse before any
form of automatic fire protection would operate. In some cases,
compresses are provided at these terminals Which further reduce
in volume or re-compress the bales received from the first
compress. The same comment as made under "Compresses" applies
in this case. It should be emphasized that under average business
conditions, the valuescf stored cotton involved in these ware-
houses are extremely high and, therefore, the expense attached
to making an electrical installation in them safe is very much
warranted.

In the case Of cotton storage warehouses Operated in
connection with textile mills, the hazard is identical to that
in the terminal warehouses, but it is probable that in the majority
of instances, the values involved will be considerably less.
Howeer, in textile mill warehouses, a fire originating there
may communicate to the mill prOper and destroy valuable machinery,
so the lack of value in the warehouse is often more than com-
pensated for.

[C

 

57
Cotton Compresses

After the cotton leaves the gin plant in banded burlap
wrapped bales, it is shipped to compresses where the bales are
pressed into bales of smaller volume. These compresses are
sometimes separately owned units, but are Often a part Of
a large terminal cotton warehouse. In any event, the hazard is
practically identical, for the usual compress plant includes
facilities for the storage of large quantities of baled cotton.
Cotton in bales, as was pointed out previously in this thesis,
while wrapped in burlap or similar material, has considerable
loose lint or fiber protruding from the bale covering. The lint
is easily ignited by any spark or heated metal, as from.the
breaking of electric light, and this fire flashes from one bale
to the next with great rapidity. In the neighborhood Of the
compressing madhine proper, there is Often considerable loose
cotton and, therefore, the hazard is that vicinity is of a
greater degree. Compresses and their associated warehouses
should be treated as Class III locations, the rules of which
Class are intended to guard against ignition of this cotton
lint from electrical sources.

Cotton warehouses

Warehouses used for the storage of cotton present hazards
identical with those described in the immediately preceding
section. In the case of warehouses at terminal points where the
cotton is stored, pending shipment by sea or rail, the buildings
are extremely large and are several acres in area. The hazard
is multiplied because of this, as a flash fire Once started, can
easily travel the entire length of the warehouse before any
form of automatic fire protection would operate. In some cases,
compresses are provided at these terminals Which further reduce
in volume or re-compress the bales received from.the first
compress. The same comment as made under "Compresses" applies
in this case. It should be emphasized that under average business
conditions, the valuescf stored cotton involved in these ware-
houses are extremely high and, therefore, the expense attached
to making an electrical installation in them safe is very much
warranted.

In the case Of cotton storage warehouses operated in
connection with textile mills, the hazard is identical to that
in the terminal warehouses, but it is probable that in the majority
of instances, the values involved will be considerably less.
Howeer, in textile mill warehouses, a fire originating there
may communicate to the mill prOper and destroy valuable machinery,
so the lack Of value in the warehouse is often more than com-
pensated for.

58

All warehouses used for the storage Of cotton should be
considered as Class IV locations and the electrical installation
made accordingly.

Cotton Mills

 

When the baled cotton is received at the cotton mill
proper, either from its own warehouse or from terminal points,
it goes first to the opener room where the bands and burlap
wrapping are removed from the bale. The cotton, somewhat loosened,
is then fed into an automatic feeder, the spikes of whichfeed
the cotton uniformly into a blower system leading to the picker
room, or what is more usual, feeds the cotton.into an Opener
picker which further loosens the stock and is then fed into the
blower system. Arriving into the picker room the cotton is
passed through pickers which further loosen the cotton, straighten
the fibers to some extent and remove dust, dirt, and short
fibers. The picker machines are made in a variety Of types
which need not be discussed here. However, it should be mentioned
that the picker room is regarded as the most hazardous location
in a cOtton mill, due to the presence of dust, refuse, and loose
cotton. In breaker and lapper pickers, the dust, short fibers,
and dirt are blown to a dust room or into a cyclone collector
for disposal. Dust rooms are necessarily hazardous.

The laps of cotton from the pickers are now trucked to
the card room where they are passed through carding machines,
the purpose Of which are to further remove dirt, short fibers,
and to straighten the fibers so that they will be in approximately
parallel lines. Lint renders this room hazardous, but probably
not as much so as picker and opener rooms. From this point the
cotton passes through various machines and processes such as draw
frames, slubbers and fly frames, to prepare the cotton for
spinning, which is done on machines called ring frames or mules.
Some lint or fly is produced by these machines with correspond-
ing hazard introduced. Where cotton yarns are manufactured, an
additional process known as combing is necessary, this being
done between the carding and drawing processes. The warp is now
prepared and this is placed in the harness of the weaving
machines or looms. There are several types of looms and various
refinements or side processes for producing certain kinds of
yarn or cloth, but these need not be discussed here. After the
cloth is woven it goes to the cloth room for inspection, napping,
if needed, and folding.

The hazards of a textile mill are, of course, represented
chiefly by the lint or "fly" produced. This is easily ignitable
and results in flash.fmes. However, the hazard decreases from the

(O

59

picker room through the process until the cloth is woven. How-
ever, through the entire process care should be taken to prevent
sparks or heated metal from incandescent lights or resistors
coming into contact with lint. Special care is needed in the
Opener and picker room where there is considerable loose cotton
and much "fly." Strict adherence to the rules of Class III
locations should be had in electrical installations in the
Opener and picker rooms and probably some parts of the carding
room. The dust room should be .regarded as'a Class II location.
In the draw frame room, the section where the slubbers or
”flyers" are located, the ring frame and mule spinning rooms

and the loom shed, it is probable that with reasonably good
housekeeping, that only the machines and their immediate vicinity
need be considered as Class III locations, the entire purpose '
being to prevent ignition of lint and "fly" by electrical arcs,
sparks or heated parts of equipment. The electrical "stop-motions"
for looms and other machines have been quite serious Offenders
in causing ignition of lint. Therefore, attention should be
given to the construction of such devices to prevent emission
of sparks or arcs. The value involved in a textile mill in the
way of machinery is quite cOnsiderable. Hence, prevention of
fire is Of great importance.

Cotton Seed Oil Mills

Reference should be made to discussion of this subject
under "Vegetable Oil Industry."

60

FABRIC AND PAPER COATING PLANTS

General

The production of rubberized fabrics, linoleum, oil
cloth, pyroxylin coated fabrics, roofing materials, wall paper,
and coated paper is usually attended by hazardous conditions
because of the character of the materials employed, and the
manner of application and drying. Flammable volatile solvents
are used to a considerable extent in the preparation Of the
coating material, and the vapors of these.solvents are present
throughout the spreading and drying operations. Where pyroxylin
coated fabrics are made, the hazards are more serious, due to
the Character of the coating materials employed. In the following
we shall discuss briefly the production of the various coated
fabrics and papers.

Linoleum

There are two types of linoleum, the felt base and the
burlap base. The felt base linoleum is usually prepared by
coating in calendar rolls the sized felt with paint to form
the undercoating which is then festoon dried in large dryers.
Designs in a varnish paint are now applied, and the sheets placed
in rack dryers after which process they are trimmed and rolled
up. In the burlap base linoleums, burlap, canvass or other cloth
is coated with a mixture of ground cork, fillers, linseed oil and
paint, and hung festoon fashion to Cry. Designs are then printed
or inlaid, and after rackdrying, the sheets are trimmed and rolled.

‘Among the hazards of linoleum factories are those ‘
introduced by the grinding of cork, and as cork dust is explosive,
it is desirable that the room where this grinding is done be
considered as a Class II location. The preparation, mixing and
application Of paints and varnishes, and the subsequent dyeing
processes involve hazards which warrant the locations where
these processes are carried on being classed as Class I locations
due to the presence Of the vapors of flammable volatile thinners
used in the paints and varnishes. If a pyroxylin varnish is used,
the attendant hazards are greater. The same comment applies
to the printing room.where<iesigns are applied by use of naphtha
thinned paints, and where the finished sheets are dried. The
warehouses for the storage of raw and finished materials are
not usually considered in the hazardous area.

011 Cloth

 

This product, as considered here, consists of a cotton
cloth treated with a vegetable drying Oil, or compounds containirg

61

chiefly these 0113, used for wagon covers, tents, and tarpau-
lins, When decorated for table covers, colors, varnishes and
other materials may be used to give the final finish. The
coating compounds vary with different processes and products,
but very often they contain naphtha or other volatile thinners.
Also, when varnishes are used, the hazard of the use of
flammable solvents is introduced. The process of coating the_
cloth is continuous. The cloth is run through rolls through a
dip tank or trough containing the compound, and thence
directly into steam heated dry rooms where the coated cloth is
hung in festoons. The classification Of the coating and dry
rooms, which will probably be the only hazardous locations
from our standpoint, depends on the character of the compounds
and varnishes used. If the use of flammable volatile thinners
or solvents is involved, these locations should bb placed

in Class I. In this case, the problem of storage, handling and
mixing of the compounds with the flammable volatile liquids

is also involved, and necessarily the sections where this is
done should also be considered as Class I locations.

Pyroxylin Coated Fabrics.

The process of producing pyroxylin coated fabrics,
which product is sometimes referred to as artificial leather,
is undoubtedly the most hazardous of the cOated fabric class,
due to the character of materials employed. The pyroxylin 13‘
received in the form of smokeless powder from surplus stocks,
as film or novelty pyroxylin stock, or as nitrated cotton
linters. The coating works may receive these in the form of a
jelly, but Whatever the form, the storage and handling of
these materials involve severe hazards. The solution of the
pyroxylin in solvents, and the addition of loading and coloring
material are processes usually required to be isolated. The '
coating is applied to the cloth by use of a spreader machine.‘
The cloth is run over a roller immediately aboveawhich is a
'doctor" or knife to cause an even spreading of the mixing as
it is fed onto the cloth. After passing the "doctor", the coated
cloth is run over a long heated table for drying, and is finally
reeled up in rolls. These spreader machines and drying tables
are often enclosed to permit ready removal of the vapors, or,
in some cases, tO permit recovery of solvents. Throughout the
process there is the possibility of considerable "droppings"
and residue abOut the machines, and hence the hazards are of a
serious nature.

Practically all parts of such a plant, including the
sections used for the storage and mixing of the pyroxylin and
solvents, the spreader room, and the dryer room, should be
considered as Class I locations.

62

Roofing Materials

 

In the manufacture of roofing materials such as tar or
asphalt coated paper, paper felt or ashpalt shingles, the chief
hazard, from our viewpoint, is that associated with the heating
of tar or asphalt to high temperatures (400 to 500 degrees F. ),
at which temperatures it is probable that flammable vapors will
be evolved.

In the impregnation process, the paper or felt is passed
through vats containing the heated tar or asphalt, and then
festoon dried in steam heated dryers.

The preparation of roofing cements is Often an auxiliary
process of roofing plants. Such cements are usually the tar or
asphalt in solution with a flammable volatile solvent. Hence,
there is present the hazard Of vapors of an explosive nature
in the rooms where the cement is mixed and placed in containers,
as well as that attending the handling and storage of the
solvents.

Wall Paper

 

There is little hazard connected with the production of
ordinary wall paper where the process consists simply of apply-
ing linseed oil paints to heavy sized paper by means of figured
rolls. If flammable volatile liquid thinned inks are used, the
hazard is measured by the care taken in the mixing of such
inks. Probably the mixing room in most plants should be con-
sidered as a Class I location. Where varnish coatings are
applied to the paper after printing, the coating room.where this
varnish is applied should be considered a Class I location due
to the probable presence of flammable vapors from the thinners
in the varnish. There is likely to be considerable waste paper
trimmings in the neighborhood of the printing machine, and in
the less modern plants this immediate vicinity should probably
be considered as a Class III location.

Wax Coated Paper

 

In coating paper with paraffin, the paper is usually
run through a trough or small vat containing heated paraffin,
and then passed over chilled rolls to festoon drying racks.
When paraffin is heated, flammable vapors may be given Off and
this fact should be weighed when plants of this type are under
consideration. In some cases, flammable volatiles are added to
the paraffin to thin the coating, in which case the coating
room definitely becomes a Class I location. In some types of

65

plants there may be considerable trimming of the coated paper
which would cause accumulations of refuse. In such instances
the application Of the rules for Class III locations is advised.

Rubber Coated Fabrics

 

Refer to section entitled "The Rubber Industry."

64

THE RUBBER INDUSTRY

Manufacturg pg Rubber

Crude rubber is received at rubber manufacturing plants
in two forms: as a "biscuit" which is smoked sap or a latex
in solid form, and as liquid latex with a small amount of
preservative, commonly ammonia, in solution. When the ”biscuit"
is received at the factory, it is passed through various wash-
ing, compounding and calendaring processes, none of which in4
volves any appreciable hazard from our standpoint. As it comes
from the calendaring process the rubber is in the form of sheets
in a soft and sticky condition and can.be moulded into any
desired shape. The rubber is now vulcanized and cured, but
these do not represent any hazardous operations, except that in
event of use of carbon bisulphide for vulcanizing, a most serious
hazard is introduced, for the vapors of this liquid are extreme-
ly flammable. Fortunately, it is a material seldom used for
this purpose.

Probably the most serious hazard in the rubber industry
is that associated with the churning process. Churn rooms are
found in various classes of rubber plants. Here rubber is dis-
solved in a flammable solvent, usually gasoline, benzine, or
naphtha, in churns which are covered iron tanks containing an
agitator or paddle to stir the mixture mechanically. The
solvents are brought to the churns in open cans, or pumped into
it from outside storage tanks through a closed system of piping.
Although the churns are usually kept closed, they are frequently
opened permitting the solvent vapors to pass into the room. In
some cases the escaping vapors are recovered by a solvent
recovery process. Necessarily, churn rooms should be considered
as Class I locations, as should the places where pumps for
handling solvents are located. The solvent recovery stills and
condensers are usually required to be in a separate room or
building, but wherever located, the recovery room is a Class I
location.

In some classes Of the rubber industry, varnishing of
the finished articles is done, especially in the case of rubber
footwear manufacture. The varnish usually consists Of linseed
oil, gum, and sulphur thinned with gasoline. This varnish is
often applied by dipping. The rooms or locations where the
varnishing is done, where the mixing of the varnish is carried
on, and where the flammable solvent, gasoline, is handled should
all be considered as Class I locations.

In many rubber plants a considerable amount of old rubber
"shoddy" is reclaimed to be mixed with the crude rubber as
received from the plantations. The reclamation processes do
not usually present any great hazards from our viewpoint, so

65

the ordinary type of electrical installation may be permitted
in the sections where the reclaiming operations proceed. How-
ever, if a churning process, such as discussed above, is
operated in conjunction with it, the location where the churns
are placed must be considered a Class I location.

Rubber Coated Fabrics

The coating of cloth with rubber is an important and
usually a hazardous process, due to the fact that the ”dough”
which is used to impregnate the fabric consists of rubber dis-
solved in gasoline or other flammable volatile solvent. The
"dough" may be applied by a spreader machine, or by friction-
ing on a calendar machine. A third method which is coming into
use is known as the latex process, -- that is, atomizing the
latex or rubber sap and causing it to be deposited on the
fabric. This method is safer than the spreader and calender
method because it does not require the use of solvents. It is
not yet generally used, however.

In the spreader method, the most common, the "dough'
made by a churning process is fed to a spreader machine. This
machine consists of a roller above which is a knife or "doctor”,
and the fabric is fed between the two from a reel. As the
cloth passes through, the "dough" is placed on it at a point ‘
Just behind the spreader knife. The cloth emerges with a coat-
ing of the "dough , passes over a long steam heated drying
table, and is then hung in festoons in a dry room for vulcaniz-
ing and curing. Here it is subjected to the fumes of sulphur
chloride, generally diluted with carbon bisulphide, benzol or
carbon tetrachloride.

Double texture goods are made by coating the surfaces
of two sheets and then pressing them together as they leave the
spreader. Coated fabrics are sometimes decorated by printing
with gasoline thinned ink, and are sometimes varnished, which
naturally introduces the hazard of flammable vapors from the
thinners in the varnish. Some double texture fabrics are
given a coating of paraffin, alum, vaseline and naphtha, a
process called "spot-proofing" to make the fabric more moisture
proof.

The hazards of the spreader method are evident, and it
is clear that the churn room, the spreader and dryer rooms,
the printing room, and the spot-proofing room are to be
_considered as Class I locations. If the gasoline and the
solvents are supplied by pump from outside tanks, the pump
room is also placed in the Class I classification.

In the friction method where the compound rubber is
pressed into the fabric in a calender machine, no hazard is
involved as the rubber so used does not contain a solvent.

Q‘s,

 

 

 

.r..

66
Dipped Goods

A large variety of rubber goods, including rubber gloves,
nipples, and similar thin elastic articles, are made by the
dipping process. The usual procedure consists of dipping metal
or pyroxylin plastic forms into a solution of rubber and gaso-
line, or other solvent, raising them to dry, and then repeating
the operation until the desired thickness of rubber is obtained.
The rubber solution or rubber cement is contained in Open dip
tanks, and this results in the evolution 0f large quantities of
flammable vapors. The process naturally involves the storage
and handling of considerable amounts of gasoline, as well as the
preparation of the cement by the churning method. Necessarily,
the churn room, solvent pump room, and the dipping room must be
considered as Class I locations.

Automobile Tires

The manufacture of tires, from our point of view, is
hazardous because of the large quantities of rubber cement used
in some types of processes. However, this cement is used in
large work rooms and applied by brush, so with reasonable care,
the hazard can be controlled to such an extent that it is not
considered necessary to designate these work rooms as Class I
locations. However, the churn rooms, where the cement is pre-
pared, are definitely Class I locations, and if the quantity of
gasoline or other solvent used is such as to require storage
tanks and pumps for handling, the pump room should also be re-
garded as a Class I location.

Hard Rubber

Hard rubber is made in the same manner as soft rubber,
except that the vulcanizing process is carried farther. There
is no great hazard in the process from our viewpoint. However,
in many hard rubber plants there is considerable reclaiming of
waste material. In this process the hard rubber is ground into
a fine powder for the purpose of mixing with new raw material.
Hard rubber dust has been found to have explosive qualities and,
therefore, the section of the plant where the grinding and
handling of the pulverized rubber is done should be subjected
to classification as a Class II location.

67
THE LEATHER AND SHOE INDUSTRY

Manufacture gf Leather

 

Up to the point where leather is received by the shoe
manufacturer there is little hazard involved from our point of
view with the exception of the barking mill used to grind bark
for the tanning operation. Bark dust is explosive when mixed
with air in the proper proportions and, therefore, the bark
mill department should be considered as a Class II location if
within the tannery buildings. Another notable exception should
be made in the case of the preparation of lacquered leather in
which pyroxylin lacquers are used to give desired finishes to
the leather. This is usually done in spray booths and, there-
fore, the same comments as made under section "Finishing
Processes" apply. The locations where such spraying is done
are definitely regarded as Class I locations, as are the mixing
and storage rooms for the lacquer.

Patent Leather

The application of a glossy varnish to the surface of a

leather results in a product which has been designated as

I'patent leather”, but sometimes referred to as japanned or
enameled leather. The production of patent leather is usually
accomplished at a plant separate from the tannery. Before the
varnish is applied, the tanned hides are degreased, which is
also frequently done at separate plants. The degreasing process
consists of immersing the hides in tanks filled with naphtha
for several hours, after which the naphtha is drained off and
warm air blown through the tanks to dry the hides. The leather
is then removed, air dried, and finally shipped to the finish-
ing plant. Sometimes the degreasing process is not followed,
but only in cases when a pyroxylin base varnish is used for

the primary finish coat. Obviously, degreasing plants are
Class I locations due to the presence of large quantities of
naphtha_vapor.

In the finishing plant, the hides are first buffed and
mounted on frames, and the priming varnish coat applied. This
is a naphtha thinned oil varnish, and is applied by heavy
brushes or poured on. The hide on its frame is now placed in
a drying oven, and when dry is lightly stoned and then given
a second coat of varnish similar to the first, except that it
is thinned to the point where it can be applied by brush.
Colors are added to this varnish. It again goes to the drier
and upon removal a second time is lightly stoned and then
brushed to remove dust. The varnish is now applied with great
care to avoid uneveness. After application is completed, the
hides are placed in large bake ovens where they are left over
night and then removed to the outside of the building for
exposure to air and sunlight, or placed in a special room and
exposed to ultra-violet light. In some cases a pyroxylin base

daub 13 used in place of the first coat, in which case the
general hazards of pyroxylin finishes apply.

 

 

 

94

 

 

 

 

68

It is obvious that the large scale production of patent
leather is attended by hazards which are of a nature similar to
those described under "Finishing Processes", and the same
comments as to the required type of electrical installation
app 1-

Shoe Manufacture

In the process of manufacturing shoes, we are concerned
almost entirely only with the use of various types of cements,
water-proofing liquids and finishes. The cements, many finishes
and water-proofing liquids, contain flammable solvents and
thinners such as gasoline or naphtha. In the well ordered
plants, the use of these materials in the main factory is well
controlled, and all mixing and storage of main supplies are
confined to a detached building. This detached building should
be regarded as a Class I location and the electrical installa-
tion made accordingly. Except in extreme cases, it should not
be necessary to class workrooms in the main factory as hazardous
locations unless heels are covered with pyroxylin plastic
(celluloid) or box toes of this material are used, in which case
the precautions mentioned under ”Pyroxylin Plastic" should be
followed to prevent ignition of this material in use and
storage. Where heels are covered with leather or satin, rubber
cement is used in large quantities. Fire prevention engineers
recommend that this operation be carried on in a cut-off room
used for no other purpose, and this room regarded as a class I
location. weed or leather heels are sometimes finished with a
pyroxylin lacquer applied by the spray process under metal
hoods. When this is done such processes should be governed by
comment under ”Finishing Processes." In cleaning white kid
shoes, ether is sometimes used, and as this is a flammable
volatile liquid, the process is usually required to be carried
on in a cut-off room treated as a Class I location. Patent
leather finishes consisting of nitro cellulose dissolved in
amyl acetate, acetone, or alcohol, are used and, especially
in the case of cheap shoes, the quantities treated may be
large due to the fact that the entire shoe is dressed with it.
In such cases the work should be done in a separate room.which
should be regarded as a Class I location.

There is a certain dust hazard connected with shoe
factories, but this is usually well controlled and probably
compliance with Class 11 rules is not justified except so far
as protection of lights in dust rooms is concerned.

69
RECOVERY OF SOLVENTS

In many industrial processes considerable quantities of
solvent vapors are released into the rooms in which the processes
are located. The need for protecting the health of employees
normally exposed to such vapors, as well as the economic waste
represented by the loss of solvents by evaporation, has led to
the development of various systems of solvent recovery. Quite
wide application of such systems has been made in the division
of the rubber industry producing rubber coated fabrics, in dry
cleaning, in the smokeless powder industry, to some extent in
the manufacture of artificial silk, and in others.

In general, the method employed for the recovery of
solvents consists of means for collecting the vapors at the
points where they are released and conveying them to the recovery
plant. Here they may be condensed to liquid form by direct con-
densation, by absorption by charcoal, silica gel, or other
solids, by absorption by liquids, or by a combination of these
methods. Distillation, condensing, clarification, and pumping
apparatus is usually associated with solvent recovery processes
to purify the recovered solvents.

. A popular type of recovery system is that employing a
charcoal absorption process. In such an installation, ventilat-
ing hoods are placed over, or often complete enclosures provid-
ed around, the machines or process from which the vapors escape.
Draft pipes connect these hoods or enclosures to a common air
trunk which leads to the solvent recovery building where the
fan establishing the suction is located. The vapor and air are
delivered to the absorber which contains a bed of specially
prepared charcoal. After the charcoal has reached its absorp-
tive capacity, the vapors from the header trunk are diverted
and high temperature live steam is turned into the bed of char-
coal. This steam carries the solvents out in the form of a
condensate, and is collected in a receiver from which the
solvent can often be drawn off separately due to differences

in specific gravity. Where the difference in specific gravity
between the solvent and water is not great, recourse must be
taken to distillation methods for separation, thus involving
the use of stills and condensers.

As has been stated, there are several other methods of
solvent recovery, but the foregoing is representative of the
nature of the hazard involved. Fire prevention engineers
recommend that the recovery apparatus be located in a well
detached building, but wherever located, the solvent recovery
department should be regarded as a Class I location.

 

 

 

 

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70
NATURAL GAS AND COMPRESSED GAS SYSTEMS

Natural Gas

In some parts of the country, natural gas is still avail-
able and is used to a considerable extent for lighting and heat-
ing purposes. Often the gas is transmitted long distance
through overland pipe lines to points where it is sometimes
mixed with manufactured gas before being introduced into the
distributing mains. In these long distance pipe lines, it is
necessary to provide pumping or booster stations at intervals
along the line to obtain the necessary pressures to permit flow.
The production of natural gas is largely one of pumping, and
the pump compressor houses, together with those buildings 0!!
played at the gas wells or at the pipe line pumping stations
for containing the meters, gauges, regulators, and valves may,
at some time, contain explosive mixtures of gas and air. There-

fore, these buildings or rooms should be considered as Class I
locations.

There are several hydrocarbon gases which might be
referred to as byproducts of the natural gas industry. Among
these gases are methane, ethane, prepane and butane, which are
obtained by the fractional distillation of liquified natural
gas. Where such operations are carried on, the hazardous area
is extended to include the compressor and still rooms used to
liquify and distill the natural gas, as both the material and
products form explosive mixtures with air. The rules for Class
I locations should be applied to these hazardous areas.

Compressed Gas Systems

The hydrocarbon gases mentioned in the previous paragraph,
especially propane and butane, are placed in heavy steel cylin-
ders in liquid form and in that form are quite widely used for
heating and lighting. There is also considerable activity in
the petroleum industry in the production of these liquified
hydrocarbon gases in which butane and propane are obtained from
cymogene, the light naphtha distillate from petroleum oil which
is largely butane. Most of these liquified gases are sold under
trade names and these are usually mixtures of propane, butane
and, in some cases, other hydrocarbons. As an example, the
liquified gas known as "Fuelite" is a compressed liquified gas
containing 50% butane and 50% propane, and is shipped in heavy
steel cylinders at a pressure of 200 pounds. ”Protane" is a
proprietary gas and is shipped in liquid form in tank cars
under its own vapor pressure of about 20 pounds per square
inch e

Compressed gas systems are of two types: Class A systems
are those introducing only gas into the buildings; and Class B

71

systems those introducing liquid into buildings and which is
vaporized at the burners. It is not intended to explain in
detail the operation of these systems, but it should be mentioned
that the rules of the H. F. P. A. provide for the installation

of the cylinders outside of main buildings, and where enclosed,
the enclosure shall be lighted only with incandescent lights in
vapor proof globes and shall contain no switches or other spark
producing devices. In effect this states the requirements for
Class I locations,which the enclosure should be considered to

be. .

Acetylene Gas Systems

Acetylene gas systems employing generators for the produc-
tion of the gas on the premises are of several types, those with
generatbrs for installation within main buildings, and those in
which the generators are required to be placed in a detached
building. The generators are usually required to be recharged
without the aid of artificial light, but should any special dis—
pensations be made in this regard, the minimum requirement in
generator houses or enclosures should be to regard them as Class
I locations.

72
HOSPITALS

There are two hazardous locations in hospitals which re-
quire special attention as to the nature of any electrical in-
stallation which may be made in them. The first of these is
the x-ray film storage room or vault when nitro-cellulose films
are employed. When acetate film is used the hazard is not any
greater than that attending the storage of paper, but unfortun-
ately nitrate film is still used to a large extent. Rigid rules
are usually enforced as to the nature of the vault or room used
for the storage of nitrate films in hospitals, especially since
the Cleveland Clinic fire in 1929 when 122 persons lost their
lives. It is not expected that any electrical equipment other
than lights will be installed and it is required that these be
enclosed with vaporproof globes and guards. Due to the low de-
composition and ignition temperatures of nitrate films, portable
lamps, whether protected or not, should not be permitted to be
used in film storage vaults. The switch controlling the fixed
lights should preferably be located outside the vault, but if
inside, should be of the type approved for Class I locations.

The second hazardous location in the hospital is the
operating room with which is often associated the anaesthizing
room and a sterilizing room. Such rooms are classed as Class I
locations due to the use of flammable gases or vapors such as
ether, propylene, ethylene, and ethyl chloride for anaesthetical
purposes. Nitrous oxide, also used as an anaesthetic, is a
supporter of combustion like oxygen and forms explosive mixtures
with the gases and vapors mentioned. While not given general
publicity, it is reported that many serious and often gruesome
explosions have occurred in operating rooms. The arrangement
of the operating rooms, or more correctly, departments, is such
that the sterilizer room and the room where the patient is
given the anaesthetic, which is sometimes separate, must be
included in the hazardous area, owing to the rapid diffusion
of the explosive gases or vapors.

Some work has been done by manufacturers of electrical
equipment toward the design and construction of lighting
fixtures, sterilizers and other equipment for use in these
locations, but there is much yet to do. Adequate lighting is
of prime importance in operating rooms, but it is also impor-
tant that lights be protected to prevent their breakage. This
can be done by locating the enclosed lights at or near the
ceiling or by providing large specially protected enclosed
units over the operating room. Any motors used should neces-
sarily be of the type approved for Class I locations for the
specific use intended. All switches or other spark producing
devices should be placed outside of the hazardous area, but
if within, should be of the explosion resisting type.’ Electric
sterilizers will probably have to be specially designed for
use in the hazardous area, as in actual practice the steriliz-
ing room must communicate conveniently with the operating room

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and, therefore, will probably contain flammable gases or vapors
in explosive mixtures with air. The writer has knowledge of at
least one manufacturer who is at work on this problem.

The use of live electrical cautery represents a problem
difficult of solution, but it is probable that by reasonable
care and by using non-flammable anaesthetics when live cautery
is employed, that trouble from this source can be avoided.

74

GRAIN ELEVATORS

Grain elevators may be said to be of three general types,
each of which performs an individual service in the business of
marketing grain and preparing it for milling or other utilization.
These are:

1. Country grain elevators,
2. Terminal grain elevators,
5. Mill elevators.

While the construction and equipment of all three classes
may, in many cases, be very much alike, there is enough distinc-
tion in their respective purposes to warrant discussing each
class separately.

Country Grain Elevators

This type of elevator will be found usually in agricul-
tural districts and is used for the purpose of receiving grain
from the trucks or wagons of farmers, storing it for a period
ranging from a few days to several months, and finally shipping
it either to a terminal elevator or to a flour mill, feed mill,
or some other factory-where it is converted into finished
products. In some country elevators, the facilities are extended
to provide for the cleaning, drying and often grinding of grain
for feed. In case of the latter activity, the elevator approaches
the feed mill in nature.

The grains handled by country elevators may include one
or more of the following: wheat, oats, corn, barley, rye, flax
and rice. Beans and peas, while not classed as grains, are
handled by some grain elevators. When corn is handled, it is
usually received in cob form, that is unshelled, in which case
corn shellers and the necessary auxiliary machinery for shelling
corn are included.

The majority of country elevators are of combustible
construction, although in the past few years many of the re-
inforced concrete fire resistive type have been built. The
usual elevator consists of the following divisions:

l. The driveway or dump shed where the grain is received
and dumped into a receiving hopper under the floor.
Conveyors of the spiral or belt type then carry the
grain into the basement of the main elevator building.

2. The elevator building preper, which consists of a
number of bins for the storage of the grain. A
part of the area, usually equal to the space which
would normally be taken by one bin, is used to house

 

75

the elevator legs (continuous belt vertical bucket
conveyors), the stairway and often the man hoist.
Surmounting a portion of the structure is the cupola
or "taxes" which contains the upper portion or "heads"
of the elevator legs, the distributor used to direct
the grain discharged by the elevator leg to anyone of
the several bins, and the necessary spouting. A
basement is commonly provided under at least a portion
of the main elevator building and here are located
.the lower portions or ”boots" of the elevator legs,
the corn sheller usually if one is provided,and the
necessary conveyors for carrying the grain from the
dump and bin to the elevator boots. If facilities
for cleaning grain are provided, the cleaner,
commonly,the shaker type,equipped with air suction,
is located in the first floor of the building or,as
is more often the case, in the cupola. If feed
grinding is done, the grinder is located in the first
floor, in the basement or may be placed in a small
addition.

3. The office building which may be attached t6 the
driveway or be detached from all budldings.

4. The warehouse often provided for the storage and
retailing of flour, sacked feeds and general supplies.
This building, if present, is sometimes detached,
but more often attached to the elevator buildings
and frequently contains the office.

5. The grain drier building, usually a separate structure,
but commonly attached to the elevator building proper.

6. Auxiliary buildings such as the dust house, corn cob
house and coal sheds.

Figure No. 1 illustrates a typical country grain elevator
as found in the wheat growing sections of the Northwest and
Southwest.

In-operating a country elevator, the grain is first
weighed in the wagon or truck and then dumped into the hoppers
or dump in the driveway of the elevator. The conveyors carry
the grain into the basement of the main elevator building where
it is discharged into the boot of an elevator leg by which it
is elevated to the upper part of the cupola. The grain is then
discharged into a spoum and directed to the desired bin through
a distributor. If cleaning facilities are provided, the grain
‘is directed from the elevator head to the cleaner where chaff,
loose dust and other foreign materialzne removed, and then is
re-elevated and distributed to the desired bin.

75

the elevator legs (continuous belt vertical bucket
conveyors), the stairway and often the man hoist.
Surmounting a portion of the structure is the cupola
or "texas" which contains the upper portion or "heads"
of the elevator legs, the distributor used to direct
the grain discharged by the elevator leg to anyone of
the several bins, and the necessary spouting. A
basement is commonly provided under at least a portion
of the main elevator building and here are located

the lower portions or "boots" of the elevator legs,
the corn sheller usually if one is provided,and the
necessary conveyors for carrying the grain from the
dump and bin to the elevator boots. If facilities

for cleaning grain are provided, the cleaner,
commonly,the shaker type,equipped with air suction,

is located in the first floor of the building or,as

is more often the case, in the cupola. If feed
grinding is done, the grinder is located in the first
floor, in the basement or may be placed in a small
addition.

5. The office building which may be attached to the
driveway or be detached from all buildings.

4. The warehouse often provided for the storage and
retailing of flour, sacked feeds and general supplies.
This building, if present, is sometimes detached,
but more often attached to the elevator buildings
and frequently contains the office.

5. The grain drier building, usually a separate structure,
but commonly attached to the elevator building proper.

6. Auxiliary buildings such as the.dust house, corn cob
house and coal sheds.

Figure No. 1 illustrates a typical country grain elevator
as found in the wheat growing sections of the Northwest and
Southwest.

In operating a country elevator, the grain is first
weighed in the wagon or truck and then dumped into the hoppers
or dump in the driveway of the elevator. The conveyors carry
the grain into the basement of the main elevator building where
it is discharged into the boot of an elevator leg by which it
is elevated to the upper part of the cupola. The grain is then
discharged into a spout and directed to the desired bin through
a distributor. If cleaning facilities are provided, the grain
is directed from the elevator head to the cleaner where chaff,
loose dust and other foreign materialzne removed, and then is
re-elevated and distributed to the desired bin.

76

Naturally, during the process of receiving, elevating,
cleaning and spouting of grain, considerable dust is removed
from the grain and in spite of all efforts to confine it, much
of it is thrown into suspension in the air and deposited finally
on floors, ledges and timbers as well as on machinery, motors
and other equipment. This dust is largely of a carbonaceous
nature, probably to a large extent starch, and therefore com-
bustible and explosive. The dust from beans and peas can be
regarded as less hazardous, generally, than that from true
grains as it consists principally of sand or earth.

In the country grain elevator there are two types of
hazards present. The first is that represented by an explosive
mixture of combustible dust and air being present when the plant
is in Operation. While dust explosions are not as frequent in
country elevators as one would expect, they are not unknown by
any means. Probably the fact that the construction is more or
less open has the effect of reducing dust explosion possibilities.
The second type of hazard and the one which gives by far the
greatest proportion of loss is that associated with the collection
of combustible dust in the windings of epen motors, in resistors,
in motor controllers, and on unenclosed incandescent electric
lights. The collection of this dust in the windings of motors
results in the impairment of ventilation to such a degree that
the motor finally overheats, the insulation breaks down and the
resulting arcs ignite the dust. The communication of fire is
then rapid because of the accumulations of dust in the neighbor-
hood of the motor and usually throughout. Grain dust can be
readily ignited when permitted to accumulate on an unenclosed
electric light and the burning dust may then fall into dust on
the floor and cause rapid spread of fire. ‘

Of the various divisions making up the country elevator
plant, all parts of the main elevator building, the driveway
and the drier house, if there is one, should be regarded as
Class II locations. The office and the warehouse are usually
reasonably free from dust and special treatment of electrical
installations in those locations is not necessary although it
is recommended that only rigid conduit wiring be employed for
any light or power installations which may be made.

While the older country elevators employ group drives
for all machinery, the machinery in the newer elevators is
almost entirely individually motor driven. The practice of
isolating electric service equipment, motor controllers, and
fuse panels to a dust-free location has been followed to a
large extent in newer installations. In other words, the service
switch and fuses, meters, fuse panels and magnetic type motor
controllers are placed in the attached office or in the warehouse,
which, being comparatively non-hazardous locations, permit the
use of ordinary dust-proof equipment. Dust-tight push button
control stations are then placed at the desired points in the

77

elevator proper. This arrangement is much to be desired from
the fire prevention point of view and also produces a less

expensive installation than if the equipment were placed in a
dusty location and the rules for Class II locations followed.

 

Figure Ho. 1.
A Country Grain Elevator

This elevator is typical of those found .

in the wheat growing states of the Northwest
and the Southwest. This is a frame iron-
clad structure with the office attached to
the driveway. In elevators so arranged,

the electric service equipment, remote type
motor controllers and panelboards can often
be conveniently located in the office thus
isolating them from the hazardous area and
permitting use of standard equipment.

