AN EVALUATION OF THIRTEEN BRANDS OF
FOOTBALL HELMETS ON THE BASIS OF
CERTAIN IMPACT MEASURES

by John Francis Alexander

The purposes of this dissertation were to evaluate
13 brands of football helmets on the bases of three measures
resultant from impact, and to analyze the data of each
measure with an analysis of variance design. Maximum accel-
eration, maximum deceleration, and rate of acceleration
were the measures used.

The methodology was to impact thirty-nine helmets at
four positions with a n.58 pound flat surfaced metal
pendulum at four different velocities. The helmets were
fitted onto a 12.2 pound wooden head which was suspended
from the ceiling by two steel cables.

Effects of impact were detected by two accelerometers
placed within the head and at the back of the pendulum.

The output from these accelerometers was fed into a dual
trace oscilloscope, photographed, projected, analyzed, and
calculated in Gs and Gs per second.

The helmets were ranked according to the lower values
for each evaluating measure at each velocity and position.
Graphs depicted the mean responses of acceleration,

deceleration, and rate of acceleration for all velocities

2
John Francis Alexander
and positions. All helmets were graphically compared at
each position and velocity.

It was concluded that, in general, leather and rubber
shelled helmets were inferior to the plaStic-type helmets.
Helmets with pliable plastic type shells and padded
suspension liners were superior to hard brittle shells with
canvas suspension liners. The worst position for all but
two brands was the back. Helmets vary according to positions
tested and velocities used. Inconsistencies in reponse to
impact were noted within brands of helmets, particularly at
the front and back positions, and at the higher velocities.
The consistently best ranking helmets were for: accelera-
tion--Mac-O, Spal-l, and Rawl; deceleration--Rid-5, Rid—h,
and Spal-2; and rate of acceleration-~Ral, Spal-l, and

W11-211.

AN EVALUATION OF THIRTEEN BRANDS OF
FOOTBALL HELMETS ON THE BASIS OF

CERTAIN IMPACT MEASURES

by

John Francis Alexander

A THESIS

Submitted to the School for Advanced Graduate Studies of
Michigan State University of Agriculture and
Applied Science in partial fulfillment of
the requirements for the degree of

DOCTOR OF PHILOSOPHY

Department of Health, Physical Education, and Recreation

1960

9/) NH

.4//b/o/

TABLE OF CONTENTS
CHAPTER PAGE
I. LHEIPROBLEM. . . . . . . . . . . 1
Statement of the problem 2
Justification of the study. 2
Limitations of the study 6
II. REVIEW OF THE LITERATURE . 8
Brain concussion and impact 8
Protective materials. . . . . . . 15
III. METHODS OF PROCEDURE. . . . . . . . 22
Experimental equipment . . . . . . , 22
Calculations . . . . . . . . . 25
Experimental design . . . . . . . 26
IV. RESULTS . . . . . . . . . . . . 31
V. SUMMARY, CONCLUSIONS, AND RECOMMENDATIONS. 109
Summary . . . . . . . . . . . 109
Conclusions. . . . . . . . . . 110
Recommendations . . . . . . . . lll
BIBLIOGRAPHY . . . . . . . . . . . . . 113

APPENDIX C O I C O O I O C O O O O O O 117

TABLE

10.

ll.

12.

LIST OF TABLES

PAGE

Analysis of Variance of Data for Maximum

Acceleration. . . . . . . . . . . 32
Analysis of Variance of Data for Maximum

Deceleration. . . . . . . . . . . 33
Analysis of Variance of Data for Rates of

Acceleration. . . . . . . . . . . 34
Helmet Rankings by Position and Velocity for

Maximum Acceleration of the Heat . . . . 50
Helmet Rankings by Position and Velocity for

Maximum Deceleration of the Pendulum. . . 51
Helmet Rankings by Position and velocity for

Rates of Acceleration of the Head. . . . 52
Totals for Analysis of Variance of

Deceleration. . . . . . . . . . . 120
Totals for Analysis of Variance of

Acceleration. . . . . . . . . . . 121
Totals for Analysis of Variance of Rates of

Acceleration. . . . . . . . . . . 122
Data Sheet—-Maximum Accelerations of the Head

in G8 . . . . . . . . . . . . . 123
Data Sheet--Maximum Deceleration of the

Pendulum in Gs . . . . . . . . . . 126

Data Sheet—-Rates of Acceleration of the Head
in Gs Per Second . . . . . . . . . 129

FIGURE

10.

LIST OF FIGURES

Yearly Percentage Comparisons of Direct

Fatalities from Head and Abdominal Injuries

Supplementary Information on Helmet Brands.

Mean Deceleration of Pendulum, Acceleration,
and Rate of Acceleration of Head Following
Four Impact Velocities at Four Positions
with Helmet Rid-4 . . . . . . .

Mean Deceleration of Pendulum, Acceleration,
and Rate of Acceleration of Head Following
Four Impact Velocities at Four Positions
with Helmet Nil-210 . . . . . . .

Mean Deceleration of Pendulum, Acceleration,
and Rate of Acceleration of Head Following
Four Impact Velocities at Four Positions
with Helmet Rid—5 . . . . . . . .

Mean Deceleration of Pendulum, Acceleration,
and Rate of Acceleration of Head Following
Four Impact Velocities at Four Positions
with Helmet Mac-O . . . . . . .

Mean Deceleration of Pendulum, Acceleration,
and Rate of Acceleration of Head Following
Four Impact Velocities at Four Positions
with Helmet Nil—211 . . . . . .

Mean Deceleration of Pendulum, Acceleration,
and Rate of Acceleration of Head Following
Four Impact Velocities at Four Positions
with Helmet Mac-5 . . . . . .

Mean Deceleration of Pendulum, Acceleration,
and Rate of Acceleration of Head Following
Four Impact velocities at Four Positions
with Helmet Spal-2. . . . . . . .

Mean Deceleration of Pendulum, Acceleration,
and Rate of Acceleration of Head Following
Four Impact Velocities at Four Positions
with Helmet Nok. . . . . . . . .

PAGE

28

36

37

38

30

MO

41

42

43

FIGURE PAGE

11. Mean Deceleration of Pendulum, Acceleration,
and Rate of Acceleration of Head Following
Four Impact Velocities at Four Positions
with Helmet Rea. . . . . . . . . . AA

12. Mean Deceleration of Pendulum, Acceleration,
and Rate of Acceleration of Head Following
Four Impact Velocities at Four Positions
with Helmet Mac-2 . . . . . . . . . 45

13. Mean Deceleration of Pendulum, Acceleration,
and Rate of Acceleration of Head Following
Four Impact Velocities at Four Positions
with Helmet Nil-201 . . . . . . . . A6

14. Mean Deceleration of Pendulum, Acceleration,
and Rate of Acceleration of Head FollOWing
Four Impact Velocities at Four Positions
with Helmet Spal-l. . . . . . . . . 47

15. Mean Deceleration of Pendulum, Acceleration,
and Rate of Acceleration of Head Following
Four Impact Velocities at Four Positions
with Helmet Rawl . . . . . . . . . A8

16. Maximum Accelerations of All Helmets Following
Impact in the Front Position at Twenty-one
Feet Per Second. . . . . . . . . . 57

17. Maximum Accelerations of A11 Helmets Following
Impact in the Front Position at Eighteen
Feet Per Second. . . . . . . . . 58

18. Maximum Accelerations of All Helmets Following
Impact in the Front Position at Fifteen
Feet Per Second. . . . . . . . . . 59

19. Maximum Accelerations of A11 Helmets Following
Impact in the Front Position at Twelve
Feet Per Second. . . . . . . . . . 6O

20. Maximum Accelerations of All Helmets FolloWing
Impact in the Side Position at Twenty-one
Feet Per Second. . . . . . . . . . 61

21. Maximum Accelerations of All Helmets Following
Impact in the Side Position at Eighteen
Feet Per Second. . . . . . . . . . 62

22. ‘Maximum Accelerations of All Helmets Following
Impact in the Side Position at Fifteen
Feet Per Second. . . . . . . . . . 63

FIGURE PAGE

23. Maximum Accelerations of All Helmets Following
Impact in the Side Position at Twelve
Feet Per Second. . . . . . . . . . 64

24. Maximum Accelerations of All Helmets Following
Impact in the Back Position at Twenty-one
Feet Per Second. . . . . . . . . . 65

25. Maximum Accelerations of All Helmets Following
Impact in the Back Position at Eighteen
Feet Per Second. . . . . . . . . . 6o

26. Maximum Accelerations of All Helmets Following
Impact in the Back Position at Fifteen
Feet Per Second. . . . . . . . . . 67

27. Maximum Accelerations of All Helmets Following
Impact in the Back Position at Twelve
Feet Per Second. . . . . . . . . . 68

