450 - a “Tr

400

350

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|
i
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300

at

105,000 "g"/ sée- onset

g
ix)
°
°
T
i

T

150

100 }—~

: \

5 10 15 20 25
TIME IN MILLISECONDS

Fieure 3. Acceleration—time—force curve of head im-
pact necessary to duplicate fracture of pilot’s helmet.

heights. DeHaven describes falls of persons in
a supine attitude that struck yielding materials
(automobiles, metal ventilators, soil) in such a
manner as to distribute the force in time and
area. In some cases average impact forces of
150 g’s (Peak=300 g’s) were tolerated without
skull fracture, loss of consciousness or subsequent
evidence of concussion. Snyder’s studies involve
large numbers of fall cases and have shown that
man can tolerate much higher decelerative forces
without concussion or skull fracture.

(3) The only study known to the author in
which the cranium was almost completely pro-
tected from deformation during impact was done
by Higgins using small primates as subjects.

Caution must be used concerning the direct
transfer of results of animal experimentation in
the study of the effects of impact energy upon
the cerebral functions of man, as there are marked
differences in the relative distribution of mass
and in the shape, size, and thickness of the two
skulls. Higgins potted the heads of his small
primates in metal helmets using plaster of Paris
to almost totally eliminate skull deformation
during head impact. However, he, like Lombard,
fixed the body, and the head impacts accelerated
the head away from the trunk. Even under
these conditions, the subjects tolerated head ac-
celerations of 1.11 to 1.91 x 10° radians/sec.?
without gross evidence of damage. Only one
suffered concussion with an acceleration of
1.56 x 10° radians/sec.2, In terms of g’s, the
author has calculated these accelerations to range
from 361 to 622 g’s.

II. Conclusions.

While thousands of research studies have been
conducted relative to the subject of human con-
cussion, only a few made any attempt to limit
the deformation of the skull. However, these
few indicate strongly that the human can with-
stand crash impact forces of 300 to 400 g’s mag-
nitude and possibly greater without concussion
or skull fracture provided provisions are made
to eliminate skull deformation.

This, in conjunction with the author’s work
concerning facial tolerances, indicates that all
lacerations and fractures of the face and cranium,
as well as concussion and more severe brain in-
jury, can be prevented during head impacts with
forces up to 300 or 400 g’s by engineering design
to distribute force in 77ME and ARPA.

Stated in more meaningful terminology, it ap-
pears that it is possible for the human head to
tolerate a deceleration from 100 ft./sec. velocity
to a complete stop in six inches of travel without
lacerations or fractures of the face or cranium
and without concussion, unconsciousness, or se-
vere brain injury. However, in view of the
limited data used in this report, experiments
should be conducted to verify the conclusions
indicated in this study.



ten showed liner deflections indicative of head
accelerations well over 200G, and three reached
values of 450G or more.” All drivers survived
and detectable neurologic residuals were not
noted. Only four men suffered temporary loss
of consciousness and of these, three were aboye
the 200 g’s level and one was below. Of interest
to note, the one suffering concussion under 200 g’s
had a history of serious head injuries during
World War II. In his summary Snively states
“Survival limits of localized head acceleration
of brief duration in man have been shown to
exceed 450 g’s.”

The author’s small contribution to this field of
knowledge bears out Snively’s work. A  heli-
copter pilot crashed at Fort Sill, Oklahoma, and
was thrown forward and slightly to the right
over his seat belt (no shoulder harness). His
head and helmet struck a solid blow against the
upper left corner of the instrument panel (Figure
1) with sufficient force to fracture his helmet
(Figure 2). Identical helmets and instrument

Fiaure 1. Photograph of helicopter instrument panel.
Corner impacted by pilot’s head is indicated.

panels were obtained from Fort Sill and attempts
were made to duplicate the fractured helmet
utilizing an instrumented dummy head. Figure
3 is an oscillograph tracing of a head impact
with sufficient force to produce a helmet fracture
similar to that shown in Figure 2. It will be

Fieure 2. Photograph of pilot's helmet showing frac-
ture pattern.

noted that the major decelerative force was a
triangular pulse with a 435-g peak, a 5 milli-
seconds duration, and a rate of onset of slightly
over 105,000 g’s/sec. The pilot, in this case
study, did. not suffer a concussion or loss of
consciousness. Rawlins states from his studies
that the upper limit for rate of onset is 200,000
g’s/sec.