78

Terminal Grain Elevators

 

The purpose of the terminal grain elevator is to receive
the grain from country elevators or from other terminal or
transfer elevators and store it pending shipment to flour mills
or other purchasers. The grain is received by boat or railroad
cars and may be shipped in like manner depending on the
transportation facilities available.

Equipment for the cleaning of grain is usually provided,
and in some,driers, washers and bleachers are included.

The newer terminal grain elevators are of fire resistive
concrete or steel construction, but there are still a relatively
few of the old type wooden elevators remaining.

Many dust explosions have occurred in elevators of the
terminal class, some of them, such as that which wrecked the
Northwestern Elevator in Chicago in 1921, being in the nature
of major disasters. The values involved are high and the
construction and arrangement such that a serious explosion
usually results in great loss of life and property.

The usual terminal elevator consists of a number of
divisions which are detailed below. Reference to Figure No. 2
will assist in obtaining a more clear idea regarding their
arrangement and construction.

A terminal elevator as ordinarily built and arranged
consists of the following sections:

1. The car shed where cars of grain are loaded and
unloaded. Under the car shed are usually unloading
sinks or heppers from which lead belt conveyors in
tunnels directly communicating with the basement of
the elevator or work house.

2. The marine legs, either stationary or movable, by
which grain is removed from the holds of vessels and
discharged either directly into the work house or
elevator through spouts or discharged onto a belt
conveyor enclosed within a gallery directly
communicating with the work:house or gallery.

3. The work house or elevator proper where the grain
is received from the car sheds or marine legs.
Here the grain is raised to the upper parts of the
building, discharged into a garner bin, thence into
the scale hopper where the grain is weighed. From
the scale hopper the grain may be discharged either
onto belt conveyors for distribution to the bins
or tanks or may be spouted to cleaners or separators

79

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure No. 2.
A Modern Terminal Grain Elevator

The view in the upper right shows the car
shed, the work house, the grain storage
tanks, and several auxiliary buildings.

The drawing below is a transverse cross-
sectional view of the same elevator which
is explanatory of the interior construc-
tion and.the placing of equipment.

 

 

 

 

 

 

 

80
where the grain is cleaned before being sent to the bins or
tanks. Such cleaners or separators are practically always
located in the work house. The work house may also contain
wheat washers, oat clippers, and other machines.

4. The drier house, although not all terminal elevators
are equipped with facilities for drying grain. Usually the
drier house is either detached from the work house or attached
to it with standard fire cut-offs. Where driers are used it
requires a furnace or boiler for supplying hot air or steam
and these are usually located in separate cut-off boiler
houses.

.5. The storage section, made up of tanks or bins, where
the grain is stored. Over the top of such tanks or bins there
is a gallery or "texas" in which are located conveyors which
carry the grain from the distributing floor of the work house
to the bins or tanks. Belbw the tank is a floor or tunnels
through which belt conveyors travel, the purpose of which is
to carry the grain discharged from the bottom of the tanks or
bins back into the work house where it is elevated to a height
sufficient for spouting or conveying directly into cars or
vessels. In the more modern elevators, the bins or tanks are
covered, thus separating one tank from the next as well as
preventing to some extent the issue of dust from the tanks up
into the gallery.

6. The shop, laboratory, office and change room depart-
ments, which are usually detached from the main elevator,
except in some of the older elevators where they may be
attached or even within the main elevator building in which
case they are usually cut-off from the hazardous dusty sections.

~ Note: In some types of elevator construction, the
functions of the work house are combined in a superstructure
built above the tanks or bins with the elevator legs, stair-
ways, etc., extending upward from the basement or first floor
in spaces between tanks or bins.

Of the above divisions, those which can without question
be placed in the hazardous class are, divisions 5, 4 and 5,
with no exceptions. Division 1, the car shed, in part, at
least, might be questioned. Usually car sheds are of semi-
open construction permitting of free air circulation, thus
eliminating to a large extent the possibility of dust explosion.
However, electrical equipment in car sheds is frequently placed
in such a location that considerable dust will collect on it.
This is especially true of motors which are often placed on
decks or in pits where maintenance work is difficult. Where
this is done, Class II equipment should be used. The locations
under the floor or track level of the car shed, such as tunnels
or unloading pits should be definitely classed as Class II
locations.

81

Harine legs, division 2, are often tightly constructed
of concrete and, therefore, the dust explosion hazard is as
serious as in the main work house. In the majority of cases,
marine legs should be classed as hazardous locations and the
electrical equipment installed to suit. Boiler houses, power
houses, transformer and switch houses should not be classed as
hazardous locations.

As in the case of the newer country elevators, the
tendency in the more modern terminal elevators is toward
individual motor drives for machinery and the isolation of
motor controllers with provisions for remote control through
push button stations. Elsewhere in this volume will be found
illustrations of several typical installations.

The dust condition in terminal elevators is more serious
than in either the country elevator or the mill elevator, due
to the large amount of grain handled and the speed at which
the various operations are carried on. The amount of dust in
suspension and accumulated depends to a large extent on the
nature of construction and arrangement, the type, if any, of
the dust collection system, and the character of housekeeping
and maintenance. However, even in the best of elevators,
conditions at times are of an extremely hazardous nature.

Mill Elevators

By mill elevators are meant those located at flour,
feed or rice mills, melting plants, breweries, linseed oil
plants, or other points where grain storage is needed. The
functions are identical with those of country and terminal
elevators, namely, those of receiving, cleaning and storage
of grain. Facilities for washing and drying grain are some-
times included. There is usually more cleaning equipment in
the mill elevator than in those previously discussed in order
that the grain may be more completely prepared for milling.

In the smaller milling plants, the grain elevator may
be very similar to the country elevator, but in the large
modern merchant milling plants, the grain storage facilities
represent what are practically terminal elevators, large
capacity being needed to insure sufficient grain to maintain
uniformity of product.

Further discussion of mill elevators is not needed as
that included under the sections on country and terminal
elevators will, with the understanding that the hazards are
practically identical, give the engineer sufficient data as
to what type of electrical installation is required.

.Iu-

 

82
FLOUR MILLS

The milling of wheat, rye, or corn is a process of
gradual reduction and separation which is accomplished by a
group of machines operating coincidently and almost always

driven by a single power unit. In brief, the process is as
follows:

When the wheat comes from the elevator it has, as
previously related, been cleaned to remove chaff, dirt, dust
and other foreign materials. However, before being milled,
further cleaning is necessary and this is done either in the
mill proper or in a division known as the cleaning or "smuts"
department cut. off from the milling division. The wheat is
spouted into the boot of an elevator leg, is elevated, usually
weighed, and passes over a magnetic separator to remove any
iron or steel which might be present and then over a cleaner
or separator similar to those used in an elevator. The grain
is now sent through a scourer which removes the tiny hair,
present in the end of the grain berry, and remaining dust by
a type of abrasive and brushing action. Foreign seeds and
grain are removed by disc type separators and this leaves the
grain ready for tempering preparatory to milling. Tempering
is done in bins or steel tanks and consists of adding a
certain small amount of water to the grain and permitting it
to remain in the tempering tanks for a period of from twelve
to twenty four hours and sometimes longer depending on the
type of grain. The tempering bins or tanks may be located in
the cleaning department or in the mill division proper.

The grain now passes into the milling process proper.
The first step is the breaking of the grain which is done in
a roller mill equipped with corrugated rolls. The broken or
slightly crushed grain, as it is discharged below the rolls,
is elevated by means of cup belt elevators and discharged
into spouts connected with a sifter or bolter which removes
the flour resulting from the initial crushing and sends the
balance or "tailings" back to another roller mill for further
grinding. This procedure is repeated a number of times. The
result of this process of gradual reduction and separation
is the production of several grades of flour, bran and
middlings which are spouted into their respective bins. The
exact process or ”flow" of a flour mill is too involved to
detail here, but it is hoped that the brief explanation given
will be sufficient for our needs.

The packing of the finished products into sacks or
barrels is done either in the mill building prOper or in a
separate packing building. If the latter, the flour is carried
by means of special conveyors or spouts into bins or tanks
located directly over the packers. When the products are
packed into sacks or barrels, auger type packers are used,
but when placed in cartons, special automatic packers are

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This drawing shows the various MUTUAL mm: pnavannon BUREAU
divisions of a flour mill anomccnmc. sen-wee. mm h
including the warehouse and Cmcmo ,LL mum «Ida’-
grain elevator. sang/L 50. PM" W

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83

found which form the carton and fill, weigh, close and wrap
them ready: to be placed in shipping cases.

There are many refinements in the milling process
such as bleaching, purifying and rebolting, which, while
important to the miller, need not be mentioned here. Figure
number 3 gives a map, cross section and an isometric draw-
ing of a modern flour mill, indicating the divisions and
general arrangement.

The following summarizes the divisions into which a
flour mill may be divided and briefly states the operations
conducted in each:

1. The office with Which is sometimes combined a
laboratory and retail sales room.

2. The elevator or grain receiving and storage depart-
ment where grain is received and stored. In the larger mills,
this division approaches in size and equipment a terminal
grain elevator.

5. The cleaning_department where the grain is cleaned
by removal of chaff, dust, etc., sometimes washed and dried,
and scoured. In some mills, this department is divided from
milling department proper by definite fire walls, but in
others it is in the same fire division.

4. The mill prOper where the grain is ground in roller
mills, bolted or sifted, purified and rebolted. The products
from this department are flour of various grades and the
offalconsisting of bran, middlings, etc. From this department,
the products go to packing bins located in the same building
or sometimes (in larger mills) located in a separate packing
building.

5. The warehouse and shipping departments where the
sacked flour and other products are stored and held for ship-
ment.

6. The shop and similar departments.

Of the above divisions, in general, divisions l, 5,
and 6 are not considered in the hazardous class unless they
are so much a part of a unit building including the main
milling operations that no definite separation.may be assumed.
Divisions 2, 3 and 4 should be regarded as Class II locations.
Division 2 may be subdivided as has already been done under
terminal and country elevators, although in the case of the
smaller mills, this division is really often a part of the
unit mill building. In the case of division 4, it is usually
found that the major portion of the milling machinery is
driven by a single motor as the relation of one machine to

84

the next is coincidental. In most cases, this motor is located
in a separate power house or motor room which, if of suitable
construction, places the motor outside of the hazardous area.
Motor control equipment is then located in the motor room. In
the case of auxiliary motors in section 4, these should be
approved for Class II locations. The same remarks can also
apply to section 3 as here, to at least a large extent, the
machines also operate together as a unit.

The divisions suggested above are based on average
conditions and hold for the majority of cases. In some instances,
however, we find that housekeeping is far above average and that
adequate dust control and collection systems have been installed
which greatly reduce the dust explosion hazard as well as the
hazard of electrical fires due to accumulation of dust on or
in apparatus or wiring. But what is the condition today may
not necessarily be true tomorrow, for some fault might develop
in the dust control system for instance, which would cause the
dust condition in the risk to be especially bad and should an
electrical fault develop at the same time, a serious dust
explosion or fire might result.

Most of the floors of such a modern flour mill, that is,
of the main mill building, are clean and the atmosphere is
remarkablyn free from suspended dust so long as the mill is
operating properly. But let a choke-up or a serious leak
develop in the spouts or elevator legs and we find that a con-
siderable amount of flour dust is thrown into suspension in
the air. Should a motor burn out, an electric light break, or
a short circuit occur at the time when this dust is in suspen-
sion, the chances of a dust explosion are good. But the point
is, that in order for this explosion to occur, a number of
conditions must prevail concurrently. The chances of a motor
burnout at just that time, for instance, may not be one in a'
thousand, but the chances of sparks from a commutator or slip
ring coming at that time are good. Hence, the definite rule
3204c (N. E. C. Article 32) which provides for enclosing such
parts of motors. Note that rule 3204f permits open squirrel
cage motors except where it is impracticable to keep them
clean.

It should be kept in mind that in flour mills we are
dealing first with grain, which, no matter how many times it
is cleaned, will shed a highly explosive dust when spouted
or otherwise handled, and second, with a finely divided
starchy material known as flour which is also highly explosive
when in suspension in air. The many explosions which.have
occurred in flour mills are sufficient to warn us of the
hazards with which we are concerned and the precautions
which must be taken to avoid these explosions and fires.

85
FEED MILLS

The process of preparing feeds for livestock and poultry
is generally a combination of grinding and mixing operations,
although some feed mills confine their activities solely to
grinding or to mixing. In any event, however, the process is
usually attended by the handling of quantities of grain, and
therefore, the dust hazard is present to a greater or lesser
degree.

Feed mills offer a wide variety of sizes and types of
arrangement ranging from the small custom feed mill to the
large commercial feed mill producing a complete variety of
feeds. It is, therefore, difficult to attempt to describe the
processes involved and the arrangement of buildings or divisions.
However, the average feed mill may be assumed to consist of
the following divisions:

l. The office with which is sometimes combined a retail
sales room.

2. The elevator or grain receiving and storage depart-
ment where grain or other feed constituents are received and
stored in bulk.

3. The grinding, mixing and packing department.

4. The warehouse or warehouses used for the storage and
handling of sacked products or sacked feed constituents. '

5. The shop, laboratory, and change room departments.

In general, divisions 1,4 and 5 are not to be considered
as hazardous locations for in these departments we rarely find
dust conditions such as to be dangerous either from the stand-
point of dust in suspension so as to introduce the dust
explosion hazard, or from the hazard of collection of dust on
or in motors or other electrical equipment so as to prevent
normal radiation of heat.

There then remain divisions 2 and 5 which should be
classed as Class 11 locations, and the electrical equipment
required to be installed accordingly.

In the small feed mill, the operations are similar to
those of the average feed mill except that they are on a
smaller scale. Also, the various divisions detailed in the
foregoing may, in many cases, be contained under a single
roof with no attempt at providing fire cutoffs. It is, there-
fore, necessary in such cases to place the entire building
in the Class II classification.

86

In the large commercial feed mill, the operations are
usually entirely given over to the grinding and mixing of feeds
in large quantities intended for shipment in wholesale quanti-
ties by truck or rail. The values involved are generally high
and, consequently, the probability of heavy damage from
explosion or fire is correspondingly great. In this type of
mill, the same departments as in the average feed mill usually
exist, but some divisions, especially divisions 3 and 4 may be
further subdivided to provide separate departments for mixing
and grinding, and often,still further subdivision of both of
these is found as pertaining to the mixing of dry feeds and
molasses feeds as well as to grinding of the different feed
ingredients. In some plants, for instance, an entirely separate
building is employed to house the cotton seed cake grinding
operations. This, however, does not affect the classification
and all such departments included under 5 and 4 must be
placed in the hazardous class. Figure number 4 is a repro-
duction of a photograph taken of a large eastern commercial
feed mill.

In the large commercial feed mills, the grain receiving
and storage department, as in division 2, approach in con-
struction and equipment that of a terminal elevator.

In feed mills it is the exception rather than the rule
to find group drives for machinery. Individual motor drive
is used because of the fact that each grinder, for instance,
is independent of the operations of a mixer and so on through
the plant. It is not uncommon to find as many as 100 motors
in the larger commercial feed mills.

So far as the hazards of dust are concerned, they are
not far different from those existing in flour mills and
grain elevators. It is usually more difficult to maintain a
feed mill in a clean and neat order owing to the more open
nature of operations, so feed mills are generally considered
more hazardous from the dust explosion standpoint than flour
mills. The matters of selection and installation of electric
power and lighting equipment for feed mills are of prime
importance to provide the necessary safeguards against
ignition of dust.

86

In the large commercial feed mill, the operations are
usually entirely given over to the grinding and mixing of feeds
in large quantities intended for shipment in wholesale quanti-
ties by truck or rail. The values involved are generally high
and, consequently, the probability of heavy damage from
explosion or fire is correspondingly great. In this type of
mill, the same departments as in the average feed mill usually
exist, but some divisions, especially divisions 5 and 4 may be
further subdivided to provide separate departments for mixing
and grinding, and often,still further subdivision of both of
these is found as pertaining to the mixing of dry feeds and
molasses feeds as well as to grinding of the different feed
ingredients. In some plants, for instance, an entirely separate
building is employed to house the cotton seed cake grinding
operations. This, however, does not affect the classification
and all such departments included under 5 and 4 must be
placed in the hazardous class. Figure number 4 is a repro-
duction of a photograph taken of a large eastern commercial
feed mill.

In the large commercial feed mills, the grain receiving
and storage department, as in division 2, approach in con-
struction and equipment that of a terminal elevator.

In feed mills it is the exception rather than the rule
to find group drives for machinery. Individual motor drive
is used because of the fact that each grinder, for instance,
is independent of the operations of a mixer and so on through
the plant. It is not uncommon to find as many as 100 motors
pin the larger commercial feed mills.

So far as the hazards of dust are concerned, they are
not far different from those existing in flour mills and
grain elevators. It is usually more difficult to maintain a
feed mill in a clean and neat order owing to the more open
nature of operations, so feed mills are generally considered
more hazardous from the dust explosion standpoint than flour
mills. The matters of selection and installation of electric
power and lighting equipment for feed mills are of prime
importance to provide the necessary safeguards against
ignition of dust.

86

In the large commercial feed mill, the operations are
usually entirely given over to the grinding and mixing of feeds
in large quantities intended for shipment in wholesale quanti-
ties by truck or rail. The values involved are generally high
and, consequently, the probability of heavy damage from
explosion or fire is correspondingly great. In this type of
mill, the same departments as in the average feed mill usually
exist, but some divisions, especially divisions 5 and 4 may be
further subdivided to provide separate departments for mixing
and grinding, and often,still further subdivision of both of
these is found as pertaining to the mixing of dry feeds and
molasses feeds as well as to grinding of the different feed
ingredients. In some plants, for instance, an entirely separate
building is employed to house the cotton seed cake grinding
operations. This, however, does not affect the classification
and all such departments included under 5 and 4 must be
placed in the hazardous class. Figure number 4 is a repro-
duction of a photograph taken of a large eastern commercial
feed mill.

In the large commercial feed mills, the grain receiving
and storage department, as in division 2, approach in con-
struction and equipment that of a terminal elevator.

In feed mills it is the exception rather than the rule
to find group drives for machinery. Individual motor drive
is used because of the fact that each grinder, for instance,
is independent of the operations of a mixer and so on through
the plant. It is not uncommon to find as many as 100 motors
in the larger commercial feed mills.

So far as the hazards of dust are concerned, they are
not far different from those existing in flour mills and
grain elevators. It is usually more difficult to maintain a
feed mill in a clean and neat order owing to the more open
nature of operations, so feed mills are generally considered
more hazardous from the dust explosion standpoint than flour
mills. The matters of selection and installation of electric
power and lighting equipment for feed mills are of prime
importance to provide the necessary safeguards against
ignition of dust.

 

 

 

 

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87
CEREAL MILLS

Cereal mills may, in general, be considered to be in
approximately the same class as feed mills with regard to the
dust hazard. This applies especially to those producing rolled
oats, for records reveal a number of disastrous dust explosions
in sumh plants. In the better type of cereal plants, such as
those producing corn flakes and other breakfast foods, the
standard of housekeeping is usually of a high grade and, there-
fore, the dust explosion hazard, as affected by the nature of
the electrical installation is not as serious as in others.
However, all cereal mills must have facilities for receiving
grain. Hence, the grain receiving department or elevator must
be considered in the same class as any other elevator. The
other departments of a cereal plant are subject to individual
study and judgment.

 

_ . .__— . , _ ,

Figure No. 4.
A Large Commercial Feed Mill.

The buildings in the background are the
feed mill and elevator divisions. The
warehouses are shown in the foreground.

88

STARCH FACTORIES

The larger part of the starch made in this country is
a product of corn. Due to the carbonaceous nature and finely
divided character of powdered starch, it has been found to be
extremely explosive. Several disastrous explosions have occurred
in starch plants within late years and, unfortunately, in most
of them, a number of lives were lost.

The manufacture of corn starch first involves means for
receiving and cleaning the shelled corn. ‘For these purposes
the starch factory buildings include a grain elevator similar
to those previously discussed. In the larger starch factories
this elevator is practically in the terminal class and it
should be so regarded.

When the shelled corn has been thoroughly cleaned in the
elevator, it is conveyed or spouted to the main starch plant
where it is placed in steeping tanks containing water, where
it is permitted to remain for from thirty to forty hours.

From this point to the point where the starch is kiln dried,

the process is of a wet nature and, therefore, the dust explosion
hazards are not present, and these divisions of the process need
not be discussed here. By the time the starch reaches the kiln
drying Operation, the hull, the steepwater or soluble protein
matter, the germ from which corn oil is made, and the gluten have
been removed, leaving starch, the main product, which constitutes
about 65 per cent of the original shelled corn. The starch is
placed in drying kilns in screened trays on wagons and after
drying about twenty-four hours, the starch is passed through a
milling process similar to that of a flour mill whereby the
starch is reduced to the size required by the particular purpose
for which it is to be used.

Edible starch is given further washing and milling to
remove impurities, while laundry starch is partly cooked with
steam to increase the solubility, then pressed, broken up and
passed through reels. After these Operations, the starch is
packed in barrels, bags, or cartons as desired.

Dextrine is made by treating dry starch with a small
amount of hydrochloride or nitric acid, and roasting until the
starch is partially cooked or dextrinized. Dextrine is used for
making glue, gum, leather dressing, cloth and carpet sizing, and
foods.

Corn syrup is made from wet starch from the filters and
the process is non-hazardous from our viewpoint. Therefore, it
will not be discussed. As a by-product in the manufacture of
the syrup, corn sugar is produced, but under ordinary conditions
the process is not hazardous so far as application of Article
52 is concerned.

89

Of the various divisions of a starch factor , the elevator
should be given the same treatment as given under ”Terminal Grain
Elevators, that is, regarded for the most part as a Class II
location. The sections of the main starch plant beginning at
and including the dry kiln room through the packing department,
should likewise be considered as Class II locations except for
offices, laboratories, or similar rooms, cut off from the hazardous
area so as to be free from starch dust, and the warehouse used
solely for the storage of finished starch in barrels, sacks
or cartons. It is likely that the larger part of the dextrine
department should also be considered as Class II locations‘
owing to the fact that dry starch and dextrine are handled.

The gluten feed department is somewhat similar in nature to
a feed mill and, therefore, requires consideration as
recommended under the section "Feed Mills."

90

RICE MILLS

In the process of preparing rice for the domestic market,
a certain amount of combustible dust is liberated, making it
necessary to regard certain parts of rice mills as Class II
locations.

Rice mills, as found in Louisiana and Texas, receive
the rough rice in sacks from the rice warehouses located
throughout the rice growing sections. In the rough form, the
rice grain is covered by a thin skin known as bran and this
by a tough hard shell or hull. The milling processes consist of
thoroughly cleaning the rough rice or "paddy", then hulling,
removing the bran, polishing and grading and finally packing in
sacks or cartons. As in the case of flour and feed mills,
facilities must be provid d for the storage of rough rice.
In the usual rice mill we, therefore, find extensive warehouses
for the storage of this rice in sacks. These warehouses,commonly
adjoin an elevator similar in nature to the grain elevators
previously discussed, and in these are located machinery for
cleaning and handling the rough rice in bulk, previous to its
being conveyed or spouted to the main mill building proper-
for processing. In handling rice in the elevator, considerable
dust is usually released, and inasmuch as rice dust forms
explosive mixtures with air, the elevator should be considered
as a Class II location as qualified by the analysis given
under "Grain Elevators." The warehouses used for the storage of
sacked rice are usually cut off from the elevator and, therefore,
need not be considrred as Class II locations.

In the processes of hulling, separating, pearling,
polishing and grading carried on in the rice mill proper,
there is considerable combustible dust liberated, in fact,
while no grinding is actually done in the ordinary rice mill,
the rice milling building is subject to the same comments as
made under "Flour Mills", and the building is regarded as
a Class II location. Where rice flour is produced, the process
is similar to that used in the milling of wheat flour and is,
therefore, to be similarly considered in establishing the
application of Article 52. After the finished rice comes from
the milling process, it is sent to the packing department in sacks or
cartons. This is usually done in a separate building attached
to, but cut off from the mill building and commonly forms a
part of the warehouse used for the storage of the finished
sacked or package rice. The packing department and waretouses
should not be considered as hazardous locations.

.‘J

91
VEGETABLE OIL INDUSTRY

Vegetable oils, such as cotton seed, linseed, soy bean
and others of this class, are not regarded as flammable volatile
liquids due to the fact that their flash points are relatively
high, ranging from 470 to 590 degrees Fahrenheit. However,
there are certain hazards attending their production and
refining which require that they be discussed briefly. It is
recognized that these vegetable oils are hazardous from the
standpoint of contributing to sportaneous ignition, but that
hazard does not immediately concern us.

Cotton Seed Oil Mills

In the manufacture of cotton seed oil, the cotton seed
is received directly from the cotton gins as removed from the
seed cotton by the ginning process. In this form the seeds
contain much foreign material sudh as dirt, bolls and twigs,
and the seeds have clinging to them considerable lint. Upon
arrival at the oil mill, the seeds are.stored in the seed
house from whence they are passed through revolving-reels or
screens to remove the foreign material. The next step is the
delinting process by which means the lint is removed from
the seeds. This is done by means of machines similar to
cotton gins. The seeds then enter the hulling machines while
the cotton linters are baled for shipment. After hulling, the
seeds are crushed, cooked and finally pressed to remove the
oil, which is then refined by filtering. The cotton seed cake
remaining from the pressing process is broken up or sold _
whole to be used in the manufacture of live stock feeds. From
our point of view, the hazards connected with a cotton seed
oil mill are those resulting from.the presence of cotton lint.
The delinting room is commonly found to have considerable
loose,easi1y ignitable lint hanging to machinery and building
members, and ignition of this lint would cause a serious
flash fire. The delinting department should be regarded as
a Class III location. The baling room, cleaning department,
and seed house are also hazardous locations because of the
presence of lint, and all should be regarded as Class III
locations.

Soy Bean Oil Mills

In plants used for the manufacture of soy bean oil, the
hazards are not partioiarly great from our standpoint unless
the solvent extraction method of separating or refining the
oil is used. If this method is used, the extraction or refining
rooms become Class I locations as do the rooms containing the

92

pumps used to handle the flammable solvents used in the process.
Attention is called to the section entitled "Extraction
Processes" under "Chemical Works." The soy beans as received

at the mill are handled and stored in a.manner similar to

that used in connection with flour mills, that is, in elevators,

This section of the plant then, is subject to the comments
under "Grain Elevators."

Linseed Oil Mills

The process of producing linseed oil is quite similar
to that used for soy bean oil, and the same comments apply.
The flax seed is received in bulk and handled and stored
in grain elevators identimfl with those used in connection
with flour mills. '

92

pumps used to handle the flammable solvents used in the process.
Attention is called to the section entitled "Extraction
Processes" under "Chemical Works." The soy beans as received

at the mill are handled and stored in a manner similar to

that used in connection with flour mills, that is, in elevators,
This section of the plant then, is subject to the comments
under "Grain Elevators."

Linseed Oil Mills

 

The process of producing linseed oil is quite similar
to that used for soy bean oil, and the same comments apply.
The flax seed is received in bulk and handled and stored
in grain elevators identimd with those used in connection
with flour mills.

93

WOODWORKING FACTORIES

In this class are included a large number of industries
producing lumber or articles manufactured from lumber such as
saw mills, piano factories, furniture and cabinet works, box
factories, wagon and auto truck building plants, wicker, veneer
and woodenware works, agricultural implement factories and
numerous others. In many of our industries, woodworking is an
important operation in the manufacture of articles requiring
other processes such as the working of metal, upholstering and
paint and varnish finishing and, therefore, we may have a
combination of different types of hazards present in a plant
normally classed as a woodworker.

Considering for the moment only the immediate hazards
of the woodworking industry as such, we find we are concerned
with one which involves the production of a great amount of
waste in the form of wood shavings, saw dust and finely
divided wood dust. The modern.woodworker is equipped with
adequate blower systems which remove this waste practically
as fast as it is produced and, therefore, the amount of waste
accumulated about the various machines isata minimum. However,
there is still usually a certain amount of waste which accumu-
lates about machines to such an extent as to collect in
objectionable quantities in open motors, in switch boxes and
on resistors and lamps. Such waste, especially when.in the
form of fine dust or as loose shavings, may readily be ignited
by sparks or arcs from electrical apparatus and wiring.

In the newer types of wood working machinery, we find
that individual motor drive has been adopted to a very large
extent, the motor and its controller being mounted directly
on the machine or built into it as an integral part. unfortun-
ately, this practice often places the motor at a point where
it is subjected to considerable dust and many motor burn-outs
and resulting fires are traced to breakdown of windings caused
by these dust accumulations. However, there now seems to be a
trend toward the use of the enclosed types of motors for use
with woodworking machinery a course which is highly commended.
In the older woodworking plants, it is common to see motors
mounted on platforms suspended from ceilings in which position
they are likely to gather considerable fine dust, and as they
are relatively inaccessible due to their location, probably
do not receive as frequent cleaning as is warranted. In many
cases, therefore, the engineer is justified in requiring that
motors be of the enclosed type. This point is definitely
covered in the rules for Class III locations, in which class
woodworkers fall.

The nature of the waste in woodworking plants is such
as to render dust explosions an improbable occurence, with
the exception of the shavings and dust vaults, in which it is
common to find a cloud of fine wood dust in suspension. These

94

vaults should be regarded as Class II locations. However,
flash fires may easily occur in the main plant, especially in
the neighborhood of sanding machines where a very fine dust is
liberated. A certain quantity of this dust passes off into the
air in spite Of dust collector systems, and finally comes to
rest on beams and other horizontal surfaces in a thin film
through which fire may pass with considerable rapidity. There-
fore, in woodworking plants, precautions should be taken to
prevent ignition.

In the application of the rules for Class III locations
to woodworkers, it is necessary to consider as Class III
locations, only those areas surrounding machines which produce
waste in quantities. The general joining, fitting and assembling
departments as usually found, may be regarded as sufficiently
safeguarded by the use of reasonable care in locating motors
and in enclosing switches, fuses and motor controllers.

Where painting and varnishing are done on any considerable
scale, the departments where this process is carried on should
be cut Off from the balance of the plant and considered as
Class I locations. This department is then "subject to the
discussion given under "Finishing Processes"

Upholstering is often an important process in woodworking
establishments, especially in those manufacturing furniture,
automobile bodies and caskets. This process usually involves
the use Of large quantities Of readily ignitable fibers and in
plants of appreciable size include the storage and picking of
such fibers. The hazards involved are similar to those dis-
cussed under "The Cotton Industry" to which reference should be
made. The upholstery departments are usually in separate
divisions and these should be considered as Class III locations.

A comparatively new industry is that concerned with the
manufacture of wood flour which is used as the basis for wood
fillers and other purposes. In the preparation of this product,
wood is reduced to a very fine powder in pulverizing mills and
is attended by the release Of considerable fine dust. Although
the writer has never had the Opportunity Of visiting a plant of
this type, the N.F.P.A. Committee on Dust Explosion Hazards has
seen fit to draw standards for the construction and arrangement
of wood flour plants in which adherence to the rules for Class II
locations is prescribed with respect to the installation of
electrical apparatus and wiring. -

I.

I‘

95

INDUSTRIES AND PROCESSES IN GENERAL

To this point we have discussed in a rather complete
manner, a number of industries and processes in Which the rules
of Article 32 apply more or less generally. There are, however,
numerous other industries or processes to which the rules of
Article 32 should be applied, probably to a small part of the
plant or to a portion of a process or operation. In the follow-
ing a few of these will be mentioned merely indicating the
probable application of the rules of article 32.

Ammunition and Explosives

 

The manufacture of these materials is in the hands of
thoroughly reliable firms who take upon themselves the responsi-
bility for safeguarding life and property. Hence, discussing
recommendations for electrical construction in factories manu-
facturing these materials would be of questionable value. In
general, motors and their control apparatus are placed outside
the hazardous area, and lighting is by the indirect method with
the lights placed in a non hazardous area.

Automobile Factories

The chief hazards from our viewpoint are woodworking,
painting, varnishing and upholstering, all of which have been
discussed under their respective headings.

Candy and Chocolate Factories

Only the sections used for the pulverizing of cocoa and
sugar should be placed in the hazardous class. Cocoa and sugar
dusts are explosive and, therefore, the rooms where these are
produced should be considered as Class II locations.

Clothing Factories

‘In the cutting of cloth considerable waste and lint are
often produced and reasonable means should be taken to prevent
its ignition. The rules for Class III locations should be
followed as far as they apply.

Coal Pulverizing and Handling

Coal dust is extremely explosive and this should be
kept in mind when considering electrical installations in
power houses or other locations where coal is pulverized. In

96

general, the coal pulverizing departments are regarded as Class
II locations. In the handling of bulk coal in coal elevators,
coal pockets and bunkers, similar consideration to the rules
for Class II locations should be given.

Combustible Fibers other than Cotton

 

In general, the same comment applies as given.under "The
Cotton Industry." Bagging factories and upholstery works should
be considered as Class III locations. Warehouses used for the
storage of fibers such as Jute, tow, hemp, etc., are included
as Class IV locations.

Electric Appliance Manufacturing

Finishing process hazards are predominant from our view-
point. Also hazards attached to the use of flammable volatile
solvents for thinning insulating varnishes applied by dipping
and baking. Reference should be made to section on "Finishing
Proceses.

Garages

Inasmuch as electrical rules for garages are contained
in Article 33 of the National Electrical Code, discussion of
them is not within the province of this thesis.

Hat Manufacturing

In the manufacture of straw hats, the practice of using
pyroxylin lacquer for sizing and varnishing is becoming very
common. Generally, this is required to be done in a cut off
room which, with.the drying room, should be regarded as a
Class I location. The hazards are similar to those discussed
under "Finishing Process.”

gattress Factories

These are usually regarded as a poor fire insurance
risks due to the presence of quantities of loose combustible
fibers. In general the sections devoted to the storage of
the fiber, the picker rooms, and the mattress filling depart-
ment should.be regarded as Class III locations.

96

general, the coal pulverizing departments are regarded as Class
II locations. In the handling of bulk coal in coal elevators,
coal pockets and bunkers, similar consideration to the rules
for Class II locations should be given.

Combustible Fibers other than Cotton

 

In general, the same comment applies as given under "The
Cotton Industry.” Bagging factories and upholstery works should
be considered as Class III locations. Warehouses used for the
storage of fibers such as jute, tow, hemp, etc., are included
as Class IV locations.

Electric Appliance Manufacturing

 

Finishing process hazards are predominant from our view-
point. Also hazards attached to the use of flammable volatile
solvents for thinning insulating varnishes applied by dipping
and baking. Reference should be made to section on "Finishing
Proceses.

Garages

Inasmuch as electrical rules for garages are contained
in Article 35 of the National Electrical Code, discussion of
them is not within the province of this thesis.

Hat Manufacturing

In the manufacture of straw hats, the practice of using
pyroxylin lacquer for sizing and varnishing is becoming very
common. Generally, this is required to be done in a cut off
room which, with the drying room, should be regarded as a
Class I location. The hazards are similar to those discussed
under "Finishing Process."

gattress Factories

These are usually regarded as a poor fire insurance
risks due to the presence of quantities of loose combustible
fibers. In general the sections devoted to the storage of
the fiber, the picker rooms, and the mattress filling depart-
ment should be regarded as Class III locations.

97

Metal werking Processes

Outside of the'hazards associated with the painting or
varnishing of finished products, the hazards of metal working
processes are light. A notable exception is that present when
dipping processes involving flammable solvents are used for the
removal of cutting oil and grease preparatory to heat treatment
or plating or for rust proofing purposes. The hazards of such
dipping processes are equivalent to those of ordinary naphtha
thinned varnish dip processes. Attention is called to the
section headed "Finishing Processes."

Oil Clothing Factories

In one step in the process of manufacturing oil clothing,
the garment is painted with a naphtha thinned varnish. General
rules usually require this to be done in cut off rooms which
should be regarded as Class I locations. This also applies to
the dry room connected with this step of the process.

Paper Industry

The manufacture of paper must be regarded in the light
of a process producing an easily ignitable material. The modern
paper factories producing newsprint and similar papers from
wood pulp are usually well ordered and all waste is promptly
removed and reworked. In paper factories producing special cut
papers, there is likely to be considerable waste and cuttings,
and in such plants extra precautions should be taken to prevent
ignition. It is probable that reasonable application of the
rules for Class III locations will be sufficient. In the
production of certain papers or paper products, such as boxes
and cartons, varnishes are used. Such processes should, in
general, be subjected to the comments made under "Finishing
Processes." Also see section on "Fabric and Paper Coating
Plants.

Printing Industny

In this industry, we are concerned chiefly with the use
of flammable liquids in the mixing of inks and cleaning of
type and presses. Usually, the amounts of such liquids used
for the latter are comparatively small and require only reason-
able care to prevent ignition of vapors. However, in some
types of inks, especially those used fer "Rotogravurs"
processes, naphtha is used for thinning, in fact some roto-
gravure inks are composed of one part ink to three parts
naphtha. In printing establishments where such inks are used,
it is apparent that rigid precautions should be taken, possibly
to the extent of enforcing all provision of the rules for Class

98

I locations, especially if the presses are located in small,
poorly ventilated rooms. Another hazard found in some types of
printing establishments is that of accumulation of waste paper
and trimmings which justifies the enforcement of the rules for
Class III locations in some instances.

Soap Manufacturing

In the manufacture of some types of soaps naphtha is
added to the extent of about 5%. The naphtha is added when
saponification is completed and is mixed with the soap at a
low temperature. Necessarily, the manufacture of such soap en-
tails the storage and pumping of naphtha and requires the
application of the rules for Class I locations to the pump
houses and the rooms where the naphtha is mixed with the soap.
In toilet soaps, of the transparent variety, alcohol is used
for the purpose of dissolving the soap and permitting the
impurities to settle, whereupon the alcohol is distilled off.
Obviously, the rooms or sections where these processes are
carried on should be regarded as Class I locations. Liquid
soap is made by dissolving a hard soap, usually made from
cocoanut oil, in warm alcohol to which potash and essences
are added. It is likely that the flammable vapors of alcohol
will be present where this process is carried on and, there-
fore, the rooms or section involved should be considered as
Class I locations. It has been discovered that soap dust is
explosive and for this reason due consideration should be
given to the application of the rules for Class II locations
to the soap pulverizing rooms.

