‘-"“ w— — n- _ l'f‘» II} II I “I [III warn”; I 't I? i .II.IIII,I|‘| III II ‘ III I. I III“: H I ”I I III I I I I I; I, n I I III I I I III I, I" I I II I w I I I4 AN EVALUATION OF THE ACCELERATION OF THE HEAD AND THE DECELERATION OF A STRIKING FORCE ON IMPACT WITH VARIOUS FOOTBALL HELMETS Thesis {or ”he Degree oI M. A. MICHIGAN STATE UNIVERSITY Lester Henry Edwards 1958 AN EVALUATION OF THE ACCELERATION OF THE HEAD AND THE DECELERATION OF A STRIKING FORCE ON IMPACT WITH VARIOUS FOOTBALL HELMETS by Lester Henry Edwards AN ABSTRACT Submitted to the College of Education of Michigan State University of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of MASTER OF ARTS Department of Health, Physical Education, and Recreation 1958 // Approved: 499/ . 2 LESTER HENRY EDWARDS ABSTRACT The purpose of this study was to compare the protec- tive qualities of existing football helmets through measure— ment of the acceleration of the head within the helmet and the deceleration of an impact producing pendulum striking selected points on the exterior surface of the helmet. This was done by inflicting a desired number of blows of five varying velocities to four specific positions on the helmets. The striking device consisted of a suspended pendulum weighing five and thirteen-hundredths pounds with a flat face. The helmets were mounted on a wooden head suspended by cables from the ceiling. At the beginning of this study eleven helmets varying in design and composition were being tested. Two had to be dropped due to damage to their shell and cotton suspension incurred during the testing. The helmets were all tested at the following five velocities: nine, twelve, fifteen, eighteen, and twenty-one feet. Four different positions: front, back, right side, and top were-tested. Three blows were inflicted at each position on each helmet for all five velocities. An accelerometer was used to measure the acceleration of the head and the deceleration of the .16 slug on impact with the helmets. The output from the accelerometer was fed into an oscilloscope. For recording the magnitude of the accelerations and decelerations, the screen of the 3 LESTER HENRY EDWARDS ABSTRACT oscilloscope was photographed with a Polaroid camera attach- ment. The magnitude of the recordings were measured and tabulated. The results were graphed and tabled. The helmets were ranked in order of their effective- ness. No statistical analysis was made of these data because only a single helmet of each type was tested. Plastic shell helmets were superior to leather helmets in all positions. It appears that helmets can not be adequately evaluated on the basis of deceleration indicating that it is necessary to measure the acceleration of the head within the helmet to obtain the critical measure desired. AN EVALUATION OF THE ACCELERATION OF THE HEAD AND THE DECELERATION OF A STRIKING FORCE ON IMPACT WITH VARIOUS FOOTBALL HELMETS by Lester Henry Edwards A THESIS Submitted to the College of Education of Michigan State University of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of MASTER OF ARTS Department of Health, Physical Education, and Recreation 1958 ACKNOWLEDGMENT The writer is indebted to many individuals for the part they have contributed to this study. Special thanks are due the following: Dr. Wayne VanHuss for his helpful suggestions, criticisms, and assistance in the testing procedure; to Dr. Henry J. Montoye who assited in the initial planning of the experiment; to Perry B. Johnson for his assistance in the testing procedure; and to Kurt E. Utley for his aid in setting up the electrical equipment. L.H.E. To Mother with appreciative memories of her inspiration. CHAPTER I. THE PROBLEM. . . . . . Statement of the problem Importance of the study. Limitations of the problem. II. REVIEW OF THE LITERATURE Medical literature Research on.protective head gear. III. METHODS OF PROCEDURE. . . . . . . The equipment used Experimental design IV. ANALYSIS AND PRESENTATION OF DATA V. SUMMARY, CONCLUSIONS, AND RECOMMENDATIONS. Summary . . . . . . Conclusions. Recommendations BIBLIOGRAPHY . . . . . . APPENDICES TABLE OF CONTENTS PAGE O\O\U'I I\)-I\J ll 18 18 21 23 45 us 46 47 49 52 LIST OF TABLES TABLE PAGE I. Composition of Helmets Included in this Study in Regard to Average Accelerations and Decelerations. . . . . . . . . . . 42 II. Helmets Ranked in Order of Effectiveness Determined by Lowest Acceharation and Deceleration Recordings at 21 ft/second at the Four Positons Tested . . . . . . 43 III. Comparison of Acceleration Characteristics in Mean Gs According to Helmet Construction. 44 FIGURE LIST OF FIGURES Acceleration of Head and Deceleration of .16 slug at varied velocities upon Impact with Helmet WF 2110. . . . Acceleration of Head and Deceleration of .16 slug at varied velocities upon Impact with Helmet WF 2010. Acceleration of Head and Deceleration of .16 slug at varied velocities upon Impact with Helmet ME 610 . . . . . . . . . . Acceleration of Head and Deceleration of .16 slug at varied velocities upon Impact with Helmet MH 620 . . . . . . . Acceleration of Head and Deceleration of .16 slug at varied velocities upon Impact with Helmet MR 612 . . . Acceleration of Head and Deceleration of .16 slug at varied velocities upon Impact with Helmet S3131 . . . . . . . . . . Acceleration of Head and Deceleration of .16 slug at varied velocities upon Impact with Helmet RTK5. PAGE 27 28 29 30 31 32 33 vii FIGURE PAGE 8. Acceleration of Head and Deceleration of .16 slug at varied velocities upon Impact with Reach Helmet . . . . . . . . . . . 3A 9. Acceleration of Head and Deceleration of .16 slug at varied velocities upon Impact with Helmet WF 2104. . -. . . . . . . . . 