While it has been shown that use of a protec-
tive head gear can protect the human head and
brain from extremely high impact forces, their
protection is limited by the short decelerative
distance afforded by the thin helmet liner and
the fracture or deformation forces of the outer
shell when striking sharp corners, ridges, knobs,
etc. In addition, only very small select popula-
tions will submit to the use of protective head

are

(2) Most of the traveling population can
better be protected from head injury and/or
concussion through the use of materials and engi-
neering design of the cabin environment to
distribute forces evenly over large areas of the
head and provide proper yield characteristics to
lengthen the deceleration time interval.

The extent to which these designs could yield
dividends is well illustrated in the early studies
of DeHaven" and later by Snyder* of persons
surviving impacts after falls from extreme


e

a

. Denny-Brown, D.:

REFERENCES

Swearingen, John J.: Tolerances of the Human Face
to Crash Impact. FAA Office of Aviation Medicine
Report No. AM 65-20, 1965.

Cerebral Concussion,
IOLOGICAL REVIEW 25 :321-325, 1945.
Protection Inc.: A Bibliography on Head and Brain
Injuries, Report No. N1-R1, Bureau of Aeronautics,
Dept. of the Navy, Jan. 28, 1956.

PHYS-

. Walker, A, Earl, M.D., Jerry J. Kollros, Ph.D., and

‘Theodore J. Case, M.D.: The Physiological Basis of
Concussion, J. NEUROSURG. 1(2) :103-116.

. Gurdjian, E. 8S. M.D. and H. R. Lissner, B.S., M.S.:

Mechanism of Head Injury as Studied by the
Cathode Ray Oscilloscope (preliminary report),
J. NEUROSURG. 1(6) :393-399, Nov. 1944.

. Gurdjian, E. S, M.D., J. E. Webster, M.D., and

H. R. Lissner, B.S., M.S.: Symposium on Head In-
juries, and: Mechanism of Scalp and Skull Injuries,
Concussion, Contusion and Laceration, J. NEURO-
SURG, 15(2) :125-135, Mar. 1958.

. Gross, Arthur, B.S.: A New Theory on the Dynamics

of Brain Concussion and Brain Injury, J. NEURO-
SURG. 15(5) :548-561, Sept. 1958.

. Gurdjian, E. S, M.D. H. R. Lissner, M.S. and

L. M. Patrick, M.S.: Protection of the Head and
Neck in Sports, J. AMER. MED. ASSN. 182 :509-512,
Nov. 3, 1962.

9. Oelker, C. E., F. H. Primiano, and H. C. Wooding,
Jr.: The Investigation of the Parameters of Head
Injury Related to Acceleration and Deceleration,
Technology Incorporated Annual Report No. TI 2610-
66-4, 1966.

10. Lombard, C. F., et. al.: Voluntary Tolerance of the
Human to Impact Acceleration of the Head, J.
AVIATION MED. 22(2), April 1951.

11. Snively, George G, M.D. and ©. 0. Chichester,
Ph.D.: Impact Survival Levels of Head Acceleration
in Man, AEROSPACE MED. 32(4) :316-320, April
1961.

12. Rawlins, J. S. P.: Design of Crash Helmets, THE
LANCET, 719-724, Oct. 1956.

13, DeHaven, H.: Mechanical Analysis of Survival in
Falls from Heights of Fifty to One Hundred and
Fifty Feet, WAR MED. 2, July 1942.

14. Snyder, Richard G., Ph.D.: Human Survivability of
Extreme Impacts in Free-Fall, FAA Office of Avia-
tion Medicine Report No. AM 63-15, Aug. 1963.

15. Higgins, Lawrence S. and Robert A. Schmall: A
Device for the Investigation of Head Injury Effected
by Non-Deforming Head Acceleration, CONF. PROC.
OF THE ELEVENTH STAPP CAR CRASH CONF.
35-46, Oct. 1967.


TECHNICAL REPORT STANDARD TITLE PAGE

T. Report No. 2. Government Accession No. 3. Recipient's Catalog No.
FAA-AM-71-13

@. Title and Subtitle 5, Report Date
TOLERANCES OF THE HUMAN BRAIN TO CONCUSSION March 1971

%. Performing Organization Code

7. Authors) 8. Performing Organization Report No.

John J, Swearingen, D.Av.T.

9. Performing Organization Name and Address 10. Work Unit No.
Civil Aeromedical Institute
P. 0. Box 25082 TT. Contract or Grant No.