28. Maximum Accelerations of All Helmets Following
Impact in the Top Position at Twenty-one
Feet Per Second. . . . . . . . . . 69

29. Maximum Accelerations of All Helmets Following
Impact in the Top Position at Eighteen
Feet Per Second. . . . . . . . . . 7O

30. Maximum Accelerations of All Helmets Following
Impact in the Top Position at Fifteen
Feet Per Second. . . . . . . . . . 71

31. Maximum Accelerations of All Helmets Following
Impact in the Top Position at Twelve
Feet Per Second. . . . . . . . . . 72

32. Maximum Decelerations of the Pendulum Following
Impact in the Front Position at Twenty-one
Feet Per Second. . . . . . . . . . 73

33. Maximum Decelerations of the Pendulum Following
Impact in the Front Position at Eighteen
Feet Per Second. . . . . . . . . 74

34. Maximum Decelerations of the Pendulum Following
Impact in the Front Position at Fifteen
Feet Per Second. . . . . . . . . . 75

35. Maximum Decelerations of the Pendulum Following
Impact in the Front Position at Twelve
Feet Per Second. . . . . . . . . . 76

vii

FIGURE PAGE

36. Maximum Decelerations of the Pendulum Following
Impact in the Side Position at Twenty-one
Feet Per Second. . . . . . . . . . 77

37. Maximum Decelerations of the Pendulum Following
Impact in the Side Position at Eighteen
Feet Per Second. . . . . . . . 78

38. Maximum Decelerations of the Pendulum Following
Impact in the Side Position at Fifteen
Feet Per Second. . . . . . . . . . 79

39. Maximum Decelerations of the Pendulum Following
Impact in the Side Position at Twelve
Feet Per Second. . . . . . . . . . 8O

40. Maximum Decelerations of the Pendulum Following
Impact in the Back Position at Twenty-one
Feet Per Second. . . . . . . . . . 81

41. Maximum Decelerations of the Pendulum Following
Impact in the Back Position at Eighteen
Feet Per Second. . . . . . . . 82

42. Maximum Decelerations of the Pendulum Following
Impact in the Back Position at Fifteen
Feet Per Second. . . . . . . . . . 83

43. Maximum Decelerations of the Pendulum Following
Impact in the Back Position at Twelve
Feet Per Second. . . . . . . . . . 84

44. Maximum Decelerations of'the Pendulum Following
Impact in the Top Position at Twenty-one
Feet Per Second. . . . . . . . . . 85

45. Maximum Decelerations Cd'the Pendulum Following
Impact in the Top Position at Eighteen
Feet Per Second. . . . . . . . . . 86

46. Maximum Decelerations of'the Pendulum Following
Impact in the Top Position at Fifteen
Feet Per Second. . . . . . . . . 87

47. Maximum Decelerations of’the Pendulum Following
Impact in the Top Position at Twelve
Feet Per Second. . . . . . . . . 88

48. Rates of Acceleration of A11 Helmets Following
Impact in the Front Position at Twenty- one
Feet Per Second. . . . . 89

viii
FIGURE PAGE

49. Rates of Acceleration of All Helmets Following

50.

51.

52.

53.

54.

55.

56.

57.

58.

59.

60.

61.

Impact in the Front Position at Eighteen

Feet Per Second.

Rates of Acceleration

of A11 Helmets Following

Impact in the Front Position at Fifteen

Feet Per Second.

Rates of Acceleration

of All Helmets Following

Impact in the Front Position at Twelve

Feet Per Second.

Rates of Acceleration
Impact in the Side
Feet Per Second.

Rates of Acceleration
Impact in the Side
Feet Per Second.

Rates of Acceleration
Impact in the Side
Feet Per Second.

Rates of Acceleration
Impact in the Side
Feet Per Second.

Rates of Acceleration
Impact in the Back
Feet Per Second.

Rates of Acceleration
Impact in the Back
Feet Per Second.

Rates of Acceleration
Impact in the Back
Feet Per Second.

Rates of Acceleration
Impact in the Back
Feet Per Second.

Rates of Acceleration

of All Helmets Following
Position at Twenty-one

of All Helmets Following
Position at Eighteen

of All Helmets Following
Position at Fifteen

of All Helmets Following
Position at Twelve

of A11 Helmets Following
Position at Twenty-one

of A11 Helmets Following
Position at Eighteen

of All Helmets Following
Position at Fifteen

of All Helmets Following
Position at Twelve

of All Helmets Following

Impact in the Top Position at Twenty-one

Feet Per Second.

Rates of Acceleration

Impact in the Top Position at Eighteen

Feet Per Second.

of All Helmets Following

90
91
92
93
94
95
96
97
98
99
100
101

102

FIGURE PAGE

62. Rates of Acceleration of All Helmets Following
Impact in the Top Position at Fifteen
Feet Per Second. . . . . . . . . . 103

63. Rates of Acceleration of A11 Helmets Following
Impact in the Top Position at Twelve
Feet Per Second. . . . . . . . . . 104

64. Wooden Head, Insert with Accelerometer and
Striking Pendulum with Accelerometer. . . 105

65. Polaroid Camera, Dual Trace Oscilloscope, and
Oscillator . . . . . . . . . . . 106

66. Wooden Head with Helmet--Pendulum Upon Impact
at the Front Position. . . . . . 107

67. Helmet Brands Used in the Study . . . . . 108

CHAPTER I
THE PROBLEM

The insurance of adequate head protection is extremely
important in the selection of football helmets. Although
concern has been shown for the improvement of protective
helmets in recent years by physicians, physiologists, design
engineers, and athletic personnel, nevertheless, a limited
amount of research has been undertaken in this vital area
of head protection.

This problem is not limited to rigorous body contact
athletic endeavors and sports car racing, but pervays into
the realms of aviation-medicine, military pursuits, and
hazardous civilian occupations. The Jet pilot, tank driver,
steel worker, and sports car enthusiast are equipped with
helmets as adeterrent to injuries of the brain and possible
death.

There is a wide range of helmet design available on
the market today. Helmet shells vary from flexible rubber-
like plastic to stiff phenolic bound fiberglass or steel.
Older modeled leather shells are yet available. Suspensions,
pads, and webbed straps are but a few of the liner types.

With the advent of the oscilliscope, criteria were
developed for measuring responses to inflicted blows.

These responses can be arbitrarily categorized into four

2
measures, namely, (1) velocity changes, (2) pressure deter-
mination localization and time duration, (3) kinetic energy
absorbtion and dissipation, and (4) rate of change of
acceleration.

The selection of helmets is based upon a compromise
between operational suitability and protective qualities.
The pertinent characteristics upon which the purchase of
these helmets is based includes comfort, shape, fit, durabil-

ity, visability, and cost.

Statement of the Problem

 

The purposes of this study are, as the result of
impact, to (1) evaluate various brands of helmets regarding
maximum acceleration and rates of acceleration of the wooden
head, and maximum deceleration of a striking pendulum; and
(2) statistically analyze the differences of each of these
evaluating criteria with a three—way analysis of variance.
The method used was to strike specific locations on all
helmets with a free swinging pendulum at different impact

velocities.

Justification of the Study

 

The use of the helmet in sports is not limited to
football, but is evidenced in ice hockey, boxing, bicycling,
and baseball. The sole purpose in this transcendental use
of the helmet is to provide protection for the head, and in

particular for the brain. According to Borgeson:

The ability of the shell and liner system to cope
with forces of impact is indicated by the amount of
acceleration transmitted to the head, and accelera-
tion and deceleration are extremely important factors
in the mechanics of brain injury. (17, p. 3)

If a blow to the head is of sufficient magnitude con-
cussionnwy'result, the severity of which is seemingly
related to the force with which the blow is inflicted, to
the rate at which the brain is set in motion, and to the
‘pressure distribution<over the brainn'The function of the
football helmet is protection of the head through a minimi-
zation of these effects, as well as prevention of skull
fracture.

Among the recommendations of the Twenty-Seventh Annual
Survey of Football Fatalities, following the 1958 season,
are listed:

1. Helmets that will further protect the (a) front
and sides of the head, and (b) top and back of
the head.

2. Regular inspection of the player's uniform for
(a) head suspension that will not allow the
head to come in contact with the helmet shell
when struck, and (b) placement of pads to properly
protect the internal organs. (1, p. 4)

This survey indicates that seventeen facilities were

directly associated with football during the fall of 1958.
The average yearly fatality incidence from 1931 to 1958 is

17.5 deaths per year.

