‘ized
a time
e sub VERTICAL RECTANGULAR

fe the

VERTICAL

Aby ACCELEROMETER
me prop ~\ HORIZONTAL “ y,
‘ig. 2). Va CONTACT.
t alu-

ona he ite
zontal CONTACT
ly 1g)
ements

inimal

, the HORIZONTAL
ractice /, ‘ACCEROMETER
ae Ga
des of ¥# : DISPLACEMENT
ote, at ] sonract
of the
sec., as
tical ac- |

Ficure 2.

Figures 3 and 4 present the 5th and 95th

, percentiles of the recorded paths of the tops of
the heads as the subjects were accelerated for-
ward and to the side over a tight safety belt.
In addition, overhead arm reach (as taken from
White® and buttocks heel measurements from
Snyder’) are superimposed with predicted paths
of motion of the arms and legs during cyash
decelerations. These curves show that the flail-
ing envelope for a singlé individual restrained
by a seat belt is a sphere nearly#10 feet in di-
ameter. Since it was found necessary to use
body measurements from four different Ko

of subjects, Table I is presented’ to permit coni-
parison of anthropometric sitting heights/of
these groups with the large Air Force sample

measured by Randall.‘
ry Tams 1’ ‘ :
2 FAA 100 in FAA 100 in
Randall White’ Snyder? Fwd. Test Side Test
= oh 88S ar Ey ete aaa |

. 3



SUMMARY

The study of motion of a human body re-
strained only by a safety belt is presented and
is briefly described as the area within the
upper two-thirds of a sphere 10 feet in
diameter.

Application of body clearance curves—devel-
oped in the study—to present aircraft seating
arrangements shows that the entire interior of
most aircraft—large or small—can be reached

one or more parts of the flailing body.

It is suggested that there is needless injury
and loss of life from impact with rigid struc-
tures in cabin/cockpit environments and in cur-
rent seats, which can be eliminated by im-
proved seat design incorporating delethaliza-
tion, especially in seat arms, seat-backs, and
rigid structures in and under the seat-back.

Current seat tie-down requirements are in-
adequate, especially in the vertical direction;
the 2 g (upward) requirement, based only on
the weight of the seat and its occupants, gives
a vertical tie-down strength of something under
1,000 pounds. It is.shown in this report that
the lifting force of the four legs of the passen-
gers seated behind the seat in question may be
expected to exceed this tie-down strength by a
factor of 2 to 5 before fracturing. In dynamic
seat testing, consideration should be given to
strike loads imposed on the rear of the seats.

In considering leg strike loads, the practice
of storing brief cases and small suit cases wader
the seat should be viewed with'suspicion, ‘since
these objects can slide forward against the
backs of the passenger's legs, fncreasing the
force of leg impact ‘against the, seat, and pos-
sibly entrapping the feet under the seat,

ACKNOWLEDGMENTS

The authors wish to express their apprecia-
tion for the assistance of other members of the
CARI staff, especially J. G. Blethrow, J. D.
Gamer, M. V. Head, and William Reed, for
their generous assistance ‘in this project. Grate-
ful acknowledgment is also given for the assist-
ance provided by Dr. Colin A, Plint, Depart-
ment of Physics, University of Oklahoma, and
Mr. John C. Earley, Aeronautical Engineer,
Buffalo, New York, in their analyses of impact
forces presented in the latter part of this paper.

REFERENCES

1. DeHaven, H. The site, frequency and dan-
gerousness of injury sustained by 800 sur-
vivors of light plane accidents. Department
of Public Health and Preventive Medicine,
Cornell University Medical College, July
1952.

2. Hasbrook, A. H. Severity of injury in light
plane accidents. Jan. 15, 1960. Space Aero-
nautics, Sept. 1960.

3. Marrow, D, J. Analysis of injuries of 1942
persons in 1422 light plane accidents. Un-
published data, CAA Medical Service Re-
cords, Washington, D. C., 1949.

4. Randall, F. E., A. Damon, R. S. Benton and
D. I. Patt. Human body size in military
aircraft and personal equipment. Army
Air Forces Air Materiel Command, Wright
Field, Ohio, Technical Report 5501.