35 10. Comparisons of Helmets WF 2110, ME 610, and RTK 5 in Acceleration of Head and Deceler- ation of .16 slug moving at various veloci- ties for Front and Back Positions . . . . 36 ll. Comparisons of Helmets WF 2110, ME 610, and RTK 5 in Acceleration of Head and Deceler- ation of .16 slug moving at various veloci- ties for Side and Top Positions. . . . . 37 12. Comparisons of Helmets MR 612, Reach, and WF 2104, in Acceleration of Head and Decel- eration of .16 slug moving at various veloci- ties for Front and Back Positions . . . . 38 13. Comparisons of Helmets MR 612, Reach, and WF 2104, in Acceleration of Head and Decel- eration of .16 slug moving at various veloci- ties for Side and Top Positions . . . . . 39 14. Comparisons of Helmets WF 2010, MH 620, and I I I S3131, in acceleration of Head and Deceler- ation of .16 slug moving at various veloci- ties for Front and Back Positions . . . . A0 viii FIGURE PAGE 15. Comparisons of Helmets WF 2010, MH 620, and S3131, in Acceleration of Head and Deceler- ation of .16 slug moving at various veloci- ties for Side and Top Positions . . . . . Al 16. Photographs of Experimental Equipment Used . . 53 CHAPTER I THE PROBLEM Research-wise very little is actually known relative to the protective qualities of the many differently designed football helmets being manufactured today. This has been due to the inadequacy of the measurement techniques and equipment used, along with the limited basic knowledge of the physical and the physiological mechanisms involved in brain injury. The design of these helmets varies consid- erably both in composition of the exterior shell as well as the interior padding and suspension. The shells are made of leather and various forms of plastic material. The interior is either fitted with some form of shock absorbent, slow recovery plastic padding material (usually a cellulose acetate, insulite), or a strong suspension of cotton webbing which fits snugly on the head. To find which material and design or combination of materials and designs provides the greatest protection is the prime objective of those con- cerned with the development of football gear. The develop- ment of sensitive accelerometers with high frequency response characteristics has led to the almost universal use of these transducers in helmet evaluation work. The measurements obtained are in terms of acceleration.1 Statement of the Problem It was the purpose of this study to compare the pro— tective qualities of existing football helmets through measurement of the acceleration of the head within the helmet and the deceleration of an impact producing pendulum striking selected points on the exterior surface of the helmet. Importance of the Study The importance of the football helmet as a standard piece of protective equipment, can never be minimized. The reasons for this protection are obvious as the head contains the nerve center of the body. A hard blow to any part of the head can have serious results. Some protection from injuries is provided by the thick shell of bones which protects the brain. An injury to the skull is only a portion of the consideration. With the head, it is important to protect the bones of the skull from being fractured as well as to guard the brain from the shock of the blow. The brain may be damaged less when the energy of the blow is dissipated by fracture of the skull, than when the skull is undamaged. One can perhaps visualize this best lEdwin Hendler and Edward Wurzel, "The Design and Evaluation of Aviation Protective Helmets," The Journal of Aviation Medicine, 27:1-65, February, 1956. by cracking an egg in which the yolk does not break and by rapidly shaking an egg in which the shell is unbroken but the inSide is scrambled. Damaging injuries to the brain and skull are thought to be caused by energy of a sharp blow being delivered to the head in a comparatively short period of time. The measure considered to be most valid to evaluate headgear is acceleration.2 A blow of high acceleration is thought to move the skull at a rapid rate. The softer tissues of the brain move less fast being forced against the impact area then rebounding to the opposite side. Research has shown the brain damage to be at either point.3 The Twenty-Fourth Annual Survey of Football Fatalities brought out that fatalities directly due to football have averaged seventeen and one-half per year.4 The head and face area accounted for 59.56 per cent of all fatalities, the spine for 20.59 per cent, and abdominal—internal for 19.85 per cent.5 2lbid. 3James B. Wilson, The Pathology of Traumatic Injury (Baltimore: The Williams and WIIEIns Company, 19467, pCI50. Committee on Injuries and Fatalities, American Foot- ball Coaches Association, Dr. Floyd R. Eastwood, Chairman, Twenty-Fourth Annual Survey of Football Fatalities, January, 1956, p. 2. 51bid., p. 3. A These data also revealed that both spine and head and face injuries result from blows to the top of the head; 80.15 per cent of all injuries were due to traumatic blows to the head.6 A breakdown of the location of blows and the percen- tage of all injuries incurred showed that:7 1. Blows to the front and side of the head 23.54% 2. Blows to the top of the head (resulting in spinal injuries) 20.59% 3. Internal injuries 19.85% 4. Blows to the back of the head 13.95% A point of interest involved with these figures is the fact that the percentage of total fatal head and spinal injuries has risen steadily since 1931 and four per cent since 1947. During the same period there had been a steady decrease in internal-abdominal injuries.8 Possibly this increase in head injuries can be attri- buted to changes in and development of the game i.e.; tech- niques and methods used, conditioning of players, speed at which players maneuver, faster and more wide open style of play, facial protective equipment inducing a stronger feeling of security and bring forth less restrictive use of the head ' in contact situations. Whatever the specific reasons for 6Ibid., p. 3. 