The causes of direct fatalities are: (l, p. 11)

 

Causes Percentage
Head injury 51.39
Spinal injury 20.86
Abdominal injury 24.73
Not specified 3.02

Further divisions of these causes indicate that the
back, right side, and left side are the sites of the head
most associated with direct fatalities. (1, p.14)

Figure 1 reveals, for the period 1931 to 1958, a
decrease in fatalities due to abdominal injuries, in con-
trast to an increase due to head and spinal injuries.

Head injuries resulting from impact are not limited
to athletic contests. Wahl reports that seventy-five per
cent of air crash fatalities result from head injuries.

He concluded that head injury is the most frequent single

cause of fatality in air craft accidents. (10, p. 8) Rawlins

claims forty per cent of all Royal Air Force war time
injuries were craniofacial, with fourteen per cent of all
fatalities due to head injuries. Rawlins further states
that fifty per cent of all motorcycle injuries are those
of the head. (12, pp. 8-9)
According to Gross,
Although most protective helmets currently in use
provide reasonable protection from scalp laceration
and skull fracture, few are designed to provide
adequate protection from brain concussion. The
reason for this is that the design and evaluation of

protective headgear has not yet been placed on a
sound scientific basis. (26, p. l)

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The preponderance of head injuries and football
fatalities establishes the urgent need for research to

determine the best means of protection for the head.

Limitations of the Study

1. Three criteria were used to evaluate the helmets.
Other factors, such as kinetic energy absorbtion and dis-
sipation, pressure development localization, and time
duration within the head, merit considerations in relation
to concussion.

2. The near solid texture of the wooden head does not
closely simulate the human head. Perhaps an aluminum head
of standard size and weight, filled with a semi-viscous
fluid, would more accurately characterize the responses of
the human head to impact.

3. The effects of extreme temperatures on the helmets
were not considered in this study.

4. The consistency of the blows, especially those of
the higher impact velocities, could not be completely
controlled. A very slight motion preceeding or during the
release of the pendulum markedly effected the response of
the helmet.

5. Angular accelerations were not accounted for in
this study.

6. Fatiguing effects of the helmet from a series of

impacts were not considered.

7. A11 blows were inflicted at right angles to the
helmet. It is obvious that many other types of impact are
subjected to the helmet during a football game. Moreover,
the four positions tested are not necessarily those covering

the vital areas of the head.

CHAPTER II
REVIEW OF THE LITERATURE

It must be stated initially that there is a paucity
of literature directly concerned with the testing of foot—
ball helmets. With this in mind, considerations must be
given to collateral experimental areas of head protection,
such as commercial and military research. Since the validity
of the three criteria for evaluating helmets is predicated
on prior medical experimentation involving concussion, it
was deemed best to devote the first part of this chapter
to a review of the relation of impact and brain concussion.
The second phase is concerned with research related to the

testing and design of protective headgear.

Brain Concussion and Impact

 

Medical literature reveals that contemporary research
on head injury began with an analysis of the mechanism by
which the skull is fractured. Although, as Wilson indicates,
skull fracture per se does not necessarily result in brain
concussion, nevertheless it does provide for more clearer
understanding of potential brain damage. (33, p. 149)

Gurdjian attempted to determine the amount of energy
necessary to produce fracture of the skull in cadaver heads

and dried skulls. Firstly, lacquered skulls were dropped a

, 9
known height onto a slab of known weight, sawed in half and
analyzed. The greater cracks were noted along the flatest
portions of the skull. Fractures were found to generally
initiate on the external surface due to an outbending at a
point considerably distant from that of impact. These
fracture lines were found to run toward the impact point,
and to the opposite direction because of a rebounding action
of the skull. Secondly, this dropping technique was used
on intact cadaver heads at four positions. The average
energies needed for a single line fracture at each position
were: frontal midline--57l inch pounds, top midline--710
inch pounds, back midline--5l7 inch pounds, and sides-~6l5
inch pounds. This is corroborrated by Wahl who, working
with the effects of impact on plastic heads filled with
liquid, concluded that fracture occurred at approximately
600 inch pounds. (10) Gurdjian concluded that the energy
requirement for a single line fracture in cadaver heads
was 400 inch pounds in contrast to 40 inch pounds for a
dried skull. The authors attribute the difference to the
absorbing property of the scalp. It was proposed that a
considerable reduction of fatalities would ensue if energy
transformation to the human head was kept below 400 inch
pounds.

Gurdjian, Webster, and Lissner, (3) in a similar study
involving the extent of fracture resulting from the fall of
cadaver heads found no correlation between the energy

absorbed and the extent of bony damage to the skull.

10
Again was noted the energy absorbing quality of the skull.

Based on the difference of energy level required to
produce fracture in skulls and in cadaver heads because of
the absorbing quality of the scalp, it is reasonable to
consider helmets which will arrest this impact energy before
it reaches the brain.

The association of acceleration and deceleration with
head injury was proposed by Gurdjian and Webster.(5) The
application of force to the head is accomplished directly
where, as the result of impact, the head is set in motion
or accelerated, or indirectly, where having struck another
object the head is decelerated. A positive correlation is
affirmed between the time duration of the acceleration of
the brain and the severity of clinical results. Rise in
blood pressure, apnea, and loss of corneal reflex were mani-
fest as the result of concussive blows causing acceleration
of 250 to 650 Gs. Pressures from concussive blows range
from 20 to 100 pounds per square inch.

Cerebral and other body responses to the infliction
of head blows have been studied. Acceleration, intracranial
pressure and time durations, as well as blood pressure and
respiration rates were studied in dogs following hammer ad-
ministered head blows. The results showed no apparent
correlation between severity of concussion and acceleration
of the skull. Time duration of intracranial pressure was
concluded to be the governing factor in the production of

concussion. The acceleration range for concussion was 250-

500 Gs.(6)

11

The effects of pressure applied to the dural sac for
varying periods of time was studied in anesthetized dogs.

Air pressure was administered by a Spring controlled cylinder
with intracranial pressure being recorded by a diaphram
strain gauge fed to an oscilloscope. Four degrees of con-
cussion were determined. The results showed no concussion
with lower pressures except with those of increased time
duration. It was concluded that, (1) the longer the

duration of pressure the lower the pressure needed to produce
concussion, and (2) the shorter the duration of pressure the
higher pressure needed for severe concussion.(7)

Research has been done for the armed services regarding
physiological responses to forces acting on the human body.
It is asserted that uniform high speeds per se do not harm
the body because rectilinear motion does not contain the
element of force. Accordingly, change of velocity may have
deleterious effects on the human body. Two salient points
linking acceleration and injury are the magnitude of the
force and its time duration.(8)

The effects of acceleration on the blood flow from
the heart to the brain were studied. If the hydrostatic
pressure developed, as the result of acceleration, is greater
than the blood pressure, the circulation is stopped.
According to Lombard, nine Gs can be tolerated for two to
three seconds in a sitting position, twelve Gs for ten to
thirty seconds in the prone position, and fourteen Gs for

ten seconds in the supine position.(8, pp. 27-28)

12

In order to adequately protect the head for military,
civilian, and athletic persuits we must first know how much
acceleration the human head can tolerate.

Lombard, et a1., tried to determine human tolerance
levels to impact of the head. Subjects, wearing various
football and airforce crash helmets, were administered
varying pendulum type blows with all accelerations being

determined. Average human tolerance levels were determined

 

 

to be:
Rate of Acceleration
Position Acceleration—-Gs G Per Second
Top 23 4,800
Front 22 5,600
Side 20 3,500
Back 18 3,700

It was felt by the authors that the psychological effect of
being injured precluded the subject from tolerating blows
of greater magnitude. Fifty-seven Gs were suggested as a
potential tolerance limit to impact.(9)

The mechanics of concussion have been reviewed by
Case (29) and Edwards (38),of Michigan State University, so
that further discussion is not warranted. However, a brief
resume of the salient features might be in order.

Gurdjian defines concussion as, "accute post traumatic
state associated with unconsciousness, pallor, and a shock—
1ike state, and is the result of derangement in the function
of the brain stem."(22, p. 690)

Gurdjian believes that anoxia is not necessarily the

cause of initial unconsciousness, but rather mechanical

13
forces acting on the intracranial contents.(22) He is in
agreement with Denny, Brown, and Russell in that portions
of the skull and brain may be damaged without resulting con-
cussion. All three state that brain contusion and lacer-
ations may occur without unconsciousness provided the brain
stem is not injured.(37)

Gurdjian proposes the following considerations relevant

to concussion as the result of impact:(22)

1. Velocity and kinetic energy of a blow govern the
amount of deformation of the skull. ’

2. Pressure level and its time duration correlate
with the severity of clinical effects. Pressure
levels of 750-5,000 mm. Hg can cause concussion.

3. Acceleration and deceleration are associated with
movements of intracranial contents. Contracoup
brain injuries are ascribed to mass movements or
to cavitation.