Sggar Refineries

 

The manufacture and refining of sugar is largely a wet
process and, therefore, there are no unusual hazards present
from our viewpoint. However, when sugar is pulverized, the
dust eXplosion.hazard is present as sugar dust is quite
explosive. The rules for Class II locations should be en-
forced in the pulverizing rooms or department.

Woolen Industry

As wool fiber is not readily ignitable and burns very
slowly, we are not concerned with the woolen industry general-
ly. However, in many types of woolen fabrics some cotton is
used which may place certain sections of what are normally
woolen mills in the hazardous class. When this is found to
be the fact, the comments made in the section entitled "The
Cotton Industry" apply.

 

2522 n

THE RULES 9;: ARTICLE _:§_2_

Containing a complete
discussion of the rules

of Article 32 with re-
ference to their intent
and application; illust-
rated to indicate apparatus
available and methods of
installation.

99

THE RULES OF ARTICLE 52

INTRODUCTORY

Having disposed of the question of classification by .
means of the foregoing discussion, it is now in order to discuss
the individual rules of Article 52 as applied to each of the
four classes into which the various types of hazardous materials
have been placed. Such discussion should be of value inasmuch
as many engineers and inspectors have requested interpretations
regarding the application of Some of the rules to definite in-
stallations and advice concerning the suitability of certain
apparatus for use in a given hazardous location. This might
seem to indicate weakness in the wording of the rules, but
before reaching the conclusion that the rules should be more
explicit, it should be remembered that an attempt has been made
in Article 52 to outline the requirements for safe electrical
construction for a host of various types of industries and con-
ditions. To mention in the rules every conceivable condition
which might arise would result in an article far too lengthy
for the practical uses of_the engineer or inspector. In fact,
it would be a volume in itself. Necessarily then, the rules
were required to be more or less general with respect to
detailed application, and yet specific enough in principle to
be capable of enforcement.

In this section of the thesis it is proposed to discuss
each rule individually. First, by stating the intent of the
rule and the reasons for its inclusion; second, by suggesting
possible forms of electrical construction to comply with the
rules; and third, by illustrating the application of the rule
with photographs or drawings of available apparatus or actual
installations. Included also is a brief outline of the
standards of the Underwriters' Laboratories and their test
methods as pertaining to the construction and required per-
formance of electrical apparatus such as motors, controllers,
fittings, and switches, intended for use in hazardous locations.
To eliminate possible confusion, each of the four classes into
which Article 52 is divided will be considered separately, and
to render unnecessary reference to a copy of the National
Electrical Code, each rule will be quoted in full.

GENERAL

Under the heading of "General" there appears a rule
(Rule 3202a) which applies to all of the four classes and
‘which states: ”The requirements of this Article shall be con-
sidered additional and amendatory to those prescribed in
Articles 1 to 19 inclusive of this Code." This rule is insert-
ed for the purpose of calling attention to the fact that the

 

 

lOO

rules of Article 32 are not complete in themselves as covering
all phases of an electrical installation, but are merely
supplementary rules to provide the necessary guidance for in-

stallations in locations more hazardous than those ordinarily
found.

101

CLASS I LOCATIONS

The first rule (Rule 5202a) of this section states: "In
locations judged to be as described for Class I in paragraph b
of section 5201, the following provisions shall be observed."
This was inserted in order to make clear that the rules of
section 5203 are to be applied when the engineer or inspector
judges the conditions present to be as described in the
definition of what should be considered as Class I location, --
in brief, where flammable gases, vapors, or highly flammable
substances are present.

In several of the rules of this Class the term "explosion-
resisting" occurs. A few words in explanation of this term at
this point will make toward a better understanding of the rules.
It has been found that it is practically impossible to make
joints in conduit or fittings, the cases of controllers, and
the enclosures of motors such as to be vapor or gas-tight. The
alternate heating and cooling of the air within the enclosures
results in an unbalancing of pressures to such an extent that
the vapor or gas is forced through even the most minute 0 en-
ings. This phenomena is usually referred to as "breathing .
Assuming, therefore, that the vapor or gas will enter the
conduit and other parts of the enclosing system, it can be
expected that the mixture of vapor or gas and air will explode
when an arc occurs within the enclosure if the mixture is with-
in the flammable limits of the vapor or gas involved. With this
in mind, it is apparent that conduit joints and fittings, motor
and controller cases, and other enclosures must be so designed
as to prevent the emission of flame or hot gases, as well as
to withstand the pressures developed within the enclosing
system. The tests of the Underwriters' Laboratories, as will
be pointed out later, are made on this basis.

Service.Equipment, Panelboards and Switchboards

 

Rule 3203b provides: "Service entrance equipment, and
all panelboards and switchboards shall not be installed.”

It was felt that there was no good reason for install-
ing this equipment within the hazardous area inasmuch as
provisions could always be made for locating service equipment,
panelboards and switchboards outside of the hazardous area.

The rule is based on a premise which is used throughout Article
-32, namely, that of eliminating as much electrical equipment
from the hazardous area as possible, consistent with sound
economics, and providing that more serious hazards, whether

of an electrical or general nature, are not introduced by such
elimination. While it may be possible to design and build
explosion resisting service and distributing equipment, the
cost would undoubtedly be excessive, especially for installa-

102

tions of any considerable size. Furthermore, the replacement of
fuses which might often be necessary during working hours would
entail Opening the enclosing cases, a procedure which is dis-
.tinctly undesirable.

In an industrial plant such as an oil refinery where the
major portion is classed as a hazardous area, the service equip-
ment, panelboards and switchboards are best located in a
separate building outside of the hazardous area or one so built
and located that explosive vapors will not be present within it.
Very often such a building can be utilized for containing auto-
matic motor controllers as well as the service and distribution
eQuipment, thus serving a dual purpose.

In other instances where only a small part of the area
is classed as hazardous the service equipment can usually
readily be placed in an adjoining room or building in which
the hazardous conditions are not present. As an illustration,
in a rubber factory where the churn room may represent the
only hazardous location, the service equipment could be placed
in the calender room, boiler room, or other similarly non-
hazardous location, and yet be convenient with respect to the
churn room.

Typg_2£ Wiring

The Code requirements for wiring in Class I locations
are contained in Rule 5203c as follows: "Rigid conduit with
vapor-tight joints and fittings shall be employed as the type
of wiring. Where it is necessary to employ flexible connections,
as at motor terminals, an approved flexible fitting of the
explosion resisting type may be used. At points where conduit
terminates, such as at motor terminal boxes, switch boxes and
similar places, provision shall be made for sealing off the
conduit by use of a suitable insulating compound to prevent
the passage of gases or vapors through the conduit system.”

It is imperative that the type of wiring employed in
Class I locations be of the safest type available. Rigid con-
duit seemed to be the only type which could be regarded as
answering this specification for the reason that, unlike
various types of wiring, it provides, (1) effective protection
against mechanical injury to the conductors, (2) a low
resistance equipment grounding circuit, (3) reasonable pro-
tection against possible arcs burning through the conduit
wall, (4) explosion-resisting threaded joints or couplings,
and (5) a type of wiring not unreasonably expensive. Other
types of wiring such as armored cable, non-metallic sheathed
cable, and open knob and tube wiring are not considered
suitable for use in Class I locations for obvious reasons._
Electrical metallic tubing or thin-walled conduit, as it is

103

sometimes called, is a comparatively new wiring material and
although having many good qualities has not yet been considered
satisfactory for hazardous locations. Its construction is such
as to necessitate the use of threadless fittings with which
there might be difficulty in making joints and connections
permanently explosion-resisting.

It will be noted that the rule requires that joints be
vapor-tight. It has been found that it is impracticable to
make joints vapor tight, due to the "breathing effect." However,
it has been established by test that the joints in successive
lengths of conduit using threaded couplings are explosion-
resisting provided that at least five threads Of each length
of corduit engage those in the coupling. From our standpoint
approval based on the joints being explosion-resisting rather
than vapor-tight is warranted. As a matter of fact, he next
edition of the Code will so amend the rule.

What has been stated in the preceding paragraph with
regard to the requirement for vapor-tight points also applies
to the various types of conduit fittings. Complete lines Of
explosion resisting conduit fittings have been develOped and
are readily obtainable. Many Of these have been approved for
Class I locations by the Underwriters‘ Laboratories which have
develOped standards for the design and test of such fittings.
-These are equipped with threaded hubs rather than the usual
"knock-out" Openings and the covers are of the screw type,
both provided with at least five engaging threads. Figure
number 5 illustrates a group of approved fittings for various
uses in Class I locations. The method of testing fittings is
very similar to that employed in testing Class I motors to
which section reference should be made. ~

Because Of the fact that in many applications, it is
necessary to provide a flexible connection at the terminals
of a motor to permit shifting the motor on its base to take
up looseness in belts, it was found necessary to make a
concession and permit a flexible fitting at the motor terminals.
In some instances it is necessary to provide some flexibility
at motor terminals to prevent breakage of the conduit or
Objectionable loosening of conduit connections.where excessive
vibration exists. It will be noted that the rule requires that
this fitting be approved, and while approved fittings for this
purpose are not yet available, it is expected that one
will receive approval shortly. This particular type con-
sists of a flexible metal tube made up Of closed convolutions
of special design and the whole covered with a wire braid.
Screw connections are fitted to either end for attachment
to the rigid conduit fitting and the motor terminal box.
To obtain approval it is, Of course, required that this

il. 1.11

 

 

 

 

 

 

 

 

 

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‘9“ 520076. >

cuSSI
cussZL 7'

 

 

 

 

 

 

Figure No. 5.
Group of Explosion-Resisting
Fittings for Class I Locations

 

 

 

TYPE EYS SEALING CONDULET

 

WIRES mpg; TYPE. EYS SEALING CONDULETS wear.

PLUG DESIGNED TO FACILITATE. SEALJNG or A
Ric-3m CONDUIT SYSTEM AS REQUIRED
ev RULE. 5203 -c or THE 1931 NATIONAL
ELECTRICAL cont WHICH READS IN, PART
J— AS rOLLows ;- AT POINTS WHERE. CONDUI‘I‘

   
 

 

 

 

 

SEALING ‘;. ...-:'- ..
COMPOUND — 1.... * /5 TERMINATES, SUCH _As AT MOTOR TERM-
‘ a / —-4:— INAL boxzs, SWITCH eons AND SIMILAR
OAKUM 331mg PLACE5,PRDV1510N SHALL DE. MADE. FOR SEAL'
commune 1N6 OFF THE. CONOUII' er THE. USE OF A
2:33:35": SUITABLE INSULATING COMPOUND To
SECTION“. VIEW OUTSIDE. DIAMETER PREVENT THE. PASSAGE OF GASES 0R
‘1‘sz BYS CONDULET orI'Hs LARGEST VAPORS THROUGH THE CONDUIT SYSTEM .

 

WlRE. OR CABLE

 

Figure No. 6.
A Type of Scaling Fitting
Designed to Prevent Travel
of Vapors or Gases Through
Conduit Systems

105

fitting be explosion-resisting. The use of such flexible
fittings should be avoided whenever possible but there are
times when the exigencies of the case require their use and
only then should they be permitted.

The provision for sealing-Off conduit runs at motor
terminal boxes, switch boxes and similar places was inserted in
the rule for two reasons. Recognizing that the conduit system,
controller cases, motors, and other enclosures are not vapor-
tight, the "breathing action” would cause the vapors or gases,
mixed with air, to enter the enclosing system where the
mixture might be ignited by an are from a motor controller, a
spark from a motor or from an arc in the wiring. As the first
consideration, it is desirable to limit the amount of vapor or
gas present in an enclosing system subject to a single source
of ignition by sealing Off the conduit at the points mentioned
and so break it up into a series of individual enclosures.

This is especially important at motor controllers, switches,
and commutator type motors where sources of ignition are
present in normal operation, but should be done at all fittings,
outlet boxes and other points as well, whether containing
normally arcing or sparking parts or not. The second considera-
tion involves the tendency of gases and vapors to diffuse.
Assuming the presence of an explosive mixture in the conduit

it would be most undesirable that this mixture be permitted to
flow through the conduit to a point beyond the hazardous area
to a service switch for instance, which being in a non-hazard-
ous area would be permitted to be of the ordinary enclosed
type. It is reasonable to believe that under some conditions

a sufficient amount of an explosive mixture of vapor or gas
and air would accumulate in this service switch to cause an
explosion when the switch was operated. The switch box not
being designed to withstand such explosion pressures would
most likely burst, causing injury or fire.

Some manufacturers have so designed their Class I
fittings, controller cases and other equipment to effect seal-
ing by providing small wells into which the melted compound
can be poured after the conductors are in place. There are
available specially designed sealing fittings which are in-
tended to be used at controller cases and similar points to
provide easy facilities for sealing. One of these will be
found illustrated in figure number 6. There are also suitable
insulating compounds on the market, some of which are specially
compounded to resist the solvent action of certain vapors and
gases and which will not soften or crack in use.

 

 

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106'

Fuses and Circuit Breakers

The text of the rule (Rule 3203d) governing the use of
fuses and circuit breakers is as follows: "Fuses shall not be
installed unless mounted within explosion-resisting enclosures.
Circuit breakers, if used, shall be of a type approved for use
in explosive atmospheres.

It is contemplated that fuses and circuit breakers
generally will be located outside of the hazardous area as
discussed under "Service Equipment, Panelboards and Switchboards."
However, there are instances where it may be desired to install
them for single branch circuit protection or for motor overload
protection in locations within the hazardous area. Obviously,
it would not be desirable to depend on ordinary pressed steel
cases for enclosing such devices in a hazardous area and there-
fore, explosion-resisting enclosures are specified for fuses and
specially approved types for circuit breakers.

At this writing, there are no assemblies of fuses mounted
in explosion-resisting enclosures approved by the Underwriters'
Laboratories. It is probable that when such an assembly is
submitted for approval that it will be as a complete device
consisting of a cut-out block mounted in an explosion-resisting
case having sufficient strength to withstand the pressures
generated by explosions of vapor or gas and air within the case
as well as those resulting when the fuses are called upon to
open on heavy ground or short circuit conditions.

It is generally recommended that when it is necessary to
use a form of circuit protection within hazardous areas, that
circuit breakers be used in lieu Of fuses. Circuit breakers
are arranged so as to be self-resetting or so as to be capable
of being reset without opening their enclosures, whereas in the
case of fuses the enclosures must be opened when renewals are
made. The latter is a decidedly unsafe practice.

There are available a variety of circuit breakers which
have been approved for hazardous locations. The demand for
such devices has been confined to a large extent to those of
comparatively small capacity, that is, up to about 50 amperes.
The units now available employ the small circuit breakers
incorporating a thermal trip of the types represented by the
Westinghouse "Sentinel." These circuit breakers are enclosed
in explosion-resisting boxes fitted with threaded hub conduit
connections and a screw type cover to permit inspection and
repair. In Figure No. 7 are reproductions of drawings of two
types of circuit breakers now available. Figure No. 8
illustrates two hypothetical installations making use of
circuit breakers and other apparatus. These are externally
operable and may be used as a switch for the control of small
motors, lights or other devices in lieu of a switch if desired.

107

l
The operating lever extends through a;hub on the enclosure so

arranged that the emission of flame or heated gases at that
point is prevented. The testing of devices of this character
follows somewhat the same plan as outlined for motors for
Class I locations.

 

 

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Figure No. 7.
Two Types of Explosion-Resisting
Circuit Breakers.

These devices consist of thermal type circuit
breaker units enclosed in explosion-resisting
fittings and arranged for manual operation.
These may be used for branch circuit operation
or as control switches for lighting circuits
or small motors.

 

 

     
 

 

 

 

 

 

 

 

 

 
 

 

 

 

 

 

 

  

 

 

 

 

 

 

 

 

 

   
   

  

  
  
  

  
     
  
  
  
  
    

 

  

 

 

 

 

 

 

 

 

 

 

 

 

 

  
  
 
 
 

  
 
 
 

 

 

  
 
 

   

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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109

Motors

Rule 3205c requires that "Motors shall be of the types
approved for use in explosive atmospheres."'

From our point of view there are two types of motors;
first, those which have sparking or arcing parts, which
includes the usual single phase commutator motors, direct
current motors, wound rotor slip ring motors and some poly-
phase self starting motors which employ open centrifugal
switches or similar devices; and second, squirrel cage
induction motors. Although motors of the first type are more
hazardous than those of the second, when operating in a
hazardous atmosphere, it was deemed necessary to require that
all motors be of types approved for operation under the par-
ticular conditions to which they will be exposed. The word
"approved" as defined in Article I means, briefly, ”acceptable
to the authority enforcing this Code." In reality, as accepted
in practice, the definition is extended to imply, so far as
equipment is concerned, test, approval and subsequent listing
by the underwriters! Laboratories, as individual inspection
authorities, rarely possessing the necessary apparatus, are
not in position to make the required tests.

A motor, to be considered safe for operation in Class
I locations must necessarily be so designed that whether in
normal Operation or in case of a fault, such as a burn out,
it will not cause ignition of the hazardous material outside
of the motor. It is recognized that an open squirrel cage
induction motor normally having no arcing or sparking parts
would be safe if positive assurance were had that it would
operate as intended at all times. However, it is a known
fact that such motors develop faults which produce arcs and
sometimes complete burnout in spite of the best of maintenance
and protection, and so even such a motor cannot be considered
safeIin Class I locations.

In order to regulate the production of motors intended
for Class I locations the Underwriters' Laboratories assisted
by the Industry Conference of the motor manufacturers have
developed standards for the design and performance of a
special type of motor. It was feund by test that the ordinary
types of enclosed motors were not suitable for several reasons.
The Underwriters' Laboratories standard covering motors for
class I locations is of too great length to repeat in full in
this thesis. However, briefly stated, the requirennnts provide
that; (l) the casing or enclosing housing of the motor shall
have sufficient mechanical strength (with certain prescribed
factors of safety) to withstand successfully the explosion of
flammable substances within the casing; (2) the fits at points
where joints are made and at the shaft openings shall be of
such width and length as to prevent the issue of flame or

 

110

heated gases or vapors produced by such explosions to the
atmosphere surrounding the motor; (5) the motor assembly shall
have sufficient heat capacity to prevent the motor casing reach-
ing a temperature which would ignite the surrounding hazardous
substances even in event of burn-out of the motor windings; (4)
the terminal leads or conductors be securely held and tightly
fitted where they pass into the motor case. (Note: This is
usually accomplished by use of a sealing compound); (5) a suit-
able terminal box be provided for motors larger than one horse
power and a terminal box or provisions for direct conduit
connection for fractional horsepower meters; (6) each motor be
marked with a name plate giving, in addition to the information
generally included, data as to the class and group for which
the motor has been approved.

As in the case of conduit joints and fittings, a motor
to comply with the above requirements need not be vapor tight,
in fact, none of them may be 30 described, but they may be
termed explosion-resisting which is all that is required to
provide safety. The standards of the Underwriters' Laboratories
for Class I motors recognize three general types of enclosed
motors as candidates for approval for Class I locations; (1)
the totally enclosed; (2) the enclosed-fan-ventilated; and (3)
the enclosed-pipe-ventilated. Of the Class I motors above the
fractional horsepower size so far approved, all are of the
enclosed-fan-ventilated type. This is probably due to the fact
that this type is the most economical to build to answer the
requirements of the standards and also the easiest to install.
The totally enclosed type requires much additional capacity
to secure rated output and, therefore, results in a very
bulky machine. For instance, what would normally be a 15 horse
power open motor may have a rating of only 7% horse power when
it is made over into the totally enclosed type. The pipe-
ventilated type, while practical for some applications, offers
objections in the way of necessitating pipes, the installation
of which is not always convenient. Figures 9 and 10 illustrate
a sectional and an assembled view respectively of typical
enclosed-fan-ventilated motors which have been approved for
Class I Group D locations. Figure 11 is a reproduction of a
label by which motors approved for hazardous locations may be
identified.

As was pointed out earlier in this thesis, the different
gases and vapors possess varying characteristics as to flamma-
bility and explosion pressures. For economic reasons, due
consideration was given to these facts in the testing and
listing of motors for hazardous locations. As a matter of fact,
the Underwriters' Laboratories for their purposes have sub-
divided Class I locations as follows: '

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112

Class I, Group A Atmospheres containing acetylene.

Class I, Group B Atmospheres containing hydrogen.

Class I, Group C Atmospheres containing ethyl ether

vapor.

Class I, Group D Atmospheres containing the vapors of
gasoline, common petroleum, ethyl
alcohol, methyl alcohol, acetone and

lacquer solvents.

These hazardous vapors and gases are arranged in the
order of their degree of hazard, so equipment designed for the
more hazardous conditions can be used for the lesser. As an
example, a Class I Group C motor which is approved for use in
an atmosphere of ethyl ether vapor may be used in a group D
location, where gasoline vapor or others of the-group are
present. However, a Group D motor is not approved for use in
a Group C, ethyl ether vapor atmosphere. This holds true in
like manner for the other groups into which Class I is divided,
and as will be pointed out later, applies similarly in prin-
ciple‘to motors approves for Class II locations. The group
classification of a particular approved motor will be found
on the motor name plate.

The tests to which Class I motors are subjected in the
Laboratories are of mu interesting nature. It is required by
the Standard that the motors be subjected to a series of
tests in the presence of specific gas or vapor-air mixtures
over the range of flammable or explosive concentrations so
as to cover (1) the maximum pressure effects of the gas or
vapor-air mixture and (2) the maximum prepogation effects of
the gas or vapor-air mixture. These tests are conducted upon
the motor with the shaft bearings machined to clearances
representing maximum wear under service conditions.

The tests are conducted by placing the motor in a test
chamber provided with gas inlet and outlet connections to the
pipes carrying the explosive mixture. The motor casing is then
tapped with threaded holes for connection to the inlet and
outlet pipes carrying the explosive vapor or gas-air mixture
and is also tapped with threaded Openings for attachment of
the explosion pressure recording device and a spark plug for
ignition. Suitable auxiliary equipment is provided to prepare
and maintain the vapor or gas-air mixture in.sccordance with
predetermined concentrations. The explosive mixture is now
permitted to flow into the motor casing and the surrounding
test chamber until all of the original air has been displaced,
whereupon samples for analysis are taken from within the motor
casing, the test chamber and from the supply line. The mixture
within the motor casing is then ignited either by the spark

 

 

Figure No. 10.
A Motor Approved for
Class I Locations.

This view shows end where
cooling air is discharged.
The outer shell directs the
blast of air from the fan
over the surface of the
enclosed inner casing.

 

Figure No. 11.
Label of

 

unbgrmriters’ SfabomtofieS

 

Underwriters' Laboratories. INSPECTED
MOTOR FOR HAZARDOUS LOCATION:
A label of this type appears EOL1E52'CLASSB GROUPE NO.-

 

on approved motors which
permits ready identification.

 

"I ’..
t' .- y

. ~ _ '

 

Figure No. 12.
Explosion-Resisting Motors
in a Petroleum Refinery.

This view shows part of'a leading rack
pump house where explosion-resisting
motors are direct connected to loading
pumps.

114

plug or by sparks from the motor. Failure of the mixture in the
test chamber to ignite and explode When the mixture within the
motor casing was fired shows that flame did not propagate from
the interior of the motor casing to the surrounding explosive
atmosphere. A series of sixty or more such tests are conducted,
both with the motor in operation and at rest, and with explosive
mixtures over the entire flammable range.

A burnout test is then made to determine the maximum
temperature reached by the casing of the motor. In this test
the motor windings are actually burned out by ”single phasing"
or other means. The maximum temperature usually reached in such
tests on motors which are otherwise satisfactory is about 500
degrees Fahrenheit, which is well below the ignition tempera-
tures of all common gases and vapors, with the exception of
carbon disulphide vapon,and possibly that of hexane. Some
solid substances, however, such as pyroxylin, have ignition
temperatures as law as 212 degrees Fahrenheit and naturally
the usual type of Class I motor will not be safe for operation
where pyroxylin dust is present and likely to accumulate on
the motor casing. .

The development of suitable explosion-resisting motors
approved for use in Class I locations has provided types of
motors Which are permitted to be installed directly within the
hazardous area except for those areas where pyroxylin lacquers
or their residues might accumulate on the motor or where
carbon disulphide vapors may be present. When substances
having such low ignition temperature are involved, it is
probable that the only alternative is to isolate the motors
from these extra-hazardous vapor atmospheres or substances.
This is the course taken with regard to the motor installations
required for pyroxylin spray booths as will be seen in the
discussion on spray booths later in this section.

Attempts at isolating ordinary open motors from hazard-
ous vapor or gas atmospheres have not always proved success-
ful, due to the fact that it is difficult to protect the shaft
openings so that entrance of the flammable gases or vapors into
the motor compartment will be prevented. The "Loss Record"
appearing as the concluding part of this thesis relates several
fires and explosions which have occurred as the result of
depending on such isolation for safety. Approved Class I motors
properly selected with respect to the vapor or gas atmosphere
group are to be preferred to attempts at isolation as a general
rule. In figures 12 to 21 will be found photographs illus-
trating typical Class I motor installations. The explanatory
notes accompanying these illustrations describe the hazardous
conditions involved and the advantages gained by the use of
Class I motors in each instance.

 

Figure No. 13.
Explosion-Resisting Motor
Driving Pump.

Pump is used for handling naphtha and
other volatile solvents. Use of explosion-
resisting motor permits its installation
directly in pump room.

 

 

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Figure NO 0 14 0
Fan Motor Installation.

4,_. I
an

   

 

This illustration shows use of explosion-
resisting motors for driving fans in gasoline
recovery plants in large Eastern refineries.
Note use of explosion—resisting motor con-
trollers.

Figure No. 15.
Explosion-Resisting Motor
Installation in Bulk
Gasoline Station.

Use of this type of motor
permits its installation in
same room with the pumps.

 

 

 

 

 

 

 

Figure No. 16.
Motor Installation in
Petroleum Refinery.

View in upper right shows explosion-resisting
motor driving caustic soda pump for scrubbing
condensed gasoline.

Lower view shows group of motors approved
for Class I locations direct-connected to
gasoline pumps. Explosive vapors occur in
this pump house due to the flammable volatile
liquids, hence need for explosion-resisting
equipment.

 

 

 

Figure No. 17.
A Modern Dry Cleaning Establishment.

The upper illustration is of a dry cleaning
room showing washers along wall and
extractors in foreground all individually
driven by motors approved for Class I
locations.

The lower installation illustrates one of
a row of tumbler driers each with its
individual explosion-resisting motor.

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Figure No. 18.
Solvent Recovery Still.

The arrow points to the Class I motor
employed to drive the pump.

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Figure No. 19.
Two Types of Solvent Purifiers.

Note explosion-resisting motors used to
provide individual drives for these machines.

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Figure No. 20.
Compressed Gas Plant.

 

   

Explosion-resistin motor installs

in "bottled" gas pfant. Such plangion
handle gases of a highly explosive nature
hence the precaution taken in the type of,
motor selected.

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Figure No. 21.
Application of Class I Motors
to Unit Heaters.

These unit heaters are intended for
installation in lacquer plants or others
Where flammable vapors are present.

120

Motor Controllers, Switches, Resistance Devices
And Similar Apparatus.

It is obvious that it would be unsafe to permit motor
controllers, switches, resistance devices and similar apparatus,
which, in their normal operation create arcs, sparks or high
temperatures, in the hazardous areas with which we are concerned
unless such apparatus were so designed and built as to comply
with certain requirements regarding type of enclosure, capabil-
ity of the enclosure to withstand internal explosion pressures,
and ability of the enclosure to prevent emission of flame in
event of internal explosion.

The rules for Class I locations cover-this situation in
Rule 5203 which states: "Motor controllers, thermal cutouts,
switches, relays, the switches and contactors of autotransformer
starters, resistance or impedance devices or other devices or
apparatus Which, in their normal operation, tend to create arcs,
or high temperatures, shall not be installed unless such
devices are of a type approved for use in explosive atmospheres."
Following this rule is a fine print note as follows: "It is
recommended that motor controllers be of the remote control
type with the main contactors located at a point where the
hazardous conditions of this class do not prevail, auxiliary
control push buttons or switches of a type approved for use in
explosive atmospheres may then be placed in the most convenient
locations.”

As in the case of motors, approval of the apparatus and
devices mentioned or implied by this rule usually involves
compliance with the standards of the Underwriters' Laboratories
for the design and test performance of such apparatus and
devices for the particular atmosphere group in which they are
intended to be used. Definite standards for construction and
test methods have been set up for industrial control devices
for Class I locations. These standards are of too great length
to repeat in full here, but it should be mentioned that two
types of control devices are recognized, viz: (1) those in
which contact is made and broken in air (air break) and (2)
those in which contact is made and.broken under oil (oil break).
Briefly, the standard for air break control devices specifies
that the enclosures be of substantial construction and capable
of withstanding certain internal pressure, (with certain pre-
scribed factors of safety), depending on the size and shape
of the enclosure, its free internal volume and on the nature
of the gas or vapor-air mixture. Joints in the enclosure are
limited to certain maximum widths with respect to the length
of the joints and definite requirements are provided with
regard to the nature of the shaft openings for re-setting or
operating mechanisms. Such joints and openings are required
to be of the metal to metal type, gaskets not being permitted.

121

The standard further states that provision for conduit
connections with threaded joints shall be made and that the
temperature of the exterior of the enclosure, assuming an
ambient temperature of 40 degrees Centrigrade, shall not exceed
safe temperatures for the gas or vapor-air mixtures under con-
sideration, which, for the various groups, are specified as
follows:

 

 

Group Mixture (Temperature D g. Cent.
A Acetylene (None given)

B Hydrogen . (None given)

C Ether 180

D Gasoline 280

The tests made by the Laboratories on air break control
devices for Class I locations are practically identical with
those made on motors, with the special provision that the
devices shall be energized at rated potential and with all
current carrying parts at maximum temperatures as based on
full rated load operating conditions. A series of fifty or
more such tests is made, covering the entire flammable range
of the vapor or gas for use in which the device is intended.
As with tests on motors, failure of the mixture in the test
box to be ignited and explode when the mixture within the
device enclosure was fired shows that flames did not propogate
from the interior of the device under test to the surrounding
atmosphere. Thus, the two principal points of the standard are
established and the approval of the device is given or it is
rejected. These tests are, of course, additional to those made
by the Laboratories on industrial control equipment generally.

In oil break control devices, it is required by the
standard to have all electrical connections, joints, terminals,
or arcing parts below the normal oil level. The enclosures are
required to be of substantial construction and shall be so
designed as to avoid any possibility of sparks being produced
above the oil level. Visible oil level indicators must be
provided to indicate minimum, normal and maximum oil levels,
and it is required that all connections, terminals, and arcing
parts be immersed to a depth of at least six inches below
normal oil level. The exterior temperature requirements are
identical with those for air break devices.

In testing oilbreak control devices the enclosure is
filled to two inches below normal level with oil specified by
the manufacturers of the device. It is then tested by intro-
ducing the particular gas or vapor-air mixture into the
enclosure above the oil and subjecting the controller to a
series of operation tests conducted at rated potential and
at full rated load. Necessarily, to pass these tests success-

 

 

 

 

 

 

Figure No. 22.
Explosion-Resisting
Switches Approved for
_Use as Auxiliaries
for Motor Controllers.

C25;

I
THE Laws ALLIS Ca.
Wu: ‘j/EE “'15

I .-

Figure No. 23.
Group of Motor
Controllers Approved
for Class I Locations.

These are of the air-break
type. Note width of flange
of switch case in illustra-
tion to left.

fully no ignition of the flammable gas or vapor-air mixture
should occur.

Although the rule specifies that thermal cutouts, relays
and similar spark producing devices be of the type approved
for use in explosive atmospheres, they are usually an integral
part of a motor controller and, therefore, are approved with
the controller as an assembled device.

Resistance and impedance devices are not commonly found
in Class I locations, but, if used, are required to comply
with the above standards for control devices. At the time of
this writing no resistance or impedance devices have been sub-
mitted to the laboratories for approval for Class I locations.
It is probable that where such devices are needed, they might
better be isolated from the hazardous area.

Switches other than those used as motor control devices
are also required to be explosion resisting and are tested in
a manner similar to that used for control devices.

Where automatic controllers are employed, it is necessary
that the auxiliary control push buttons or switches, if in the
hazardous area be of the type approved for Class I locations
of the particular group of gases or vapors involved.

The manufacturers of motor control equipment have placed
on the market complete lines of motor controllers and auxiliary
control push buttons or switches for Class I, Group D locations.
They are made in both the oilbreak and air break types and
arranged for either manual or automatic operation. In figures
22 to 24 inclusive are illustrated several representative types
of motor controllers, with their auxiliary push buttons and
switches, which have been approved for Class I locations.

The fine print note following this rule should receive
special mention. In many cases it is convenient to isolate the
principal control equipment from the hazardous area in a
manner similar to that suggested under "Service Equipment,
Panel Boards and Switchboards." This course should be followed
whenever possible as isolation of controllers always results
in a safer installation than is the case when controllers are
placed within the hazardous area, even if the latter
controllers are of the types approved for such hazardous
locations.

"l' ~‘tu 3H}.
HI‘HHUH

 

 

Figure No. 24.
Explosion-Resisting Motor Controllers.

The controllers illustrated are of the oil

break type. The interior construction is
illustrated in the views showing the oil
tanks removed.

 

 
 
   
  

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‘Heating Appliances

Permitting the installation of heating appliances in
hazardous areas without definite control as to what type of
heating appliance would be used, would result in the intro-
duction of serious hazards. The temperatures reached by heating
appliances are often far above the apparent ignition tempera-
tures of the various gases and vapors in the atmospheres of
which they may be installed and so would furnish an excellent
source of ignition to cause an explosion.

To control sudh a situation, the following rule (3203g)
was inserted: "Electric heating appliances shall not be used
unless they are of a type approved for the particular location
or type of material in or with.which they are used." This rule
again contemplates approval of such heating appliances by the
Underwriters' Laboratories in practically all cases.

So far as the writer is aware, no heating appliances
have yet been submitted to the laboratories for examination
and test and there apparently has been no demand on the
Laboratories for a standard to guide manufacturers as to what
would be required in order to secure approval of a heating
appliance for Class I locations.

It is not likely that there will be any extensive use
of electrical heating appliances in hazardous locations except
for very special uses, such as sterilizers for use in hospital
operating rooms where the sterilizer may be in an ether or
ethylene air’atmosphere. Another possible exception are the
specially designed heaters used in connection with spray paint-
ing. Undoubtedly the development of suitable and safe appliances
for these purposes will require much study and experimental
work.

Switches for Lighting Circuits

Rule 3203k states that: "Switches controlling lighting
circuits shall not be installed unless of a type approved for
use in explosive atmospheres."

This rule requires little comment as the situation is
similar to that discussed under "Motor Controllers, etc."
Such switches are subjected to tests similar to those used
for air break motor controllers and are required to have the
same qualities with regard to non-emmission of flame and
maximum temperature of the housing.

It will be seen that the rule implies the possibility
of locating the switches outside of the hazardous area. This
is done in many cases, especially when the hazardous area is

126

represented by a single room or cut-off section of an establish-
ment of considerable extent. As an example, the switches for
controlling the light circuits of a dry cleaning room may be
placed just outside of this room, and then such switches may

be of the ordinary type, providing, of course, that the room

in which they are located is not also a hazardous location.

In event of lighting installations of considerable size,
a possible solution is to extend each circuit to a point well
outside of the hazardous area, fuse each circuit separately
and control the entire group of circuits by a single magnetic
contactor type switch actuated by means of an explosion-resist-
ing auxiliary push button or switch located within the hazard-
ous area. Such control would be both convenient and safe.

Suitable explosion-resisting switches for lighting
circuits have been developed and are available. In figure 25
are illustrated two types for use in Class I, Group D, locations.
The switching mechanisms of these switches are housed in
explosion-resisting cases having the operating shafts extend-
ing through long-path, smalléclearance bearings or sleeves
which successfully prevent the emission of flame to the outside
should an explosion occur within the housing.

The circuit breaker assemblies mentioned under "Fuses
and Circuit Breakers," are also suitable for use in Class I
locations for controlling lighting circuits. -

Lamps in Fixed Positions

In rule 52051 it is required that: "Lamps in fixed
positions shall be enclosed in a manner approved for explosive
atmospheres and shall be properly protected by substantial
metal guards or other approved means where exposed to breakage.
Lamps shall not be of the pendant type unless supported ridig-
ly by conduit hangers. Where rubber covered wire is used, it
shall have insulation not less than 3/64th inch thick."

The proper guarding of lamps is of extreme importance
as the breakage of a lamp results in an intense flash or are
and is usually accompanied by the falling of incandescent
metal, either of which may accomplish ignition of hazardous
substances. Also the temperatures reached by some parts of an
electric lamp, especially one of high.wattage, is often hi
excess of the apparent ignition temperatures of certain
vapors and gases. By providing such lamps with enclosing
globes or with specially designed fixtures with heavy glass
lenses, the maximum temperature of exposed parts is consider-
ably reduced. The enclosing globe or fixture assists to some
extent the purpose of the required guard, as it is found
that the strength of the globe or fixture is sufficient to

 

 

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Figure No. 25.
Types of Lighting Circuit Switches.

The upper switch is especially designed
for gasoline pump dome lights.

 

127

withstand a considerable shock or blow and thus serve to help
protect the lamp from breakage.