7Ibid., p. 3. 8Committee on Injuries and Fatalities, American Foodball Coaches Association, Dr. Floyd R. Eastwood, Chair- man, Twenty-Fifth Annual Survey of Football Fatalities, January 7, 1957. this increase may be are unknown. However, these figures clearly indicate the need for more knowledge and research involving the structure and composition of the helmets manufactured today if this football fatality and injury picture is to be materially decreased. Limitations of the Problem 1. There are many over-all factors that have to be considered and evaluated before it can be concluded that one type helmet is more protectively effective than another. 2. It was possible to test only one helmet of each type. It is possible the intra helmet comparisons could be greater than the inter helmet values. 3. It would have been desirable to test helmets through the range of sizes. Only one size was measured in this study. 4. Fit of the helmet was not controlled. Seven and one-quarter sizes vary considerably as to fit. 5. Maximal accelerations and decelerations only were recorded in the present study. The time relationship associated with recording the full envelope of the blow from the oscilloscope was not recorded. The absence of these data is a serious limitation of the present study. CHAPTER II REVIEW OF THE LITERATURE In reviewing the available related literature to this problem it was considered desirable to first gain some insightinto the pathology of injuries to the central nervous system and to become acquainted with some of the (experimental work in the medical field involved with con- cussive effects on the skull and fractures. Secondly, research work involving different types of protective head gear carried on by branches of the armed forces, educational institutions, and private organizations was reviewed. Medical Literature It can be ordinarily stated that (in wounds of the head) it is never the injury to the skull which really matters, but rather the amount of damage to the underlying tissue and its coverings.9 The problem involving the mechanism of head injuries still remains incompletely understood. Wilson states that when the head in rapid motion is stopped by a stationary or resistant mass, or when this head is at rest and it is struck by a fast-moving object, damage to the brain not 9Wilson, op. cit., p. 149. only occurs at the point where the force is acting, but actually the maximum cerebral injury takes place at the pole directly opposite the spot of impact. Many debatable theories have been expressed involving this reaction but the one which probably best fits in with the known facts and pathology of the lesions found is one developed by Holbourn.lo He believes it is the shear strain which causes the injury and not the compression and rarefaction strain which many consider to be important. Holbournll also theorizes that distribution of shear strains can be predicted and, therefore, the locations of injuries from various types of blows. It was further stated that rotational acceleration forces are the main cause of brain injury and that it can be shown that linear, centrifugal,and coriolis forces produce little in the way of shear force and are thus of little account in the pro- duction of head injuries.12 13 Gurdjian, gt al, showed that acceleration, decel- eration, and compression may cause deformation of the skull, 10Ibid., p. 150. 11Ibid., p. 151. 12lbid., pp. 153-154. 13E. S. Gurdjian, J. E. Webster, and H. R. Lissner, "Observations on the Mechanism of Brain Concussion, Contusion, and Laceration," Surgery, Gynecology, and Obstetrics, 101: 682, December, 195 . distortion of the skull and dural septa, a sudden increase in intracranial pressure at the time of impact, mass move- ments of the intracranial contents, shearing off of a portion of the head and contents without necessarily pro- ducing an increase in intracranial pressure at the time of impact, and shearing and tearing with high levels of in- creased intracranial pressure. Distortion of the skull is most severe near the site of the blow and consists mainly of indentation, whether fracture occurs or not shear strain in the brain is local and superficial and seldom serious in itself. Shears due to skull distortion are so small as seldom to cause tearing of large vessels, but when fractures occur tearing of dura and rupture of large vessels are almost inevitable.14 Fractures have been grouped according to location and type. They may be linear, depressed, or penetrating. Lin- ear fractures are most frequent. Their production depends on certain elastic qualities of the skull. If sufficient force is brought against it, the skull will be shortened in one diameter, lengthened in another, and fracture results from increasing its equatorial circumference. Almost invari- ably the line of the fracture follows the direction of the shortest meridian. Naturally, linear fractures have various locations and peculiarities because the offending forces l“Wilson, op. cit., p. 151. differ in intensity and direction and because the cranium is not a perfect sphere. At first the fracture line separates but immediately springs together. Since the base of the skull is its weakest part, it is the most common site of fracture.15 When the various weaker lines and areas are taken into consideration, and when the direction and site of the applied force are known, one is generally enabled to foretell with considerable