4. Concusion is the result of major damage to the
brain as the result of its closed cavity dynamics.

An interesting theory on the dynamics of brain concus-

sion has been advanced by Gross who premises his research on
the fact that if certain detectable physical phenomena

within the head can be ascribed to concussion it may be
possible to determine concussion threshold information from
impact research with cadavers. The results of this research
would then be used as criteria for the testing and evaluation

of helmets. (26, p. 1)

14

Gross's explanation of concussion is based on the
assumption of potential traumatic effects due to the violent
collapsing of cavities within the brain due to impact (27,
p. 21) In a simple hydrodynamic experiment involving impact
upon a closed test tube partially filled with liquid, it was
discovered that the fluid was accelerated in the opposite
direction of the blow by the tensile force of the fluid
itself. Should the tensile force, resultant from impact,
be greater than the tensile strength of the liquid itself,
the fluid will tear apart into gaseous cavities. The ap-
pelation given this tearing apart action is "cavitation."
The tensile stress developed is greatest as the point
opposite the impacted end.(27, p. 3)

In a subsequent experiment involving impactment of a
sealed test tube completely filled with fluid, it was con-
cluded that the fluid was accelerated by both pressure from
the impacted end and tension from the opposite end of the
tube. This contralateral effect is called "contracoup
cavitation." It is assumed by the author that the same
principles of coup and contracoup cavitation can be applied
to the human head following impact.

A limitation to this theory is that brain damage, as
the result of coup and contracoup cavitation, is of a focal
nature near the surface of the brain. It does not explain
contusions found elsewhere in the brain.

A third form is "resonance cavitation." In response

to impact of sufficient magnitude to a sealed fluid medium,

l5
radtfl.oscillations were initiated as the result of the violent
collapsing of coup cavities. The result was cavitation of
a dispersed nature.(27, pp. 13-16)

The importance of Gross's research lies in the possi-
bility of determining concussion thresholds applicable as
criteria for the future testing of football helmets. A
second feature was his practical experimental set-up, which
simulated responses of the human head. A third value was a
generous chronological listing of literature related to the

mechanism of brain concussion and brain injury.

Protective Materials

 

Research from the fields of aviation medicine and
commercial endeavors are herein presented to fully discuss
the topic of protective headgear.

Protective head padding may generally be categorized
into resilient or non—resilient materials. Resilient or
energy storing material have rapid recovery from deformation
following impact. Examples are spring steel and rubber.
Non-resilient substances are energy dissipating or absorbing
materials and, following deformation, are slow to recover.
Examples of these materials are polystyrene foam and cellulose
acetate foam. The cushioning effect observed by the crushing of
a lump of sugar by a hammer blow serves to illustrate an
energy dissipation process.

Lombard, et al., considered various approaches toward

maximizing energy absorbtion and minimizing acceleration,

l6
resultant from impact to the head. .Accordingly, the dis-
advantage of resilient material is that following deflection,
as a result of energy storing, it rebounds with considerable
force. In contrast it was asserted that non-resilient
materials dissipate energy with no subsequent rebound.
Foamed or cellular plastic products are listed as satis—
factorily tested non-resilient products. Of these latter,
cellular cellulose acetate was found to be superior to
foamed or cellular plastic because of its deformation resis-
tance to blows of great magnitude.(13) Borgeson, however,
points out that the optimal thickness of non-resilient type
liners varies according to the material used. Such a
variable might pose problems regarding fit, size,comfort,
and visibility in designing football helmets. He also states
that this type is crushed with heavy impact blows.(17)

Dye lists four essential considerations, in the deter—
mination of materials, designed to give head protection
against impact:(l6, pp. 8-11)

1. Materials of low density such as polystyrene foam,

cellulose acetate foam, and sponge rubber.

2. Energy absorbing features as exemplified by

ensolite.

3. Resiétance to deformation.

4. Enough padding to allow satisfactory distribution

of pressure before bottoming.'

To evaluate helmets Hendler advocates: (1) high

impact velocity, and (2) measurement of the pressure

17
distribution over the head. It is suggested that, by proper
helmet design, force can be strategically distributed over
the head. Two consideration for determining force distri-
bution are offered: (1) helmets which distribute force to a
low uniform pressure, and (2) helmets which distribute force
to stronger areas of the skull.(18, pp. 64-70)

Rawlins, of England, lists seven essentials in the
design of aviation and commercial crash helmets: (1) pro-
tection against penetration, (2) protection against skull
deformation, (3) reduction of rotational acceleration of
the head, (4) reduction of average linear acceleration of
the head, (5) reduction of peak acceleration, (6) absorbtion
of kinetic energy, and (7) distribution of impact forces.

To accomodate these critera, helmets should be "tough, rigid,
smooth surfaced, without projections and with the ability to
dissipate the force of impact over the head."(l2, p. 721)

He advocates that the shell be made of Resin-bonded contin-
uous-filiment nylon as designed by the Royal Aircraft-
Establishment for the Royal Air Force. The lining should be
made from nylon tape for best impact distribution. Regarding
padding within the helmet, polyvinyl chloride is superior

to foam polysterene or natural cork for peak force distri-
bution.(12)

The effects of impact on two types of protective
helmets were studied by Strand in a technical report for
the United States Air Force. The Protection, Incorporated,

Toplex Helmet, a stiff shelled helmet with cellular cellulose

18
acetate lining, and the USAF—~Pl Helmet, a similarly stiff
shelled helmet with webbed suspension, were impacted at two
velocities on four positions. Accelerations and deceler-
ations were determined for all velocities and positions.

In terms of lower acceleration at both velocities, the Pl
helmet was found to react best to blows from the back and
worst to blows from the side. The best position of the
Toptex was its top with the worst being at the back. Among
the recommendations for further study, Strand lists the
inclusion of the rate of change of acceleration.(l5)

Head injury has been a perplexing problem to sports
car enthusiasts. Research has been done by Snively of the
Snell Study Plan. Evaluating crash helmets on the basis of
one severe impact he concluded that the above mentioned
Toptex Helmet with fiberglass shell and non-resilient liner
provided the best protection because of its small transmis-
sion of impact force to the head. Snively estimates 500
foot pounds as the upper tolerance limit to impact to the
head. Accordingly, this is equivalent to the helmet striking
a fixed surface at a speed of 34 miles per hour.(1l)

It should be understood that Snively's preference for
this helmet is based on the helmet giving best protection
against a single high energy impact as experienced by the
racing driver in a crash. Football helmets, in contrast,
are subjected to blows of lower magnitude, but of a repeated

nature.

19

In terms of survivable high energy impact levels,
Lombard recommends that, using a one quarter slug pendulum
mass with contact velocity of 20 feet per second, the head
not exceed accelerations of 250-300 Gs, and the rate of
acceleration not exceed 100,000 Gs per second.(Personal
correspondance--Lombard)

Dye suggests limits of 60 Gs for acceleration of the
head, 20,000 Gs per second for the rate of acceleration, and
400 pounds per square inch as the intensity of pressure sus-
tained in line with the blow. His figures are based on a
twenty pound pendulum impacting the helmet at a velocity of
17 feet per second.(34, p. 4)

Edward R. Dye, formerly of the Cornell Aeronautical
Laboratory, Incorporated, experimented with the design of
football helmets. Believing that helmets offer inadequate
protection around the "equator," and are only 1/300th as
stiff as the human skull, he proposed to: (l) lessen the
kinetic energy transmitted to the wearer by padding, and
(2) distribute the force of the blow. Sixteen experimental
models were designed and tested by "static" and "dynamic"
tests. The general constructional patterns were hard shells
of phenolic canvas and fiberglass cloth, beam pads of
ensolite, muslin foam, cushion rubber, plastifoam, and sus-
pension liners of webbed belt or "geodetic" cotton. The
"beam pad" was a circular disk laterally placed between the
shell and suspension liner. The "static" test was adminis-

tered by the pressure of'a hydraulicpress on the helmet the

20
results of which were recorded in terms of deformation on
an "injury meter." The "dynamic" test was accomplished by
the infliction of blows onto the unsupported helmet by a
twelve pound striker. Results were determined from fractures
to a liquid filled ten pound head within the helmet.
Although Dye's work is the first step forward in the testing
and design of protective football helmets, nevertheless his
computational methods are somewhat unorthodox.(2l)

Lombard devides blows to the head received in football
into: (1) low energy, and (2) high energy impacts. It is
stated that current football helmets provide protection
against low energy impacts. He states,

To improve the protective value of football helmets
it follows that protection against the high energy
impacts must be provided. To accomplish these two
tasks in one helmet is possible by requiring that
the helmets have (1) a resilient energy attenuating
property for repeated low order energy impacts and
(2) an energy absorbing property with the ability to
handle high order of energy impact.(36)

Recently football helmet research has been undertaken”
at Michigan State University.