Oklahoma City, Oklahoma 73125

13. Type of Report and Period Covered

12. Sponsoring Agency Name ond Address
Office of Aviation Medicine
Federal Aviation Administration OAM Report
800 Independence Avenue, S.W. 14. Sponsoring Agency Code
Washington, D.C. 20590

15. Supplementary Notes

Research performed leading to preparation of this report was done under
Tasks AM-A-69-PRS-37, AM-A-70-PRS-37, and AM-A-71-PRS-37.

16. Abstract

This report reviews the pertinent literature and adds additional evidence
indicating that the human brain may be able to tolerate head impact forces
in the range of 300 to 400 g's without evidence of concussion or other
detectable neurologic sequelae, provided that provisions are made to prevent
deformation of the cranium.

17. Key Words 18. Distribution Statement
Availability is unlimited. Document may

Head, Impact Shock, Crash Injury, be released to the National Technical

Tolerances Information Service, Springfield,
Virginia 22151, for sale to the public.
19. Security Classif. (of this report) 20. Security Classif. (of this page) Zi. No, of Pages | 22, Price
Unclassified Unclassified 4 $3.00

Form DOT F 1700.7 (e-69)







TOLERANCES OF THE HUMAN BRAIN TO CONCESSION

I. Introduction.

A report! published in 1965 showed conclu-
sively that the human face and frontal area of
the cranium can withstand crash impact forces
in excess of 300 g’s without lacerations or frac-
tures, provided that the structure impacted has
been properly designed to distribute loads over
large contour areas of the head and has adequate
yield characteristics. Accepting the data given
in this report as fact, the question of brain
trauma during such severe impacts arises. It is
the purpose of this report to review the pertinent
literature and to add some additional test data
to attempt to answer this question.

A complete review of all the literature con-
cerned with studies of concussion is beyond the
scope of this paper. The most extensive standard
literature review was written by Denny-Brown
in 1945.2 Since then, a bibliography by Gross*
published in 1955 lists over 1000 separate research
studies in this area and there have probably been
as many more in the past 15 years. However,
by far the largest portion of this research in-
volved studies of hammer blows or similar im-
pacts on the heads of various animals or cadavers
in which the cranium of the test subject was
allowed to deform. Numerous authors*® have
expressed the opinion that concussion, contrecoup,
and more serious brain injuries are a direct re-
sult of skull deformation with or without frac-
ture.

On the other hand, Oelker® proposed in 1966
that, due to the suspension of the brain in a fluid
having approximately the same specific gravity
of the brain, it is improbable that any significant
relative motion between brain and skull can be
obtained for purely translational accelerations
in which the skull is not deformed.

It is the purpose of this report to discuss these
few studies of human tolerance to concussive
forces in head impact situations where skull
deformation is prevented or largely reduced.

IL. Discussion.

In general, three separate areas of research
indicate that concussion and brain injury may
be prevented or significantly reduced if the skull
is not allowed to deform during head impact.
Studies of (1) helmet protection, (2) survival
in fall cases, and (3) tolerances of the brain to
head impacts with the cranium embedded in a
cast are presented in the following discussion.

(1) Helmets of numerous designs have been
worn by military personnel, motorcycle riders,
race drivers, football players, and others. While
the details of construction vary, most of them
consist of an outer rigid shell to prevent pene-
tration and distribute the force over a larger
area, and a crushable liner to better distribute
the force over the shape of the head and to
slightly lengthen the deceleration time during
the crush phase of the liner. Lombard*® and his
co-workers voluntarily tolerated 38-g frontal
impacts while wearing helmets without any indi-
cation of concussions. He states that he was sure
the human head could tolerate much higher im-
pact forces and that the tests were stopped be-
cause of local bruising, tension loads on the liga-
ments or ligamental attachments of the neck
muscles, or sharp burning pains in the joints of
the cervical vertebrae. In these tests the subject
sat in a chair and the head, covered with a
helmet, was struck by a 13-pound weight on a
pendulum. This technique accelerated the head,
but not the trunk, and would not be the same as
if the head and trunk were both in motion.

An empirical study by Snively" in 1961 of
helmeted racing drivers involved in crash de-
celerations provides more realistic data concern-
ing brain tolerances provided against impact
forces by utilizing crash helmets. His technique
was to duplicate the depression of the «helmet
liners of ten race drivers involved in crashes.
Crash impact force readings during the duplica-
tion testing with an instrumented dummy head
ranged from 115 to over 450 g’s. “Six of the