accuracy the probable transbasic course of the fracture. Fractures of the skull may be divided into three cate- gories where they might occur. The area of primary stress level is the weakest region in the skull and it is here a fracture may start. The area of secondary stress level is the region where a second fracture line may be initiated with additional energy. The area of tertiary stress level is the region where still further fracture lines will be caused by more energy, usually resulting in a stellate pattern. The area of primary stress level varies in dif- ferent skulls.l6 The time duration of the pressure exerted upon the brain is believed to be an important causative factor in concussion. A study on experimental concussion by Gurdjian, 15Frederick Christopher (ed.), Textbook of Surgery, by American Authors (fifth edition; PhiladeIphia and London: W. B. SEUnders Co., 1949), p. 447. 15E. s. Gurdjian, J. E. Webster, and H. R. Lissner, "The Mechanism of Skull Fracture," Radiology, 54:3:338, ‘March, 1950. IO 17 P.3i’ concluded that the longer the duration of the pressure exerted upon the brain, the lower the pressure required for a severe concussion. The shorter duration, the higher is the pressure required for a severe concussion. Concussion and brain damage may be more readily caused when a direct blow contacts the head in a relatively fixed position than if the head were free to move at impact with the blow. This is due to the time duration of the pressure on the brain which lasts for a longer period of time on con- tact with the head when in a fixed position. After impact by a direct blow there is an area of inbending immediately beneath and around the point of the blow. If the time duration is long enough or the velocity is sufficiently high, the area of inbending may fail, resulting in a depressed fracture. If the inbending at the boundary of the inbended area is not severe enough to cause a fracture, the skull rebounds. The outbending may be so severe that a linear fracture results. Thus the fracture line extends both toward the point of impact and in the opposite direction.18 It should also be understood that differences in thickness of scalp, thickness of skull, and shape of skull 17E. S. Gurdjian, H. R. Lissner, J. E. Webster, F. R. ‘Latimer, and B. G. Haddad, "Studies on Experimental Concus- sion," Wayne University Neurosurgical Service, March, 1954, p. 678 18E. s. Gurdjian, J. E. Webster, and H. R. Lissner, "0bservations on Prediction of Fracture Site in Head Injury,‘ Radiology, 60:2:226, February, 1953. I 11 may have important bearing on the individual's susceptibility to concussion and fracture. Research on Protective Head Gear It is assumed that a head injury is the result of force applied to the head and its contents. Because accel- eration is directly proportional to force for a constant mass, the terms force and deceleration can be used inter- changeably. The development of sensitive accelerometers with high frequency response characteristics has led to the almost universal use of these transducers in helmet eval— uation work. The measurements obtained, therefore, are in terms of acceleration. The usual unit, g, is used in expressing magnitudes of acceleration.19 Forces applied to the exterior surface of a protective helmet are tramsmitted through the padding to the surfaces and contents of the head primarily, and to the supporting tissues of the neck and back to a lesser degree. Distri- bution of force can be achieved by proper helmet design, and can do much to provide increased head protection.20 21 It is known that certain portions of the skull are inherently stronger than others, and that blows to certain 19Hendler and Wurzel, op. cit., p. 65. 2Olbid., p. 66. 211bid., p. 67. 12 parts of the head can result in more extensive internal damage than similar blows directed to other parts. The protective helmet which distributes forces to parts of the head in proportion to the ability of these parts to with- stand injury is preferable to one without this characteris- tic. A helmet capable of insuring such wide distribution of applied forces that local pressures all over the head would be reduced to non injurious levels could achieve an equally desirable effect. Lombard, gt al,22 * conducted what was probably the first clear experimental work concerning the limits of voluntary tolerance to accelerations of the human head due to impact and to determine the limiting factors. Apparatus consisted of two different weight pendulums, one of thirteen pounds and the other 9.44 pounds. Each was used on seven different football helmets. Difficulty encountered with the support of the thirteen pound pendulum made it necessary to change the suspension and to use the 9.44 pound pendulum. In the steel head of the pendulum a strain gauge type accel- erometer capable of measuring in excess of 500 gs was mounted. For recording the pattern and magnitude of accel- eration, the face of the oscilloscope was photographed by a 35 mm. streak camera. 22Charles F. Lombard, Ames Smith, Herman P. Roth, and Sheldon Rosenfeld, "Voluntary Tolerance of the Human To Impace Accelerations of the Head," The Journal 3: Aviation Medicine, 22:2:109-16, April, 1951. 