Case (29) measured peak deceleration of an impacting
pendulum on nine different football helmets. Blows were
inflicted at six velocities and at four positions on each
helmet with the average of five blows at each velocity being
considered. Characteristics of the blows were photographed
from an oscilloscope by a hand cranked l6 millimeter camera.

Among his conclusions were the superiority of plastic to

leather shelled helmets, and the optimal combination of a

21
hard plastic shell with a snugly fit canvas suspension in
describing an ideal helmet.

Edwards(28) subsequently evaluated nine individual
football helmets on the basis of acceleration of the head
and deceleration of the pendulum. The experimental design
was similar to that of Case with the exceptions of five
impacting velocities being used, and oscilloscopic photo—
graphs being made by a polaroid camera attachment. The
results of his study supported those of Case. Although
measurement of acceleration was included, it must be men—
tioned that two limitations persist, namely, (1) inability
to measure both deceleration and acceleration simultaneously
because of the single channel osciolliscope, and (2) use of

only one helmet of each type.

CHAPTER III

METHODS OF PROCEDURE

Experimental Equipment

 

The impacting device was a metal pendulum bob weighing
4.58 pounds (.143 slug mass). This was selected to approxi-
mate the weight of the knee. The striking surface was flat
to provide for uniformity of blows (Fig. 64). The pendulum
was suspended from the ceiling by two steel cables which
were attached to either side of the bob in order to preserve
a constant position throughout its descent. An accelero-
meter was permanently attached to the back of the pendulum.
A protruding core atop the pendulum was inserted into a
solenoid switchbox to which was attached a chain which could
be hoisted to any height corresponding toca desired impact
velocity. The release of the pendulum was controlled by an
electro-switch adjacent to the oscilloscope.

The head was made of laminated wood, weighed 12.2
pOUfldS, and was d8818ned to accommodate a size seven and a
quarter football helmet. An iron insert, measuring two and
one-half by two and onefhalf by ten inches long and bearing
a second accelerometer, was inserted into the center of the
head so that the proper aXis of the accelerometer was in
line with the direction of the blow. The accelerometer

could be rotated to respond to blows on any position of the

helmet. The combined weight of the wooden head plus the
insert and accelerometer was 15.1 pounds.

The head was suspended from the ceiling by two steel
cables, each of which could be raised or lowered by turn
buckles fastened to the four extremities of the head (Fig.
66). In this manner the precisely desired height and degree
of levelness could be had. It was possible to detach and
turn the head to accommodate any desired striking position
on the helmet. Masking tape was applied to the extremities
of the turn buckles to minimize angular motion of the head.

Two Schaevitz, type VG—250, linear variable differen-
tial transformers were the accelerometers used (Fig. 64).
The opperation of these accelerometers was based on the
principle of displacement of the spring supported core, so
that voltage differences between the two coils could be
portrayed as visual signals on the oscilloscope. The line
was operated on 3,000 cycles per second and was controlled
by a model 200 CD wide range oscillator which fed into the
primary coil of the transformer.

A Hewlitt Packard oscilloscope (Fig. 65) model 150A
with dual trace amplifier was used to display the signals
from the accelerometers. This oscilloscope can be operated
on 115 or 230 volts A.C., and can be used as single trace
high grain amplifier or dual trace amplifier. The advantage
of the latter is the simultaneous portrayal of signals from
both accelerometers making possible the determination of

both acceleration and deceleration. Any signal up to a

24

frequency of 10 M.C. per second can be displayed on the
oscilloscope. Sweep time can be varied between .1 MSEC and

5 seconds per centimeter. Independently controlled vertical'
sensitivities are variable from .05 volts to 2 volts per
centimeter.

To photograph the signal traces the oscilloscope was
set to trigger internally, upon activation of the input
signal, so that one sweep per impact was diSplayed across
the grid. The sensitivities and sweep times were set
according to the expected deflection as a result of the
magnitude of the impact velocity. The complete envelope,
depicting maximum deflections and time duration, could,

. therefore, be studied. Photographs of the deflections on
the grid were made by a Beattie-Varitron Polaroid Camera.
This was attached over the grid surface, and was equipped
with a mirror system enabling the operator to View the face
of the oscilloscope prior to and during impact; 400-ASA
Polaroid Film was used in the camera. Calibration was accom-
plished by photographing the signals displayed as a result
of the difference in position of the linear variable differ-
ential transformer turning from the null position to one
where its axis was maximally effected by the forces of
gravity, and back through the null position to the.opposite
axis. This difference is equivalent to two Gs. Sweep time
and vertical sensitivity for this callibration were set at

5 seconds per centimeter and .05 volts per centimeter,

respectively. The equivalence to one G in millimeters was

25
determined for each sensitivity setting for both deceleration
and acceleration. Calibration was done prior to each testing
session.

For optimal operational efficiency two technicians were
required. The operation of the oscilloscope, camera, and
pendulum release switch were controlled by the first tech—
nician. Manipulation of the helmets and change of intended
impact velocities were done by the second.

All photographs were individually projected on a flat
surface by a Beseler Van Lyfe II projector. This projector
was meticulously placed four feet from, and at right angles
to, the projection surface. It had been determined that
this position produced the clearest image, with an absolute
minimum of optical distortion. The exact position of the
projected picture was marked on the projection surface with
masking tape, as were the positions of the legs of the
projector on the floor. This permanent tape on the wall,
framing the projected picture, insured that all photographs
were in the exact same centermost position in the projector.
These projected figures were traced onto graphing paper
(twenty squares to oneinch). Measurements of the figures

were made in millimeters with sliding Vernier calipers.

Calculations

 

Determination of the G level was done by measuring
the highest deflection on either side of the base line,

subtracting out the base line, and dividing by two. This

26
residual, representing the increase in voltage due to the
impact, when divided by the appropriately calibrated
sensitivity factor, resulted in Gs.

A smooth curve was drawn through the extremities of
all deflections on the graph paper. Rate of acceleration
was calculated from the point of initial rise from the base
line to the peak of the curve. Knowing the indicated sweep
time and the distance from the initial rise to the peak it
was possible to determine the time elapsing between these
two points. Maximum acceleration divided by the time re-
quired to reach the maximum was construed to be the rate of
acceleration.

Observance of the projected tracings indicated that a
few of the envelopes were blank at the side corresponding
to the beginning of the sweep on the oscilloscope. In these
cases the most uniform portion of the slope was considered.
This condition prevailed irregularly at the lowest impact

velocity of twelve feet per second.

Experimental Design

Thirteen brands of football helmets were struck by a
free swinging pendulum at impact velocities of l2, l5, l8,
and 21 feet per second (Fig. 67). These represent the foot—
ball helmets most currently in use by high school, college,
and professional teams. There were three helmets of each
brand which were labeled one through three for identification

purposes. Each helmet was tested at four positions: front,

27
side, back, and top. The infliction of blows was at right
angles to the position being tested. Each position on all
39 helmets was struck once at each of the four impact .
velocities. Oscilloscopic responses of the head and

pendulum to impact were analyzed according to the previously

discussed method.

The shells ranged from stiff, rigid, non-penetrating
surfaces, through pliable materials,to leather (Fig. 2).
Cotton suspensions, padded suspensions, webbed straps, and
geodetic suspensions represent the liners used in this
study. Liner materialsvwnxacomposed of resilient and non-
resilient materials. Ancillary information concerning the
helmets was secured from a questionnaire sheet forwarded to
the manufacturers (Appendix A). All but one manufacturer
responded to this questionnaire.

A three-way layout design was set up to include
thirteen brands of helmets, three replicates of each brand,
four impacting velocities, and four helmet positions. This
design was applied individually to the measures of acceler-
ation, deceleration, and rates of acceleration. A three-way
analysis of variance was performed on each impact measure.
The variances due to the three main effects of brands,
positions, and velocities were statistically analyzed with
F ratios, as were the interactions of brand and position,
brand and velocity, position and velocity, and the triple

interaction of brand and position and velocity.

28

 

 

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30

Any bias from fatiguing effects of the helmets was
minimized by randomizing the striking order of the veloci-
ties across helmet brands and positions.

The order of impact, by positions, was (1) front,

(2) side, (3) back, and (4) top. The striking order for
helmet brands was the same across positions, so that a
particular replicate number was hit at four randomized
velocities across all brands for a position. The procedure
was to test a given replicate of' all brands at all veloci-
ties for a given position in one testing session.

The helmets were ranked in order of efficiency as
determined by the lowest value of the evaluating measure
in question. For purpose of rating a brand of helmet, the
mean of its three replicates was considered for a given
position and velocity. This was done at each velocity and
position for all three evaluating measures.