It will be noted that the rule requires that the lamp
shall be protected by substantial guards or other approved
means where exposed to breakage. Thus, lamps which are mounted
at or near the ceiling may not be required to be provided with
guards, due to their position. It should also be pointed out
that a possible substitute for metal guards might be heavy
glass lenses properly fitted to a lighting fixture. Lighting
units of such design are available and, undoubtedly, are
sufficiently rugged to withstand any shock or blows which
might be reasonaUW'expected. Probably lighting units of such
types will be found suitable for the operating rooms of
hospitals.

In order that the temperature of enclosing fixtures be
reduced, it is to be recommended that the installation of a
few high wattage lamps in a hazardous area be avoided in favor
of a large number of lower wattage lamps to obtain the same
intensity of illumination. Another procedure which should be
followed is that of using oversize enclosing fixtures in order
to provide increased radiating surface. For instance, it is
advisable to employ a 100 watt size fixture to accomodate none
larger than a 60 watt lamp. The temperatures reached by certain
parts of so-called vapor proof fixtures are excessively high
when the higher wattage lamps are used. Attention is called
to the drawing accompanying the section on spray booth light-
ing (Figure 27) which gives some definite information on
this matter.

The Underwriters' Laboratories have developed a tenta-
tive standard for the design and testing of lighting fixtures
for Class I hazardous locations. This standard, in brief,
provides that, (l) the enclosure mhall be of sufficient
strength to withstand the pressures developed by vapor or
gas-air explosions occurring within it, (2) the glass of
which the globe or lens is made shall be free from internal
strain and of sufficient thickness to resist breakage by
internal explosions, (5) the joints of the enclosure shall be
of the metal to metal type and of certain width and length
specifications and (4) that protection in the form of guards
shall be provided unless the fixture design itself adequately
protects the globe or lens against breakage. Several other
specifications are included regarding provisions for
connection and sealing-in of conductors. The temperature
requirements are identical with those mentioned under "Motor
Controllers, etc.," this referring to both the internal and
external temperatures. The internal temperature limitation
is necessary in order to prevent the repeated ignition and
possible explosion of mixtures within the fixture and which
is possible when such mixtures can enter and accumulate.

128

Again the "breathing action" is involved in a manner similar
to that which has been discussed previously.

The tests to which such fixtures are subjected are
similar to those made on motors for Class I locations so far
as the explosion tests are concerned. Gas or vapor air
mixtures are introduced within the globe or fixture and
fired, and if flame does not pass out of the fixture to
ignite the mixture in the test box, it is assumed to be
explosion resisting. A series of fifty or more such tests
are made. Temperatures, both internal and external are also
determined when a lamp of the maximum wattage for which the
fixture is designed is in place and operating at rated
voltage. Vibration tests to determine the security of
assembly of the fixture complete the tests.

To date no lighting fixtures have been approved as
complying with this standard, although one manufacturer has
'just recently developed a fixture which he believes will be
approved.

As a temporary substitute for lighting fixtures
especially approved for Class I locations, inspection
authorities have been accepting fixtures of the so called
vapor-proof type, a group of which are illustrated in
figure 26.

It will be seen from the rule that ordinary flexible
cord pendant supports for lamps are not permitted. This is
for the reason that such pendants are readily subject to
injury, to undue wear by coming into contact with vibrating
objects, and because such injury or wear may cause exposed
arcs or sparks. There remain then two alternatives, the
first, use of rigid conduit hangers and the second, attach-
ing the fixtures direct to the circuit conduit.

The final sentence of the rules requires the
insulation of conductors used for wiring fixtures to be
5/64 inch thick when rubber covered wire is used. This was
inserted as a precaution against break-down and injury.

 

 

 

The above units are suitable
where not exposed to breakage.

 

 

 

Fixed lighting unit
equipped with guard
and vapor-proof globe.

 

 

 

Unit designed for use
in automobile greasing
pits.

Figure_No. 26.
Group of Vapor-Proof Lighting Fixtures.

These should be regarded as temporary
substitutes pending development of light-
ing fixtures especially approved for
Class I Lecations.‘

150

Electrical Equipment in Spray Booths

 

 

Owing to the low temperatures at which pyroxylin
varnish residues decompose and ignite (ignition at temperatures
of 212 degrees Fahreheit and possibly lower) it was found
necessary to provide definite rules for the exclusion of
electrical equipment in spray booths. Rule 5205j, which
relates to this states: "No motor, lamps, or lighting
fixtures of any type shall be located within spray booths,
in ventilating ducts connected therewith nor in any location
where there is a possibility of the spray lodging upon them."
This is followed by a fine print note as follows: "Motors in
spray painting establishments that are located outside of the
paint spray booths and ventilating ducts and are judged by
the authority enforcing this code to be outside of the
hazardous area may be of any standard totally-enclosed type
or of the open induction type having no brushes, make-and-
break contacts, collectors or other arcing or sparking parts."

Closely associated with the foregoing is rule 5205k
which provides that: "The auxiliaries of mercury-vapor lamps
shallnbe offset at least ten feet from spray booth working
face.

It should first be pointed out that the above rules
apply to all spray booths and not only those in which
pyroxylin varnish sprays are used. One can never be certain
that a booth used in connection with ordinary oil varnish
spraying operations willnot be changed to accomodate pyrox-
ylin; varnish spraying without notice. Furthermore, even
with the less hazardous oil varnish sprays it is found that
objectionable coatings of varnish are formed on any motors,
and lighting fixtures with which it comes in contact, often
in such quantities as to prevent normal radiation of heat
from such motors and fixtures. Hence, the desirability of
rule 5205j.

With regard to pyroxylin sprays, it should be repeated
that with them a combination of hazardous materials is in-
volved, first, the pyroxylin itself; second, the solvent
such as amyl acetate; and third, a thinner, such as acetone
or alcohol. In the application of such pyroxylin sprays we
not only have to deal with the explosive vapors of the
solvents and thinners, but also with a fine highly flammable
dust or residue placed in suspension in the air within the
booth and ventilating ducts. Quantities of this residue
accumulate in the booth and in the ducts in spite of the
ventilating system, and if meters or lighting fixtures are
located in these places it is a foregone conclusion that
considerable residue will collect on them. The normal heat
of a motor or lamp is sufficient to cause decomposition
and ignition of this residue and this often results in a

131

flash fire or literally an explosion.

The Underwriters' Laboratories conducted a series of
tests about four years ago to determine whether or not so-
called vapor proof lighting fixtures could be safely installed
directly within spray booths in which pyroxylin sprays were
employed. The answer provided by these tests was an emphatic
"No", for it was found that ignition of the pyroxylin dust
was obtained at various points on the fixture and globe when
pyroxylin varnish was sprayed directly at them. Flaming
ignition occurred at a frequency of one trial out of five, in
some cases ignition occurring at the moment the spray came in
contact with the surface and in others a few moments later.

In the tests not producing actual ignition it was found that
the residue was decomposed with the evolution of the character-
istic explosive vapors or fumes. By means of thermocouples

the temperaturesof various points on the globes and fixture
were determined. These ranged from 295 degrees Fahrenheit on
the neck of the fixture to 471 degrees Fahrenheit on the
surface of the globe.

The tests also included an investigation of the
temperatures of various parts of a mercury vapor lamp and of
the resistance coils of its auxiliary. The spray test using
pyroxylin varnish.was also made on this lamp and on the
auxiliary. Ignition occurred at the upper end of the lamp
where the temperature was found to be 455 degrees Fahrenheit
and also on the main resistance coils of the auxiliary where
a temperature of 758 degrees Fahrenheit was recorded. The
latter is sufficient explanation of the reason why mercury
vapor lamp auxiliaries are required to be placed at a distance
of at least ten feet from the working faces of.spray booths
and the entire test is offered in support of the rule prohibit-
ing the installation of lamps and lighting fixtures within
spray booths. Obviously, this also excludes portable lamp
units for use in spray booths.

While no actual tests have been conducted to determine
the possibility of ignition of pyroxylin varnishes by motors,
it is a safe assumption that if ignition is obtained on an
enclosed lamp with a temperature of 471 degrees Fahrenheit
that igntion would certainly occur in event of burnout of a
Class I motor during which it is known to reach a temperature
of 500 degrees Fahrenheit. Hence, the exclusion of meters of
any type from spray booths or ventilating ducts connected
with them.

The tests referred to above are reported in some detail
in an article by Mr. A. H. Nuckolls, Chemical Engineer of the
Underwriters' Laboratories, which appeared in "Laboratories'
Data" issue of March, 1928. The article contains some
valuable and interesting data. Through the courtesy of Mr.
Huckolls it is possible to reproduce a graphic record of the
results of the tests. This will be found in Figure 27.

 

 

 

 

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Figure No. 27.

The above illustrations record graphically
the results of tests conducted by the
Underwriters' Laboratories to determine
ignition characteristics of pyroxylin
lacquer with respect to lighting units.
The upper drawing indicates the results of
the tests using a 100 watt lamp in vapor-
proof fixture. The lower drawing gives
similar data when a mercury vapor lamp and
its auxiliaries were used in the tests.

155

The motors driving the fans for ventilating spray booths,
being required to be placed outside of the booths and ventilat- '
ing ducts, can be located in any of the several places with
safety. In ventilating systems using the indirect method, the
motors and fans may be placed on the roof or in some other
equally non-hazardous place. Where the fan proper is placed
directly within the duct the motor driving the fan is located
outside of the booth and duct, usually in the rear of the booth
where it will not be exposed to the spray. In such locations,
it will be noted that the rules permit the use of any standard
type enclosed motor or an open induction motor of the non-
sparking type. However, where there is any possibility of
diffusion of the flammable solvent or thinner vapors to the
area where such motors are located, the type approved for
Class I locations should be specified. Figure 28 illustrates
two methods of spray booth ventilation and shows approved motor
installations for them.

Inasmuch as lamps are not permitted directly within
spray booths it is necessary to place them outside of the booth
in such a manner that sufficient light will be provided so as
not to interfere with the quality of the work produced. There
are several plans which have been used successfully which will
be described briefly.

In a large automobile body factory which the writer
visited, the owners had provided openings in the walls of the
booths which openings were covered with wire glass. Behind the
glass were installed mercury vapor lamps outside of the booth
and where they would not be subjected to accumulations of
varnish residue. In another plant, high wattage flood lights
with reflectors were placed at a distance of about ten feet
from the face of the booth and the lights focused on the
articles being sprayed. This method is probably the safest
of all. In long tunnel type spray booths it is common to
find openings at intervals along the length of the booth
through which openings light from vapor proof flood lights
was directed. This method has found considerable use in rail-
road coach finishing shops.

For the smaller booths a reasonably safe lighting in-
stallation can be provided by placing vapor proof lighting
fixtures on special brackets so attached to the top of the
booth that the fixtures are fairly well away from the booth.
In such installations a baffle is provided to prevent the
spray from coming into contact with the fixture.

The practice of placing lighting fixtures in such a
position as to project inward from the wall of the booth is
to be condemned, as in such a position not only will residue
collect on the fixture, but the fixture is subject to
mechanical injury. This applies, whether the fixture is of
the vapor proof type or not.

 

 

 

Figure No. 28.
Two Methods of Spray Booth Ventilation.

The upper view illustrates the direct
method and procedure of placing motor
outside of the booth and duct.

The lower illustration shows application
of the indirect type of ventilation.

Note that motor driving fan is outside of
the booth in a place which permits use of
open non-sparking type.

155

In the illustrations (Figures 29 and 50) will be found
representative examples of spray booth lighting of the types
mentioned above. There are included in Figure 51 two types of
vaporproof floodlights which are suitable for mounting at a
distance from the face of the booth or for providing light
through openings in the side walls of tunnel type booths.

Portable Lamps

 

Portable lamps and their cords are without a doubt the
most hazardous pieces of equipment used and, as will be seen
by referring to the "Loss Record" of this thesis, they have
been responsible for many losses Which have occurred in Class
I locations. Any attempt to produce a portable lamp assembly
for use in a Class I location is but a concession to necessity
or convenience. However, it must be recognized that such
portable lamp assemblies will be used and rather than leaving
the matter to the judgment of the individual, rule 52051 was
inserted which states: "Sufficient general illumination shall
be provided by fixed lighting units to eliminate, so far as
possible, the need for portable lamps. When portable lamps
are necessary, they shall be enclosed in a manner approved
for explosive atmospheres and shall be properly protected by
substantial metal or other approved types of guards to prevent
breakage. Sockets for portable lamps shall be of the keyless
moulded composition type with no exposed metal parts."

The importance cf providing sufficient illumination by
means of fixed lighting units should be strongly emphasized.
In many cases, portable lights would not be needed were the
general illumination properly designed originally. Illumination
by fixed lighting units should be designed with respect to
machines or work benches for by so doing it is probable that
the need for portable lamps will be greatly reduced. The
Underwriters' Laboratories have not yet developed a standard
for design and test of portable lamps specifically, but it is
assumed that the standard for lighting fixtures generally will
apply to portable lamps. As this standard has already been
discussed, nothing further need be said. To the knowledge of
the writer no portable lamp assemblies have yet been sub-
mitted to the Laboratories for examination and test. However,
the practice has been to accept the so-called vapor proof
portable lamp assembly for use in Class I locations, again
a concession to necessity. Such an assembly is illustrated
in Figure 52. ~

It should be mentioned that there are some places
where portable lamps of any type should be prohibited because
of the rather high temperatures reached by the surface of
the enclosing globe. Such locations may be in factories
manufacturing articles from pyroxylin plastic, nitrate film

 

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Figure No. 29.
Illustrating Various Methods of
Spray Booth Lighting.

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Detailed View of Small Spray Booth.
Note location and protection of
lighting fixture.

 

Figure No. 51.
Two Types of Vapor-Proof Flood
Lights for Spray Booth Lighting.

Fixtures of this type may be placed at a
distance of ten feet from the working face
of the booth and the light directed into

the booth interior.

158

storage vaults, sections of establishments Where carbon disul-
phide is used, and others. The materials mentioned have low
ignition temperatures and might easily be ignited by the heat
from a portable lamp, even though the lamp is enclosed.

It is reQuired that the exposed metal portions of a
portable lamp assembly be grounded, but this is specifically
cared for in rules 5205m and 5205p, discussion of which will
follow. A grounding terminal is usually provided within the
lamp assembly to which the grounding conductors may readily
be connected.

Portable Cords

Sub-standard portable cords have caused many fires and
explosions in Class I locations and are placed in the same
category as portable lamps from the point of view of being
concessions to necessity. Their use should be avoided whenever
possible, but when it is necessary to employ portable cords,
they should be of as short a length as practicable to
accomplish the purpose desired.

Recognizing the fact that portable cords must be used
under some circumstances, guidance as to the types Which
should be selected is given by rule 5205m which provides
that: "When necessary to use portable lamps or other portable
current- -consuming devices, approved flexible cord designed
fer hard usage such as Type S or Type PA shall be used. Such
a flexible cord shall contain one extra insulated conductor
which shall be properly connected to form a grounding
connection for metal lamp guards, motor frames, and all other
exposed metal portions of such portable lamps and devices."

The Type S cord referred to is a heavy reinforced
rubber-jacketed cord which is designed to withstand very
rough usage. Of any portable cord, it is probably the most
desirable for Class I locations. The type PA cord has a steel
armor over the rubber insulation and while having enduring
qualities, it is not nearly as flexible as the type S cord
which may, under some circumstances, be a point against its
use.

It will be noted that an extra conductor is required
to provide for grounding of the exposed metal parts of the
lamp assembly or other portable device. This extra conductor
is connected to the grounding terminal in the lamp assembly
or device and also to the grounding connection in the
attachment plug, or to the conduit system when portable
cords are attached directly to the supply conductors. The
metal armor of type PA cord is not to be accepted as a
grounding circuit, due to its probable high resistance and
the doubtful character of the terminal connections.

a. «sw- -

 

159

Connection 23 Portable Cords

 

 

Rule 5205m provides for attachment of portable cords
direct to the supply conductors as follows: "Connections of
portable cords direct to supply conductors shall first be made
mechanically secure and shall then be soldered and heavily
taped. In addition, the cord shall be securely supported so
that the probability of a break in the conductors at this
point will be minimized. This rule is in recognition of
possible installations such as over a long row of work benches
where permanent attachment of portable cords is desired. The
importance of removing the strain from the connections is to
be emphasized. There are fittings on the market which were
specially developed to comply with this rule. These are of the
type which attach directly to the conduit by threaded joints
and provide means for gripping the conductors securely to re-
move the strain from the connections. Facilities for sealing-
off the conduit are also provided. It is not expected that
this method of attaching portable cords to the supply
conductors will be very generally employed.

The separable connections as provided for by rule 5205c
will probably be used in the large majority of cases for
connecting portable cords to the supply. This rule states:
"Receptacles and attachment plugs, if used, shall be so
connected as a part of a unit device with an explosion-proof
inter-locking switch that the plug cannot be removed while
the switch is in the "on" position or approved devices which
seal the are, made when current is interrupted, by means of
an explosion-resisting or vapor-proof enclosure shall be used.
Such receptacles and plugs shall be of the polarized type,
providing a connection for the grounding wire of the portable
cord. .

It is admitted that the wording of this rule is rather
involved and the exact meaning not clear to one not familiar
with the intent. An attempt will be made to clarify this rule
for the next edition of the Code.

The intent of the rule is to provide for attachment
plugs and receptacles which will not permit an arc to occur
in the hazardous atmosphere when the plug is removed from the
receptacle. This may be done by two methods as follows:

1. By designing an assembly consisting of a circuit
switch and a receptacle.which are so interlocked
that the plug cannot be inserted in the receptacle
unless the switch is in the "off" position, and
when once in the receptacle, the plug cannot be
removed while the switch is in the "on" position.
While the rule now reads "explosion-proof" it is
intended that the switch and receptacle assembly
be "explosion-resisting" in accordance with the
requirements for switches in general.

 

 

 

llllll’llll

140

2. By a specially designed plug and receptacle in which
the are developed when the plug is removed is con-
tained within an explosion-resisting enclosure. This
may be accomplished by providing a long sleeve plug
fitting closely over the shell of the receptacle with
prongs or contacts of such length that the circuit is
broken before the plug has travelled a sufficient
distance to permit the emission of flame from any
explosion which might occur within the chamber made
by the plug and receptacle. It will be noted that the
plug and receptacles of both types are required to
be polarized to eliminate the possibility of the plug
being incorrectly inserted. An extra contact is
provided to accomodate the grounding conductor.

Devices of both types are available. One complying with

the second specifications above will be found illustrated in
figure 55.

Grounding

 

The proper grounding of the non-current carrying metal
parts of equipment is very important because of the fact that
should an accidental ground occur anywhere in the system with-
in the hazardous area, the service fuses or other circuit
protection should open immediately and clear the circuit. With
a high resitance grounding circuit, or an installation operat-
ing without an equipment ground, it is probable that serious
arcing would result, possibly to the extent of burning through
the conduit. Rule 5203p provides that: "The exposed non-current
carrying metal parts of equipment, such as the frames or metal
exteriors of motors, fixed or portable appliances, fixtures,
cabinets, cases, and conduit shall be grounded as provided in
Article 9 of this Code. The locknut-bushing and the double-
locknut type of contact shall not be depended upon for bonding
purposes, bonding jumpers or other approved means being re-
quired to assure an effective grounding circuit."

It will be noted first, that it is required that equip-
ment grounding be provided in accordance with the rules of
Article 9 Which is the article of the National Electrical Code
dealing with the subject of "Grounding." The second sentence
of the rule is intended to provide for a low resistance
grounding circuit in that part of the conduit system outside
of the hazardous area to the point where the connection is
made to the water pipe or grounding electrode. It is not
thought safe to rely on locknut and bushing types of contact
between conduit and cases as very often excessively high
resistance is introduced into the grounding circuit by im-
properly made or loosened conduit connections at cases or
similar points. For this reason the requirement for bonding

141

jumpers at such points is provided. Inasmuch as positive
threaded connections are used at all points within the hazard-
ous area, bonding jumpers are not required, for the threaded
connections are sufficient in themselves. Suitable bonding
bushings and flexible jumpers are available by which the bond-
ing can be neatly done within the cabinets or cases. Figure

34 illustrates the use of such devices. As an alternative
method, exterior bonds employing clamps and jumper conductors
are permitted by the rule.

For the grounding of equipment in a Class I location,
every effort should be extended to secure a ground connection
of low resistance. Preference should always be given to a
continuous water piping system as the grounding electrode.

Live Parts

 

 

Rule 3203q requires that "There shall be no exposed
live parts." This rule requires no comment, as in reality,
compliance with all of the preceding rules of the Article
automatically fulfills the conditions imposed by this rule.

‘gasoline Discharge Devices

The Underwriters' Laboratories have established
standards for the design and test performance of motor driven
gasoline discharge devices for filling stations. Where former-
ly the pump itself was examined and tested as an individual
device, the new procedure provides for the examination, test-
ing and listing of the entire pump assembly, including the
motor, its control switch, and wiring as a complete unit.

When a dome light is provided on the top of the device, this
also is included in the consideration.

The standards provide requirements which are in
thorough conformity with the rules for Article 32, Class I
locations. The motor is required to be of the type approved
for Class I, Group D locations. The same requirements are
made of the motor control switch and dome light and switch,
if any; Rigid conduit wiring with explosion resisting joints
and fittings are specified.

As the device is usually received at the filling
station for installation, the device is completely wired down
to the explosion resisting junction fitting located in the
base of the pump. The installer runs a circuit from the fill-
ing station building to the pump and makes the necessary
conduit connection to the junction fitting in the base of
the pump and then seals off the conduit at the fitting in
the base of the pump with a suitable compound. Attention is
called to the discussion on "Filling Stations" appearing
under "The Petroleum Industry" of Part II of this thesis.

   

Bondin‘ Jumper Bondin‘ Bushing

I mums amuv
_M6
mam” “WW”
\ anmsmmwn
mwv
fifML
cwmwf‘

Showin‘ Interior of Cabinet to Illustrate Use of Bonding
Bushm‘s and Jumpers. These devises result in
nest and efl'ective bonds

 

 

 

 

Figure No. 34
This Illustrates Hethod
of Bonding using Bonding
Bushings.

 

Figure No. 52.

A Vapor-Proof Hand
Lamp Assembly with
Live Rubber Handle.

 

 

 

Gilliiiifia-
4%—>
<h2§i’

 

 

 

 

 

 

 

PLUG REMOVED

 

 

 

Figure No. 33.

Receptacle and Plug Intended for
Use in Class I Locations.

143

CLASS II LOCATIONS

As the introductory rule of this section, the following
appears: "In locations judged to be as described for Class II
locations in paragraph c of section 3201, the following
provisions shall be observed:" This rule was inserted for the
purpose of providing a definite reference back to the defini-
tions for the various classes, where Class II locations are
described briefly, as those where combustible dust is present.

Before beginning the discussion of the rules of this
class, it should be pointed out that it is practicable to
exclude dust from within the enclosure of electrical apparatus.
As the discussion of the rules proceeds, it will be noted that
they specify dust-tightness in certain instances. This section,
then, differs in this respect from that pertaining to Class I
locations for which explosion-resisting, rather than vs or or
gas-tight, equipment is specified. The term "dust-tight as
applied to enclosures is defined as: "so constructed that dust
will not enter the enclosing case."

The intent generally, of the rules for Class II
locations is to prescribe types of enclosures for electrical
apparatus and wiring which will, first, prevent the occurrence
of electrical arcs or sparks in the immediate presence of .
combustible dust which is likely to be in suspension in the
atmosphere; and second, prevent the ignition of combustible
dust which may have accumulated in or on motors, lamps, or
other electrical devices in such quantities that normal
radiation of heat from such devices is prevented.

Due to the presence of combustible dust in the atmos-
phere in places judged to be Class II locations, it is
obviously necessary to take proper precautions to not only
enclose sparking or arcing parts of apparatus, but also to
design such enclosures that dust will not enter them. Lamps
must be protected to guard against their breakage when
exposed to mechanical ihjury and must be enclosed in
enclosing globes to prevent ignition of the dust by the heat
of the bare lamps. These requirements are satisfied by com-
pliance with the rules which we shall now discuss.

The supposition is sometimes made that because a
device is approved for Class I locations, it is automatically
approved for Class II locations. This is not necessarily
true, in fact, may be decidedly untrue in some cases. Whether
or not a Class I device is suitable for installation in a
Class II location can be determined only by specific examina-
tion and test. Some electrical manufacturers have requested
dual listing of the Underwriters' Laboratories for certain
pieces of equipment and in some instances such dual listing
will be found.

 

 

 

 

 

 

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144

Service Equipment, ggnelboards and Switchboards

Service and circuit protection equipment involves
switches, fuses, circuit breakers, metering equipment and
associated apparatus which in their operation entails the
production of arcs and sparks which, if occurring in the
immediate presence of an atmosphere of combustible dust, may
result in an explosion. Hence, the need for either adequately
enclosing such apparatus, or removing it to a location where
combustible dust is not present. Rule 5204b provides as
follows: "Service entrance equipment, and all panelboards and
switchboards shall not be placed in locations of this class,
but, if impracticable to locate elsewhere, all live parts
shall be enclosed in dust-tight metal cases or cabinets having
provisions for external operation only, or shall be located
in a separate dust-tight room built of or lined with substan-
tial non-combustible materials and having a self closing door,
so constructed and installed as to adequately exclude dust."

In the large majority of instances,especially in new
construction, convenient arrangements can be made to place
the main service equipment, panelboards and switchboards in
some comparatively dust-free location judged to be outside of
the hazardous area. This is a procedure much to be preferred
over any other. In the larger establishments, such as large
capacity flour mills or terminal grain elevators, space for
this equipment is ordinarily provided in a power house of
non-combustible construction, either attached or detached
from the main plant, or oftentimes a special switch house is
built for this particular purpose. In the smaller plants,
such as the smaller flour and feed mills and country elevators,
there will commonly be found an attached building regarded as
out of the hazardous area in which the service equipment can
be installed. This may be an office, warehouse, or power
house,which are usually divisions of such plants.

Where it is not practicable, from an economic or con-
venience standpoint to provide such an arrangement, and
installation within the hazardous area is required, recourse
can be taken to the portion of the rule which permits the
eQuipment to be so installed provided it is located in a
room of suitable construction. In plants of fire resistive
construction, the room should be built completely of non-
combustible materials such as concrete, tile or brick, but
where the building is of a combustible nature, a room of
steel lath and cement plaster on a framework of wood or
steel is permitted. Necessarily, there should be no exposed
combustible material within the room, which requires that
the floor be covered with concrete. Any openings from the
room into the main plant should be provided with tight-fitting
fire doors so arranged as to be self closing. It is important
that the room be sufficiently large to permit of ready .
entrance by persons for operation and maintenance work. In
general, rooms lined with sheet metal, asbestos, or similar
fire-retardant materials are not suitable, for they are rarely

145

found to exclude dust adequately and do not have the necessary
qualities to confine fire within the room. In the section
entitled "Motors" will be found complete instructions for the
construction of a suitable steel lath-cement plaster room.

It is often feasible to provide a room of the above
description to contain, not only the service and circuit
protection apparatus, but the motor controllers as well,

especially when controllers of the remote control t e are
used. This plan is coming into quite general use an with

complete satisfaction.

In the larger elevators and mills it is often found'
necessary to provide sub-feeder distribution panelboards in
certain portions of the plant to obtain a more economical
and convenient installation. This can be readily provided for
by building rooms of the style previously suggested at or near
the load centers, and in them locate the panelboards.

It is not generally required that panelboards located
in such rooms be enclosed in cases or cabinets because of the
fact that they are regarded to be accessible only to qualified
persons. However, if there is a possibility that the room
will be accessible to all workmen, it may be advisable, in
the interest of safety, to provide the necessary cases or
cabinets which when so located may be of the ordinary dust-
proof type.

Only When lack of space or possible great inconvenience
dictates, should the portion of the rule permitting the use
of dust-tight metal enclosures for service equipment, panel-
boards and switchboards be resorted to, for as in the case
of Class I locations, a hazard of no small degree is intro-
duced when it is found necessary to renew fuses or do other
maintenance work at a time when the plant is in operation.

There is available, one type of dust tight metal
enclosed panelboard, but so far as the writer is aware, none
has yet been approved by the Underwriters' Laboratories.
There is also a dust tight fused service switch available
and, of course, various types of oil circuit breakers, some
of which may answer the specification for dust-tightness,
but to the knowledge of the writer, none has been specific-
ally approved for service switch duty in hazardous locations.

Fuses and Circuit Breakers

Rule 5204c provides that: "Fuses shall not be placed
in locations described in this class unless enclosed in
dust-tight metal cabinets or cases." Circuit breakers shall
be of the dust-tight or dust-tight oil immersed type.”

145

found to exclude dust adequately and do not have the necessary
qualities to confine fire within the room. In the section
entitled "Motors" will be found complete instructions for the
construction of a suitable steel lath-cement plaster room.

It is often feasible to provide a room of the above
description to contain, not only the service and circuit
protection apparatus, but the motor controllers as well,

especially when controllers of the remote control t e are
used. This plan is coming into quite general use angpwith

complete satisfaction.

In the larger elevators and mills it is often found'
necessary to provide sub-feeder distribution panelboards in
certain portions of the plant to obtain a more economical
and convenient installation. This can be readily provided for
by building rooms of the style previously suggested at or near
the load centers, and in them locate the panelboards.

It is not generally required that panelboards located
in such rooms be enclosed in cases or cabinets because of the
fact that they are regarded to be accessible only to qualified
persons. However, if there is a possibility that the room
will be accessible to all workmen, it may be advisable, in
the interest of safety, to provide the necessary cases or
cabinets which when so located may be of the ordinary dust-
proof type.

Only When lack of space or possible great inconvenience
dictates, should the portion of the rule permitting the use
of dust-tight metal enclosures for service equipment, panel-
boards and switchboards be resorted to, for as in the case
of Class I locations, a hazard of no small degree is intro-
duced when it is found necessary to renew fuses or do other
maintenance work at a time when the plant is in operation.

There is available, one type of dust tight metal
enclosed panelboard, but so far as the writer is aware, none
has yet been approved by the Underwriters' Laboratories.
There is also a dust tight fused service switch available
and, of course, various types of oil circuit breakers, some
of which may answer the specification for dust-tightness,
but to the knowledge of the writer, none has been specific-
ally approved for service switch duty in hazardous locations.

Fuses and Circuit Breakers

Rule 3204c provides that: "Fuses shall not be placed
in locations described in this class unless enclosed in
dust-tight metal cabinets or cases." Circuit breakers shall
be of the dust-tight or dust-tight oil immersed type."

146

Practically the same comment is in order on this rule as
was made in the case of "Service Equipment, Panelboards and
Switchboards." Every effort should be made to have fuses and
circuit breakers placed in rooms of the types suggested, as
this procedure is by far the safest.

In installations of the older type and possibly in
isolated instances in new construction, it may be found neces-
sary to provide for the installation of fuses in the hazardous
area. In such an event, the rule is invoked and such fuses are
required to be enclosed in a case so constructed that dust will
not enter. It should also be required that certain temperature
limits for the enclosing case be prescribed in accordance with
the discussion which will appear under "Motors."

It should be noted that circuit breakers are required
to be of the dust-tight or dust-tight oil immersed type if in-
stalled in the hazardous area, but not in rooms of the type
which has been mentioned. Such circuit breakers should be of a
type meeting the requirements for "Motor Controllers" generally,
which will appear later in this section.

Type 2; Wiring

The requirements as pertaining to the type of wiring for
Class II locations is contained in Rule 5204d which states;
"Rigid conduit shall be the wiring method employed. Where it is
necessary to employ flexible connections, as at motor terminals,
a short length of flexible steel conduit may be used."

As in Class I locations, the type of wiring for Class II
locations should be the safest available and for this reason
rigid conduit was specified.kIt offers, (1) effective protection
against mechanical injury, (2) a low resistance equipment
grounding circuit, (3) reasonable protection against destruc-
tive arcs within it,-(4) dust-tight joints when threaded
couplings are used, and (5) a type of wiring not unreasonably
expensive.

It is the understanding that threaded connections are
required at couplings, cabinets and eases, no recognition
having been given threadless fittings.

The present rule does not indicate whether fittings,
such as "ells" or ”tees", are required to be of the dust-tight
type. It was not the intention at the time when this rule was
drawn to require such fittings to be dust-tight as it was not
felt that the small amount of dust which would enter such
fittings could, by any stretch of the imagination, cause an
explosion or do any other damage. To avoid differences in
interpretations on this point, the matter will be referred to

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147

- the Article 52 Committee who will so amend the rule as to be
explicit.

The same may be said with regard to pull boxes, Junction
boxes and similar enclosures which do not contain, normally,
arcing or sparking parts. In general, it has not been the
practice to require such boxes to be of the dust-tight type,
not to require that conduit connections to such boxes be made
through threaded hubs, as it was felt by the majority that the
small amount of dust that would enter such boxes could do no
damage. It is admitted, however, that the rule is not explicit
with regard to the matter, and so proper amendment is in order.

It has been found that in order to render switch
cabinets, fuse boxes, controller cases, and other enclosures
containing normally arcing or sparking parts permanently dust-
tight as required by the rule, it is necessary to specify
that the conduit connections to them be of the threaded type,
that is, so as not to depend on the locknut and bushing type
of attachment. However, with enclosures for normally non-
sparking parts such dust-tightness does not appear to be
necessary, although opinions vary on this point. It is
important, however, that when the locknut-bushing type of
attachment for conduit is used that proper bonding be provided
around and to such enclosures as will be discussed under
"Grounding."

It is often necessary to provide flexibility at motor
terminals in order to permit the motor to be shifted on its
base for the purpose of tightening the drive belt. A
concession has been made to care for this by permitting the
use of a short length of flexible steel conduit to enclose
the terminal wires. This should be as short as is practicable
and usually need not exceed three feet in length. This
flexible conduit is required by the general rules of the
Code to be attached to the terminal box of the motor and to
the rigid conduit by means of clamps or fittings approved
for the purpose.

Motors and Generators

 

 

There are three rules in the section pertaining to
Class II locations which deal with the design, construction
and installation of motors and generators. To avoid confusion,
these will be quoted and discussed separately. The first rule,
(Rule 3204c) relates to motors which might be referred to
as of the "sparking type", and states: ‘Where explosive dusty
atmospheres are likely to be present, as in (l) of paragraph
c of section 3201, motors or generators having brushes or
sliding contacts shall have such contacts enclosed in sub-
stantial dust-tight housings or shall be of the totally-
enclosed, totally-enclosed-fan-cooled, or totally-enclosed-

148

pipe-ventilated types or>shall be enclosed in separate dust-
tight rooms or housings, built of or lined with substantial non-
combustible materials, and so constructed as to adequately ex-
clude dust, and properly ventilated from a source of clean air."
Following the rule is the fine print notes: "It is recommended
that al 1 motors installed in dusty locations be of the totally-
enclosed, totally-enclosed- ~fan- -cooled or totally-enclosed—pipe-
ventilated types.”

The intent of this rule is only to guard against
ignition of the explosive mixture of dust and air by sparks or
arcs from unenclosed brushes, collectors, centrifugal switches
or other so-called sparking parts. Such sparks or arcs may
occur to some extent even when the motor or generator is in
normal operation, but more serious sparking occurs when the
machine is overloaded, is being started, or when faults develop
in the windings.

The rule should be interpreted that such guarding is
necessary in any Class II location, as it is practically
impossible to have accumulations of dust in motors and other
equipment without at some time having explosive mixtures of
dust present in the atmosphere. The reverse is not always true,
however, as will be pointed out later.

The rule suggests several methods for compliance with
its provisions. The.first, that of enclosing the sparking
parts in dust-tight housings, may be conveniently used for
the larger slip ring wound rotor motors or for certain types
of the centrifugal switch self-starting polyphase motors.
Figure 35 illustrates a slip ring would rotor motor having
its slip rings enclosed in a dust-tight housing.

 

Figure No. 35.
Slip Ring Motor with Enclosed Slip Rings.

In this type of motor, the slip rings are
arranged for out-board mounting. Although
the hazard of normally sparking parts is
removed by such enclosure, the windings of
the motor are still exposed to accumulations
of dust.

 

I.

149

However, for some types of slip ring wound rotor motors
it is difficult to provide an enclosure for the slip rings, in
which case, it becomes necessary to employ some other method
to secure the necessary protection of the sparking parts.

While the enclosed types of slip ring,wound rotor motors
are available, it is found that the cost of the larger sizes,
such as used for main drives in flour mills, is excessively
high and it is usually more economical to locate such motors
in a special fire resistive motor room, or in a power house
outside of the hazardous area. In either of these latter cases
it is permissible to use the standard open motor without en-
closures for the slip rings.

The comments in the preceding paragraph also hold true
for generators, direct current motors, the smaller slip ring
motors, and single phase motors of the commutator or centri-
fugal switch type, except possibly in the comparatively small
capacities when totally-enclosed or totally-enclosed-fan-
cooled or pipe-ventilated types of machines may be economical-
ly employed, all of which are available.

The construction of a motor room in or in connection
with a plant of fire resistive construction should necessarily
be of equally fire resistive construction. The walls may be of
brick, tile or concrete; the floor and ceiling or roof of
concrete or tile; and so built that there will be no unpro-
tected combustible material within the room. Door openings
into the main buildings should be protected by tight-fitting
approved fire doors so arranged as to be self-closing. The
shaft opening should be protected by slides of non-combustible
or tin-clad wood construction, fitting tightly around the
shaft. The room should be of sufficient size so that a person
can readily enter the room to perform the necessary mainten-
ance work.