13 Helmets were selected which subjectively fitted the subject. The subject was positioned so that the blow could be delivered approximately in line with the center of the Inass of the subjects head from the front, side, back, or top positions. The subject was questioned as to his feelings immediately after receiving the blow to the head. The results showed in general that the upper limit of linear acceleration which the human can tolerate voluntarily due to impact blows to the head was not reached. Always the effect of the locally applied force caused bruising, and other discomfort caused the subjects to limit exposure to no higher energy impacts. The voluntary limitation of the energy of the blows to the head by the various subjects in nearly all cases reflected their reluctance to tolerate local bruising and pain. However, it is believed by the authors that psycho- logical factors play a most important part in the limitation. From this study the value of further human studies seems questionable since the impacts subjects are able to tolerate are at the levels where there are relatively little differ- ences in helmets. To meet the problem of impact resistance pilot 23 helmets have been fabricated, in the past, of resilient 23"NewHelmet Protection Theory Advanced," Aviation Week, 50:4:18, January 24, 1949. l4 material designed to distribute the impact force and provide protection against penetration of the helmet by sharp objects in the event of crash. However, recent investiga- tions indicate that brain injury can also result from acceleration of the head. It is important, therefore, to provide for maximum energy absorption to limit the accel- eration of the head. Investigation revealed that not only should the outer shell of the head gear possess both maximum force-distri- buting and penetrating-resisting characteristics, but the space between the shell and head should be filled by an essentially non-resilient, energy-absorbing material. A material which has been particularly effective is a foamed polystyrene plastic. The advantage of the material is that foaming can be controlled and that it is particularly shock absorbent. The disadvantage is that the cell structure is destroyed by a blow making its protection a "one shot affair." Styrafoam is such a plastic. The molded insert of the "Toptex" crash helmet is of "Dylene" a trade name of Koppers Plastic Company, Pittsburg for the same type of plastic. Greatest disadvantage of resilient material for the job of energy absorption is that during deflection it stores rather than dissipates energy. As it is deflected, an increasing restoring force is created which reaches a max- imum at the point of maximum deflection and the energy is returned in the form of a rebound of the helmet from the ob- ject. fie std-fifhbhihfit, .1 Er I..d!u EFT... Eh. 15 Strand24 conducted a test to evaluate the acceleration of the head and the deceleration of the impact producing pendulum on two types of protective helmets. The two helmets were tested at four different positions. Three impact-shapes were used at two impact velocities. The energy absorbing qualities were found to be the same. In evaluating the results of other characteristics it was concluded that on the point of uniform protection over the entire head one helmet could be considered to be superior than the other. In studying the protection afforded to the head by any kind of helmet one must have knowledge of: (1) The inagnitude of the maximum acceleration that the cushioning perndts the head to reach; (2) The form of the acceleration- time relation; and (3) The strength, natural frequencies of 'vibration and damping of the structural elements of the head.25 Of these three factors, only the first two may be lneasured under given conditions in the case of a head en- <2losed by a protective helmet. The third factor concerning tflqe mechanical properties of the head and its contents, is undetermined . 26 2”Oliver T. Strand, "Impact Effect on Two Types of Pruatective Helmets," Air Force Technical Report No. 6020, May, 1950), Index- iii. 25Hendler and Wurzel, op. cit., p. 65. 26Ibid., p. 65. l6 Snively27 discovered in the Snell study of crash helmets that few persons concerned with the use, manu- facture, or sale of helmets in this country possessed ade- quate data concerning the helmets' efficiency. The first phase of the Snell28 study was designed to compare the efficiency or protection provided by the more popular brands of helmets against a single, severe impact. This was a maximum stress type of test, deliberately set to approximate the upper limits of impact force at which if the head could be protected, survival might reasonably be expected. The site of impact selected was the temple area; this was chosen after an analysis of statistics had shown temple blows to be more common, and more apt to be fatal than blows to other areas of the skull. The helmets were tested on human cadavers. It was believed this made a more reasonable comparison with actual accident situations than if an artifical head was used. The cadaver head could also be directly examined and X—rayed for fracture after a test was made. Six different makes of crash helmets were used in this study. Defects determined from the examination of 27George G. Snively, "Skull Busting for Safety," Sports Cars Illustrated, July, 1957. [Reprinted] 8 2 Ibid. * 17 the constructional characteristics after testing are as follows: surface projections should be removed for they served to concentrate most of the striking force onto one small area, preventing its distribution. Severe fractures may occur even though the shell of the helmet itself remains unbroken. This shows how impact forces may be transmitted through the shell without significant change in the shell itself, when there is no energy-absorbing liner material utilized. The best protection in this test was provided by a, Toptex, police motorcyclist model helmet. This could not be attributed to a superior shell, for its shell did not differ significantly from the other shells, all of which were fiberglass. The vital difference was in the type of liner used. The Toptex was the only helmet fitted with a completely non-resilient, energy