Graphs were plotted to show: (1) the average deceler-
ation, acceleration, and rate of acceleration compositively
for all velocities and positions; and (2) the individual
responses of the three replicates of all brands at each

position and velocity for all three evaluating measures.

CHAPTER IV

RESULTS

Based on thirteen brands, four positions, four velocities,
three replicates, and 624 determinations, the allocation of
degrees of freedom were: Total—-623, Brands--l2, Positions--3,
Velocities-~3, Brand x Velocity--36, Brand x Position—-36,
Position x Velocity--9, Brand x Position x Velocity--108, With-
in Position-—8, and Error-—408. Because an attempt was made to
keep the calibration effect constant throughout each replicate
involving a given position and all brands and velocities, two
degrees of freedom were apportioned for each position, or eight
for all positions for the within position variance.

The variance due to replication was found significant at
the one per cent level for all three evaluating measures
(Acceleration, F = 15.17, Deceleration F = 35.29, Rate of
Acceleration F = 5.93). Analysis of the contribution, by
position, to this variance for the three measures showed that,
for deceleration the front position contributed more than all
other positions combined (Table 7, Appendix B), and for acceler-
ation (Table 8, Appendix B), and rates of acceleration (Table
9, Appendix B), the back position contributed more than all
other positions combined.

Results of the three way analysis of variance are shown
for each measure in Tables 1, 2, and 3. With 408 degrees

of freedom in the error term a very low F ratio was

required for significance.

significant for the three impact measures.

ANALYSIS OF VARIANCE OF DATA FOR MAXIMUM ACCELERATION

F ratios for all sources were

TABLE 1

32

 

At
a

 

Variation D.F. Squares Square F F.95 F.99
Total 623 3,333,576.81

Brands 12 227,620.25 18,968.35 49.57 .78 .23
Position 3 1,417,485.11 472,495.03 1234.76 .62 .83
Velocity 3. 882,191.79 294,063.93 768.47 .62 .83
Brand x °

Velocity 36 90,710.69 2,519.74 6.58 .45 .69
Brand x

Position 36 116,364.86 3,232.36 8.45 .45 .69
Position x

Velocity 9 202,748.57 22,527.62 58.87 .90 .46
Brand x

Position x

Velocity 108 193,883.29 1,795.22 4.69 .28 .42
Within

Position 8 46,448.38 5,806.05 15.17 .96 .54
Error 408 156,123.87 382.66

 

TABLE 2

ANALYSIS OF VARIANCE OF DATA FOR MAXIMUM DECELERATION

33

 

 

Source of Sums of Mean
Variation D.F. Squares Square F F.95 .99
Total 623 18,788,713.30
Brands 12 1,443,538.42 120,294.87 50.23 1.78 .23
Position 3 3 7,222,281.72 2,407,427.24 1005.30 2.62 .83
Velocity 3 4,531,996.21 1,510,665.40 630.83 2.62 .83
Brand x

Velocity 36 513,408.86 14,261.36 5.96 1.45 .69
Brand x

Position 36 1,523,729.71 42,325.83 17.67 1.45 .69
Position x ’

Velocity 9 721,569.90 80,174.43 33.48 1.90 .46
Brand x

Position x

Velocity 108 1,179,033.06 10,916.97 4.56 1.28 .42
Within * ‘
Position 8 676,104.59 84,513.07 35.29 1.96 .54
Error 408 977,050.83 2,394.73

 

 

34

 

 

TABLE 3
ANALYSIS OF VARIANCE OF DATA FOR RATE OF ACCELERATION

Source of Sums of Mean
Variation D.F. Squares Square F F.95 .99
Brands 623 382,588,179

Types 12 31,297,468 2,608,122.33 31.04 1.78 .23
Position 3 131,002,960 43,667,653.00 519.62 2.62 .83
Velocity 3 84,192,425 28,064,141.60 333.95 2.62 .83
Brand x

Velocity 36 13,970,519 388,069.97 4.62 1.45 .69
Brand x

Position 36 41,299,050 1,147,195.83 13.65 1.45 .69
Position x

Velocity 9 30,324,942 3,369,438.00 40.09 1.90 .46
Brand x

Position x -

Velocity 108 12,229,847 113,239.32 1.35 1.28 .42
Within .

Position 8 3,983,749 497,968.62 5.93 1.96 .54
Error 408 34,287,219 84,037.30

 

Note: Data coded with division of each determination by

one hundred.

35

It was felt that part of the within variance could
have been attributed to experimental fluctuations. An adjust-
ment was, therefore, made on the values within each position
based on a percentage above and below the mid replicate total
for each position (Tables 7, 8, and 9, Appendix'B). All
graphical repreSentation were made on the basis of these
adjustments. These adjustments were not applied to the values
used in the three analyses of variance.

Figures 3 through 15 are graphs comparing the means of
the three evaluating measurements across all velocities
and positions.

The similarity of response between acceleration and
rate of acceleration was evident throughout most helmet
brands. Decelerations were consistently higher than the
accelerations. This is reasonable because of the greater
mass of the head compared to that of the pendulum.

The front and back positions appear to be inferior to
the side and top positions for all three measurements. The
wider distance between the shell and liner at the side and
tops in most of the helmets may partially explain this dif-
ference. For all three measures at 21 feet per second the back
is the worst position for all brands except for helmets Mac-0
and Mac-5. The front is the worst position at all velocities
for all three measures of evaluation with helmets Mac-0 and
Mac-5.

It was of interest to note the lower deceleration
values at impact velocity of twenty-one feet per second,.

compared to those at eighteen feet per second. Observed in

the front and back positions, this was nOted in helmets

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49'
Rea (Fig. 11), Nok (Fig. 10), and Nil-201 (Fig. 13), ail of
which rated poorly for these positions. It was thought that
the softer shells of these helmets may have sufficiently
given with the blow without bottoming so that the pendulum
decelerated more slowly.

The worst position for all three evaluating criteria
was the back. This was most noticeable in helmet Nok. This
newly designed helmet had a shell of vulcanized rubber and
leather, and a web suspension type liner. The Rea and Mac—2,
both leather helmets, also responded poorly in the back
position at the higher velocities. Values at this position
often exCeeded 250 Gs, the limit as recommended by Lombard.(38)

Tables 4 through 6 are the rankings of all brands of
helmets of all three evaluating measures for each position
and velocity. These rankings are supplemented with a break-
down of helmet brands into the individual responses of their
constituent replicates in Figures 16 through 63.

The best helmet in regard to maximum acceleration of
the head at all velocities in the front position was Nil-211
(Table 4). The shell of this helmet is a flexible plastic
(Etholite) and the liner is a double suspension cotton type.
The average response of this helmet to impact at twenty-one
feet per second was 135 Gs. Second and third in the front
position at this velocity were Rid—4 and Rid-5 with average
values of 140 and 143 Gs, respectively. All liners of
these three helmets were very similar but with the shells

of the Rid-4 and Rid-5 being noticeably more rigid than

.hHo>Hpoonop .moHpHoOHo> cooprm 0cm NSON pom mxcop ho Hop0p Sop
oocHEpopoo mmcchog oprOQEOo 0cm COHpHmOQ HmopmoHHQop oopnp ho comfi Eosh oocHspopoo mxcom

 

 

 

%, m m m s H m N e H e m o N m m m m N m o N Hzom
N H H H H m m H N w m m m e .o 0H m e m H m H1Hoom

NH mH NH mH mH mH MH HH MH mH mH oH m NH mH mH N o N m m HoNnHHz

oH m m 0H m m .0H m OH OH HH H H m s N m 0H 0H m oH Nuooz

mH oH H HH NH HH NH NH NH NH NH HH HH HH oH HH mH m NH mH mH mom

HH NH mH NH HH oH HH mH HH HH 0H m m N N m m w m 0H NH xoz

m oH m N oH NH m m m m m m o o m H H s m m s N1Hoom

m N HH m o N H N m H N H H H N m NH NH HH NH HH msooz

o m 0H m m N m 0H m m o o m 0H m s H H H H H HHN1HH3

H H o N N H m o m m H H N N H N HH mH mH HH m 01ooz

N o N m N m m m H N e mH mH mH NH w m N s m m m1on

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UocHEhopoU mxsom

 

 

 

 