When the plant is of combustible construction, the same
type of motor room as specified in the preceding paragraph
may be used, especially if the motor room is outside of the
main building. If it is required that the motor room he with-
in the building and in the hazardous area, a lighter form of
construction may be necessary, due to the danger of overload-
ing floors. In this case, a motor room built of steel lath
and cement plaster on a frame work of wood or steel may be
used, the other requirements of the preceding paragraph as to
shaft and door protection, being the same. Figure 56 illus-
trates two types of motor rooms or enclosures which have been
found very satisfactory in combustible flour mills, feed
mills, and grain elevators. Some details as to construction
are given which, will be of assistance. In general, and for
motors or generators of from 7% to 50 horsepower inclusive,
the enclosure pictured in the upper illustration may'be used,
in which case, one having dimensions of six feet by six feet

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Figure 1

 

 

 

 

 

 

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Figure 3

Figure No. 56.
Suggested Methods for
Construction of Motor and
Controller Rooms.

 

 

 

Figure 2

Figure 1 illustrates the standard motor
enclosure which should be used for all
motors larger than 5 horsepower.

Figure 2 illustrates the construction of
the asbestos lumber slides which should
fit tightly around the motor shaft and
yet permit moving motor on its rails

for adjusting the belt.

Figure 3 illustrates an enclosure for
motors of 5 horsepower and smaller
and for motors so located that space is
limited.

See typewritten specifications for size of
enclosure and ventilating space recom-
mended.

 

MOTOR ENCLOSURE
SPECIFICATIONS

ENGINEERING IERVICE DEPT.

CHICAGO. ILL. DATE Ill/2.
SCALE—_—

 

 

MUTUAL FIRE PREVENTION BUREAU

PRINT No. 120.

 

151

by six and one half feet high has been found satisfactory. For
small motors up to seven and one half horsepower, where space
is restricted, the enclosure shown in the lower illustration,
having dimensions of a three foot cube, may be employed. Sheet
metal or asbestos lined frame motor rooms should not be
recommended.

The ventilation of motor rooms or enclosures is important,
as without adequate ventilating facilities overheating of the
motor may result and defeat, to a large extent, the purpose of
the enclosure. When a motor room is a separate structure,
sufficient ventilation can usually be secured by means of
window openings or louvres in an outside wall, but when the
motor room or enclosure is within the building, it is necessary
to extend inlet and outlet vent pipes to the outside of the
building to a source of clean air. To secure the needed ventila-
tion there must be provided a certain difference in level between
the upper end of the outlet pipe and the lower end of the outlet
pipe, this depending on the size of motors, the diameter of the
vent pipes and other factors. For motors larger than 25 horse-
power, when enclosed in the 6' x 6' x 6%' enclosure, it is
usually necessary to employ an exhaust fan in the outlet pipe
to insure sufficient flow of ventilating air.

The construction of sheet metal housings for motors
should be discouraged as such attempts at protection are seldom
of any value, due to difficulties encountered in making them
dust-tight, and in providing the needed ventilation. In many
instances, such housings are worse than none at all. Figure
57 illustrates the use of such housings on the two motors of
an attrition mill. It is only in exceptional cases that hous-
ings of this type are successful. Usually dangerous heating of
the motor occurs, or the operator, falsely believing that he
possesses dust-tight housings for his motors, neglects to
open the housings for inspection of the interior. This often
results in the burning out of the motors sometimes with dis-
astrous results because of the failure of ordinary sheet metal
to retard spread of fire.

, -

 

Figure No. 57.
Illustrating
Attempts to
Protect Open
Type Motors
From Dust.

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z

 

 

 

 

 

 

 

 

152

When motor rooms are provided, it is often convenient to
locate service equipment, switchboards, and controllers in it,
thus making a safe and satisfactory arrangement.

The fine print note following rule 3204c recommends the
use of the totally enclosed types of motors in all dusty
locations whether or not conditions are such as to require the
application of rule 3204f. The enclosed types of motors are
much to be desired throughout the hazardous area, even though
the motor be of the squirrel cage type without sparking parts.
As a matter of fact, various fire insurance underwriters have
recognized the value of such procedure by granting liberal
credits in the fire insurance rates applying when this is done.

In rule 3204f, there appears the following: "Where it
is impracticable to prevent combustible dust from collecting
in dangerous quantities on or in motors as in (2) of paragraph
c of section 5201, all motors shall be of the totally-enclosed,
totally-enclosed-fan-cooled, or enclosed-pipe-ventilated types,
or shall be enclosed in separate dust-tight rooms or housings
built of or lined with substantial non-combustible materials
and so constructed as to adequately exclude dust, and properly
ventilated from a source of clean air." Following this rule,
this fine print note is found; "The above conditions often
exist in sugar, cocoa, and coal pulverizing rooms, cupolas,
head-houses, basements and other points in grain elevators,
flour mills and feed mills, where grains are spouted, and in
similar locations. Where the installation and maintenance are
such that the hazardous conditions do not exist‘ the foregoing
requirements are not called for and are waived.

The intent of this rule is to provide protection for
motors which are located in areas where they are likely to be
exposed to combustible dust in such quantities as to seriously
interfere with the radiation of heat. It is clear that when
combustible dust accumulates in the ventilating ducts or on
the windings of a motor that it is impossible for the motor
to radiate heat as intended by the designer. The overheating
thus caused, eventually results in the breakdown of the wind-
ings of the motor with accompanying arcs or sometimes by
ignition of the dust in and about the motor. Very often the
condition is aggravated by spillage of oil by careless
attendants or leakage from defective bearings. This 011 mixed
with the dust not only causes the dust accumulations in the
motor to build up rapidly, but destroys the insulation of the
windings in a comparatively short time.

By referring back to the discussion appearing on pages
17 to 19 inclusive and 24 to 26 inelusive, of this thesis,
it will be clear that there are several factors which have
bearing on the question as to what motors should be required
to be guarded against dust accumulations in the manner pre-

153

scribed by the rule now under discussion. The location of the
motor with respect to accessibility in an important factor, for
there is a natural tendency to neglect a motor which is more or
less out of reach. The character of the operation or process in '
the vicinity of the motor is also an important consideration.
An attempt is made in the fine print note following rule 3204f
to suggest the general nature of the processes or operations
which are likely to produce excessive quantities of dust.

However, each type of process in the industries producing
combustible dust must be considered separately and only after
considerable experience will the engineer be in a position to
judge beforehand where dust in excessive quantities will be
likely to occur.

Attention is called to the discussion beginning on page
75 of this thesis in which will be found recommendations as to
the treatment of motor installations in grain elevators, flour
mills and feed mills.

While it is admitted that ordinary open type squirrel
cage motors may be operated with comparative safety in some
parts of plants which involve the production of combustible
dust, it should always be kept in mind that for all locations
in such plants, the enclosing of motors or the use of the
enclosed types of motors is always to be preferred. This re-
moved the need for considering such factors as housekeeping,
efficiency of dust collection systems and general maintenance.

From an economic standpoint, the enclosed motor is
also favored, for even in the cleanest location in a grain
handling risk an open motor is bound to collect considerable
dust which can be removed only by means of compressed air or
by disassembling the motor and.thoroughly cleaning it.
Necessarily such maintenance work entails considerable
expense, all of which can be avoided by employing the en-
closed types of motors.

It is seen that the provisions of rule 3204f, with
regard to the protection of motors from dust accumulations,
is similar to that in rule 5204a except that the latter rule
permits the enclosing of the sparking parts only as one means
of compliance, whereas rule 5204f requires the enclosing of
the entire motor. The distinction between the two rules is
that in rule 32049 it is contemplated that dust will be
present in the atmosphere of the location in explosive quan-
tities, but not necessarily so as to cause accumulations of
the dust in motors so as to prevent normal radiation. Thus,
the condition considered in rule 3204s can be present with-
out that outlined in rule 3204f. However, the conditions
considered in rule 3204f almost always involve those of rule
5204a also. '

154

There are now on the market a wide variety of the
various types of enclosed motors, and are available in all
standard sizes up to 150 horsepower. All motor manufacturers
of any importance have developed complete lines of such motors
to answer the demands of not only those industries coming
under the Class II designation, but others of the non-hazard-
ous classes as well. In figures 58 to 41 will be found illus-
trated several of the various types from Which can.be obtained
a good idea as to their construction and operation. Several
photographs are included showing application of enclosed motors
to grain elevators. These will be found in figures 42 to 47.

Although there are three general types of enclosed
motors available, viz; the totally enclosed, the totally-en-
closed-pipe-ventilated and the totally-enclosed-fan-ventilated;
the totally-enclosed-fan-ventilated has had by far the widest
application, at least in capacities up to 50 horsepower. The
advantages of this type are represented chiefly by the facts
that vent pipes are not required, that the weight is but
little more than that of the open motor of like size, and
that the mounting dimensions are in most cases identical with
those of the open motor of the same size. The totally enclosed
non-ventilated motor is out of the question, except in sizes
of two horsepower or less because of its great size and weight,
in comparison to its output. The totally enclosed-pipe-venti-
lated type is often objectionable, due to the necessity for
providing vent pipes which is not always convenient where
space is limited. However, in the larger sizes (50 HP and
larger) the pipe ventilated type is often used for economic
reasons.

The Underwriters' Laboratories have developed standards
for the construction and test performance of enclosed motors
intended for use in Class II locations. These standards are
available in printed form and, therefore, will not be repeated
here, except to mention briefly the general considerations
involved. As was the case with motors intended for installa-
tion in Class I locations, it was found that various dusts
possessed varying degrees of hazard and, therefore, rather
than grouping all motors for Class II locatiOns together, a
division was made with respect to the type of dust. These
divisions are as follows:

Group Mixture
E Metal Dust
F Coal or Carbon Black Dust
G Grain Dust

The construction requdrements of the Standards recognize
enclosed motors of all of the three types which have been
discussed and prescribed that they shall be enclosed in a
casing of substantial dust-tight construction. Metal-to-metal

 

 

 

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Figure No. 38.
Cut-Away View Showing Interior
Construction of Totally-Enclosed-
Fan-Ventilated Motor.

Note that windings and rotor are completely
sealed against the entrance of dust. Also
note external fan for forcing cooling air
between inner and outer casings.

 

Figure NO 0 59 e
Sectional View of Totally-Enclosed-
Fan-Ventilated Motor to Show Path of
Cooling Air.

 

 

 

 

 

Figure No. 58.
Cut-Away View Showing Interior
Construction of Totally-Enclosed-
Fan-Ventilated Motor.

Note that windings and rotor are completely
sealed against the entrance of dust. Also
note external fan for forcing cooling air
between inner and outer casings.

 

Figure No. 59.
Sectional View of Totally-Enclosed-
Fan-Ventilated Motor to Show Path of
Cooling Air.

156

joints with a metal-to-metal surface of at least 5/16 of an inch
in width when assembled, are required. Gaskets are not permitted
except on those parts subject to removal for inspection and
maintenance. The shaft openings are required to have a length

of path of not less than 1/2 inch for a maximum radial clearance
of .005 inches. For greater lengths of path larger clearances are
permitted, complete information on which is contained in the
standard. The terminal leads are required to be securely held
and tightly fitted where they pass into the casing. This is
accomplished by sealing the conductors by means of a suitable
insulating compound. A terminal box, arranged for condlit
connection is also required, add finally the motor is required
to be marked with a label on which is stated the Class and

dust group for which the motor is intended.

In testing a motor submitted for approval for Class II
locations, it is placed in a special test chamber of sufficient
size to prevent other than normal heating of the motor. This
chamber is about six feet by six feet by five feet high, the
bottom of which is hoppered. Means are provided for causing
continuous circulation of dust, which dust is held in suspension
in the chamber by means of a blower fan directing the dust
through nozzles placed at various points in the interior.

The motor shaft extends through a protected opening in a wall
of the chamber and is caused to drive a generator Which permits
testing the motor under actual load conditions. Tests are made
under both continuous and intermittent operation. In the latter
test, the motor is pennitted to operate fully loaded until
normal temperature rise has been attained and is then allowed
to cool to ambient temperature when the test is repeated.

The purpose here is to determine the possible influence of

the "breathing" action in causing dust to be forced into the
motor casing. These tests are cnntinued for a period of time
sufficient to determine the dust-tightness of the motor under
these conditions. Naturally, if dust enters the motor casing
which surrounds the working parts, the motor is not dust-tight
and is not eligible for approval. Figure No. 55 illustrates
the test chamber and auxiliary apparatus used in the Under-
writers' Laboratories for testing Class II motors.

A further test is now made for the purpose of deter-
mining whether the temperature attained by the motor casing,
when operating fully loaded and when blanketed with dust is
sufficiently high to cause ignition of the dust. This tem-
perature is measured by the thermocouples placed on the eas-
ing, and the dust is examined for evidence of charring and
ignition. Temperatures produced on burn-out of the windings
of the motor are also determined. The ignition temperature
of Group G dusts, (grain dusts, etc.), is taken at 500 degrees
Fahrenheit.

Practically all of the important motor manufacturers
have been successful in obtaining approval of their motors

 

 

Figure No. 40.
Group of Totally-Enclosed
Fan-Ventilated Motors.

The upper illustrations are of squirrel
cage motors while the lower is of a
single phase motor.

158

for Class II, Group G locations. All of those so far approved
are of the totally-enclosed-fan-ventilated type, and so far

as the writer can learn, none has been submitted for approval
for Group E and Group F dusts.

When motors are enclosed in motor rooms which require
vent pipes, or When motors are of the totally-enclosed-pipe-
ventilated type, it is very important that the vent pipes
be prOperly installed. This is provided for in Rule 5204g
which states: "When motors of the enclosed-pipe-ventilated
type are used, or When motors are enclosed in rooms or hous-
ings, the vent pipes shall extend to the outside of the
building to a source of clean air. The vent pipes shall be
of metal, substantially constructed and with each section
attached to the next by riveting, welding, or other approved
methods. When motors are intended to be moved on their bases,
a slip or universal joint, tight enough to prevent the entrance
of dust shall be provided in the vent pipes. The outer ends
of vent pipes shall be suitably screened to prevent the entrance
of animals or birds."

It is not thought that this rule needs much special
comment. It should be mentioned, however, that both the in-
let and outlet vent pipes are required to be extended to the
outside of the building. It is sometimes found that only the
inlet vent pipe is so extended, but this is likely to cause
accumulations of dust within the motor or room, due to the
possible reversal of direction of flow of air when the motor
is not in operation. The screening of both pipes at their
outer ends is also important lest birds or rodents build
nests in the pipeaAand so cause obstructions to the flow of
air. .
The size of vent pipes and required pressure head
should be calculated for each installation in order to pre-
vent overheating of the motor. This is especially true when
the motor is enclosed in a comparatively small room and long
lengths of vent piping are needed to reach the outside of the
building. _

A number of typical motor installations in the dusty
industries will be found illustrated in Figures No. 42 to
47, inclusive. .7

Figure No. 55.
Test Chamber and Auxiliary
Apparatus Used by Under-
writers' Laboratories for
testing Class II Motors.

 

AN

"1"

  

Figure No. 42.

The photograph to the right
illustrates actual installation
of a totally-enclosed-pipe-
ventilated motor in a grain
elevator.

Figure No. 41
Group of Totally-Enclosed-
Pipe-Ventilated Motors.

The illustration to the left
shows a motor of this type
direct-connected to a feed
grinder.

 

 

 

 

Figure No. 45.
These Photographs Illustrate Application
of Totally-Enclosed-Fan-Ventilated Motors
to Grain Elevators.

The upper photograph is taken in the cupola
of a country elevator and shows motor
driving elevator leg. The lower illustrates

motors driving car dumpers located under the
car dumping shed.

 

 

 

at
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Figure No. 44.
Totally-Enclosed-Pipe-Ventilated
Motors Driving Belt Conveyors in

Bin Floor of Large Terminal Elevator.

.00 h u;-
u..‘.

 

 

 

 

Figure No. 45.
Totally-Enclosed-Fan Ventilated
Motor Employed to Drive Receiving
Belt under Car Shed..

0'00.

0.......‘

 

 

 

 

Figure No. 47.
Totally-Enclosed-
Fan-Ventilated

Motor Driving Grain
Separator in First
Floor of a Country =
Elevator. I

Figure No. 46.
Totally-Enclosed-
Fan-Ventilated
Motor Driving
Air Compressor
in a Country
Elevator.

 

165

Motor Controllers, Switches, Resistance Devices

and Similar Apparatus

 

Rule 5204h requires that: "Motor controllers, thermal
cutouts, switches, relays, the switches and contactors of auto-
transformer starters, resistance or impedance devices, or other
devices or apparatus which, in their normal operation, tend to
create arcs, sparks, or high temperatures, shall not be
installed in these locations unless such devices or apparatus
are enclosed in dust tight cases or cabinets or are of the
dust-tight or dust-tight-oil-immersed type, and so designed
that the device may be operated.without opening the cabinet or
case." A fine print note follows the main rule which states:
"It is recommended that motor control devices be of the remote
control type, with the main contactors located in separate
rooms or compartments, built of non-combustible materials so
constructed as to exclude dust. The remote control push buttons
or switches of the oil immersed or dust-tight type may then be
placed in the most convenient locations."

It will be seen that this rule is practically identical
with that which covers the same subject for Class I locations
except that it is provided that the enclosures be dust-tight,
rather than explosion-resisting. Because of the similarity of
principles involved, it is not necessary to include detailed
discussion of the provisions of the rule at this point. It
should be obvious that the purpose of the rule is, (l) to
prevent the occurrence of arcs, sparks or high temperatures
in the immediate presence of combustible dust and so cause
ignition and probable explosions and, (2) to prevent accumu-
lations of dust on or in the apparatus mentioned or implied
by the rule so as to introduce the possibility of ignition of
such dust through overheating. These purposes are accomplished
by requiring that (l) the apparatus be enclosed in dust-tight
cases with certain limitations as to maximum temperatures
attained by such cases or (2) that the apparatus be isolated
from the immediate hazardous area by installing such apparatus
in a non-combustible room.

The second procedure is recommended as being the safest
in all instances and should always receive first consideration.
.The various possibilities of this method have already been
discussed under "Service Equipment, Panelboards, and Switch-
boards" of this section to which reference should be made. It
has also been suggested, under "Motors" that it is often
feasible to install remote type motor controllers or even
those of the manually operated type in the motor rooms, thus
isolating all electric power equipment from the hazardous
area, excepting the auxiliary control switches which may be
located at convenient points throughout the hazardous area to
provide means for regular and emergency operation. It will be
noted that such auxiliary switches are required to be of the

llalfI|i§iL

 

 

164

dust-tight or dust-tight-oil-immersed type.

When it is not practicable or economical to thus isolate
controllers and other similar equipment, and it becomes
necessary to install all or some of them directly in the hazard-
ous area, the precautions mentioned in the main body of rule
52041 are required to be enforced, that is, such controllers
or other devices or apparatus Which, in their normal operation,
tend to create arcs, sparks, or high temperatures are required
to be enclosed in dust-tight cases or cabinet, or to be of the
dust-tight or dust-tight-oil-immersed type. An outstanding

application of the principle of isolation of control apparatus
is shown in figure 48.

A large variety of motor controllers complying with the
specification of dust-tightness has been developed and are
available. Many of these are of types approved and listed by
the Underwriters' Laboratories, which organization has developed
standards for the design and test performance of such equipment.

The Underwriters' Laboratories' Standard recognize both
air-break and oil immersed control equipment, but both are
required to be enclosed in substantial dust-tight enclosures
or cases. Joints, if of the metal-to-metal type which, when
assembled, are required to have a contact surface at least
5/16 inches in width. Such joints are to be preferred to those
which employ gaskets which, while permitted, are sometimes
capable of being easily removed. The standard prohibits the
use of rubber for gasket material because of its liklihood of
becoming cracked and otherwise defective in aging. If gaskets
are used, they must be mechanically attached, not glued, to
the case body or cover. Shaft openings for operating or reset
mechanisms are required to have a length of path not less
than 1/2 inch with a maximum clearance of .005 inch. For
greater clearances, longer paths are specified.

The standard further prescribes that the exterior
observable temperature of the case or enclosure based on a
40 degree Centigrade ambient shall not exceed the safe tempera-
tures for the dust-air mixtures under consideration. For grain
dust this temperature is assumed to be 500 degrees Fahrenheit.

The tests made on controllers and such apparatus are
almost identical with those used for the testing of motors
intended for Class II locations. The controller is placed in
the test chamber and exposed to the dust-air atmosphere while
operating at full rated load. Temperatures on the exterior of
the enclosing case are measured just as with motors. A special
additional test is made when oil break controllers are under
consideration. This consists of subjecting the device to a
series of operation tests under full load, during which
samples are withdrawn from above the oil level to determine

 

 

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tr

 

Figure NO e 480
A View of the Interior of a Fire Resistive
Controller Room in a Large Terminal Elevator.

0n the switchboard shown are mounted automatic
controllers for several synchronous motors
which drive elevator legs. To the right of
the photograph are shown the steel cabinets
containing branch circuit fuses.

 

Figure No. 49.
Group of Magnetic Type Motor Controllers
Approved for Class II Locations.

166

whether or not a dangerous amount of hazardous gas or vapor
has been produced. Thus, the tests determine whether the device
is dust-tight or whether the maximum temperature of the case

is sufficiently low to prevent ignition of dust which may have
accumulated on it.

Resistance or impedance devices, relays, thermal cutouts
and similar apparatus are usually not installed in the hazard-
ous areas unless they are integral parts of a controller.
Resistors used in conjunction with the controllers for slip
ring wound rotor motors should be located in the motor room or
control room, but when such rooms are not provided, such
_resistors must be enclosed in dust-tight cases. It may be found
necessary to ventilate such cases to the outside to prevent
excessive temperature rise, especially if the resistors are
used for other than intermittent duty.

The accompanying illustrations (Figures 49 to 52
inclusive) show several types of motor controllers suitable
for use in Class II locations.

Electric Heating Appliances

It is not contemplated that electric heating appliances
will be installed in Class II locations. However, rule 5204i
provides for their installation by specifying special approval.
The rule states: "Electric heating appliances shall not be
used unless of a type approved for installation in dusty
atmospheres."

The temperatures reached by electric heaters of any
type are usually above the ignition temperatures of any
combustible dusts likely to be generally encountered. A
possible exception is the electric immersion type radiator
heater which employs an enclosed heating unit extended into
the header of a radiator filled with water. Such heaters have
been used, but not with entire success. No heaters especially
approved for dusty locations have yet appeared.

The rule does not imply forced exclusion of "Strip"
type or other electric heaters from cut-off dust-free loca-
tions, such as the weighmasters' and foremens' offices often
found in grain elevators, even though these are in the
elevator building proper.

Lamps 12 Fixed Positions

 

Rule 5204j provides that: "Lamps in fixed positions
shall be enclosed in approved dust-tight globes, and where
exposed to mechanical injury, shall be protected by substan-
tial guards. Heavy fixtures used as pendants shall be

I0

 

.fi-hmgllq # .g {j
e ';‘
? 1

Figure No. 51.
Dust-Tight Auxiliary
Switch for Use in
Connection with Magnetic
Type Controllers.

 

Figure No. 50.
Magnetic Type Motor Controllers
for Class II Locations Shown
with Cover Removed.

 

Figure No. 52.

Open and Closed Views of Automatic
Starter Approved for Class II Locations
in Which is Incorporated a Disconnect

Switch.

168

supported by conduit hangers or chains to prevent strain on
the wires. Where rubber covered wire is used, it shall have
insulation not less than 3/64 inch thick. Sockets and
receptacles shall be of the keyless type, and unless individual
switches are provided, shall be located at least 7% feet above
the floor, or shall be otherwise so located or guarded that
the lamps cannot readily be backed out by hand. This is
followed by a fine print note which states: "When light is
required for the interior of bins, hoppers, elevators, con-
veyors and similar equipment or construction, it is recom-
mended that such light shall, whenever practicable, be
supplied by means of lamps, enclosed in dust-tight globes
prOperly protected against mechanical injury, and mounted
flush in the walls or floors of the equipment or construction.
No wiring or fixtures should be permitted inside of bins,
hoppers, elevators or conveyors.

It is important that every precaution be taken to
prevent ignition.of suspended dust or dust which accumulates
on lamps, by providing enclosing globes for lamps in all dusty
locations, and in addition, guards, where lamps are so
located as to be exposed to mechanical injury.

The use of unguarded lamps in dusty locations has
resulted in many fires and explosions, for when such lamps
are broken while lighted an intense flash follows accompanied
by the emission of incandescent metal.

An equally important matter associated with the hazards
of the unenclosed lamp is the fact that when combustible dust
accumulates on the bare lamp a heat insulating effect is
produced. The heat generated by the lamp is confined by the
blanket of dust until the temperature of the dust immediately
in contact with the lamp builds up sufficiently to cause
charring and finally ignition. This can and does occur even
with lamps as small as the 60 watt gas-filled type, the clean
surface temperatures of which do not exceed 252 degrees
Fahrenheit.

In an investigation made by the writer, it was found
that ignition of a small cone of wheat dust on a bare 60 watt
inside frosted incandescent lamp occurred in seven minutes,
starting at the room temperature of 74 degrees Fahrenheit.
The temperature recorded by a thermometer placed on the
surface of the lamp under the dust cone was 502 degrees
Fahrenheit when ignition was observed. A similar test was
made using the same lamp, but enclosed in a standard vapor
proof fixture and it was found after continuing the test for
7% hours that the maximum temperature reached by the surface
of the enclosing globe was 324 degrees Fahrenheit. In this
test, ignition did not occur and the dust immediately in
contact with the globe showed only a very slight discolor-
ation. The tests made involved several other types of lamps,

168

supported by conduit hangers or chains to prevent strain on
the wires. Where rubber covered wire is used, it shall have
insulation not less than 5/64 inch thick. Sockets and
receptacles shall be of the keyless type, and unless individual
switches are provided, shall be located at least 7% feet above
the floor, or shall be otherwise so located or guarded that
the lamps cannot readily be backed out by hand. This is
followed by a fine print note which states: "When light is
required for the interior of bins, hoppers, elevators, con-
veyors and similar equipment or construction, it is recom-
mended that suhh light shall, whenever practicable, be
supplied by means of lamps, enclosed in dust-tight globes
properly’protected against mechanical iniury, and mounted
flush in the walls or floors of the equipment or construction.
No wiring or fixtures should be permitted inside of bins,
hoppers, elevators or conveyors.

It is important that every precaution.be taken to
prevent ignition of suspended dust or dust which accumulates
on lamps, by providing enclosing globes for lamps in all dusty
locations, and in addition, guards, where lamps are so
located as to be exposed to mechanical injury.

The use of unguarded lamps in dusty locations has
resulted in many fires and explosions, for when such lamps
are broken while lighted an intense flash follows accompanied
by the emission of incandescent metal.

An equally important matter associated with the hazards
of the unenclosed lamp is the fact that when combustible dust
accumulates on the bare lamp a heat insulating effect is
produced. The heat generated by the lamp is confined by the
blanket of dust until the temperature of the dust immediately
in contact with the lamp builds up sufficiently to cause
charring and finally ignition. This can and does occur even
with lamps as small as the 60 watt gas-filled type, the clean
surface temperatures of which do not exceed 252 degrees
Fahrenheit.

In an investigation made by the writer, it was found
that ignition of a small cone of wheat dust on a bare 60 watt
inside frosted incandescent lamp occurred in seven minutes,
starting at the room temperature of 74 degrees Fahrenheit.
The temperature recorded by a thermometer placed on the
surface of the lamp under the dust cone was 502 degrees
Fahrenheit when ignition was observed. A similar test was
made using the same lamp, but enclosed in a standard vapor
proof fixture and it was found after continuing the test for
7% hours that the maximum temperature reached by the surface
of the enclosing globe was 324 degrees Fahrenheit. In this
test, ignition did not occur and the dust immediately in
contact with the globe showed only a very slight discolor-
ation. The tests made involved several other types of lamps,

168

supported by conduit hangers or chains to prevent strain on
the wires. Where rubber covered wire is used, it shall have
insulation not less than 3/64 inch thick. Sockets and
receptacles shall be of the keyless type, and unless individual
switches are provided, shall be located at least 7% feet above
the floor, or shall be otherwise so located or guarded that
the lamps cannot readily be backed out by hand. This is
followed by a fine print note which states: "When light is
required for the interior of bins, hoppers, elevators, con-
veyors and similar equipment or construction, it is recom-
mended that such light shall, whenever practicable, be
supplied by means of lamps, enclosed in dust-tight globes
properly protected against mechanical injury, and mounted
flush in the walls or floors of the equipment or construction.
No wiring or fixtures should be permitted inside of bins,
hoppers, elevators or conveyors."

It is important that every precaution be taken to
prevent ignition of suspended dust or dust which accumulates
on lamps, by providing enclosing globes for lamps in all dusty
locations, and in addition, guards, where lamps are so
located as to be exposed to mechanical injury.

The use of unguarded lamps in dusty locations has
resulted in many fires and explosions, for when such lamps
are broken while lighted an intense flash follows accompanied
by the emission of incandescent metal.

An equally important matter associated with the hazards
of the unenclosed lamp is the fact that when combustible dust
accumulates on the bare lamp a heat insulating effect is
produced. The heat generated by the lamp is confined by the
blanket of dust until the temperature of the dust immediately
in contact with the lamp builds up sufficiently to cause
charring and finally ignition. This can and does occur even
with lamps as small as the 60 watt gas-filled type, the clean
surface temperatures of which do not exceed 252 degrees
Fahrenheit.

In an investigation made by the writer, it was found
that ignition of a small cone of wheat dust on a bare 60 watt
inside frosted incandescent lamp occurred in seven minutes,
starting at the room temperature of 74 degrees Fahrenheit.
The temperature recorded by a thermometer placed on the
surface of the lamp under the dust cone was 502 degrees
Fahrenheit when ignition was observed. A similar test was
made using the same lamp, but enclosed in a standard vapor
proof fixture and it was found after continuing the test for
7% hours that the maximum temperature reached by the surface
of the enclosing globe was 324 degrees Fahrenheit. In this
test, ignition did not occur and the dust immediately in
contact with the globe showed only a very slight discolor-
ation. The tests made involved several other types of lamps,

‘\ _,

Figure No. 54.
Two Types of Guarded Lighting
Units Suitable for Installation
in Dusty Locations.

 

 

Figure No. 55.

Showing an Approved Lighting
Installation in Conveyor
Gallery of a Large Terminal
Elevator.

170

including the 100 watt gas filled, 50 watt mill type, and 16
candle power, carbon filament lamps, and the results, while
interesting, would be too lengthy to detail here. The data

given above should be sufficiently convincing so that the im-
portance of providing enclosing fixtures for lamps in dusty
locations can be appreciated. As a matter of fact many fires

are caused by the dust accumulated on bare lamps being ignited
and falling into additional dust in the vicinity. The "Loss
Record" included in this thesis reports several such occurrences.

The Underwriters' Laboratories have drawn standards for
the design and test performance of lighting fixtures intended
for use in Class II locations. These are comparative to those
which have been described for Class I locations except that for
Class II fixtures they are required to be dust-tight and the
maximum exterior temperature below certain prescribed values,
depending on the dust group for which approval is desired. For
the grain dust group (Group G) this maximum temperature is 500
degrees Fahrenheit and these maximum temperatures are required
not to be exceeded, either when the fixture is clear or
blanketed with dust. The tests are made in a manner similar
to those used in testing Class II motors with due recognition
of the "breathing" effect.

To the knowledge of the writer no fixtures have yet been
approved for Class II locations but as a temporary measure,
authorities are permitting the use of standard vapor-proof ,
fixtures, several of which are illustrated in Figures 26 and
54. A typical lighting installation in the conveyor gallery
of a grain elevator is shown in figure 55.

It will be noted that the rule requires that heavy
fixtures be adequately supported by conduit hanger or chains
in order that dependence on ordinary pendant cords for such
support be eliminated. Key sockets and receptacles are also
ruled out, due to the possible ignition of dust by arasor
sparks from the operation of these devices.

The fine print note is intended to recommend means for
elimination of the need for using portable lights in bins,
hoppers and similar spaces. The method suggested in this note
has been used to a considerable extent in starch factories,
but has not yet been adopted for grain elevators due to the
fact that the bins are usually so deep and the dust so dense
that lights placed in the upper part of-the bin are ineffective.

,‘

 

 

171
Portable Lamps

The importance of designing illumination for Class II
locations in such a manner that the need for portable lamps
will be eliminated should be strongly emphasized. Portable
lamps are distinct hazards no matter how well made or how
carefully used.

It seems almost impossible to so build a portable lamp
fixture as to render it sufficiently resistant to breakage,
especially when accidentally dropped from any appreciable
height. Also when an enclosed portable lamp is buried in dust
or grain with the lamp burning ignition of the dust or grain
will occur if left for a sufficient length of time. In tests

 

 

 

 

 

 

Figure 56
Portable Lamp Assembly and
Plug and Receptacle for
Class II Locations

made by the writer, it was found that a 60 watt gas filled
incandescent lamp enclosed in a unit such as illustrated in
figure 56 and buried in a box of wheat dust, that ignition
of the dust was obtained after 2§ hours operation at a
temperature of 506 degrees Fahrenheit. It is granted that
the enclosed unit is safer from this point of view than a
base lamp, for in a similar test with a bare 60 watt gas
filled lamp buried in dust, ignition occurred in eleven
minutes. But the hazard is present whether the lamp is used
bare or enclosed, due to the possibility of the lamp being
buried and forgotten.

173

Appreciating that portable lamps will be used even
though authorities go to the extent of drawing rules prohibiting
their use, the rule providing for their design is more or less
a concession.

Rule 5204k treats the subject of portable lamps as
follows: "Sufficient general illumination shall be provided by
fixed lighting units to eliminate so far as possible the need
for portable lamps. When portable lamps are necessary they
shall be enclosed in dust-tight globes properly protected by
substantial metal or other approved types of guards to prevent
breakage. Sockets for portable lamps shall be of the moulded
composition or metal jacketed porcelain, keyless type."

The standards of the Underwriters' Laboratories for
Class II lighting fixtures also apply to portable lamps. How-
ever, none have yet been listed by the laboratories for
especial use in Class II locations. There are available several
types of portable lamp assemblies classed as vapor proof,
which are probably also, at least in most instances, sufficient-
ly dust-tight to be permitted. A representative type is found
illustrated in figure number 56. This particular unit has a
live rubber handle, a dust tight globe, and an aluminum guard
and designed so as to not subject the connections of the cord
to the socket to strain.

Portable Cords

 

Rule 52041 states: "When necessary to use portable
glamps, or other portable current consuming devices, approved
flexible cord designed for hard usage‘such as Type SorType PA
shall be used. Such a flexible cord shall contain one extra
insulated conductor which shall be properly connected to form
a grounding connection for metal lamp guards, motor frames,
and all other exposed metal portions of such portable lamps
and devices." It will be noted that the wording of this rule
is identical with the parallel rule for Class I locations
(Rule 3205m) and, therefore, the same comment will apply.

As in Class I locations, substandard or defective portable
cords have caused many fires in mills, elevators, and
similar establishments included under Class II locations.
The importance of selection of the proper types is to be
emphasized.

Connection pf Portable Cords

 

 

The methods used to connect portable cords to supply
conductors through separable connections are of importance.
It would be extremely undesirable to employ a plug and
receptacle of such a design as to permit the occurrence of

 

 

 

 

174

an are or spark in the immediate presence of an explosive dust-
air mixture. Rule 5204m provides adequate precautions against
this possibility as follows: "Receptacles and attachment
plugs, if used, shall be so connected, as a part of a unit
device with a dust-tight interlocking switch that the plug
cannot be removed While the switch is in the "on" position or
approved devices which seal the arc, made when current is in-
terrupted, by means of an explosion-proof or vapor-proof en-
closure shall be used. Such receptacles and plugs shall be of
the polarized type providing a connection for the grounding
wire of the portable cord. "It will be noted that the rule,
although written to provide precautions for a dusty atmosphere
specifies that the arc or sparks be confined within an
explosion-proof or vapor-proof enclosure. A better wording
would be had were the requirement worded so as to specify
dust-tight enclosures and undoubtedly this change will be

made in the next edition of the Code.

Except for the fact that our considerations in this
rule are based on prevention of exposed arcs or sparks in a
dusty atmosphere rather than a gas or vapor-air atmosphere,
discussion of this rule would be identical with that of the
parallel rule, (Rule 32050) which appears under the rules for
Class I locations. For this reason the discussion is not
repeated here.

In figure 56 will be found an illustration of a suit-
able type of receptacle and attachment plug for class II
locations. Others of this type are also available, as well as
those included as a unit device employing an interlocked
switch.

The manner of connecting portable cords direct to
supply conductors is treated in rule 5204h as follows:
"Connections of portable cords direct to supply conductors
shall first be made mechanically secure and shall then be
soldered and heavily taped. In addition, the cord shall be
securely supported so that the probability of a break in the
conductors at this point will be minimized."

Such a manner of connecting portable cords is not
used to any great extent in Class II locations, the separable
type of connection being used almost entirely. The rule is
identical with rule 5205n as applied on the same subject to
Class I locations, and the comments to be made are the same.

Grounding

 

The rule treating this subject (Rule 52040) states:
"The exposed non-current carrying metal parts of equipment,
such as the frames or metal exteriors of motors, fixed or
portable appliances, lighting fixtures, cabinets, cases,

175

and conduit, shall be grounded as provided in Article 9 of

this Code. The locknut bushing and double-locknut type of
contact shall not be depended upon for bonding purposes, bonding
jumpers with prOper fittings or other approved means being
required to assure an effective grounding circuit."

It will be seen that this rule is identical with Rule
5204p covering the same subject under the rules for Class 1
locations. 0n the whole, the same comment as previously given
applies at this point and so will not be repeated. It should
be pointed out, however, that whenever pull boxes, junction
boxes, and similar enclosures are used which are not definitely
required to have threaded type conduit connections, they should
be bonded, either by use of the grounding bushings illustrated
in figure 54 or by suitable clamps and bonding jumpers
connected to the conduit runs and boxes on the exterior. It is
recommended that this system of bonding be extended to
electrical wiring throughout the premises. It is also
recommended that a copper bonding jumper be provided to shunt the
flexible steel conduit at motor terminals which such flexible
connections are used.