absorbing type of liner material (Dylene), which absorbed rather than transmitted most of the impact force. A limitation of the Snell study was that the effec- tiveness was determined by the fractures present when the cadaver heads were X-rayed. The fracture is a questionable criterion due to the amount of brain damage which can occur with no fracture. Severe fracture occurs in dissipating the energy,a fracture in itself might be desirable in severe impact as opposed to no fracture. It is hoped the persons connected with the Snell study will continue their excellent work by studying accelerations and brain damage. CHAPTER III METHODS OF PROCEDURE The methods of procedure are divided into two parts: (1) an explanation of the equipment, and (2) the experi- mental design. The Equipment USed A strong wooden head fashioned to fit a football helmet of size seven and one-fourth and weighing 13.7 pounds minus insert was used. With insert in place the weight of the head was 16.7 pounds. The insert (see Figure 16) referred to was a steel frame measuring two and one-half inches square times ten inches in length. This insert could be placed in the center of the head thus enabling the accelerometer to be positioned as near to the center of gravity of the mass as possible. The insert was held secure by a screw which enters through the side of the head and tightens into the insert. To the sides and end of this insert an accelerometer can be attached so that acceleration of the head can be recorded at any desired position the head may be placed. The head was fastened by two steel cables with a sling arrangement attached at the ceiling and free to move at impact (see Figure 16). Four turnbuckles were 19 used, one at each corner, to raise or lower the head when adjustment was necessary. The striking device consisted of a pendulum weighing five and thirteen-hundredths pounds with a flat face (see Figure 16). It was attached with a suspension consisting of two steel cables to the ceiling. This weight was used because it was the maximum the electrical release could hold. The pendulum could be raised or lowered by a small chain to the desired heights. The release of the pendulum was controlled from a switch box placed beside the oscillo- scope. 0n the back of the pendulum the accelerometer could be securely fastened for the measurement of deceleration. The accelerometer used was a Schaevitz29 linear variable differential transformer (L.V.D.T.). It measures the force of deceleration or acceleration accurately up to 500 Gs by the displacement of a spring supported core. The output from this accelerometer was fed into a Hewlett- Packard30 Model 130A oscilloscope. For recording the magni- tude of acceleration, the face of the oscilloscope was photographed by a Beattie-Varitron model X5 Polaroid camera. This camera was attached directly over the oscilloscope 29Bulletin AA-lA,"Notes on Linear Variable Differential Transformers," Schaevitz Engineering, Camden, New Jersey. 30"Operating and Service Manual for Model 130A Oscillo- scope," Hewlett-Packard Company, Palo Alto, California. 2O face with a viewer arrangement on it enabling you to look through and follow the pip on the oscilloscope screen. A model 200 CD wide range oscillator which fed the 2000 cycle and 10 volt current supply into the accelerometer was used (see Figure 16). The setting of calibrations on the oscilloscope varied between helmets and velocities. These changes in calibra— tion were made to provide a visual recording which could easily be measured as well as to keep the height of the visual recording on the screen. The oscilloscope was so constructed that a linear relationship existed between millivolts per centimeter and the height of the recording. A vernier caliper was used to measure the mangitude of the recordings recorded on each picture. At the onset of the study eleven of the finest helmets in use today were included. These helmets varied in design and composition. The shells were made of leather and various forms of plastic materials (Tenite, Kralite, Etho- lite). The suspensions varied from resilient blow absorbent materials against the plaster or leather shells to cotton suspensions. They were all size seven and one-fourth. The helmets studied were as follows: Company ‘Stylg Code Number 1. Wilson F2110 (Suspension) WF2110 2. Wilson F2010 - WF2010 3. MacGregor E610 (Geodetic with ME 610 Beam Pad 4. MacGregor H620 MR 620 5. MacGregor H612 MR 612 21 Company Style Code Number 6. Spalding 3131 S3131 7. Spaldin 31 3122 (Suspension) S3122 8. Riddel ?Tenite)32 RKA (Suspension) RK4 9. Riddle Kralite) TK5 Suspension KTK5 10. Reach Reach 11. Wilson (Etholite) F2104 WF2104 Experimental Design The helmets were all tested at the following five velocities: nine, twelve, fifteen, eighteen, and twenty- one feet per second. Four different positions: front, back, right side, and top were tested. Each helmet was tested three times at each velocity starting at nine feet per second and working up to twenty-one feet per second. The few times that a glancing blow was believed to have been struck a repeated fourth blow was then made. One person was capable of conducting this experiment but it was discovered not to be feasible or desirable. Therefore, two and three persons worked together when col- lecting the data. The three man team proved to be the most efficient and desirable. One person checked the position of the helmet and adjusted it following each blow. The head was motionless before each blow was struck. To insure the helmets from not falling off when struck, a lacing held 31Stitching in the cotton suspension gave way so this helmet was dropped from the study. 