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m H H H H N N N N N NH m s H N HH m N N m N H1HooN
NH mH N mH mH NH HH HH HH mH N oH H OH NH NH m N N m oH H0N1HH3
N N e N m m 0H N oH oH HH N N m m N N 0H m N s N1ooz
mH NH N NH NH HH NH NH NH HH m NH oH HH HH NH HH m HH mH N mom
HH HH 0H 0H oH OH NH NH mH NH 0H m m N N oH N s OH oH m soz
N N N a HH mH N m N m N H m H H H s N N s N N1HooN
m N oH N N H H m m N N oH N NH NH m NH NH NH HH N m1ooz
s e N m H N N oH m N N N HH N N s H H H H H HHN1HH3
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H H H N N m N m H 3 3 N 3 H m 3 m m m m m Hzmm
N N m H H w m N N N m m H m m m N m m 3 m . HIHNQm
NH MH mH MH MH NH HH OH NH NH HH m N m MH MH m N w w NH HONIHH3
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HH NH HH NH OH OH NH MH MH HH NH m w m 3 N OH 0 HH HH MH xoz
m HH m N HH MH m 0 OH m w H m N H N 3 m 3 N m NIHQO
m N NH 0 m N H 3 m N N N m N N m MH NH OH MH HH mlowz
m m m m m N w HH w m N 3 N 3 N m H H H N H HHNIHH3
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N w OH m w 3 3 H 3 w m MH mH MH NH m N N N m N mIUHm
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3 m m OH N m m m N H 0 HH m OH HH NH m 3 m H m 310Hm
opHmoQEoo mpoEHom
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w mum<e

53
that of the Nil-211 (Fig. 2). Helmets Mac-5,Nok, and Rea
ranked eleventh, twelfth, and thirteenth, at twenty-one feet
per second with maximum Gs of 203, 206, and 227, respectively.
Mac-5 had a plastic type shell (duralite), and a combination
pad-suspension liner. Nok and Rea are soft shelled helmets.

Intra-helmet variations were noted at the highest
impact velocity among helmets Rid-4, Mac-5, and Spal-2 (Fig.
16). At the velocity of twelve feet per second Spal-l,
Nok, and Rea had the widest replicate variation (Fig. 19).

Helmets Spal-2, Mac-0, Mac-5, and Nil-211 were ranked
the best four at the side position at twenty-one feet per
second. At this velocity Nil-201 had the highest acceler-
ation at 198 Gs. The consistency of Spal-2 and Wi1-211 at
the front and side positions was in direct contrast to that
of Mac-O and Mac—5 for these two positions. Intra—helmet
variations were noted among helmets Rea and Rid-4 at twenty-
one feet per second to a lesser extent (Fig. 20). Rid-5 was
ranked thirteenth at both impact velocities of fifteen and
twelve feet per second. For the side position at twenty-one
feet per second the values ranges from 31 to 198 Gs.

At twenty-one feet per second in the back position
the three best helmets were Mac—0, Mac—5, and Spal—l. The
acceleration of the best helmet Mac—0 was 156 Gs as compared
to 324 Gs for the worst, Wil-201. The range of replicate
values of Nil-210 at this velocity is 164 Gs.

The definite superiority of Mac-0 at the top position

(twenty-one feet per second), with an average of 30 Gs was

54
in direct contrast to that of Nil—201 with an average of
177 Gs (Fig. 28). The manufacture of this brand of football
helmet (Nil-201) has been discontinued. Most helmets in
this position show little replicate variation.

The most consistently low ranking helmet for all
velocities and positions in regard to acceleration of the
head was Mac-O. The characteristics of this helmet are a
firm pliable plactic-type shell (Duralite) and a geodetic
padded liner (Bedford Vinyl).

Regarding maximum deceleration of the pendulum at all
velocities in the front position it was found that Nil-211
consistently ranked first (Fig. 6). Mac-O was ranked
thirteenth at all velocities for this position except at
eighteen feet per second, where it was rated twelfth.

The most consistently low ranking helmet across all
velocities for the side position was Spa1-2. The worst at
the side position was Rea.

Best over-all protection from the back was afforded
by Rid-5 while the least protection, in terms of deceleration
of a striking pendulum, was given by Nok.

Rid-M, Rid—5, and Spa1-2 are the persistently lowest
ranked helmets for the measure of deceleration across all
positions. Intra-helmet variation was more noticeable,
particularly in the front position for deceleration as com—
pared to acceleration. This was more pronounced at the
highest impact velocity (Fig. 32). It was observed that

factors such as whipping motions of the descending pendulum

55
cables, projections at the ear level, and rims along the
axis of the helmets, often resulted in inconsistent blows.
These were mostly produced at the higher impact velocities.

' The rankings of helmets by rates of accelerations
(Table 6) were markedly similar to those by maximum acceler-
ation.

At twenty-one feet per second in the front position
Wi1-211 was ranked first with an average rate of 96,772 Gs
per second (Fig. 48). In spite of it being impacted with
the highest velocity possible in this experiment, it was
yet within the limit of 100,000 Gs per second as advocated
for football helmets by Lombard.(38)

Mac-O was ranked first at twenty—one feet per second
in the side (8,872 Gs per second), back (93,818 Gs per second),
and top (7,200 Gs per second) positions. However, it ranked
seventh at twenty-one feet per second in its poorest position
the front with 172,688 Gs per second. At the back positions
the ratings of Mac-0, for acceleration and rates of acceler-
ation, are nearly identical.

The two lowest cumulative rankings for all positions
are, in order, those of Rawl and Spal-l. The shells of
these two helmets are almost identically constructed (Cycoloc),
with the liners being made of non-resilient ensolite. Their
resemblance to the liners of the Mac—0 was noted.

The results of this chapter may be summarized:

1. Except for the side position of Mac—2, leather

helmets are inferior to plastic shelled helmets.

56
While somewhat alike at the low impact velocities,
the responses of helmets are considerably more
variable as the result of blows of greater magni-
tude.
Helmet types differed significantly according to
position. The back was generally the worst
position. The within variance was significant
for all three evaluating measures. lntra-helmet
variation was found least at the top position.
Firm pliable plastic like shells with suspension
padded liners are seemingly superior to rigid
shells with canvas suspension liners.
F ratios of all sources of variance are
significant.
The best helmet for all three measures at the
front position Wil-2ll. Its shell was of a firm
pliable plastic material (Etholite) with the liner
being a cotton suSpension type.
The consistently best three ranking helmets were
for:
Acceleration-~Mac-0, Spal—l, and Rawl,
Deceleration-~Rid—5, Rid-b, and Spa1-2, and

Rates of Acceleration-~Raw1, Spal-l, and Wi1-211.

57

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Upon Impact at the Front Position.

 

 

108

 

 

 

 

Fig. 67. Helmet Brands Used in the Study

CHAPTER V

SUMMARY, CONCLUSIONS, AND RECOMMENDATIONS

Summary

The purposes of this dissertation have been to: (l)
evaluate thirteen brands of football helmets regarding
maximum and rate of acceleration of the head, and maximum
deceleration of a striking pendulum; and (2) statistically
analyze the data on the basis of the responses of the helmet
to impact.

The evaluation was done by ranking the helmets
according to their responses at various impact velocities
and positions. A separate analysis of variance was applied
to each of the three evaluating criteria involving the
variance of the three main effects and four interactions.

The experimenting was done by impacting thirty-nine
helmets, which were mounted on a wooden head, with a free
swing flat surfaced pendulum. The helmets were tested at
four randomly distributed impact velocities (12, 15, 18, and
21 feet per second), and at four positions, front, side,
back, and top). The reaponses to impact were measured by
two accelerometers mounted within the head and at the back
of the pendulum, the output of which was fed into a dual
trace oscilloscope. Oscilloscopic traces resulting from

these impacts were photographed by an attached polaroid

llO

camera, projected, analyzed, and measured in terms of Gs,

and Gs per second.

The helmets were ranked according to their efficiency

in terms of lower values for all three evaluating criteria.

Graphs were plotted to show the mean responses of each

helmet brand for all velocities and positions, and to com-

pare the responses of all helmets at a given velocity and

position for each measure of evaluation.

Conclusions

 

l-

Helmet brands, positions, and impacting velocities
are significantly different for all three eval—
uating measures. The highest F ratios are for
position: acceleration F = 1234.76, deceleration
F = 1005.30, rates of acceleration F = 519.62.

For all three evaluating criteria, brands vary
significantly according to the position and the
impact used. Helmets varied mostly at the highest
impact velocities. Excepting for helmet Mac—O

and Mac—5, the back is the worst position for

all brands.

Helmets responded differently to the various impact
velocities within all given positions. The back
position contributed mostly to the within variance
for measures of acceleration and rates of acceler-
ation. The front position produced the most

within variance for the measure of deceleration.

111
Leather and rubber shelled helmets were generally
inferior to other types of helmets. Mac-2, con-
sistently among the best helmets at the side
position, is the only exception to this.
Firm, pliable plastic-type shells with suspended
padded liners were seemingly superior to rigid

plastic-type shells with webbed suspension liners.

Recommendations

 

1.

Various combinations of assorted types of shells
and liners should be tested to determine the

best football helmet.

Fatiguing effects from a prolonged series of
impacts on the helmets should be studied.