Live Parts

It would be undesirable to permit any exposed live
parts and, therefore, rule 5204p was inserted to care for the
matter. This rule states: "There shall be no exposed live
parts." As a matter of fact, however, compliance with the
remaining rules for Class II locations automatically results
in no live parts being exposed to contact.

176

CLASS III LOCATIONS

It is not the intention to discuss the rules for Class
III locations in detail because of their similarity to the
rules for Class II locations which have been discussed in con-
siderable detail. It may be desirable, however, to point out
the distinction between the two classes. In Class II locations,
it will be recalled, we were concerned with the probability of
sparks or arcs from electricalequipment igniting an explosive
mixture of dust and air, as well as the probability of
sufficient dust accumulating on or in such equipment as to
prevent prOper radiation of heat and so cause ignition either
directly or indirectly through burnout of a motor resulting
from.dust accumulations. In Class III locations explosive
mixtures are not present in the atmosphere, but there is
likely to be present a quantity of easily ignitable lint or
other light material on machines and building surfaces Which,
if ignited, would result in the rapid spread of flames through
the area where the material is present. In some instances,
eSpecially in the delinting rooms of cotton seed oil mills,
the picker rooms of cotton mills and in some woodworking
plants, the problem represented by objectionable accumulations
of lint, sawdust and such materials in or on electrical
apparatus, especially in the windings of Open type motors,
becomes a serious consideration.

Therefore, in the rules for Class III locations it will
be found that provisions are made to (l) prevent ignition of
lint and similar substances by arcs, sparks or high tempera-
tures, and (2) prevent accumulation of such substances on or
in electrical wiring and apparatus in sufficient quantities
to be hazardous frmn the standpoint of preventing the proper
radiation of heat.

From the discussion which has previously appeared
under "Classification" with particular reference to Class III
locations, it will be understood that the rules must be
applied with judgment owing to the wide range of conditions
which are likely to be encountered. Some guidance is also
given in the section "Classification as to Industries and
Processes", especially those parts entitled "The Cotton Industry"
and "Woodworkers".

In the following the rules for Class III locations
will be stated, but discussion will be confined to only those
rules about the application of Which questions may arise.

The first rule of the section (Rule 5205a) states
that: "In locations judged to be as described for Class III
locations in paragraph d of section 5201 the following
provisions shall apply:" This rule is for the purpose of
referring the user to the definitions of various classes.

177

Service Eguipment, Panelboards and Switchboards

 

Rule 5205b: "Service entrance equipment and all switch-
boards and panelboards shall not be placed in locations of
this class, but if impracticable to locate them elsewhere, all
live parts shall be enclosed in dust-tight metal cases or
cabinets with provision for external operation only, or shall
be located in separate dust-tight rooms built of or lined
with substantial non-combustible materials and with self-
closing doors, so constructed and installed as to adequately
exclude flyings or lint."

This requirement is identical with that prescribed for
Class II locations and needs little comment. In most instances
it is possible to place such equipment outside of the hazard-
ous area, but where this cannot be done, the other provisions
of the rule are invoked. Reference should be made to page 144
of this thesis where the details of the rule are explained.
It will be noted that the term "dust-tight" is used, although
the material involved in Class III locations is usually of
a linty nature. It was felt that owing to the uncertain degree
of fineness of the lint or light material, that dust-tightness
should be specified. In other words, where such equipment is
required to be installed within the hazardous area, that
apparatus approved for Class II locations may be used.

Fuses and Circuit Breakers

 

Rule 5205c: "All fuses shall be enclosed in dust tight
metal cases or cabinets. Circuit breakers shall be of the
dust-tight oil-immersed type, or shall be enclosed in dust-
tight metal cases." Comment appearing under the same subject
in discussion of the rules of Class II applies.

Type 22 Wiring

Rule 5205d: "Rigid conduit shall be the wiring method
employed. Where it is necessary to employ flexible connections,
as at motor terminals, a short length of flexible conduit may
be used."

Here again it was felt necessary to prescribe the
safest available type of wiring inasmuch as we are dealing
with locations where every precaution should be taken to
prevent ignition. With regard to fittings, boxes, and similar
enclosures not containing normally sparking or arcing parts,
the discussion under the subject for Class II locations
applies.

178

Motors and Generators

 

Rule 5205e: "Where it is impracticable to prevent lint
and flyings from collecting in dangerous quantities on or in
motors, as in cotton gins or the seed cleaning and linter
rooms of cotton seed oil mills, all motors shall be of the
totally-enclosed, totally-enclosed-fan-cooled or totally-
enclosed-pipe-ventilated types, or shall be enclosed in
separate dust-tight rooms or housings built of or lined with
substantial, non~combustible materials so constructed as to
adequately exclude lint or flyings and be properly ventilated
from a source of clean air. Elsewhere, if motors or generators
having brushing or sliding contacts are used, they shall:

"1. Be of the totally-enclosed, totally-enclosed.
fan-cooled, or enclosed-pipe-ventilated
types, or

"2. Be enclosed in separate rooms or housings
as specified above, or

"3. Have brushes or sliding contacts enclosed
in substantial tight metal housings, or

"4. Have upper half of brush or sliding contact
end of motor enclosed by a wire screen or
perforated metal cover and lower half on-
closed by solid metal covers. No dimension
of any Opening in the wire screen or
~perforated metal cover shall exceed .05
inch, regardless of the shape of the open-
ing and of the material used."

It will be noted that this rule provides not only for
the prevention of ignition of lint or other light materials
by arcs or sparks from the brushes or sliding contacts of
motors and generators, but also for the prevention of accumula-
tions of lint or "flyings" in the windings of open motors of
any type whether having brushes or other sliding contacts or
not.

In addition to motors in cotton gins, and the seed
cleaning and linter rooms of cotton seed oil mills, it is
often found that the motors in some woodworking establish-
ments become fouled with excessive sawdust, turnings and
similar light material. In such cases it is decidedly
advantageous to adopt one of the enclosed types of motors,
not only from the standpoint of fire prevention, but also as
a money saving measure.

In figure 57 there appears a photograph which illus-
trates an attempt at motor protection. It will be noted from

 

179

the photograph that no provision has been made for ventilation
of the motor and unless the motor is much larger than actually
needed, or is Operated only intermittently, it is certain that
overheating and ultimate breakdown of the windings will result.
A much safer procedure would have been to have adOpted the
enclosed-fan—ventilated motor for this duty and location.

Where the amount Of lint or light material present is
not sufficient to cause it to collect in dangerous quantities
in motors, but prevention of ignition is still important, there
are four methods suggested in the rule to provide the necessary
safeguards. Of these, the last(numbered 4)is the least
desirable owing to the liklihood of the screens which are
mentioned becoming clogged with lint or dust and impairing the
flow of cooling air through the motor.

Undoubtedly, the best method is that of providing
motors of the totally-enclosed or totally-enclosed-fan-cooled

type.

The dangers associated with the Operation of Open motors
in places where considerable lint is present has been recognized
for some time, as evidenced by the develOpment of the textile
motor some years ago and, the recommendations of the Associated
Factory Mutual Insurance Companies advocating the protection
of motors against lint accumulations.

Reference should be made to the discussion of the rules
for Class II locations with reference to 'Motors and Generators"
beginning on page 147 of this thesis, much of which also
applies to Class II locations.

The use of Class II motors for those parts of Class III
locations where excessive lint may be present is permitted and
recommended.

Rule 5205f: "When motors of the enclosed pipe-ventilat-
ing type are used, or when motors are enclosed in rooms or
housings, the vent pipes shall extend to the outside of the
building to a source of clean air. The vent pipes shall be of
metal, substantially constructed and with each attached to
the next by riveting, welding, or other approved methods.
When motors are intended to he moved on their bases, a slip
or universal joint tight enough to prevent the entrance of
dust shall be provided in the vent pipes. The outer ends of
vent pipes shall be suitably screened to prevent the entrance
of animals or birds."

This rule is identical with that which appears on the
same subject under the discussion of Class II rules and needs
no additional comment.

180

Motor Controllers, Switches,
Relays and Thermal Cutouts.

 

 

Rule 5205g: "Motor controllers, thermal cutouts,
switches, relays, the switches.and contactors of autotransformer
starters, or other devices or apparatus which in their normal
operation tend to create arcs or sparks shall not be installed
unless such devices or apparatus are enclosed in dust-tight
metal cases or cabinets, or are of the dust-tight-Oil-immersed
type, and are so designed that they may be operated without
opening the cabinet or case."

In the matter of motor controllers the plan of selecting
controllers of the automatic remote control type immediately
suggests itself and it is probable that this plan can be made
use of very generally. When this plan is followed, it is then
necessary to place only the auxiliary push button or switches
in the hazardous area. The method of locating the controllers
and such equipment in specially built controller rooms is also
recommended so that lint and light material will not collect
in or about such equipment.

For extreme cases when it is necessary to place
controllers and such equipment directly in a location where
considerable lint or light material is present, the apparatus
shall be of the dust-tight design. Apparatus approved for
Class II locations will be permitted and is recommended.

Rheostats and Resistance Devices

Rule 5205h: "Rheostats, resistance boxes, or other
resistance devices, shall be enclosed in non-combustible cases,
so constructed as to adequately exclude flyings or lint."

It would be decidedly unsafe to permit open resistors
or other resistance devices in places where lint or other
light combustible material is present. Hence, this rule which
prescribes the necessary enclosing of resistors in non-
combustible cases or enclosures. It is not required that this
case be dust-tight, it will be noted, but it should be
sufficiently tight to prevent the material from entering. In
many instances a switch enclosure can be built of compressed
asbestos lumber or similar non-combustible material.

When such resistors are employed in conjunction with
motor contrOllers and a control room is provided, or the con-
trollers are isolated from the hazardous area, the resistors
should be mounted in the control room or near the isolated
controllers.

181

Electric Heating Appliances

 

Rule 32051: "Electric heating appliances shall not be
used unless of a type approved for installation in locations
where combustible flyings or lint are present."

This rule is identical with the parallel rule appearing
in the discussion of the rules for Class II locations except
that it is specified that the appliances be approved for
locations where combustible flyings or lint are present.

Heating appliances with exposed heating units are
necessarily not to be permitted in the hazardous areas.

Lamps i2 Fixed Positions

 

Rule 5205j: "Where there is a possibility of flyings
or lint collecting about lamps in fixed positions, such
lamps shall be enclosed in globes of the dust-tight type, and
- when exposed to mechanical injury, shall be protected by sub-
stantial metal or other approved types of guards to prevent
breakage. Heavy fixtures, used as pendants, shall be supported
by conduit hangers or chains to prevent strain on the wires.
Where rubber covered wire is used, it shall have insulatiOn
not less than 5/64 inch thick. Sockets and receptacles shall
be of the keyless type and, unless individual switches are
provided, shall be located at least 72 feet above the floor,
or shall be otherwise so located or guarded that the lamps
cannot readily be backed out by hand."

Where a considerable amount of lint or finely divided
light material is present in the atmosphere Of picker rooms,
delinting rooms, and in some locations in woodworkers it may
be possible that a blanketing effect of the same nature as
discussed under Class II locations will occur to cause
ignition of the lint or light material. Such instances are
rather infrequent and the portion of the rule requiring the
use of enclosing globes need not be applied except in extreme
cases. It is important, however, that lamps be guarded, as
provided by the rule, when they are exposed to injury, for
the breakage of a lamp may cause immediate ignition of lint.

Portable Lamps

 

Rule 5205k: "Sufficient general illumination shall be
provided by fixed lighting units to eliminate, so far as
possible, the need for portable lamps. When portable lamps
are necessary, they shall be enclosed in dust-tight globes
properly protected by substantial metal or other approved
types of guards to prevent breakage. Sockets for portable
lamps shall be of the keyless moulded composition type with
no exposed metal parts."

182

While portable lamps in Class III locations may not
create as severe a hazard as when such lamps are used in gas,
vapor or dust and air atmospheres, it is still important that
they be of the proper type. Breakage of a portable lamp in the
presence of lint would be likely to cause a flash fire, so it
is necessary that the lamp be equipped with an enclosing globe
and a substantial guard.

It will be noted that the rule is identical with that
appearing in the rules for Class II locations. The portable
lamp units suggested in the latter are suitable for use in
Class III locations.

Portable Cords

 

Rule 32051: "When necessary to use portable lamps, or
other portable current-consuming devices, approved flexible
cord designed for hard usage such as Type S or Type PA shall
be used. Such a flexible cord shall contain one extra con-
ductor, which shall be properly connected to form a grounding
connection for metal lamp guards, motor frames, and all
exposed metal portions of such portable lamps and devices."

This rule is identical with that on the same subject
in the rules for Class II locations and the same comments

apply.

Connections 23 Portable Cords

 

Rule 5205m: "Connections of portable cords direct to
supply conductors shall first be made mechanically secure
and shall then be soldered and heavily taped. In addition,
the cord shall be securely supported so that the probability
of a break in the conductors at this point will be minimized."

This is the only rule which appears in this section
providing for the connection of portable cords to supply
conductors and is identical with that appearing in the
discussion of the rules for Class II locations. The same
comment as previously made applies.

Owing to the absence of any other rules on the subject
of connection of portable cords to supply conductors in this
section, permission is automatically given to employ any
approved separable attachment plug and receptacle. It is
recognized that the use of an eXDosed device for this purpose
would introduce considerable hazard if opened under load in
the presence of quantities of lint. For this reason Article
32 Committee has now under consideration a new rule to care
for this matter. It is probable that the requirements will
be somewhat similar to those for Class II locations on this
point.

185

Groundigg

 

Rule 3205n: "The exposed non-current carrying metal
parts of equipment such as the frames or metal exteriors of
motors, fixed or portable appliances, lighting fixtures,
cabinets, cases, and conduit shall be grounded as provided in
Article 9 of this code. The locknut-bushing and double-lock-
nut type of contact shall not be depended upon for bonding
purposes, bonding jumpers with proper fittings or other

approved means being required to assure an effective grounding
circuit."

This is identical with the rule on Grounding which
appears in.the discussion of the rules for Class II locations.
No additional comment is needed.

 

Figure 57
Illustrating Attempt to Protect
an Open Motor in a Woodworking
Establishment by Use of Sheet
Metal Housings. Such Methods
May Result in Overheating and
Burning Out of the Motor.

184

CLASS IV LOCATIONS

As has been previously discussed under "Classification",
the hazards in Class IV locations are similar to those of
Class III locations in that both are involved with easily
ignitable combustible fibers. However, where Class III loca—
tions are concerned with manufacturing plants where combustible
fibers or lint are produced or used, Class IV locations are
concerned only with warehouses and storage facilities for these
combustible fibers. In most respects the rules for Class IV
locations are more rigid than those for Class III, for the
reason that the warehouses involved are of large area and the
property values usually very high. Consequently, a fire once
started spreads with great rapidity due to the easily ignit-
able nature of the fibers.

The rules for Class IV locations are designed to prevent,
so far as possible, ignition of the fibers from arcs, sparks
or high temperatures resulting either during normal operation
or when faults occur. The hazard represented by accumulations
of excessive quantities of lint on or in apparatus, such as
motors, is not usually present, except possibly in warehouses
where compresses are used. However, it will be seen that rules
prescribe enclosed motors, protection of resistance devices,
dust-tight enclosures for or isolation of motor controllers,
prOper placement and enclosing of lighting fixtures and
certain requirements with regard to cranes and battery
charging equipment. All of these requirements are made for
the purpose of safeguarding all possible sources of ignition.

Due to the similarity of the rules for Class IV
locations to those of the other Classes previously discussed,
detailed comment on many of them is not needed.

Rule 3206a: "In locations judged to be as described
for Class IV locations in paragraph 6 of Section 3201, the
following provisions are to be observed:"

This is an introductory rule which refers back to the
section containing the definitions of the various classes.

Service Equipment, Switchboards and Panelboards

 

Rule 3206b: "Service entrance equipment and all switch-
boards and panelboards shall not be placed in locations of
this class, but, if impracticable to locate them elsewhere,
all live parts shall be enclosed in dust-tight metal cases
or cabinets with provision for external operation only, or
shall be located in separate dust-tight rooms built of or
lined with substantial non-combustible materials and with
self-closing doors, so constructed and installed as to
adequately exclude flyings or lint."

"$

185

This rule is identical with that which appears in the
rules for Class II and Class III locations. In the modern large
terminal warehouses the service equipment and switchboards are
usually placed in a switch house especially provided for the
purpose. In the older warehouses a separate room built as
specified by the rule may be conveniently provided, either
outside of or within the warehouse. Reference should be made
to the discussion on the same subject in the treatment of the
rules for Class II locations.

When it is impracticable to isolate this equipment as
provided for by the rule, it is, of course, necessary to permit
its installation in the hazardous area, but only if the equip-
ment is enclosed in dust-tight metal cases or cabinets.

Fuses and Circuit Breakers

Rule 3206c: "Fuses and circuit breakers shall prefer-
ably not be installed in storage rooms, but if impracticable
to locate them elsewhere, all live parts shall be enclosed in
dust-tight metal cases or cabinets or shall be located in
separate dust-tight rooms built in accordance with the
provisions of paragraph b of this section."

The same comment as made on service equipment applies
to fuses and circuit breakers. In most cases it is practicable
to isolate or enclose them in non-combustible rooms, but
when conditions are such that this cannot be done, they may
be located within the warehouse on condition that they are
enclosed within dust-tight cases or cabinets.

Type 2E Wiring

Rule 5206d: "Rigid Conduit shall be the wiring method
employed. Where it is necessary to employ flexible connections,
as at motor terminals, a short length of flexible steel
conduit may be used."

"It is recommended that pilot lights be installed on
the outside of storage rooms to indicate when the
current in the rooms is "on" or "off. "

Note that rigid conduit is specified as in the other
classes of this article and for the same reason.

The recommendation for the installation of pilot lights
outside of storage rooms applies to the more modern terminal
cotton warehouses which are often found divided into a number
of separate compartments, each cut off from the next by fire
walls and cutoff from the working alley on aisle by fire

186

walls with openings protected by fire doors. Under these
conditions, greater safety is obtained when all light or power
circuits supplying each compartment or room are disconnected.
Hence, the need of pilot lights for warning attendants.

Motors and Generators

Rule 3206a: "Motors and generators shall be of the
totally-enclosed, totally enclosed-fan-cooled, or enclosed
pipe ventilated types, or shall be enclosed in separate dust-
tight rooms or housings built of or lined with substantial
non-combustible materials and so constructed as to adequately
exclude flyings or lint and properly ventilated from a source
of clean air.

The requirements in this rule are identical with those
in rule 3204f for Class II locations and the discussion.
included under this rule applies here. However, the reason
for such a rule applying to fiber warehouses is not because
of accumulations of lint in the motor, but to protect against
ignition of fibers in event of burnout of a motor. It is felt
that the expense attached to the use of enclosed motors, or
the enclosing of Open motors in non-combustible rooms is
warranted, due to the high property values which are affected
by possible fires.

Rule 5206f "When motors of the enclosed-pipe-ventilating
type are used, or when motors are enclosed in rooms or housings,
the vent pipes shall extend to the outside of the building to
a source of clean air. The vent pipes shall be of metal, sub-
stantially constructed and with each section attached to the
next by riveting, welding, or other approved methods. When
motors are intended to be moved on their bases, a slip or
universal joint tight enough to prevent the entrance of dust
shall be provided in the vent pipes. The outer ends of vent
pipes shall be suitably screened to prevent the entrance of
animals or birds."

No comment is needed on this rule. Reference should be

made to the discussion of the parallel rule appearing under
Class II locations.

Resistance Devices

 

Rule 3206g: "Resistance devices, unless installed in
rooms such as described in paragraph b of this section shall
be enclosed in especially approved metal cases of dust-tight
design. These shall be so constructed that ignition of lint
or flyings by direct contact with the enclosing case, whether
in normal Operation or in case of accident, is avoided."

 

‘...

187

It has been found that great care must be taken to guard
resistance devices to prevent ignition of baled fiber or loose
lint by direct contact with resistance devices or their
ordinary enclosing cases. As usually interpreted in the field,
it is required that the ordinary enclosed resistance device be
enclosed in a somewhat larger outer case in order to permit
dissipation of heat generated during normal operation or in
case of burnout, without resulting in unduly excessive surface
temperatures on the outer enclosing case.

Obviously, the safest procedure is to install such
resistance devices in a room such as described in Rule 3206b.

Motor Controllers, Switches, Relays

 

and Thermal Cutouts

 

Rule 5206b: "Motor controllers, thermal cut-outs,
switches, relays, switches and contactors of auto—transformer
starters, impedance devices, or other devices or apparatus
used in connection with the control of power or other circuits
shall not be installed in these locations unless such devices
or apparatus are enclosed in dust-tight cases or cabinets,
and so designed that the device may be operated without open-
ing the cabinet or case.

"It is recommended that motor control devices be of
the remote control type with the main contactors
located in separate rooms or compartments built of or
lined with substantial non-combustible materials so
constructed as to exclude flyings or lint. The remote
control push buttons or switches of the oil-immersed
or dust-tight type may then be placed in the most
convenient locations.’

The provisions of this rule are similar to those for
Class II locations on the same subject. In general, controllers
and similar devices are required to be of the type approved
for Class II locations unless located in rooms of the type
mentioned in the note following the main rule.

Electric Heating Appliances

 

 

Rule 52061: "Electric heating appliances shall not be
used unless of type approved for installation in locations
where combustible flyings or lint are present."

It is obvious that electric heating appliances should
not be permitted in combustible fiber warehouses where they
may cause ignition of baled cotton or other fibers, or lint.

 

 

I.

188

It is probable that the usual radiant or strip type heaters
will be permitted in offices, shops or similar locations in
which lint is not present.

Lamps 12 Fixed Epsitions

 

Rule 32063: "Sufficient general illumination shall be
provided by fixed lighting units to eliminate so far as
possible, the need for portable lamps. Lamps shall not be in-
stalled where they are likely to be injured when bales are
being tiered or handled. Lighting fixtures shall be wired with
not less than No. 14 wire, and the fixture wiring shall be en-
closed in rigid conduit or the equivalent in thickness. Lamps
may be in receptacles attached directly to the outlet box
covers. Lamps and their sockets shall be so enclosed that in
the event of a burn-out of the lamp or socket no spark or hot
metal can escape from the enclosure."

It should be noted that very rigid precautions are
taken to prevent the ignition of baled fiber or "flyings" by
the breakage of lamps or faults in their fixtures or wiring.
Breakage of lamps by careless handling of baled cotton or
other fibers has been a common cause of fire. The wording
of the rule is such that both its intent and application are
clear.

Portable Lamp

 

Rule 5206k: "When portable lamps are necessary they
shall be enclosed in dust-tight globes properly protected by
substantial metal or other approved types of guards to prevent
breakage. Sockets for portable lamps shall be of the moulded
composition or metal-jacketed porcelain, keyless type."

As in the other types of hazardous locations, portable
lamps in fiber warehouses are regarded as a severe hazard.
Hence, the provisions of the rule specifying the types
described for Class I and Class II locations. Here again
should be emphasized the need for so designing general
illumination by fixed units that portable lamps will not be
necessary.

Portable Cords

 

Rule 52061: "When necessary to use portable lamps, or
other portable current consuming devices, approved flexible
cord designed for hard usage suCh as type S or type PA shall
be used. Such a flexible cord shall contain one extra

189

insulated conductor which shall be properly connected to form
a grounding connection for metal lamp guards, motor frames,
and all other exposed metal portions of such portable lamps
and devices."

Here again, the safest available types of cord are
specified. The provision for an extra conductor for grounding
purposes is made as in the rules for the other classes of
Article 52.

It will be noted that no requirements are made as to
the method to be used in connecting portable cords to supply
conductors. This omission has been criticized and undoubtedly
a rule will be added to care for this point. It is probable
that a rule similar to that for Class II locatiOns 3204m will
be adopted.

Electric Cranes

Rule 3206m: "Electric cranes Operating over combustible
fibers shall not be operated on a system with a grounded
conductor. Feeders for electric cranes shall be provided with
a recording ground detector, and protected by a relay which
will automatically open the feeder circuit breaker in the
event of the insulation of the system falling below 1000
ohms. Bare conductors for cranes operating in rooms used for
the storage of combustible fibers shall be protected by suit-
able barriers so arranged as to prevent any escape of sparks
or hot particles, and the moving current collectors shall be
so designed as to minimize sparking at sliding contacts.

"It is recommended that where the distance of travel
permits, current to the crane be supplied through

Type S or PA portable conductors equipped with approved
type of reel or take-up device."

In the more modern tenninal fiber warehouses, electric
cranes are coming into use for handling baled fibers. As
usually employed, the crane travels on rails over the load-
ing dock or platform and can be shunted into the various
compartments on shunt rails in order to remove bales from
the compartment or deliver them. The crane motors are
supplied from bare conductors from which current is obtained
through "shoes" sliding on the conductors. Necessarily every
precaution is required to be taken to prevent sparks or arcs
produced by imperfect contact on the bare supply conductor
igniting accumulated lint or heated particles falling to the
cotton below and causing ignition.

The writer had occasion to inspect a terminal cotton
warehouSe in Which a crane installation made in accordance

190

with the rule under discussion was in operation and, from all
he could learn, it has given entire satisfaction. It.will be
noted that the system supplying current to the crane is re-
quired to be of the ungrounded type. Compliance with this re-
quirement, together with that providing for the use of an
automatic recording ground detector, enables the operator to
detect any accidental grounds which may occur.

For small crane installations, the type of crane motor
current supply mentioned in the recommendation can be employed
to good advantage.

Storage Battery Charging Equipment

Rule 3206n: "Storage battery charging equipment shall
be ofapproved type located in separate rooms built of or lined
with substantial non-combustible materials so constructed as
to adequately exclude flyings or lint, and shall be well
ventilgted. Electric trucks shall be charged only in such
rooms.

Inasmuch as the Operation of storage battery charging
equipment involves the frequent production of arcs or sparks,
the requirement for its installation in a separate non-
combustible room is warranted. necessarily also, the charging
of electric trucks should be confined to such a room.

Grounding

 

Rule 32060: "The exposed non-current carrying metal
parts of equipment, such as frames or metal exteriors of motors,
fixed or portable appliances, lighting fixtures, cabinets,
cases and conduit, shall be grounded as provided in Article
9 of this Code. The locknut-bushing and double-locknut type
of contact shall not be depended upon for bonding purposes,
bonding jumpers with proper fittings or other approved.means
being required to assure an effective grounding circuit. The
wheels of electric trucks shall be provided with rubber tires
or made of non-conducting material.

This rule, both in application and intent is identical
with those appearing in the other sections of this Article and,
therefore, needs no special comment. It should be noted that
wheels of electric trucks are required tobe provided with
rubber tires. Electric trucks for use in cotton warehouses
are usually made subject to special approval by the inspection
authority involved.

190

with the rule under discussion was in operation and, from all
he could learn, it has given entire satisfaction. It.will be
noted that the system supplying current to the crane is re-
quired to be of the ungrounded type. Compliance with this re-
quirement, together with that providing for the use of an
automatic recording ground detector, enables the operator to
detect any accidental grounds which may occur.

For small crane installations, the type of crane motor
current supply mentioned in the recommendation can be employed
to good advantage.

Storage Battery Charging Equipment

Rule 5206n: "Storage battery charging equipment shall
be ofapproved type located in separate rooms built of or lined
with substantial non-combustible materials so constructed as
to adequately exclude flyings or lint, and shall be well
ventilgted. Electric trucks shall be charged only in such
rooms 0

Inasmuch as the Operation of storage battery charging
equipment involves the frequent production of arcs or sparks,
the requirement for its installation in a separate non-
combustible room is warranted. Necessarily also, the charging
of electric trucks should be confined to such a room.

Grounding

 

Rule 32060: "The exposed non-current carrying metal
parts of equipment, such as frames or metal exteriors of motors,
fixed or portable appliances, lighting fixtures, cabinets,
cases and conduit, shall be grounded as provided in Article
9 of this Code. The locknut-bushing and double-locknut type
of contact shall not be depended upon for bonding purposes,
bonding jumpers with proper fittings or other approved means
being required to assure an effective grounding circuit. The
wheels of electric trucks shall be provided with rubber tires
or made of non-conducting material.

This rule, both in application and intent is identical
with those appearing in the other sections of this Article and,
therefore, needs no special comment. It should be noted that
wheels of electric trucks are required tobe provided with
rubber tires. Electric trucks for use in cotton warehouses
are usually made subject to special approval by the inspection
authority involved.

190

with the rule under discussion was in operation and, from all
he could learn, it has given entire satisfaction. It.will be
noted that the system supplying current to the crane is re-
quired to be of the ungrounded type. Compliance with this re-
quirement, together with that providing for the use of an
automatic recording ground detector, enables the operator to
detect any accidental grounds which may occur.

For small crane installations, the type of crane motor
current supply mentioned in the recommendation can be employed
to good advantage.

Storage Battery Charging Equipment

Rule 5206n: "Storage battery charging equipment shall
be ofapproved type located in separate rooms built of or lined
with substantial non-combustible materials so constructed as
to adequately exclude flyings or lint, and shall be well
ventilgted. Electric trucks shall be charged only in such
rooms.

Inasmuch as the Operation of storage battery charging
equipment involves the frequent production of arcs or sparks,
the requirement for its installation in a separate non-
combustible room is warranted. Necessarily also, the charging
of electric trucks should be confined to such a room.

Grounding

 

Rule 32060: "The exposed non-current carrying metal
parts of equipment, such as frames or metal exteriors of motors,
fixed or portable appliances, lighting fixtures, cabinets,
cases and conduit, shall be grounded as provided in Article
9 of this Code. The locknut-bushing and double-locknut type
of contact shall not be depended upon for bonding purposes,
bonding jumpers with proper fittings or other approved means
being required to assure an effective grounding circuit. The
wheels of electric trucks shall be provided with rubber tires
or made of non-conducting material.

This rule, both in application and intent is identical
with those appearing in the other sections of this Article and,
therefore, needs no special comment. It should be noted that
wheels of electric trucks are required tobe provided with
rubber tires. Electric trucks for use in cotton warehouses
are usually made subject to special approval by the inspection
authority involved.

 

2.4.3.2 V

LOSS RECORD

Containing a number of
typical reports of fires
and accidents from elect-
rical causes in establish-
ments in which hazardous
processes or materials
were involved.

192
LOSS RECORD ’

TYPICAL FIRE AND ACCIDENT REPORTS
INVOLVING HAZARDOUS MATERIALS AND PROCESSES

 

In the following will be found a number of abbrev-
iated reports of fires and accidents which have occurred in the
hazardous industries through electrical causes. These have been
included to illustrate and emphasize the need for the types of
electrical installations prescribed by Article 52.

It should be pointed out that, because of the nature
of the hazardous materials, it is frequently difficult to determine
even the approximate causes of fires and explosions which occur '
in plants where they are present. Very often eye witnesses are
killed or are so badly injured that little can be learned of the
causes or conditions which brought about the explosion or fire.
Furthermore, in the more serious accidents, all material evidence
is generally destroyed, with the result that the fire or explosion
is classed as from.unknown cause.

It will be noted that the actual property losses in
many of the reports given involve comparatively small sums of
money. This is not to be taken as an indication that such is
usually the case. As a matter of fact it is the exception rather
than the rule, but it is usually only in the case of these smaller
losses that we are able to determine the cause with any degree of
accuracy.

In these reports, details as to available fire
protection and methods of extinguishment have largely been omitted
as we are not immediately concerned with this angle of the case.
Our problem.is one solely of prevention of ignition of hazardous
materials from electrical causes. -

Acknowledgment should be made to several persons
and agencies who obliged by furnishing many of these reports. The
office of the National Fire Protection Association, through the
kindness of Messrs. Moulton and'Walker, contributed a large volume
of the reports involving finishing processes. Free reference was
also made to loss reports which have appeared in various issues
of the "Quarterly"of the R. F. P. A., and in the Associated
Factory Mutual "Record." Messrs. Forsyth, Stewart, Adkins, Smith,
Daniel,‘Wise,‘Wellman and other members of the International
Association of Electrical Inspectors also contributed valuable
reports. For fire and explosion reports involving the grain and
flour industry, the loss records of the Mutual Fire Prevention
Bureau were made use of to a considerable extent. The actual
names of the plants involved in these reports are deleted for
obvious reasons.

195
FINISHING PROCESSES

SPRAY PAINTING

Automobile Body Factory, Grand Rapids, Michigan, February 11th, 1926.

A workman.was engaged in cleaning out a vent connected to a tunnel
type spray booth after operations for the day had ceased. He was
standing on a ladder and partly entering the duct, using an un-
guarded electric light on an extension cord of unknown character.
The lamp was broken and a smouldering fire occurred which.was
quickly followed by a flash and explosion. The flash spread rapidly
into connected tunnels and vents, but the prompt operation of
automatic sprinklers held the fire loss to the nominal amount

of $1,800.00. However, the employee was fatally burned and his
assistant suffered serious burns.

Automobile Body Plant, Detroit, M1chigan, September 9th, 1926.

An automobile body was being conveyed through a tunnel type spray
booth where it was being painted. One door of the body was
accidently left open and this struck a protruding vapor proof
lighting fixture inside the booth and tore it from its supports.

A short circuit followed and the flash caused ignition of the
spray vapor and residue in the booth. The fire was extinguished by
sprinklers with negligible damage.

Automobile Body Plant, Detroit, Michigan, April 23rd, 1927.

The fire or explosion originated on the third floor of a five
story building where lacquer spraying was done. It was due to

the ignition of pyroxylin dust or residue by a spark from.cr the .
overheating of a mercury vapor lamp over a spray booth. The first
explosion was enough to shake the pyroxylin dust into suspension
in.the air and this, together with.the gases formed by the
decomposition of residue resulted in a second explosion of

great violence. Several workmen were killed outright by the blasts
and others died later of their burns. In all, twenty three lives
were lost. Property loss was $2,000,000.00.

Automobile Body Plant, Detroit, Michigan, March 19th, 1929.

A worker entered the vent duct of a spray booth with an unguarded
portable lamp in his hands which.was strictly against orders. The
light bulb was broken and ignited by pyroxylin dust in the booth

and vents. The workman was fatally burned‘before he could escape

from the booth. Property loss $400.00. .

Furniture Factory, Lenoir, North Carolina, November 50th, 1926.

A spray gun was being cleaned in close proximity to unprotected
electric lights. The bulb at the booth entrance was broken and there

,1

1“

194

was an immediate flash of the flammable vapors throughout the
second floor. The fire developed sufficient heat to ignite the
spray materials stored near the booths and the lacquer residue
accumulated on the floor near booth. One man was burned to
death and eight were injured. Property loss $260,000.00.

Airplane. Wing Factoyy, Englewood, Colorado, April 20th, 1928.

The fire occurred in a building used for the assembling and
treatment of airplane wings. Lacquer was applied by spraying

and also by brush from an open fifteen gallon can. Lacquer spraying
of plane cowls and metal parts was done in the basement. Neither

in the first floor nor in the basement were booths provided for

the spraying operation and no artificial ventilation existed except
that by motor driven fan in an outside wall. There was a mild
explosion coupled with a dull roar followed by two more severe
explosions which filled the building with flame, blew the doors
closed and piled debris against them.in such a.manner that those
who got out escaped only with difficulty. The first explosion
appeared to be from ignition of the lacquer vapors and the
explosion that followed from the ignition of the deposit or -
residue which was to be found throughout the room. The investigators
state that just before the first explosion, one of the surviving
employees had seen a spark from the fan motor. Eleven deaths and
seventeen injured is the toll taken by this accident. The building
and contents were totally destroyed with a loss of about
$25,000.00. Incidently, the coroner's jury declared the owners
guilty of criminal negligence and of "involuntary manslaughter"

on hearing the testimony. _

Automobile Plant, Detroit, Michigan, February 12th, 1931.

 

The rumble seat of a car being painted closed down on an extension
cord, cutting it:in two. This resulted in a short circuit which
caused a fire. Loss negligible.

Automobile Pactogy, Chester,'§g., September 21st, 1911.

 

The process involved in this fire was the spraying of truck parts
with grease dissolved in naphtha to prevent rusting during shipment
to foreign countries. This was carried out in a spray booth
through which the parts travelled on a conveyor. The spray nozzles
were supplied with the grease mixture by pumping from a 750 gallon
open tank located beneath the floor of the booth. Early in the
morning of the day of the fire employees filled the tank with the
thinned grease mixture and operated the pump a few minutes to

make sure the nozzles were clear, but did not start the ventilating
fans. Naphtha vapors accumulated and two hours later when the
foreman pressed the switch button located just outside the booth

to start the tank agitator pump, there was a flash in and around
the booth. It seems apparent that the flammable vapors were

ignited by an electric spark from the switch. The contents of the
tank caught fire immediately and the flames spread rapidly.

A large portion of the plant was destroyed.

.7.

195

Spray Paint Shop, New York City, Date not available.

An ordinary direct current desk fan was mounted in the rear of a
paint spray booth to force vapors out of doors. The windings of

the motor broke down and the arc ignited the waste spray in the

hood. The fire spread causing a loss of $22,626.18.

Automobile Paint Shop, Dallas, Texas, July 6th, 1928.

It is thought that a short circuit in electric wiring to an
exhaust fan caused this fire which resulted in a property loss
of $8,724.00.

Auto Body Factory, Detroit, Michigan, April 26th, 1926.

A short circuit in the electric switch terminal of an old style
mercury lamp in a spray booth ignited pyroxylin-dust on the switch
box. Loss was confined to $500.00 damage.

Auto Body Féctory, Detroit, Michigan, September 21st, 1926.

The fire started in a pyroxylin spray booth and was probably
caused byen.electric spark from.a mercurial arc lamp or its
connections which ignited pyroxylin waste. The loss was small.
Auto Body Factopy, Mifflinburg, Pa., October 4th, 1926.

An employee was using gasoline to clean paint from.the inside of the
spray booth. A spark from an open light socket caused a spark
which ignited gasoline fumes. The fire was extinguished without
pr0perty loss.