32A crack developed in the front of the plastic shell of this helmet making it necessary for it to be dropped from the study also. 22 them secure to the head. The second person placed the pendulum in the release box after each impact, and changed the velocity level when necessary. Care was taken here also to be sure there was no sway in the pendulum, and that it was motionless before it was released. The third person operated the switch button to release the pendulum and photographed the picture. This individual also made the necessary dial changes on the oscilloscope and recorded the millivolts per centimeter used at the different veloc- ities. This information was recorded on the back of each picture as it was developed. Each time data were collected an accelerometer cali- bration was taken and recorded due to the possibility of current fluctuations. The identical procedure was followed in collecting the data of deceleration of the blow as in the acceleration of the head. The only difference being in the changing of the placement of the accelerometer from the back of the pendulum for deceleration to the inside of the wooden head for acceleration. On completion of the testing the magnitude of the 'Dips were measured with a vernier caliper and recorded. The averages were taken on all helmets at each position and velocity, and were transferred to measurement in Gs. The results were tabulated, graphed, and tabled. CHAPTER IV ANALYSIS AND PRESENTATION OF DATA The present study was undertaken to compare the pro- tective qualities of football helmets being seld commer- cially. The comparisons were made through measurement of the acceleration of the head within the helmet and the deceleration of a .16 slug pendulum striking selected points on the exterior surface of the helmet. Measurements were made electronically using an accelerometer, oscillator, and an oscilloscope. Oscilloscope tracings were photographed using a Polaroid camera. Acceleration and deceleration records were made at five velocities (nine, twelve, fifteen, eighteen, and twenty-one feet/second) of the pendulum, and for four positions (top, side, back, and front) for all helmets. The accelerations and decelerations recorded for each helmet are presented graphically (Figures 1-9). The helmets are graphically compared at the four positions as to both the acceleration and deceleration characteristics (Figures 10-15). Table I presents the average accelerations and decelerations at the four positions, and five velocities for all helmets, permitting further comparisons. The helmets were ranked in order of their effectiveness (see Table II). 24 This ranking was made using the recordings of acceleration and deceleration at twenty-one feet/second at all four positions. Low acceleration and deceleration values are indicative of a superior shock absorbing quality. At the lower velocities the helmets are very similar. In fact, within voluntary human tolerance values (under 40 Gs deceleration) several of the leather helmets which are so poor at the higher velocities show up more favorably. Helmet WF 2110 was the only helmet that ranked consis— tently high at all positions. This helmet has a plastic (Etholite) shell with a Riddell type cotton webbing suspen- sion. The remaining helmets all fluctuated considerably in their rank order from one position to another. The highest recordings for the four positions in terms of deceleration of the blow was at the back position. The lowest average recordings for deceleration was at the side position. The highest average recordings for the four positions in terms of acceleration of the head was at the front posi- tion. The lowest average recordings for acceleration was at the side position. Study of the graphs and tables reveals that a helmet with a low acceleration at a specific position does not necessarily have a low deceleration at the same position. The ranking of a helmet by its deceleration may be consid- erably different from its ranking according to acceleration. 25 Rank order correlations were calculated for the nine helmets using the rank order of the helmet at the highest velocity, twenty-one feet/second. The correlations, cal- culated for each position are as follows: front r = -.016, back r = .10, top r = .932, side r = .90. The correlations for the top and side are statistically significant. Obvi- ously the other two are not. From the results it appears that helmets can not be adequately evaluated on the basis of deceleration indicating that it is necessary to measure the acceleration of the head within the helmet to obtain the critical measure desired. The helmets are very similar in characteristics at the lower velocity levels. It is not until the higher velocities are reached that the differences are most striking. In Table III all of the helmets tested in the present study were roughly graphed according to materials and type of construction. No statistical analysis was made of these data because the intra helmet variation is unknown. Con- clusions based on these data could be misleading. The means should be regarded as trends only and it should be recalled that the results are based on repeat testing of a single helmet of each type. The trends which appear are as follows: 1. Plastic shell helmets were superior to leather helmets in all positions. 26 The plastic helmet with a cotton webbing suspen- sion appears to be slightly superior to the plastic-insulite padded helmets. This is parti- cularly true in blows to the front. The plastic M—610 helmet with geodetic suspension is superior to other helmets in blows from the top. 6") RA T I ON OF H LOCITIES UPON ‘ I .LJ sw ELI-{ET WF 2110 U (\V / "r1 1. FIGURE 1 ' DF HEAD AND DECEL - VARI ITITH . \ p . J’ .. .. 