Because of the range in temperatures experienced
in football games, the effects of both temperature
extremes on helmets should be studied.

Much of the literature relates concussive levels
to pressure distribution over the head. It would
be beneficial to test the effects of impact in
terms of pressure distribution and its time
duration at selected points on the head as the
result of impact.

For comparable results, standardized testing equip-
ment should be used in future testing of this kind.
Mass, texture, size, and content of the head, as
well as mass and shape of the impacting pendulum

should be uniform.

112
Kinetic energy, absorbtion, and dissipation by
the head as a result of impacting the helmet
should be determined.
The incidence of concussive head injuries incurred
in games and practices in relation to the brands
of football helmets used should be studied.
More research must be done to determine the
various types and magnitudes of impact incurred

in football games.

BIBLIOGRAPHY

 

BIBLIOGRAPHY

Committee on Injuries and Fatalities, American Football
Coaches Association. Dr. Floyd R. Eastwood,
Chairman. Twenty-Seventh Annual Survey of Foot—
ball Fatalities, January, 1959.

Gurdjian, E. S., H. R. Lissner, and J. E. Webster.
"Mechanics of Skull Structire,” Proc. Soc. Exp.
Stress Analysis, 7:61-70, 1949.

 

 

Gurdjian, E. S., J. E. Webster, and H. R. Lissner.
'"The Mechanism of Skull Fracture," Radiology,
54:3:313-339, March, 1950.

Gurdjian, E. S., J. E. Webster, and H. R. Lissner.
"Observations on Prediction of Fracture Site in
Head Injury," Radiology, 60:2:226-235, February,
1953.

Gurdjian, E. S. and J. E. Webster. "Recent Advances
in the Knowledge of the Mechanism, Diagnosis, and
Treatment of Head Injuryn" American Journal of the
-2

Medical Sciences, 226:21 20, August, 1953f__

 

 

[A

 

 

Gurdjian, E. S., H. R. Lissner, F. R. Latimer, B. F.
Haddad, and J. E. Webster. '"Quantitative Deter-
mination of Acceleration and Intracranial Pressure
in Experimental Head Injury," Neurology, 3:6:417-
423, June, 1953.

 

Gurdjian, E. S., H. R. Lissner, J. E. Webster, F. R.
Latimer, and B. F. Haddad. '"Studies on Experi-
mental Concussion," Wayne University Neurosurgical
Service, March, 1954.

Lombard, Charles F. "How Much Force Can Body Withstand,"
Aviation Week, 50:3:20-28, January 17, 1949.

 

Lombard, Charles F., Smith W. Ames, Herman P. Roth, and
Sheldon Rosenfield. "Voluntary Tolerance of the
Human to Impact Accelerations of the Head," The
Journal 9; Aviation Medicine, 22:2:109-116, AEFii,

1951.

Wahl, N. E. and A. A. Whiting. '"Head Impact Investi-
gation," Cornell Aeronautical Laboratory, Inc.,
Report No. OG-537-D-9, December 22, 1948.

 

 

 

11.

12.

13.

14.

15.

16.

17.

18.

19.

20.

21.

22.

23.

24.

255.

115

Snively, George G. '"Skull Busting for Safety," Sports
Cars Illustrated, July, 1957.

 

H

Rawlins, J. S. P. ‘"Design of Crash Helmets,

Lancet,
2:271:719-724, October, 1956.

'"New Helmet Protection Theory Advanced," Aviation Week,

 

50:4:18-20, January 24, 1949.

Strand, 0. T. '"Protective Helmet Impact Testing Equip—
ment," Air Force Technical Report No. 5820, May,

1949. pp. 1-9.

Strand, 0. T. '"Impact Effect on Two Types of Protective
Helmets," Air Force Technical Report N9. 6020,
May, 1950,‘Index iii.

 

 

Dye, Edward R. "Protecting the Head from Impact
Injuries," Safety Education, April, 1953, pp. 8-11.

 

Borgeson, Griff. '"Helmet Design: Comfort or Survival,"
SportsCaIs.Illustrated, July, 1958.

 

Hendler, Edwin and Edward M. Wurzel. ‘"The Design and
Evaluation of Aviation Protective Helmets," The
Journal of Aviation Medicine, 27:1:64-70, February,

1959. -—-

"Auto Racing M.D. Seeks Better Helmets," Scope Weekly,
21:15-16, May 27, 1959.

 

 

."

"Aviation Engineers Develop Football Helmet, Scope
Weekly, 3:48:15, November 26, 1958.

Dye, Edward R. '"Development of the Beam-Pad and Geodetic
SuSpension Helmet," Cornell Aeronautical Laboratory,
Inc., Report N9. 0G—674-D—3,‘April 30, 1952.

 

 

 

Gurdjian, E. 8., J. E. Webster, and H. R. Lissner.
"Observations on the Mechanism of Brain Concussion,
Contusion, and Laceration," Surgery, Gynecology,
and Obstetrics, 101:680-690,9December, 1955.

 

 

 

Snively, George. Notes on Instrumentation Provisions,
"Comparative Impact Tests."

White, William H. "Armor That Does As Much Harm As
Gooi,"-Sports Illustrated, October 31, 1955, pp.
"4’6- 7.

 

Wilkinson, C. 5., Jr. "Electronic Pendulum for Evalu-
ating Impact Absorption of Foam Material," Goodyear
Tire and Rubber Company Research Contribution No.
222: September, 1957, pp. 8414851.

 

 

26.

27.

28.

29.

30.

31.

32.

33.

34.

35.

36.

37.

38.

116

Gross, Arthur G. "On the Impact Thresholds of Brain
Concussion," Gross Research Laboratories, Inc.,
Final Report Contfact NOnr 1647(00), May 15, 1957.

 

 

Gross, Arthur G. ‘"A New Theory on the Dynamics of Brain
Concussion and Brain Injury," Gross Research Lab—
oratories, Inc., Report GR-Rl, May 15, 1957.

 

 

 

Edwards, Lester Henry. "An Evaluation of the Acceler-
ation of the Head and the Deceleration of a
Striking Force on Impact with Various Football
Helmets." Unpublished M.A. thesis, Michigan State
University, 1958.

Case, Wayne Floyd. "An Investigation of the Impact-
Absorbing Qualities of Various Football Helmets."
Unpublished M.A. thesis, Michigan State University,

1957-

Goulden, Cyril H. Methods 9: Statistical Analysis.
New York: John WiIey and Sons, Inc., 1956.

 

"Notes on Linear Variable Differential Transformers,"
Bulletin AA-lA, Schaevitz Engineering, Camden,
New Jersey, 1955.

Doyle, Joseph T., David W. Richardson, and Edith L.
Hardie. '"The Circulation in Induced Acute Head
Injury." Albany, New York and Richmond, Virginia.
Unpublished paper.

Wilson, James V. The Pathology of Traumatic Injury.
Baltimore: The Williams and Wilkins Company, 1946.

 

 

Eastwood, Floyd R. Chairman, Injury and Fatality Com—
mittee. '"Confidential Report on Present Research
on Football Helmets and Future Study Needs."
Unpublished paper, Los Angeles State College,
December 31, 1956.

Lombard, Charles F. "Football Helmets," June 1, 1956.
Unpublished paper, Protection, Incorporated.

Lombard, Charles F. ‘"Football Helmet Design," June 1,
1956. Unpublished paper, Protection, Incorporated.

Denny-Brown, D. and W. R. Russell. ‘"Experimental
Cerebral Concussion," Brain, 64:93, 1941.

Lombard, Charles F. Protection, Inc., 6521 West Blvd.,
Inglewood 3, California. Personal correspondence
dated May 24, 1960.

APPENDIX

APPENDIX A

SAMPLE QUESTIONNAIRE SENT TO MANUFACTURERS

Football Helmet Statistic Sheet

 

Please be specific:

Helmet Model

 

 

Shell Composition: Fiberglass, leather, p1exiglass,etholite,
other
Shell Thickness inches (nearest one hundredth)

 

 

Liner Type: Strap, pad, suspension, geodetic suspen-
sion, other

 

 

Liner Material Styrefoam, ensolite, polystyrene, polye-
thylene, cotton, suspension, other
Liner Thickness inches

 

 

Distance between
liner and inside of
shell at the:

 

 

 

-—top inches (nearest one hundredth)
--back inches
—-sides inches
--front inches

 

 

Total weight of
helmet without
face and nose quards lbs. (nearest one hundredth)

 

 

Attachment material Cotton stitching, metal rivets, cotton
of liner to shell rivets, other

 

 

Comments:

Other worthy physical
features of helmets
not included above

 

APPENDIX B

 

120

 

 

 

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5.9 455.3 211.2 255.3
7.6 509.7 267.9 113.7

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