Casket Factory, Pittsburg, Pa., November 20th, 1924.

Lacquer solvent fumes in a spray booth were ignited by a spark
from a ventilating fan motor located in the path of the fumes.
The loss was $2,679.00.

Furniturg Factory, North Bennington, Vermont, January 5th, 1924.

A spark from a motor in a s ray booth ignited varnish.spray inside
of the booth. The loss was 4,500.00.

Furniture Factogy, St. Louis, Missouri, September 24th, 1924.

Sparks due to short circuit in a fan motor ignited vapor from.the
spray guns. The loss was small.

Furniture Factory, Martinsville, Virginia, February 12th, 1925.

 

In lifting a bucket of varnish an employee accidently struck and
broke an electric light bulb close to the spraying cabinet which
ignited varnish fumes in and around the cabinet. The loss was
$14,454.00.

196

Furniture Factory, Pulaski, N. Y., December 50th, 1926.

 

An employee threw an Open electric switch while holding a spray

gun and the gasoline with which he had washed his hands was

ignited by the spark. He dropped the gun on the floor where varnish
residue was ignited. The loss was 89,208.00.

Furniture Factory, Los Angeles, California, April 25rd, 1927.

A spark from a fan.motorignited vapors in a spray booth causing a
flash fire with loss of $4,518.00.

Furniture Factory, Savannah, Ga., April 25th, 1927.

 

The fire started in a spray booth and was due to a spark from the
motor of a ventilating fan. The loss was $52,268.00.

Furnitup§_Factopy, Bassett, Virginia, February 25rd, 1925.

 

The fire started at a spraying machine when a spark from a motor
ignited the vapor. The loss was $500,000.00.

Furniture Factory, McGraw, New'York, June 4th, 1926.

 

The fire was due to a hot bearing on a‘motor located in the exhaust
vent of a lacquer spray booth. This ignited the lacquer vapor around
the motor. The loss was $6,800.00.

Furniture Factory, Montoursville, Pa., June 12th, 1926.

Fire was caused by a spark due to a short circuit at a motor under
an all metal spray hood. The loss was large.

Furniture Factor , Atlanta, Georgia, June 15th, 1926.

 

The fire started at a motor in a shellac spraying booth which had
not been cleaned for some time. The trouble was due to the motor
being "gummed up" and arcing from a short circuit. The loss was
$13,966.00. '

Furniture Factopy, Bostozn Massachusetts, August 18th, 1926.

An electric light bulb in a spray b00th.was accidently broken. This
ignited the flammable vapors. The loss was $197,000.00.

Tannepy, Peabody, Massachusetts, December 24th, 1926.

Butyl acetate vapor and lacquer in a spray booth.were ignited by a
hot bearing on the booth fan motor. The loss was $567.00.

Metal Worker, New York City, July 25th, 1924.

A spark from.an electric motor ignited lacquer residue on the
inside pf a spray hood. The loss was moderate.

197
Metal Worker, Keene, New Hampshire, August 14th, 1924.
A surge had occurred in the power supply and when the current
was turned on after repairs had been made the wiring to the spray
gun equipment heated or short circuited. This ignited the lacquer
residue on the equipment. Fire followed with a loss of $5,100.00.
Metal Worker, Binghamton, New‘York, June, 1926.
A small loss occurred when sparks from.an electric motor, used to
revolve a table on which.parts to be sprayed were laid, ignited
lacquer~residue.

Furniturg_Factory, Thomasville, North Carolina, May 19th, 1927.

 

Vapors which had accumulated in the spray booth.were ignited by a
short circuit in an electric heater at the booth. Loss of $17,205.00.
resulted.

Furniture Factopy, Shelbyville, Indiana, July 19th, 1927.

'A spark from an electric switch ignited some lacquer which had just
been spilled. Fire flashed into the booth badly burning the operator.
A large loss followed.

Furniture Factory, Philadelphia, Pa., March 8th, 1928.

The fire started at a varnish spray booth due to a short circuit in
a small electric heater or connections used to adjacent to the
booth. The loss was small.

Furniture Factory, New York City, June let, 1929.

 

A fire caused by the ignition of varnish in a spray booth from.a
short circuit in an extension cord did considerable damage.

Metal Worker, New'York City, December lst, 1927.

A.fire started in a spray booth when an electric light was broken
igniting fumes from lacquer and drawing the flame into the vent
duct. The loss was small.

Metal Worker, Buffalo, New York, October 8th, 1928.

The fire was due to the practice of spraying pyroxylin lacquer
and varnish in the Open without spray hoods. Residues collected
not only on the various construction and finish features, but also
on the motor switch, and were ignited when employees Opened the
switch. The flash was almost instantly followed by burning of
residue on nearby walls, ceiling, floors and equipment. The loss
was moderate.

198
Metal Worker, New Brighton, Pa., May 50th, 1929.

The case of the fan motor for the fan in a spray booth was removed
to clean the commutator shortly after lacquer spraying had.been
done. Fumes were ignited when the meter was started for inspection
after being cleaned. The loss was small.

Metal Worker, Binghamton, New York, August 1926.

A.small loss followed when a flash fire occurred in a spray booth.
It is believed that the source of ignition was furnished by a spark
from.the booth fan motor.

Metal Worker, St. Johns, Quebec, December 7th, 1926.

While an employee was changing an electric light in a spray booth
an arc resulted, igniting varnish on the walls of the booth. The
loss was $700,0 . ' '

Metal Worker, Detroit, Michigan, December 16th, 1926.

Sparks from a motor ignited fumes from lacquer in a spray booth.
The fire which resulted caused a damage of $1,085.00.

Metal Worker, Brooklyn, New York, June 29th, 1927.
A short circuit in sub-standard wiring to a light and a motor

in a spray booth ignited the highly flammable lacquer. The loss
was small.

Metal Werker, New'York City, June let, 1929.

The fire occurred in the lacquer spray hood when a short circuit
of electric wiring ignited lacquer on the sides of the hood.
Moderate loss occurred when the fire spread to other spray hoods.

Metal Worker, Cambridge, Massachusetts,. December 7th, 1929.
Fire was discovered during the night in the rear of a spray booth

and was due to an overheated motor which had been started by mistake.
The loss was small.

Metal Bed Factor , Boston, Massachusetts, August 50th, 1926.

Paint and lacquer in a spray booth were ignited by a short
circuit in a fan.mot0r. The loss was small.

Automobile Factory, Flint, Michigan, July 50th, 1924.
The fire was due to a short circuit in a fan motor inside a spray

booth.which ignited the lacquer residue in the exhaust vents. The
loss was small.

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199

Automobile Factory, Philadelphia, Pa., October 19th, 1925.
While an employee was spraying some metal parts he broke an
electric light bulb in the spray booth. Vapors from the paint
caught fire and a loss of $500.00 resulted.

Automobile Factory, Flint, Michigan, May 21st, 1925.

An ordinary incandescent light was being used in a spray booth.
The lamp became coated with lacquer which decomposed and was

ignited by the heat of the lamp. A flash fire followed causing
a loss of $500.00.

Automobile Factory, Norwood, Ohio, June 5rd, 1925.
A small can partly filled with lacquer was in a spray booth and
a small motor driven pump was used for supplying the spray gun.

When an employee raised the cover on the can, fire flashed due to
either static sparks or sparks from the motor. The loss was small.

Automobile Factory, Arabi, La., August 15th, 1926.

An employee was cleaning a spray booth.and accidently dr0pped an
extension light, the globe of which.broke and caused pyroxylin
lacquer to ginite. The loss was $168.00.

Electric Appliance Facto , New‘York City, September 2nd, 1926.

The fire originated under a lacquer spray booth and was caused by
a spark from an electric motor. The loss was small.

Electrig Appliance F ctor , New'York City, October 6th, 1926.

The fire was caused by the breaking of an.electric light bulb
over a lacquer spray hood. The loss was small.

Electric Appliance Factor , Milwaukee, Wisconsin, June 2nd, 1928.

A spark from.a fan motor ignited lacquer in a spray booth which
resulted in a fire with.amall loss.

Electrig Appliance Factor, New'York City, November 7th, 1928.

A spark from.a motor started a fire in a small lacquer spray hood.
The loss was small.

Electric Appliance Factory, Chicago, Illinois, March 30th, 1929.

A short circuit in electric wires on a spray machine ignited spray
material. The resulting fire caused a loss of $53,920.00.

..

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200
Automobile Factory, Detroit, Michigan, March 1st, 1927.
The fire started inside the ”coil box” of a mercury arc lamp
whichwas attached to the side of the spray booth. A short circuit
occurred in the "coil box" - the arc igniting dust on the wire

and the fire spread to the lacquer residue on the top of and
inside the spray booth. The loss was small.

Electric Appliance Factory, New'York City, October 24th, 1925.

Fire originated in a lacquer spray hood as the result of a spark
from.a switch.used to control the fan motor. The loss was small.

Electric Appliance Factory, Syracuse, New'York, April 2nd, 1926.

 

Fire in a lacquer spray booth was caused by trouble with the
electric fan.motor located directly in the exhaust pipe. The
loss was small.

Electric Appliance Factory, Hamilton, Ontario, August 28th, 1926.

The fire was caused by the breaking of an electric light bulb
hanging in a spray booth. The loss was $200.00.

Display Tray Factor , Providence, Rhode Island, October 26th, 1928.

Jewelers display trays were being finished by spray process in a
spray room when the lacquer solvent vapors were ignited by sparks
from a ventilating fan motor. The loss was small.

Piano Factor , St. Therese, Quebec, May 19th, 1929.

A spark occurred when the motor drive exhaust fans were started,
igniting vapors rising from a pail of lacquer suspended nearby.
About twelve employees were injured and heavy preperty damage
occurred.

Metal Werker, Cuyahoga Heights, Ohio, December 17th, 1927.

An employee accidently broke a lighted portable electric light
bulb at one of the spray booths. The heated filament was struck
by the spray and a violent flash.immediately occurred which.spread
the fire rapidly. The loss was $50,000.00.

Radio Equipment FactoryI New'York City, August 7th, 1925.

Fire occurred in a lacquer spray hood from.a short circuit in
electric light wiring inside of the hood. Loss was small.

 

 

 

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C 9

201
Furniture Factor , Oakland, California, June 15th, 1928.

 

The fire was caused by the accidental transmission of high potential
to motor circuits which caused the exhaust fan motor inside spray
booth to flash. The residue on the sides of the booth ignited and
fire spread to wood trusses and roof. The loss was $18,000.00.

Radio Equipment Factory, Boston, ‘Massachusetts, November 18th, 1926.

 

An electric spark from a motor ignited volatile fumes from pyroxylin
spraying. The loss was $240.00.

Radio Equipment Factory, Brooklyn, New York, March 2nd, 1929.

 

The fire was caused by a short circuit in an electric light
socket causing a spark which ignited spray mixture and loose
lacquers on the sides of the spray booth. The fire was confined
to the coating of residue inside of the booth.

woodworking plant, McGraw, New'York, June 20th, 1927.

The fire occurred when an employee turned on a switch.mounted on a
frame partition to start the lacquer spraying process. A spark from
the switch ignited lacquer residue on the partition and the fire
spread rapidly. The loss was $2,000.00.

W00dw0rking Plant, Sales, MassaChusetts, August 11th, 1924.

The fire started near an enamel spray booth due to sparks from an
electric fan switch. The loss was $590.00.

Automobile Body Plant, Detroit, Michigan, March.19th, 1929.

The fire occurred when a gas filled lamp on an extension cord
in use by cleanup man broke and caused a flash which ignited
lacquer residue and dust in.booth. The clothing of both cleaners
caught fire and one was so badly burned that he died later. The
property loss was $400.00.

Metal Partition Manufacturipg Plant, Elkhart, Indiana, November 20th,
—— ""— 1929 .

Lacquer residue and dust in a spray booth were ignited from a
broken incendescent lamp used to illuminate the spray booth while

it was being cleaned. The loss was $65.00.

Silver plated ware Mfg., Plant, Taunton, Mass., June let, 1925.
A spark from a motor located inside of'a spray booth ignited

lacquer fumes and caused a flash fire. Lacquer on the sides of
the booth ignited and the fire spread to a dip tank. Loss $5,000.00.

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Automobile Truck AssemblingPlant, Detroit, Michigan, June 20th, 1919.

The blowing of a fuse in the circuit to a ventilating fan motor in
the paint spraying section ignited the flammable vapors and the
fire quickly spread along the paint soaked walls. Loss $106,000.00.

‘g. g. Hauserman Cgmpany, Cleveland, Ohio, About 1928.

An.unprotected electric light bulb was broken while pyroxylin was
being sprayed in a booth. The flash ignited the spray and caused

the explosion of three barrels of lacquer which s cattered the
‘flaming liquid over the entire plant, resulting in considerable loss.

Furniture Factory, Ionia, Michigan, About 1928.

 

A fire originating in.the sprayingreoniswept the third floor of the
furniture factory. The blaze was caused by a short circuit in
electric wiring. Timely work in removing several barrels of lacquer
liquids stored on the third floor was thought to have lessened the
probable loss considerably.

Manufacturing Plant, Detroit, Michigan, December 16th, 1926.

A spark from a fan motor ignited lacquer vapors in a spray booth.
Spray booths, electric wiring and ceilings were damaged to the
extent of $1,085.00.

Sewing Machine Factory, St. Jehns, Quebec, December 7th, 1926.

As an openflnr screwed ah electric light bulb into a socket in a
varnich spray booth.igniting varnish residue on the booth walls.
The fire burned the cotton rope supporting a five gallon varnish
container, spilling the varnish which ignited when it fell.

The loss was estimated at from 700.00 to $800.00.

Metal Worker, Cleveland, Ohio, October 6th, 1927.

A spark from.a motor ignited lacquer residue in the duct to a
spray booth in which.metal cabinets were being finished. The loss
from the fire and water damage was from $5,000.00 to $5,000.00.

DIP TANKS AND DRYING OVENS

Metal Worker, New‘York City, Date not available.

An electrically operated crane was used to dip bundles of metal
parts into a dip tank. An electrical fault in the crane motor
permitted molten metal to drop into the tank and ignite the.paint in
it. The resulting fire caused a loss of $11,654.50.

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205
Automobile Factory, Racine, Wisconsin, October 8th, 1929.

Fire in pull box due to short circuit. Pull box was mounted
on.the side of an oven.used to dry fenders and frames coming from
dip tanks e

Automobile ManufacturingPlant, Detroit, Michigan, August 5rd, 1919.

An employee dipping a fender in a naphtha bath hit an insulated
wire causing an arc. An explosion occurred and the resulting fire
caused a loss of $40,000.00.

WOOd Worker, Kansas City, Kansas, November 15th, 1928.

The fire originated in the painting department Of a factory producing
wagon and truck bodies. A workman accidently struck an unprotected
electric light with a scoop board, breaking the light and igniting
naphtha vapors from adjacent Open dip tanks. The flash fire which
resulted spread rapidly and soon involved the entire building.

Loss was $22,000.00.

Electrical Manufacturing Plant, East P1ttsburg, Pa., April 25rd, 1927.

 

Workman were handling small steel plates during repair work when
one Of the plates came in contact with a bare spot on an electric
light wire, producing a spark which fell into and ignited varnish
in a dip tank. The loss was $256.00.

GASES

 

nguid Petroleum Gas Station, Madison, Wisconsin, December 12th, 1951.

A motor driven pump was being used to pump liquid gas from.a tank
car into underground tanks. The building housing the pump was
divided into two parts by means Of a metal partition, with the
pump in one compartment and the motor and its control apparatus

in the other. An attempt had been.made to make this partition
vapor proof, but apparently it was not, as consequences proved.
The motor was Of the open squirrel cage type and the controller

an ordinary magnetic switch in non-explosion resisting case.

Some difficulty had.been experienced with the pump and it was shut
down and cleaned. The pump was again started but did not seem to
Operate properly so the attendant made some adjustments, and while
doing so an explosion occurred in the compartment housing the
motor and controller. Flames passed through the partition,
seriously burning the Operator and another employee. It was found
the cover Of the controller case and also that Of the power
service switch were blown Open. It was apparent that the explosive
mixture Of liquid gas and air was ignited and exploded.

11

 

 

 

204

FLAMMABLE LIQUIDS - GENERAL

Bleachery, Pawtucket, Rhode Island, August 12th, 1924.

Two pails of benzol had been added to the warm.water in a washing
machine when an explosion occurred due to ignition Of the benzol
vapors by a spark from.an electric motor. An employee operating
the machine was fatally burned. PrOperty loss was small - $100.00

An interesting record Of fires of previous electrical origin
Occurring in buildings in metropolitan New York City, where
flammable vapors were present, is given in the following:

 

 

Year Number 9; Fires Location A_m0_upt_ 21: £925
1918 6 $88,409.49
1919 4 40,726.96
1920 5 55,402.94
1921 7 59,694.65
1922 5 600.00
1925 .6 1,210.00
1924 16 8,850.00
1925 21 10,155.00
1927 ll Spray Booths 57,000.00
” l2 Hat Cleaners 855.00
" 5 Garages 70.00
” 5 Alcohol Fumes 700.00
1928 -8 Spray Hood 5,400.00
" 21 Varnish Remover 8,996.00
2 14 Eat Cleaner 4,226.00
a 2 Garages . 225.00
5 Alcohol Fumes 5,751.00
1929 9 Spray Booths 18,696.00
2 20 Hat Cleaner 2,280.00
” 8 Varnish Remover 1,851.00
" 5 Alcohol Fumes 10,648.25
1 Paint 2,000.00
1950 10 Spray Booths 8,986.00
" 12 Varnish Remover 5,028.00
" 14 Hat Cleaner 6,118.97
$380,360.25

Previous to 1927 the record does not indicate the type or plant or
occupancy involved.

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205

Metal Working Plant, Turtle Creek, Pa., July 2nd, 1927.

Varnish and benzine stored in buried tanks were handled by means
Of pumps located in an underground pump house nearby. The engineer
entered the pump house to start the varnish pump and it is
presumed that he turned on the electric light switch just before
passing down the stairway. Immediately an explosion occurred,
caused, no doubt, by a spark at the switch igniting an explosive
mixture of the flammable vapors and air. The engineer managed

to escape, but he was so badly injured that he died a short time
after reaching the hospital.

Radio Tube Factor , Salem Massachusetts, Date not available.

A young woman tipped over a can of alcohol on a machine at which
she was working and the liquid spilled on the sleeve Of her dress.
When she stOpped her machine a spark from the switch ignited the
alcohol soaked sleeve. The girl ran about the room causing the
fire to spread and inflict severe burns over almost her entire
body which caused her death.

Paper Products Factory, Monroe, Michigan, About 1929.

Fire is said to have originated in the grinding room and as the
flames spread, a series Of explosions involving tanks of alcohol,
benzine, glycerine and other explosive liquids wrecked the plant
and spread the blaze in all directions. The loss was reported

to be $40,000.00.

Printipg_Establishment, Milwaukee, Wisconsin, August 27th, 1951.

The rolls Of a five color press were being cleaned with gasoline
when a spark from the ”inch switch" ignited the gasoline vapors.
The loss was confined to the press, on raved plates, and driving
connections for an amountin excess Of 1,500.00.

PYROXYLIN PLASTIC INDUSTRY
Motion Picture Film.Lab0ratopy, Fort Lee, N. J., February 7th, 1925.

A short circuit ignited exposed film.in the joining room. The fire
‘was followed by an explosion Of gases caused by rapid decomposition
which lifted the building from its foundations and forced out one
wall. Twenty employees and firemen were injured, two of whom died
from their injuries. Property loss was $1,000,000.00.

Drafting Supply Factory, St. Louis, Mo., September 25th, 1928.

Plant was engaged in the manufacture Of tee squares and triangles
from wood and celluloid stock. A defective lamp socket ignited scrap
celluloid on the floor causing a fire which did considerable damage
to the building and contents.

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206
Box Toe Company, Lynn, Massachusetts, November 8th, 1928.

 

The plant was used for the manufacture of pyroxylin—impregnated
cotton flannel from which box toes for cheaper grades of shoes
are cut. They also mix box toe softener and make an adhesive
similar to rubber cement for the use Of shoe manufacturers. All
processes involved the use of flammable solvents. Pyroxylin
plastic scrap was dissolved in ethyl acetate and denatured alco-
hol in mechanically agitated churns, and cotton flannel was then
impregnated with this mixture, applied by drawing the flannel
strips through an Open tank of the mixture. A wooden knife then
removed the excess and the flannel was festooned over steam coils
on an Open dry rack. The adhesive was made from gum mixed with
benzol in mechanically agitated mixers. The box toe softener is
a mixture of diacetone and denatured alcohol and was sold to the
trade in five and ten gallon cans. While some attempt had been
made to have the electrical equipment conform to the standard for
hazardous occupancies, it was reported that there were several
ordinary snap switches, a motor starting box, three small A. C.
motors on the ceiling, and several small window fan motors, none
Of which were of the vapor proof type. It is also reported that
there was at least one electric light not enclosed in a vapor
proof globe. The fire which occurred in the North end of the
building was followed by several explosions Of terrific force.
The cause could not be definitely ascertained, as Of the fifteen
male employees, thirteen were killed and seven other perons liv-
ing in adjoining dwellings died from burns. The prOperty loss
to the plant was $15,000.00.

Hospital, Boston, Massachusetts, April 25th, 1925.

A fire occurred in the X-ray film room in the basement, caused,
it is said, by the ignition of the film by the heat Of an un-
protected electric light bulb which accidently came in contact
with the film. '

Clothinngactory, Toronto, Ontario, March 15th, 1927.

 

An unprotected electric light had been permitted to lay lighted

in a tray Of celluloid buttons. The celluloid started to decompose
and presently the vapors were ignited. The fumes prevented fire-
men' from entering which greatly increased the extent of the

loss. The damage was estimated at_from $10,000.00 to $20,000.00.

 

Advertising Novelty Factory, Newark, New Jersey, April 27th, 1927.

Celluloid advertising novelties were stored in Open crates in

a vault.' Smoke was discovered coming from the vault and investi-
gation indicated that the celluloid had begun to decompose either
Spontaneously or frcm.heat from an incandescent drOp light,which
had then burst into flame. Only about three quarters Of the
celluloid was consumed, but the remainder was badly discolored.
The smoke left a brownish deposit throughout the upper floors

of the building necessitating repolishing some Of the g00ds.Loss
was $8,500.00.

207

CO§TING P TS

Shade Cloth Factory, Oswego. New York. November 2nd, 1923.

A drum of-benzine was spilled at the bottom of an elevator
shaft. This was ignited it is reported. by an electric spark.
Three lives were lost. but the fire was extinguished with no
prOperty loss. .

Igtegproof canvag Manufacturing‘Plggt, Poughkeepsie, New York.
March 14th. 1921.

The fire was caused by a short circuit due to warn insulation
of an electric light extension cord, igniting fumes near the
impregnating machine. There was no explosion. but the fire
caused a loss of $1,358.00.

ngther Finisher Wogks, Boston. Massachusetts. January 5th, 1929.

The fire occurred in the mixing room of the plant where a mixture
was being prepared from alcohol. lacquer. thinner and other
ingredients. The mixing was done in three tanks. each of which
had a capacity of 250 gallons. During the process the liquid in
these tanks was ignited by a spark from a loose connection on

the mixer motor. The operation of automatic sprinklers confined
the fire somewhat. yet the loss was considerable due to the
highly flammable contents of the building.

CLEAN. ING fl BEING
,figg.Cleaning‘Establishment. washingtongD. 0., November 16th, 1928.

An explosion occurred when gasoline vapor was ignited by a spark
from an electric motor in a bootblack shOp while a hat was being
blocked and cleaned. Three of the ten persons who were in the
she at the time were more or less burned and damage amounting
to 1,000.00 was done to the building and contents.

iDry Clegging Plggt. Harvey, North Dakota. March 19th, 1928.

A.spark from.an electric switch ignited gasoline vapor and caused
33 explosion in a small detached cleaning room. The loss was
50.00.

CHEMIC INDUSTRY

Industrial Plant. Detroit, Nfichigan. January 4th, 1931.

A damaged extension cord in the vicinity of wooden vats used for
storage of alcohol short circuited and ignited the alcohol vapors.

The loss was small.

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208

Alcohol Manufacturing Plant, New Orleans, La., August 31st, 1928.

Two men were engaged in filling 50 gallon drums with denatured alcohol
in a warehouse when an explosion occurred. The fire spread rapidly
from.the point of origtiand the buildings involved were completely
envelOped in flames by the time-the first fire companies arrived.
Several additional explosions occurred in quick succession. A
fireman was killed by an exploding drum.which was thrown about

100 feet into the air. Several firemen were also overcome by the
intense heat. The exact cause of the explosion could not be
determined but was apparently due to the ignition of alcohol vapor.
Investigators stated that the most probable causewas ignition of
the vapors by an electric spark from defective wiring or short
circuiting of a storage battery used in connection with a weighing
device. Total loss to buildings and equipment was approximately
$220,000.00.

Chemical Laboratory, Ossining, New York, November 27th, 1929.

A short circuit in an electric cord ignited a pail of powdered
paraffin which was the base of a secret waterproofing compound
being made. The woman chemist lost her life when her clothing was

Alcohol Still Plgnt, Cadillac, Michigan, December 12th, 1907.

 

A fire occurred when an employee started to look for a leak in one

of the alcohol stills. He used an extension light which was protected
by a wire guard, but had no vapor proof globe. Alcohol vapor

escaping from the still ignited. The fire spread rapidly causing
total destruction of the buildings for a loss of $48,000.00.

Alcohol Plant, Binghamton, New York, January 26th, 1917.

 

An employee removed the manhole cover from.an alcohol still while
it was in Operation in order to investigate the interior of the
still. He used an incandescent lamp on an extension cord which was
provided with a wire guard. During his investigation he thrust the
lamp inside of the still, but in so doing he struck the side of

the still and alcohol vapors ignited and blew through the manhole,
seriously burning the employee. A ball of fire is reported to have
passed up through a hoist Opening, the trap of which was blown Off
and the monitor ignited. The property loss was slight.

Chemical Plant, Niagara Falls, New'York, January 6th, 1921.

Toluol was being chlorinated in ten gallon glass carboys in the
presence of heat and light which was furnished by a.high wattage
nitrogen filled incandescent lamp. It is believed that the lamp
broke and ignited the vapors. The fire spread with great rapidity
and the building was a total loss.

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208

Alcohol Manufacturing Plant, New Orleans, La., August 3lst, 1928.

Two men were engaged in filling 50 gallon drums with denatured alcohol
in a warehouse when an explosion occurred. The fire spread rapidly
from.the point of orighland the buildings involved were completely
enveloPed in flames by the time-the first fire companies arrived.
Several additional explosions occurred in quick succession. A
fireman was killed by an exploding drum which was thrown about

100 feet into the air. Several firemen.were also overcome by the
intense heat. The exact cause of the explosion could not be
determined but was apparently due to the ignition of alcohol vapor.
Investigators stated that the most probable causewas ignition of
the vapors by an electric spark from defective wiring or short
circuiting of a storage battery used in connection with a weighing
device. Total loss to buildings and equipment was approximately
$220,000.00.

Chemical Laboratory, Ossining, New York, November 27th, 1929.

A short circuit in an electric cord ignited a pail of powdered
paraffin which was the base of a secret waterproofing compound
being made. The woman chemist lost her life when her clothing was
ignited 0

Alcohol Still Plant, Cadillac, Michigan, December 12th, 1907.

 

A fire occurred when an employee started to look for a leak in one

of the alcohol stills. He used an extension light which was protected
by a wire guard, but had no vapor proof globe. Alcohol vapor

escaping from the still ignited. The fire spread rapidly causing
total destruction of the buildings for a loss of $48,000.00.

Alcohol Plant, Binghamton, New York, January 26th, 1917.

An employee removed the manhole cover from an alcohol still while
it was in Operation in order to investigate the interior of the
still. He used an incandescent lamp on an extension cord which was
provided with a wire guard. During his investigation he thrust the
lamp inside of the still, but in so doing he struck the side of

the still and alcohol vapors ignited and blew through the manhole,
seriously burning the employee. A ball of fire is reported to have
passed up through a hoist Opening, the trap of which was blown Off
and the monitor ignited. The property loss was slight.

Chemical Plant, Niagara Falls, New‘York, January 6th, 1921.

Toluol was being chlorinated in ten gallon glass carboys in the
presence of heat and light which was furnished by a high wattage
nitrogen filled incandescent lamp. It is believed that the lamp
broke and ignited the vapors. The fire spread with great rapidity
and the building was a total loss.

209

Chemical Laboratories, Chicago, Illinois, August 8th, 1921.

A leak:Occurred in the rotary drier used for extracting water from
alcohol. Before the power could.be shut off an explosion occurred,
killing two men and seriously injuring four others. The explosion
was due to a spark from.cr an arc in an electric motor at the
dryer, igniting fumes of alcohol escaping from.the dryer. The
automatic sprinkler operated and held fire loss to a small amount.

Chemical WOrks, Chicago, Illinois, June 30th, 1922.

Fire occurred when a.spark:from.an electric motor ignited alcohol
vapors in a still room. There was no explosion and the automatic
sprinklers held.the fire iradheck. The prOperty loss was small.

Coal Tar 2:2 Stuffs Factogy, Buffalo, New‘York, September 25th, 1923.

A tank used in a.process involving the recovery of benzol leaked and
was accidently filled during the night. The benzol leaked through

a hole to the first floor where it was ignited at a motor starting
switch. The fire flashed to the tank of the second floor and

upwards through the stair openings to the third floor. The loss

was held to moderate proportions by automatic sprinklers.

Chemical le , Belleville, New Jersey, September 6th, 1930.

Fire was caused by the ignition of gasoline fumes by an abctric
motor used in pumping a solution of phosphorous oxy-chloride
phenol and gasoline from.the maxing tank to the crystalizing vat.
Fire occurred when an employee started the electric motor which
caused the ignition of the gasoline fumes. The fire was held in
check by sprinklers. The loss was $2,700.00._

Chemdcal Works, Everett, Massachusetts, September 8th, 1930.

Fire started at a lacquer filter press machine and was due to
either a faulty electric light globe aéthe breaking of a globe.
The fire was extinguished by sprinklers and an automatic
carbon dioxide systems The loss was $267.00.

Coal Tar 2:: Stuff Factor , Buffalo, New‘York, January 7th, 1924.

Naphthalene which drOpped from the floor above was ignited by

a heated electrical connection to inductor coils for heating an
autoclave. A flash took place which ignited the woodwork which
was saturated with naphthalene. Automatic sprinklers held the
loss to small proportions.

Chemical Works, Perth, Amboy, New Jersey, February 12th, 1926.

Alcohol was being pumped through a rubber hose which either brOke
or became disconnected. The room.was filled with alcohol vapor.

210

A spark from the electric pump motor ignited the vapors and an
explosion occurred in which one life was lost. The property loss
was considerable. *

Chemical WOrks, Shawinigan, Quebec, February 13th, 1929.
Employees were cleaning a steel churn used for mixing ethyl acetate.
A flash fire occurred when an electric extension light was lowered

into the manhole of the churn. Two employees were burned when the
fire flashed from.the manhole. Sprinklers checked the fire.

Stove Polish.Manufacturing, Plant, Buffalo, New York, April 16th, 1924.

 

Fire occurred when an electric drop cord short circuited against

a steel tank in the room.where stove polish was being manufactured.
A spark from the short circuit ignited naphtha fwmes in the room.
The main.portion of the East end of the one story frame building
was destroyed by the fire which.followed.

PAINT AND VARNISH FACTORIES
Paint Factory, Racine, Wisconsin, 1931.

A tank in whiqh dyes were mixed had been.drained preparatory to
being cleaned. An employee drOpped a nonpstandard extension cord
into the tank. It is reported that the cord was defective and short
circuited, igniting the vapors in the tank and the fire spread to
adjoining tanks causing considerable damage.

Paint and Varnish Works, Reading Pa., August 28th, 1928.

Fire occurred in a paint mixing roon.where tanks were located. There
were eleven 225 gallon tanks located on a-turn table on which was
also located an electric light on a drOp cord which was used to
examine the tanks occasionally. This light was apparently unguarded
and it is thought that it broke directly over a tank and ignited
vapors. An employee who was present did not see the bulb break,

but heard glass filing and saw flames shoot from.the tank
immediately afterward. The loss was $110,000.00.

Varnish Remover Factor , Newark, New Jersey, October 27th, 1924.

The mixing room was one story with desk floor on one side, con-
taining several 250 gallon tanks of alcohol and acetone, two benzol
and one all alcohol. These liquids were pumped from.the drums to
the tanks and thence drawn to mixing kettles beneath in order to
see the gauge glasses on the tanks from.the floor below, an electric
light provided with a wire guard but no vapor proof globe was

hung near the gauge glasses. While filling the tank with acetone,
more or less vapor was given off which ignited either from.the
electric light bulb or a short circuit in the wire, and a.flash
fire resulted. The fire was extinguished with some difficulty. The
loss was $262.00.

211

Varnish Works, C1eveland, Ohio, June 30th, 1925.

This fire was caused by the breaking of a connection between an
extension cord and a socket near a point where cans were being
filled with varnish remover. The spark which.resulted ignited
the flammable vapors. The fire was held to small proportions by
automatic sprinklers.

Paint Factor , Frankford, Pa., August 22nd, 1924.

Fumes from paint mixing and grinding process collected at the
ceiling around an electric motor and were apparently ignited by

a spark from.the motor. Fire extended to the second floor through
an open hoist causing a loss of $10,000.00.

' Shellac Varnish Factory, Broom, New York, October 11th, 1924.

Fire occurred in a building in which spirit shellac was manufactured
and barreled. After closing down, an employee was cleaning the
interior of a small wooden varnish tank. To obtain light he was
using an electric extension light which in some way became broken,
causing the fumes within to ignite and loose varnish in the tank
also ignited. Fortunately, the employee was able to escape from the
tank uninjured. The fire was held to small proportions by the
operation of automatic sprinklers.

Varnish.Works, Pittsburg, Pa., January 15th, 1919.

A tar composition for roofing paint was being thinned down in two
steam heated metal tanks. The process was nearly completed when
an electric light globe located directly over and about five feet
above one of the tanks was accidently broken, and the resulting
spark was sufficient to ignite fie naphtha fumes present. A flash
occurred immediately, but the operation of automatic sprinklers
confined the loss to small propertions.

Shellac'ggg Paint Factor , New York City, N. Y., February lst, 1925.

A flash fire occurred in a large wooden shellac mixing vat. In the
vat were large metal paddles run by an induction.motor with.knife
switches in the room. Considerable dust was created when.shellac
was poured into the vat, and alcohol was then added to be mdxed
with.the shellac. This process was not cut off from the remainder
of the room and there was not even a cover for the vat. Alcohol
fumes were ignited either by a spark from the motor or from.a
starting switch. The loss was confined to the contents of the vat.

,0

r.

212

PETROLEUM INDUSTRY

REFINERIES.
Oil Refinery, Fort Worth, Texas, April 9th, 1927.

An employee attending.a motor driven pump used to pump gasoline
from a tank car into storage tanks, discovered that the pump was
leaking. As he opened the switch which.was located in the pump
room, the arc ignited the gasoline vapors and resulted in an
explosion which destroyed the building and severely burned the
operator.

Gasoline Tank, Shreveport, Louisiana, February 25th, 1928.

Two men were assigned to clean out an all steel gasoline tank.
While at work, one of them.dropped a portable extension lamp which
was unprotected, on the floor of the tank. The spark which resulted
ignited the gasoline vapors in the tank, causing an explosion which
blew the men from the tank, badly damaged the tank itself and
ignited the oil refuse outside the tank. The fire spread to another
tank and nearby buildings. The men were but slightly injured, but
the property loss was $97,500.00. '

Gravity Filter Building, Warren, Pa., December 12th, 1922.

Defective electric light wiring is thought to have been responsible
for a flash fire which occurred at an Open barrel capacity tank
containing light filtered motor oil. The fire spread to the
contents of sixteen other tanks located in the building and to

the roof of the filter house and adjoining boiler house. The loss
was $45,000.00.

BULK GASOLINE DISTRIBUTING STATIONS.
Flying Field, Madison, Wisconsin, September 6th, 1931.

A motor driven pump, used to pump gasoline from.tank cars to
storage tanks, was located in a concrete pit near the railroad
tanks. The pit was divided into two parts, with the pump in one
compartment and the motor and its control switch in the other.

The motor is reported to have been of the approved explosion
resisting type, but the switch was of the ordinary type in a non-
explosion resisting case. The unloading had been completed and the
attendant had gone into the pit to stop the motor. When the switch
was opened there was an explosion. Apparently there were sufficient
gasoline vapors in the motor compartment to form an explosive
mixture in spite of the tile partition which divided the pit. The
attfindant was seriously burned about the hands, face, arms and

1100 e

213

Bulk Gasoline Sation, Wichita, Kansas, May 11th, 1931.

A motor driven pump was employed to pump gasoline from.ctorage
tanks to a tank truck. The motor and its control apparatus were
decidedly sub-standard, the motor being of the Open brush type and
the control switch of the ordinary type. When the switch was
Opened the are ignited the accumulated gasoline vapors in the
pump house. The building was wrecked and the man in charge
dangerously burned. Only good work on the part of the fire
department prevented the fire spreading to the adjoining

gasoline storage tanks, thus averting a major disaster.

Bulk Gasoline Sation, Berlin, Wisconsin, June 20th, 1925. _

The manager had driven his truck into the wagon house for filling
direct from a tank car. A motor driven pump controlled by an
ordinary knife switch was used for this purpose and these were
located in the wagon house. As the switch was closed to start the
pump motor, the arc ignited the gasoline vapors which.seemed to
fill fie'building and in a moment the entire building was in flames.
The manager was badly burned and only his presence of mind saved
him from death.