3'71 J1. LERA T1 (‘1 IMPAI’ . l6 SL1 9.. [SOC—J a I . .. . A I . L T . a T... . a .l . . . . ... «IIIfiI Mk: I III_WIIIV .I..~.II IIW 4.1 v MI T d III—III” I I IL +I.II24IJO.LW . . . I . x ,_ H L”. .. . _ . _ ~ . . l _ .II II..I II III L 1.. .II . ti I_-II I II A III .IIJIIIh _ . . .. n . . _ I _ . n H . . . N _ H _ . L H “I . m ~ . u . M n . I: , mm . -I . _. a. .. , + I I I - LIIII a _m_ . . n H . m _. “ . . T a _ , .7 - a _ , h ._- I ._ 1 . . l . . . I . .5. _ "WW” 1 . .1 1L _ w m I 1. . _ l ,, L . a _ _ . .1- V” .M m r L - - - .r 4 n - L .1 . n ._ . . . . m . . 2 . . D u Anew m l . . l . . u _ _ ... 2, N h 7L0 M M i W . u i l O. . “IL . .vIIII , a. -..II:IIII'I. u IIIII II III- I III lroIl IIII‘IIIIII- III .IIIIIua I'I IAVOIII IIII4II III IIIII.IL. - . .. - . T . . . a . . fit I . . i m I , _ . _. H . . a . Rmm .. u . _ . .H 19 m . .7 U l .1 r. 9-. D N O A . . . . u . . . . _ . . _ P h . _ . . . H . . . 3 m1 I 0L 1. p .II.I.W, -..-.Im. ...... .t. .-.., - — o vI.Iv-.-.- . Ia .I--|IA.... . , w . .I . . ... w I H . ._ U H . _ _ . .. m “HUD“ _ . , . L O _ m Lo . V 7.2.1 . l , . _ . . . _.. PL ill.-- -OT'EETTEE'.T-'II-’|||'E 'EII'- .. . ,PET--l--‘--'4---.|-‘E‘E---.'E--l-"-- . T 1 WILD “ .4 ., x J. , J a . _ m . .3 _ . n n . . H . _ . I . _ .1 4 WI IRm.- I .«r I.III IIIIqII II’I. IIIWIII+III1 no.1. I IIIIIIoIIIIIOIII IJI,III I. IIII.-. - - . _ t ._ _ _ 4 _ . 2 l. . . _ a _ 3. _ “MW ,. . n . .. . H v .I n...“ ,. . 1 B Y XV . _ 1.1.. , i- p I l. , i m . .— p l _ _. n l. C _ . i. a - . I L TiII I00 4. . II. fi N w _ u. .0 l, H . v _ .T. T _ . . h T I - Q5“ «‘9 hnij-A n I 1 I . _ -1 LEGEND- - LLKBIIUN I. .F.. -I'R I ‘I I I r I I :ACCIELERA MK! I I _ r-..—...ut__—_.y-- . . ' I I I I +4 120 WISE _, r :1 i i— , -_§i_.___ Iec —- -I I-— I40 I 2 FIGU.F ACCELERATION OF HEAD AN 0 T V IOI UPC} RAT ELE DEC .16 SLUG AT VARIOUS f‘ F 3 FIGU “LFRATION OF HEAD .16 SLUG AT VARIED VELOCITIES UPON ECELERATION OF AND "1 J I C A I) CURE 4 EAD AND DEC FT LUG AT VARIED VELOC LEILATION OF E) UPON 7-1 a LJ Y R ACCELERATION O [‘1 .14 TI T D .16 4 '1 RD m D U1 FIGURE 5 RATION OF H ATION CF ‘fif“" 7-. .LJ‘J I L74 TDD EAD AI LE ACCE LOC ITIES UPON q J .16 SLUG AT VARIED V' HART 612 IITH RF [V ACT .1!“- FIGURE 6 RATION OF HEAD AND DEC LERATION OF .16 SLUG AT VARIED VELOCITIES UPON E J J ACCEIE IXCJ.3LERATI("I\T ‘I; "’ k7~ . 9—4 VA. "' LEJl’1‘J .16 SLUC- AT VARIEI acr— ' .‘sIID D YE- DC «a ., \J H T',‘ "I "11) \JJ.) 441.111 ATIdz TIES UPON CF F 8 FIG LLOCITIES UPON .l6 SLUG AT VARIED .w/ FIGURE 9 ATION CF F” OF ON I AT VARIED VELOCITIES UPON ERAT “a EOE AD AND D .E .1 ”I - .J Adi CCE \ .C J. SLUG .l6 FIGURE 10 D AN D A US HE IN ACCELERATION OF T.) 5 OF HELNE iPARISON I. 0 C01 'I .16 SLUG MOVING AT VARIC OF H LERATII LOCITTE DECE 0 7" OSITIOT IT AND BACK F OR FRO! F C: - k) VE 7- RATION OF HEAD AND 7-1 11. IE 11 CC C. I GO If .16 SLUG MOVING AT VARIOUS VELOCITIES FOR SIDE AND TOP POSITION“ is DECELERATION OF FG‘U" . r” T“ *cc~l PATION 0F 'EAD 5ND 3 ‘I.'.’l"-’sRISCITS OF HELILSIS if. WWI... CELLRATION OF .1 S UG MOVII'IG AT VARIOUS EL CIT S “I“ FR ND BACK POSITIONS TD R a D EAD OVING AT VARIO T 5- AL S RRATICN OF A! f .16 SLUG I ELOCITIES FOR SID 'D TOP POSITIO IN ACC AN ‘ E VETS ‘ l S OF HE IPARISOF DECELERATION 0F 7.’ st. CO 14: IN ACCELERATION OF HEAD AN FIGURE 8 OF HELMETS ARISO ’ DECEUERATION OF I. V.- CC} OVING AT VARIOUS VELOCITIES FOR FRONT AND BACK POSITIONS T . 16 SLUG I‘ o I 41 FIGURE 15 I OF HEAD AN ACCELERATIOI LUG'MOVING AT VARIOUS “N :""I.‘~ .'. a; .I fifi Li ‘31-}.- h RISONS OF DECELERATION OF .1 P ? I T ‘ COT I' I .-1 '\ 0 «LI: S FOR S AND TOP POSITIONS r1 ‘2; \ .. I u. -1 if. VELOCITI c~v T 131/3 COHPCSITION OF HELMETS IRJLUDED IN THIS STUDY IN REGARD TC.AV£RAGE ACCE ERATIONS AND DECELERATIOUJ F1 1 F4 Lp .4 FRONT BACK SIDE TOP 3175. Gs AVE. Gs AVE. Gs AVE. 8s HELMET VELOCITY ACC. DEC. ACC. DEC. ACC. DEC. 400. DEC. fi?’2110‘“9?t/5ec 11 19 14 23 5 22 4 21 12 15 31 18 31 7 29 5 25 15 18 79 23 35 9 40 7 30 18 33 113 32 85 13 43 17 39 21 41 195 51 143 18 53 19 75 HF 2010 9ft/sec 11 39 19 32 3 18 4 18 12 22 95 40 99 4 23 5 24 15 , 42 157 70 184 7 32 12 42 18 ' 52 219 91 211 39 89 58 148 21 95 259 118 252 52 172 ..95 250 ME 510 9ft/seo 13 34 14 21 3 19 3 25 12 20 59 23 31 4 28 5 31 15 32 119 25 48 5 33 5 35 18 55 254 37 53 8 37 11 41 21 85 266 49 86 10 45 14 42 NH 520 9ft/sec 20 54 15 30 4 19 3 14 12 41 103 29 80 8 59 5 18 15 58 155 58 132 43 121 8 45 18 93 215 82 182 54 179 29 104 21 95 257 123 254 81 221 55 224 NH 512 9ft/sec 20 44 17 34 3 14 3 18 12 38 95 41 85 5 24 5 29 15 55 141 58 132 8 34 9 53 18 77 193 92 173 20 51 31 117 21 91 239 124 255 29 55 57 185 S 3131 9ft/sec 12 32 15 55 4 21 3 18 12 30 74 21 89 5 29 5 24 15 47 118 32 148 8 38 5 27 18 73 173 38 299 19 45 18 49 21 115 244 90 447 24 71 54 146 COMPOSITION OF HELKETE'INELU 15 REGARD TO AVFRAGE ACCELERATIONS \hv- P‘LJtT. T I‘ "‘1me AND DECE ERATIONS J11“. ‘ . DED IN THIS STUDY \ I FRONT BACK SIDE TOP _§VE. Gs AVE. Gs AVE. Gs AVE. Gs HELKET VELOCITY ACC. DEC. ACC. DEC. ACC. DEC. ACC. DEC. R TK5 9ft/sec 21 51 16 45 5 22 4 52 12 59 61 57 119 7 27 7 41 15 59 105 59 229 9 54 14 48 18 72 126 72 520 21 56 57 64 21 '97 182 96 448 24 45 65 114 REACH 9ft/sec 24 26 11 61 5 21 4 18 12 55 6O 21 145 7 52 5 20 15 58 118 44 267 19 42 6 45 18 82 175 71 579 27 58 50 152 21 111 229 98 451 54 85 65 225 HF 2104 9ft/sec 10 30 5 58 5 27 4 22 12 16 50 ll 94 6 56 5 5O 15 25 88 14 107 9 48 7 52 18 51 14 19 215 20 55 12 56 21 85 252 51 294 24 67 19 64 008H22.0am H<0HezmmH n '- camp: wEHADmZH 05.2.5 uvoam E... 02H8044 mangmzH mmmeamq m0mm qumaaHmv ZOHmzmmmam ma>z<0 188H5u4m20 0Hemqgm .028 m 02H002¢0 AMBHgomamv 0HemHBommhm MO memo ZH Dam/Hg memufimm JTd ‘.I¢.%J\Ci LII“: r. 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