Bulk Gasoline Station, Plentywood, Montana, About 1922.

An accident similar to the foregoing case occurred when a knife
switch was operated to start a motor driving a gasoline pump. The
are ignited accumulated gasoline vapors which resulted in an
explosion causing total destruction of the entire station. The
attendant, fortunately, escaped without serious injury.

Gasoline Pump House, Linden, New Jersey, Februmy 12th, 1929.

The pump Operator was preparing to load a long line of tank cars

at the loading rack and pressed the button to start the pump. A
sudden flash ignited gasoline vapor and enveloped the room. It

is thought that a short circuit in the electric pump was responsible
for the ignition of the flammable vapor. The loss was estimated at
from $50,000.00 to $100,000.00.

Gasoline Pump Hause, Everett, Massachusetts, April 14th, 1922.

An explosion of gasoline vapors occurred in a space under an air
compressor room. It is thought that a spark from defective wiring
was responsible for the explosion. The concrete floor was raised
about six inches and four reinforced concrete beams were cracked. The
fire was confinedto the pit, but one man was killed and several
injured. The property loss was about $5,000.00.

Bulk Gasoline Sation, Minot, North Dakota, July 3rd, 1928.

Two persons lost their lives and two others were badly burned in a
fire following an explosion in the basement of the warehouse of an

214

oil company. A spark from.an electric motor used to operate the
pump which pumped gasoline and other petroleum.fr0m the tank cars
to storage tanks i nited an accumulation of flammable vapors. The
prOperty loss was 23,820.00.

Bulk Gasoline Station, Wilmington, Ohio, January 26th, 1929.

Gasoline was beinglnmped from a storage tank to a tank truck. An
employee was in the filling house at the time, and it is thOught
that he opened the switch to stop the Operation of the pump. The
Electric are caused by the operation of the switch is thought to
have ignited gasoline vapors which filled the building. The
operators were fatally burned. All buildings and tanks, together '
with a nearby bulk gasoline station were destroyed. The property
loss was $22,000.00.

Bulk Gasoline Station, Clearwater, Florida, March 1st, 1924.

Gasoline vapor, due to overflowing of a tank, accumulated in the
motor room.and was ignited by sparks from.the electric motor which
was not enclosed. The office, motor room and one tank were destroyed
by the explosion which followed. The loss was $8,000.00.

Bulk Gasoline Station, Houston, Texas, April 19th, 1927.

Gasoline vapor accumulated and was ignited by a spark from.an
electric switch which controlled the motor driving a pump which
was used to pump gasoline from one tank to another. Several
thousand gallons of gasoline and lubricating oil were destroyed
together with considerable building property. The total loss
was $28,265.00.

Bulk Gasoline Station, Green Bay, Wisconsin, August 22nd, 1929.

A 1,000 gallon loading tank located inside a building was being
filled. The pump was left unattended with the result that the tank
overflowed. An employee threw the electric switch to shut off the
pump and a spark from.this switch ignited the vapor and caused a
terrific explosion. Three men were killed and four others injured.
The property loss was $50,000.00.

Bulk Gasoline Station, Desmet, South Dakota, April 12th, 1930.

An explosion occurred when an employee threw an electric switch
in the station. Accumulated vapors were apparently ignited by a
spark from the switch. One man died as a result of burns received.
The station was totally destroyed.

Bulk Gasoline Station, New Orleans, Louisiana, January 7th, 1952.
An underground tank was being filled with gasoline from.a tank car

by means of a motor driven pump. The pump was located out in the
open, but the driving motor and its control, together with a.motor

, 215

driven air compressor were located in a small pump room. The pump
shaft extended through the wall of the pump house. The meter was
an open single phase brush type motor of about 2 horse power
capacity and the control switch and service equipment were of the
ordinary enclosed type. It appears that the tank became filled and
overflowed through the vent pipe, spraying the attendant with
gasoline. He immediately went into the pump house to open the
motor control switch, but as he did so the gasoline vapors were
ignited by the are at the switch contacts and his clothing was set
afire. The attendant died from.bis burns. Considerable damage
resulted to the pump house and its equipment as well as to the
attached office.

GASOLINE FILLING STATIONS
Gasoline Filling Station, Rock Rapids, Iowa, July 21st, 1950.

One man was killed when gasoline fumes which.had accumulated in the
basement of the building at a filling station exploded. The vapors
were ignited by a spark from.the switch of an automatic air pump.

Gasoline Fjlling Station, Hartford, Conn., August 19th, 1930.

A man.was burned to death as the result of an explosion of gasoline
vapors which had accumulated in the basement of an office at a
filling station. A pipe line from.the storage tanks to the filling
pumps had developed a leak and gasoline had filtered into the
basement. The victim of the fire was using a broom.to sweep up

the gasoline and it is believed that his broom broke an electric
light bulb which ignited the vapors.

Filligg Station Buildigg, Pittsburg, Pa., January 23rd, 1920.

An.employee in a gasoline filling pit accidently broke an un-
protected electric light bulb. The resulting spark ignited gasoline
vapor and an explosion followed. The building was destroyed with
1arge loss.

Filligg Station, Rock Rapids, Iowa, July let, 1930.

One man was killed when gasoline fumes, which had accumulated in

the basement of the building at a gasoline filling station, exploded.
The explosion was due to the ignitiOn of the fumes by a spark from
the switch of an automatic air pump.

The writer has been told of numerous explosions originating in

motor driven gasoline pumps, the causes of many of which were
attributed to improper wiring at the pumps. In a certain city in
Illinois, six such.explosions occurred within one year. One explosion
resulted in the rupture of the pump assembly, one half being thrown

216

into the filling station shelter and the other half across a
street and into the wall of a church. It is unnecessary to point
out the possible results of such an explosion should it occur on
a busy corner of a large city.

_GARAGES
Garage, Providence, Rhode Island, December 11th, 1950.

Four garage employees were burned, three of them.fatally, when an
electric light bulb dropped into a pit in which they were working.
The light was broken and ignited gasoline on the floor of the

pit. The flames spread rapidly, fed by the oil and gasoline on
the floor of the garage and before they could reach.the door,
which was closed, three of them were so badly burned that they
died later in the hospital

MISCELLANEOUS
Residence, Boston, Massachusetts, July 17th, 1926.

The residence was being renovated during the process of which
painters were using a paint remover. A fire occurred, thought to
have been caused.by ignition of the vapors by the are from a switch.
One of the painters was trapped in the burning building and suffered
death by suffocation.

Building under Construction, Boston, Massachusetts, January 15th, 1927.

A plastic floor covering containing a volatile flammable solvent

was being laid, when a spark from.a broken electric light bulb

ignited the vapors. An explosion followed and one workman was

burned so badly that he died. Three others were knocked down by

the force of the explosion. .
INDUSTRIES PRODUCING COMBUSTIBLE DUST

COUNTRY GRAIN ELEVETORS.

 

Grain Elevator, Abilene, Kansas, August 12th, 1921.

A motor was enclosed in a poorly constructed non-standard enclosure.
Considerable dust had collected in and about the motor. A poorly
made connection at the terminals of the motor caused sufficient
heat to ignite the dust. Flames passed out through the belt opening
in the enclosure to the main plant and did considerable damage. The
loss was $167.00.

 

 

217

Grain Elevator, wessingon Springs, South Dakota, October 17th, 1927.

A five horse power squirrel cage motor in the cupola of a grain
elevator burned out due to accumulations of dust in the windings
and ventilating ducts. The motor was found in flames and the fire
was extinguished only after considerable effort. The cupola walls
were badly damaged and the motor destroyed. The loss_was $143.00.

Grain Elevator, Calamus, Iowa., September 27th, 1921.

'A ten horse power single phase commutator type motor was mounted

on a platform.about 12 feet above the cupola floor of this fire
resistive elevator. Circumstances indicated that dust had collected
around the commutator and had been ignited by sparks from the brushes.
This burning dust fell onto dust on the platform.and destroyed the
motor. The loss was $456.00.

Grain Elevtor, Little River, Kansas, June 13th, 1926.

An unguarded portable electric light was left burning in a dump
pit and the pit was filled with grain. This forced the light '
against a wood partition and a fire resulted. The loss was $15.00.

Grain Elevator, Oberon, North Dakota, May 18th, 1925.

.The manager left an.unguarded portable electric light burning in a
pit. The next morning he found a fire smouldering in the pit which
was easily extinguished. The loss was $10.00.

Grain Elevator, Capron, Oklahoma, October.31st, 1921.

An open squirrel cage meter in the cupola burned out from overload
or insulation breakdown. The flames spread rapidly and caused the
.total destruction of the building and contents. The loss was
$10,799.00.

Grain Elevator, Park Rapids, Minnesota, January 11th, 1921.

Several days before the fire electricians had replaced the brushes
on a motor and in so doing had removed the enclosure from the motor
and had not replaced it. Considerable dust accumulated on the

motor and a spark from.the brushes ignited the dust which fell to
the flOor igniting dust there. The flames then.spread through the
cupola but prompt action by employees prevented further damages.
The loss was $164.00.

Grain Elevator, Dalton, Missouri, April 22nd, 1930.

A fifteen horse power single phase commutator type motor was enclosed
in a.sub-standard metal lined enclosure in the cupola of the
elevator. A defective brush spring lodged against the rotor causing
sparks and finally a fire which.was just beginning to burn through

218

the enclosure when discovered. The fire was extinguished with water
but the owners report that had it not been discovered when it was,
the elevator would have been a total loss. The loss was$168.00.

Grain Elevator, Kingsley, Kansas, January 6th, 1930.

An Open motor located in the cupola had accumulated so much dust
that its ventilation was impaired. The motor was discovered in
flames and prompt action with an extinguisher held the loss to
$50.00. The motor windings were ruined.

Grain Elevator, Morrison, Iowa, January 10th, 1931.

A defective dr0p cord on a lighting circuit caused this fire
according to the investigator's report. The elevator building
and contents were a total loss in the amount of $7,016.85.

Grain Elevator, Clear Lake, Iowa, May 2nd, 1931.

An Open squirrel cage motor in the cupola burned out during the
afternoon, but was discovered and cooled with an extinguisher and
the motor disconnected. Apparently dust about the motor was ignited
and smouldered for the fire broke out early the following morning
causing tetal destruction of buildings and contents with a loss

of $8,637.00.

Grain Elevator, Marshfield, Wisconsin, March 21st, 1929.

A short circuit in undersize open conductor serving two fifteen
horse power motors or an attrition.mill caused the ignition of a
frame wall. The flames followed the wall up to the roof, causing
considerable damage. The loss was $1,905.00.

Grain Elevator, Lake Andes, South Dakota, December 1st, 1926.

A seven and one half horse power single phase motor was located
in a substandard metal lined wooden room.in the cupola. According
to the report, the motor failed to start when the controller was
thrown in, probably because of defective brush mechanism. When the
operator went to the cupola to look for the trouble he discovered
fire, and by the time help was summoned the flames had come
through.the walls of the motor room. Considerable damage to
buildings and contents resulted before the fire was extinguished.
The loss was $481.00.

Grain Elevator, Palmyra, Missouri, June 13th, 1929.
This fire was caused by the burning out of a twenty horse power

open squirrel cage meter probably from dust accumulations in the
motor or overloading. The loss was $131.00.

219
Grain Elevator, Java, South Dakota, April 13th, 1931.

 

A single phase motor was being started by means of an open
resistance type starter. At the same instant a dust explosion
occurred damaging the building considerably and seriously
butning three men. The loss was about $2,000.00.

Grain Elevator, Burdett, Kansas, 1931.

The odor of smoke was detected in the elevator at closing
time, but, although a thorough search was made, no fire

was discovered. The next morning the odor was more pronounced
and after further search, dust accumulated in a pit was

found to be on fire at a point directly under an unprotected
electric light. Apparently, dust collected on the light bulb
had ignited and dropped to the dust below.

Grain Elevator, Blackwell, Oklahoma, January 8th, 1920.

Two unprotected incandescent lights in the boot pit of the
elevator were installed in a horizontal position. Dust which
had collected on them became heated to the ignition point,
dropped into the dust in the boot pit and caused fire. The
flames spread and considerable damage resulted. The loss

was $2,874.00.

 

 

a‘. I
t‘ltl}: I ‘1‘: [tar-9:3: ., .-

DUST EXPLOSION IN A LARGE TERMINAL GRAIN ELEVATOR IN THE MIDDLE WEST. ALL THE SIx WORKMEN
IN ELEVATOR AT TIME OF EXPLOSION WERE KILLED: PROPERTY DAMAGE OVER $3,000,000

220

Grain Elevator, Webster City, Iowa, October 27th, 1927.

An Open squirrel cage motor was enclosed in a small frame box in
cupola. The bearings of the motor were permitted to wear to such
an extent that the rotor came in contact with the stator1 thus
damaging the windings. This caused a fire which resulted in a
damage loss of $114.00.

Grain Elevator, Belle Plain, Kansas, December 31st, 1926.

A five horse power single phase open type motor located in the
cupola burned out, probably from.breakdown of insulation. The
gupola was practically destroyed before the fire was extinguished.
he loss was $246.00.

Grain Elevator, Huntington, Indiana, October 18th, 1926

An Open squirrel cage motor located in the cupola had burned

out during the afternoon. The motor had been removed for rewinding
at which time there was no evidence of fire. However, late that
night fire broke out in the cupola, probably from.a spark smoulder-
ing in accumulated dust, and total destruction resulted. The

loss was $21,985.00.

Grain Elevator, Sleepy Eye, Minnesota, January 13th, 1925.

An Open.type motor in a substandard metal lined enclosure in
cupola burned out and burst into flames. The operator summoned '
the fire department, but frozen hydrants rendered them helpless.
The plant burned to the ground for a loss of $44,975.00.

Grain Elevator, Elk Mound, Wisconsin, October 1st, 1925.

A fire was located at a seven and one half horse power single phase
motor in the basement and, although the Operator thought that it
had been extinguished, the fire spread rapidly and resulted in
total.loss to the building and contents in the amount of $5,089.00.
Grain Elevator, Danville, Kentucky, March 2lst, 1928.

The resistance grids used in connection with a wound rotor motor

became overheated, igniting nearby combustible equipment and
construction. The loss was $187.25.

FLOUR AND FEED MILLS.

 

Feed M111, South Bartonville, Illinois, January 1st, 1919.

An electric spark is given as the cause of an explosion and fire in
the grinding and.mixing plant. The estimated loss was reported as
$750,000.00 to buildings and contents. -

221

Feed Mill, Buffalo, New'York, November 22nd, 1921.

An employee was using an improperly guarded portable electric light
to inspect the interior of an elevator head which was not dis-
charging properly. In some manner the steel buckets of the
elevators struck the lamp, crushed the light wire guard and

crushed the lamp. An explosion followed. The prOperty loss was

but $4,000.00.

Flour Mills, Czegled, Hungary, About twelve years ago,

The breaking of an electric light in a flour bin caused a flour
dust explosion. Complete details could not be secured.

Feed Mill, Milwaukee, Wisconsin, Date not available.

A serious explosion of grain dust occurred which, according to
the investigation, was caused by the breaking of a portable electric
light.

Hogan Mill Feed Company, Kansas City, Missouri, August 22nd, 1930.

A dust explosion resulting from ignition of ground screenings and
wheat scourings resulted in the death of two employees and injury
to two others with property loss of $75,000.00 - a total loss.
The cause was not definitely ascertained although first reports
stated that the explosion occurred when a motor starting switch
was thrown in.

Flour Mill, Crete, Nebraska, April 16th, 1923.

A two horse power open type motor burned out from.unkn0wn cause.
The fire spread to surrounding equipment. The loss was $129.00.

Feed M11 , waverly, New York, May 26th, 1923.

A double disc attrition mill was driven by two ten horse power

open squirrel cage motors. An employee smelled smoke and looking

up observed the attrition mill in flames and surrounded by smoke.
Quick action with chemical extinguishers checked the fire. Both
motors were found to have been.burned out due, apparently, to '
overload. The overload relays did not operate. The loss was $180.00.

Flour Mill, Neodesha, Kansas, November 30th, 1921.

Indications point conclusively to a short circuit in substandard
electric light wiring as the cause of this fire. The loss was.
$21,971.00. -

Flour M 11, Crookston, Minnesota, July 8th, 1924.

A direct current motor was enclosed in a substandard enclosure which
permitted considerable dust to collect in.the motor. The motor

I.

222

burned out Or a spark from the brushes ignited the dust in the
enclosure and the fire spread causing considerable damage. The
loss was $1,211.00.

Flour Mill, Shelbyville, Indiana, January 23rd, 1928.

Defective electric light wiring of the open knob and tube type
is reported to have caused this fire. The loss was $969.00.

Feed M111, Russellville, Kentucky, November 28th, 1927.

All evidence points to improperly installed Open power wiring
as the cause of this fire which practically completely destroyed'
the building and cements. The loss was $8, 696.00.

Food Mill, Byesville, Ohio, July 13th, 1930.

A short occurred in a run of steel armored cable in the basement
of the mill. The original installation light wiring was in rigid
conduit, but this armored cable was an extension to the original
40b. Three holes were found.burned through the cable by the are.

he fire burned through the first floor and caused heavy damage

to buildings and contents with a loss of $5,407.72.

Feed M111, Noy, Ohio, May 15th, 1930.

A motor driving a hammer mill burned out and then discovered

was in flames. It is reported that the meter was not overloaded
and that the overload relays and bearings were in proper order.
It is probable that the burnout was caused by breakdown of the
insulation due to dust accumulations. The loss was $200.00.

Feed M 11, Hannaford, North Dakota, October 5th, 1931.

A small open squirrel cage motor burned out and set fire to
nearby construction and dust in several places. The fires were
thought extinguished and the motor replaced. The next day the
fire broke out anew and caused practically total destruction
of the mill and attached buildings. The loss was $19,580.00.

Flour Mill, Toledo, Ohio, April 5th, 1929.

A defective abctric light socket ignited a pile of flour in
aper sacks causing considerable damage to flour. The loss was
231.00..

All indications point to this fire as having been caused by an
overloaded 40 horse power open squirrel cage motor. The fire
brde out while the men were at lunch and was beyond control
when discovered. The motor had been "running hot" previous to
the fire. The loss was $18,840.00.

225

Feed M111, NOble, Illinois, May 29th, 1929.

This fire is reported to have originated at the service switch
cabinet of the electric power installation. Trouble had been
experienced from.the blowing of the transformer primary fuses
so it seems probable that there was a short circuit in the
cabinet or wiring. The building and contents were a total loss
amounting to $15,056.00.

Food Mill, Springield, Illinois, May 27th, 1927.

A fifteen.horse power three phase open type squirrel cage motor was
operating ”single phase" due to the blowing of a fuse in one of
the circuit wires. This caused the motor to heat and finally

burst into flames. Prompt action with extinguishers saved the

plant from destruction. The loss was $261.00.

Flour Mill, Wichita, Kansas, April 30th, 1929.

A 100 horse ppwer motor located in a standard metal lath and
plaster motor room.burned from unknown cause. The fire was confined
entirely within the motor roOm, the damage being to belting, motor
room.vents and similar parts. This demOnstrates the value of a
standard motor room. The loss was Tl38.00.

Flour M311,‘Yakima, washington, December 7th, 1926.

A seventy five horse power 2200 volt motor with its control
equipment was located in a standard metal lath and plaster enclosure.
The fire originated in an oil circuit breaker and intense heat was
generated. However, the fire was confined to the interior of the
enclosure until the fire department was called and the flames
extinguished. The fact that the loss was but $511.00 demonstrates

the value of locating electrical equipment in standard rooms.

Flour Mill, Lawrence, Kansas, April 13th, 1930.

The night superintendent lowered a portable light into a metal flour
bin. As he did so a dust explosion occurred burning him.about

the arms and face. The tOp was blown from the bin and dust was
scorched for a distance of 30 feet from it. The resulting fire
spread to several separated sections of the plant through screw
conveyors and Opened nine sprinkler heads in the frame elevator
building. The lamp unit which was recovered was found to be of
unapproved type consisting of a brass shell socket, a wooden handle,
and wire guard. The light bulb was intact after the explosion, so
it was apparent that the explosion was caused either by a defective
socket or a ground to the metal guard. The loss was about $925.00.

224

Feed Mill, Liverpool, England, November 24th, 1911.

In this dust explosion thirty nine persons lost their lives and

one hundred and one others were injured. According to the reports

a drive belt brOke and caused a dense cloud of dust to tbe thrown
into suspension. This dust, it is reported, was ignited by the
blowing of a fuse on a temporary switchboard in the hazardous area.

Feed M 11, Chicago, Illinois, February 5rd, 1929.

The plant manager visited the plant at 11:00 oclock A. M. Sunday
morning and found.it filled with smoke. The fire department was
sum;oned and located the fire in an elevator boot pit which was
filled with ground.tankage. Immediately over the pit hung an
unprotected incandescent electric light. It is apparent that

the fire was started by burning dust falling from the light into
the tankage. The loss was $50.00.

TERMINAL'GRAIN.ELEVATOHS.
Grain Elevator, Akron, Ohio, December 2nd, 1913.

 

An employee was examining the interior of an elevator leg, using a
portable light to enable him to see. Details are not clear as to ‘
whether or not the lamp caused the explosion. However, the

explosion occurred in the elevator leg which.was being examined
after after the explosion the lamp was found to have been burned out.
No lives were lost and the property loss was confined to damaging
the 1980 '

Terminal Grain Elevator, Kansas City, Missouri, Sept. 13th, 1919.

Fourteen men were killed, ten injured and property in the amount

of $500, 000.00 was destroyed in this explosion. All evidence indicated
that it originated in the basement of the elevator near the receiving
legs where men were engaged in cleaning. It is suspected that the
source of ignition was furnished by defective electrical devices

such as substandard extension cords or unprotected electric lights

or switches. The exact cause could not be discovered.

MISCELLANEOUS
S;arch.Factor , Argo, Illinois, March 12th, 1919.
Two men.were seriously injured in an explosion which.followed when a

portable light lowered inn a starch bin was broken. Theproperty loss
was not large.

Sugar Refinery, Chicago, Illinois, June 16th, 1920.

An arc from an electric switch which ignited the sugar dust in the
air is assigned as the cause of an explosion in the sugar pulverizing
section. Fire following caused considerable dmnage.

Rubber Recovegz Plant, Muskegan, Michigan, August 18th, 193).

In this plant hard rubber scrap was first broken up into small
pieces, then pressed between steam heated rollers and finally
pulverized. Large quantities of fine dust was produced. An
explosion of this dust occurred in which eight men lost their
lives and one‘was seriously injured. Property was damaged to the
extent of $25,000.00. All evidence as to the origin of the spark
which ignited the dust was destroyed, but one of the sources
advanced by the investigation was the breaking of an electric
light.

COMBUSTIBLE FIBERS

COTTON MILLS. .
Cotton Mill, East Newark, New Jersey, April 28th, 1927.

An operator had thrown a switch to start a motor driving a ring
spinning frame- when an electric arc occurred blowing off the
cover of a fuse box and ignited the operators clothing and the
lint and banding on five adjoining frames. The employee died from
his burns. Loss $500.00.

Cotton M111, Lancaster, South Carolina, December 15th, 1926.

A short circuit in an oil switch started a fire which damaged three'
cards, although‘it was extinguished by a single automatic sprinkler.
Damage was $217.00.

Glove Lining Factor , Fonda, New York, May 28th, 1927.

In the ”mule" spinning room the electric lights hung by ordinary
suspension cords from the conduit. The cover of an outlet box was
accidently detached by a drive belt and the sharp edges of the cover
were the insulation from the cord until a short circuit occurred.
This ignited the lint accumlated on the cord and fire dropped to
the mule carriage below and to the‘floor. The total fire and water
damage was estimated at from $9,000.00 to $10,000.00, and the use

and occupancy insurance loss at between $2,500.00 and $5,000.00.

Textile Mill, Newton, New Jersey, October 25rd, 28th, 1951.

A weaver suddenly discovered that a fire had started in a Jacquard
loom about which there was considerable fine lint. The fire spread
rapidly, but the operation of automatic sprinklers checked the fire,
though not until loom harhesses, cylinders, warps and cloth had been
damaged to the extent of $1,100.00. Five days later a similar

,‘I

fire occurred, but the damage was held to less than $500.00.
The reports state that both of these fires were started by
defective electric light cords or by a spark from the electric
warps stop—motion.

MATTRESS FACTORIES.
Mattress Factory, Derry, N. H., May 22nd, 1929.

The fire was caused by ignition of loose flammable stock by
an are from an electric motor driving a sewing machine
located between two mattress forming machines. Fire flashed
rapidly over floor causing the death of an elderly woman.
Property 1033 was $50,000.00.

Bedding Factory, St. Paul, Minnesota, January 17th, 1927.

The greatest single fire loss on record in St. Paul involving

a loss of $600,000.00, originated in a bedding factory. While
the fire was not of electrical origin, the circumstances em-
phasize the need for every care in preventing sparks from any
cause whatever in or about places where cotton is handled or
stored. In this case it is believed that the spark came from a_
piece of metal passing through the rolls of a carding machine.
Suddenly, as the "camel back' of the machine Operated, flames
burst out on its under side. The flames spread so rapidly from
the carding machine to baled cotton in the room that one of the
Operators of the carding machine who attempted to fight the fire
was not able to escape from the building before he was so badly
burned that he was forced into hospital confinement for two
months, and will probably be partially disabled for the remain-
der of his life. The building was practically totally destroyed
and considerable damage resulted t0 dwellings in the neighbor-
hood. The raw material in a plant of this type is very flam-
mable, and the type of process is usually such as to coat every-
thing in the plant with fine lint or dust of an easily ignitable
nature. The slightest spark, are or molten metal coming into
contact with this material will cause an immediate flash fire
more like an explosion in speed of prOpagation than a fire.

BAG FACTORIES.

 

Bagging Factory, New Orleans, La., September 2nd, 1929.

This factory was engaged in working over old burlap bags, scrap
gunny, etc., into bagging material. This material was run through
pickers in the picker room where it was reduced to a fluffy material
(jute shoddy), and then conveyed by air to a condenser. Under

each condenser was a hOpper which discharged the fiber to a belt
which carried the fiber to the carding machines. It is reported that
an unprotected portable electric light was hung in the hopper under

227

the condenser while some adjustments were being made. It appears
that this lamp was in some manner broken.and the flash ignited the
fiber on the conveyor. The machinery was shut down thereby averting
a heavy loss. The damage to the madhines was estimated at $3,000.00.

Bag Factory, New Orleans, La., November 9th, 1927.

Several workmen were inside a drier,used for drying sugar sacks,
repairing a blower fan. A portable light equipped with a cheap wire
guard was accidently dropped. The light was broken by the fall

and the resulting flash.ignited accumulated lint resulting in a
small flash fire within the dryer. The damage was small.

MISCELLANEOUS (Hosiery Mills, etc.).
Hosiegy Mill, Philadelphia, Pa., April 8th, 1927.

An employee started a motor driving a fan connected with a hosiery
drybox and in so doing an are at the rheostat ignited greasy lint.
The fire spread was but extinguished by workmen. The loss was

esti mated at from $200.00 to $400.00.

Hosiegy Mill, Macon, Georgia, December 17th, 1926.

Sparks from a.switch.controlling the card room.motor ignited
accumulated cotton lint clinging to the wall. The fire flashed
up through an Old elevator tower and into the attic. Automatic
sprinklers held the fire in check, but when the fire department
responded considerable water was thrown into the building causing
heavy water damage. The loss was estimated at from.$2,000.00 to .
$4,000.00.

Carpet Factory, Thompsonville, Conn., February 11th, 1950.

While a repairman was making repairs on a Jacquard loom, he dropped
a wrench.which broke an unprotected electric light bulb. The hot
filament ignited lint and fire flashed over the loom. It was
extinguished by prompt action of automatic splinklers before it
spread to other looms. The loss was about $2,250.00.

 

Telephone Factory, Kearney, New Jersey, January 27th, 1952.

An accumulation of lint on a braiding machine used for making telephone
cord was ignited by a spark from a broken wire in an electric
”stop-motion" device. The fire flashed over twenty.0f the braiding
machines before being extinguished, resulting in a loss estimated

at $5,000.00.

Textile Mill, York, Pa., December 18th, 1951.

An electrician had removed the motor from a Jacquard loom and failed
to tape the ends of the cirmuit conductor. Several days later a
workman closed the circuit switch not knowing that the motor had
been removed. An arc occurred at the loose ends of the conductors

and ignited lint on the loom.and the flames spread to the harness

._._ a

228

and cards. The fire was extinguished by sprinklers and first aid
equipment, but damage resulted to the extent of about $850.00.

Textile Mill, Shamokin, Pa., December 16th, 1951.

A weaver heard falling glass and looking up saw fire in a nearby
Jacquard loom, The cause was determined to be from an are caused
by a worn pendant cord coming into contact with a grounded steel
beam._The cord had been in contact with.the beam.and the vibration
had caused the cord to be worn until the bare conductors were
exposed. The fire was extinguished by sprinklers, but fire and water
damage was estimated at between $10,000.00 and $15,000.00.

WAREHOUSES.
Terminal gotten yarehouse, New Orleans, La., June 5th, 1919.

This fire was caused by the breaking of one of the cast iron
collector shoes on an electric crane and short circuiting the
collector rail. A slight arc resulted and molten metal fell on
a quantity of baled cotton ten feet below, igniting scme loose
lint. The fire was discOvered promptly and the damage confined
to five bales Of cotton. Two fires of similar type caused by
defects originating in the crane current collectors occurred
in this same warehouse on March 10th and 16th, 1916. The first
resulted in‘a lossrof about $1,000.00 and the second in a loss
of about $2,500.00.

PAPER MILLS

 

Paper Mill, North Chattanooga, Tennessee, February 29th, 1928.

Sparks from a short circuit in a two piece plug connector in

a portable cord connected to a portable electric elevator in a
paper warehouse ignited loose paper. A fireman was suffocated in
fighting the fire. Loss $45,544.00.

Paper M111, Kalamazoo, Michigan, May 27th, 1951.
Fire originated in a section of the plant where waxed paper was
prepared. A spark from.a.short circuit in an overhead uncovered
junction box ignited bales of waste waxed paper. The blaze was
held in check by automatic sprinklers and finally extinguished
by firemen. The loss was nearly $700.00.

WOODWOHKING PLANTS
Woodworkers (Dust Hazard)
Veneer Factory, Rhinelander, Wisconsin, Date not available.

Directly over the center of a long wooden dry box hung a pendant
light. The cord rested against a top member of the box in such

.6

229

fashion that the vibration caused the cord to wear until finally
a short circuit occurred and a small flame passed up the cord. An
employee attempted to extinguish the fire, but in doing so he
stirred into suspension accumulations of wood dust Which in turn
‘were ignited. This produced other dust flashes and the entire
plant was destroyed. The employee's clothing was burned before

he made his escape, an indication of the rapidity with which the
flame spread.

 

 

 

This photograph illustrates the effects of
an explosion of gasoline vapor in a bulk
oil station pump house in Wichita, Kansas.
The vapors were ignited by the are from
an ordinary enclosed knife switch used to
control an open single phase motor.

 

‘ This circular was prepared by the
writer following a disastrous flour
dust explosion. Eight thousand of
these were distributed to mills and
elevators throughout this country
and Canada .

09‘“ 'i \V‘ a “:3;
Lbs ”Va "‘ emf“
B a“? ‘ £an Vim“ 005.69”?
f9: ffifi . - C C'
0 5‘“ C a“ ' “ cc
\0 $33M $£3.;gbb\ ‘\\\$ COQ‘L“ 01 ch‘ej
0 \O~ I9 \3
a“ e ‘3 e5 . er? AW“ ce‘
0“ ‘k‘ ‘0“63“ d“S\« W t 0

Have You Taken

Precautions to

 

 

Prevent This

Happening in
..Your Plant..

 

 

 

 

 

 

ll :1

 

View to left is from a photo'
graph taken after the eprOv

sion and fire.

The portion in ruins was a
two story frame iron clad
packing department attached
to the mill building. Heavy
damage also occurred to the

mill and its equipment.

 

 

[a TI

 

 

 

Here Is T/oe Story

URING the early afternoon of December 18, 1931, a terrific explosion followed by
fire occurred in the packing department of the Nebraska Consolidated Mills at
Omaha, Nebraska. The packing building, a two story frame iron clad structure,

was practically totally destroyed and considerable damage was done to the mill and other
attached buildings. The accompanying photographs show clearly the effects of the
explosion. ‘

One Man Dead and Seven Injured

is the toll taken by this accident. The operator of the packer, referred to on the opposite
page, was blown upwards and onto the roof of the adjoining mill building from which
the firemen rescued him. His injuries were so serious that he died twelve hours later
Several of the injured were buried under the debris.

 

 

 

F 1]

 

The view to the right illus'
trates the effects of the explo’
sion. Note how the roof and
walls were completely blown
out. Neighbors report that
the blast rocked their houses.

That flour dust has explosive
qualities approaching that of
dynamite cannot be doubted
after seeing what flour dust

did in this instance.

 

 

F J

 

 

 

The Damaged Property Can Be Replaced But Lost Life Never!

‘W/Jaz‘ Caused It?

HE operator of a flour packer wished to determine what quantity of flour remained
in the steel bin over his packer. He used a portable electric light on an extension
cord to enable him to see the interior of the bin. As he lowered the light into the
bin the lamp was broken and there followed a terrific explosion, the effects of which are

so well illustrated in this circular.

The portable light assembly was found after the explosion and although the rubber
cord was burned somewhat by the fire, the socket and a portion of the lamp remained

as proof that—

The Lamp Was Not Equipped With a Guard!

 

 

 

 

 

 

 

II n

 

HERE ARE THE

REMAINS OF THE

CORD, SOCKET
AND LAMP

Note the fragment of lamp
still in the socket and no evir
dences of a guard ever having
been attached. Also note the
ordinary key type brass shell
socket which is in itself un’
safe for use with portable
lights in dusty locations. The
cord, itself, however, is of
the correct type.

 

 

 

Unguarded Electric Lights in Dusty Locations Are Serious Hazards

The Lessons Tang/2t

IRST,we are again shown that flour dust in suspension and mixed with air in proper
Fproportions constitutes a perfect setup for a terrific explosion. All that is needed is

a tiny flash or spark to ignite the mixture. In this case the flash incidental to the '
breaking of an electric lamp was sufficient to cause destruction.

Second, this explosion illustrates the absolute necessity of properly guarding all electric
lights in dusty locations, but more especially, portable lights. A- proper portable light unit
consisting of a keyless socket of proper construction, a dust tight globe, and a substantial
guard made up into a single assembly should be adopted for all dusty locations. Only
heavy rubber jacketed cord, known as Type S, should be used.The various cotton covered
cords are distinctly unsafe. An excellent portable unit, cord, attachment plug and recept'
acle are illustrated below.

 

 

 

 

E _JJ

 

To the right is illustrated an
excellent type of portable
light assembly. Note that the
socket, dust tight globe and
guard, with handle is made
up into a convenient unit.
Also note that cord is of the
heavy rubber jacketed Type
S, rugged and long wearing.
The receptacle and plug are
well adapted to use in mills

and elevators.

 

 

 

E J

 

 

 

 

Properly Guard the Lights in Your Plant Before it Is Too Late!

For advice or assistance in making your plant ligbting safe, write your
Mill Mutual insurance oflice.

THE MILL MUTUALS

Mutual Fire Prevention Bureau

230 East Ohio Street , , . CHICAGO, ILLINOIS

1

BIBLIOGRAPHY

 

BIBLIOGRAPIQ

 

Associated Factory Mutual Insurance Companies,

Electric Light and Power Equipments
Fires in Cotton Mills

Cotton Conveying Systems

Factory Mutual Record

Crosby-Fiske-Forster,
Hand Book of Fire Protection.

Dana and Milne,
Industrial Fire Hazards

International Association of Electrical Inspectors,
News Bulletin

Mutual Fire Prevention Bureau,

Electrical Code
Fieldmen's Manual

National Fire Protection Association

A Table of Common Hazardous Chemicals

The Quarterly (1924 to 1952)

Proceedings of Annual Meetings (1924 to 1931)
Spray Application of Flammable Finishing Materials

National Board of Fire Underwriters (and N.F.P.A.)
Regulations on following:

Electrical Wiring and Apparatus (National
Electric Code)

Storage and Handling of Combustible Fibers

Prevention of Dust Explosions

Nitrocellulose Motion Picture Films

Installation of Pulverizing Systems for Sugar
and Cocoa

Installation of Pulverized Fuel Systems

Storage, Handling and Use of Pyroxylin Plastic

Construction and Operation of Pyroxylin Lacquer
Manufacturing Plants

Installation of Blower and Exhaust Systems

Installation and Operation of Acetylene Equip-
ment for Lighting, Heating, and Cooking

Safeguarding Dry Cleaning and Dry Dyeing Plants

Finishing Processes (other than Spray Painting)

Installation and Operation of Compressed Gas
Systems

Price and Brown

Dust Explosions

Underwriters' Bureau of New England

Report No. 165 -- Explosives
Underwriters! Laboratories, Inc.

Laboratories "Data" (Various Issues)

Method for Classification of Hazards of Liquids

Outline of Method for Examination and Tests of
Industrial Control Equipment for Hazardous
Locations .

Standard for Motors for Use in Atmospheres of Com-
bustible Dust

Outline for Examination and Test of Electric Lighting
Fixtures for Use in Hazardous Locations

Outline for Examination and Test of Explosion-Resist-
ing Electrical Fittings for Use in Hazardous
Locations

Standard for Construction and Performance of Power-
Operated Discharge Devices

Standard for Electric Motors for Use in Hazardous
Gas or Vapor-Air Atmospheres - 30 HP or Less

Report on Propogation of Flame in Pipes and Effective-
ness of Arrestors

I AN STATE UNIVERSITY LIB ARIES

 

mlllll Ill Illll llllllllllll I
3 1293 11062 0102