5. Snyder, R. G. Anthropometric measure-
ments of 400 air traffic control operators.
Unpublished data, CARI, Oklahoma City,
Oklahoma. |

6. White, R. M. Anthropometric measurements
of 500 army aviators. Unpublished data,
Quartermaster Research and Development
Center, Natick, Massachusetts.



but data on

injuries causing death were not presented be-
cause reliable autopsy data are rarely obtainable
in instances where civilians are fatally injured.
However, due to the large number of head and
chest injuries among the survivors, death was
probably associated most frequently with in-
juries to these body areas. This is substanti-
ated by Marrow’s report,’ in which head and
chest injuries accounted for 337 of 342
fatalities.

x

Ficure 6. 2

The pattern of fatal and non-fatal injuries
in commercial transport crashes closely parallels
that presented herein for the private pilot.
There is one notable post-crash difference; un-
conscious and incapacitated passengers in com-
mercial transport accidents are often trapped
and die in the smoke, fumes and fire that follow
the crash—light aircraft seldom burn.

When the flailing curves are applied to pre-
sent day commercial transport seating arrange-
ments (Fig. 8, 9, 10), it becomes obvious that,
because of the overlap of body movements and
the extensive arc necessary to protect even one
individual, almost every square inch in the
cabin is covered by the combined body move-
ments of all the passengers; therefore, all rigid
objects and structures within the cabin may be
considered as having a lethal potential. Since
the sphere in which an individual should be
protected from injury is nearly 10 feet in di-
ameter, it would be necessary to limit even our
largest jet transports to one row of seats down
the middle, spaced five feet apart, in order to
offer adequate protection without delethaliza-
tion, Such spacing is obviously impractical.
Therefore, efforts to increase crash survival
must be aimed at (a) delethalization to main-
tain impact forces below human tolerance levels
and (b) improved seat anchorages to insure
that seats remain in place until the cabin
disintegrates.

+>

Fioure 8. 3



SADC A RR RG ER

BODY MOTIONS RELATED TO AIRCRAFT

To determine aircraft structures that are in
the path of the flailing body, the 95th percentile
curves of the subjects were superimposed on
scale drawings of aircraft seating and cockpit
arrangements, Since the head clearance curves
were established with -the safety belt adjusted
as tightly as possible during the tests, delethali-
zing the areas within the curves would provide
protection for those persons in the upper per-
centiles with tight belts, and would allow cei
tain degrees of freedom for these in the lows
percentiles wearing the belt loosely adjusted.

Figure 5 shows the 95th percentilé forward
body clearance curves superimposed on a scale.
drawing conglomerate of a number of late

model light aircraft. Since the head and torso *

are the usual sites of fatal lesion, the area with-
in the head clearance curve may be considered
the lethal area and the additional area swept
over: by the arms and legs might be classified
“as the “incapacitating” area.

Figure 5. |

Figure 6 relates the lateral body clearance
curves to a scale drawing of one of the largest
personal type aircraft. Examination of
Figures 5 and 6 discloses that almost all of the
interior of the aircraft is within the lethal curve
area.

The only body areas that are reasonably pro-
tected from structure are within ten to twelve
inches of the seat belt. Studying the statistics
of injuties in survivable light plane accidents,
it is not surprising to find that the number of
injuries increases with increased distance from
the seat belt. Figure 7 displays the pattern of
injury of*800 survivors of light aircraft acci-
dents, as reported by DeHaven’; this appears

_ to correlate well with the incidence of severe

and fatal injury shown in the more recent study
of 913 light plane accidents studied by Has-
brook.’ A large number of injuries to the head,
upper trunk, and lower one-third of the extremi-
ties is shown in DeHaven’s study, as demon-
strated in Figure 7. A number of fatalities oc-
curred in this group of accidents, but data on

-4—

inj
cat
in:
Ho
che
pro
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ate:
che
fate

ee


in some
may also

ct velocity
ft./sec., in
perience a

the weight of the seat itself, due to lack of
readily available, precise data on weights and
centers of gravity of passenger seats of current
design.

Assuming that the head and lower leg can
deliver blows equal to 200-300 g, the floor loads
experienced under seat No. 1 increased appre-
ciably as a result of the impact of the heads
and legs of the occupants of seat No. 2, as in-
dicated by the reactions shown parenthetically
in Figure 11,

NOTE: ecard
rey
‘open Oot wt

ekpecstet

37088,

wade 18800 gaan aad,

eae,

THEORETICAL SEAT LOAD ANALYS#

Ficure 11.

For example, the total vertical tension load
on the two back legs of seat No. 1 was in-
creased from 4,600 to 13,664 pounds By the
impacts of the occupants ik seat No, 2. In
other words, over two-thirds of the total force
acting to pull the back legs of the seat out of
the floor is imposed on the seat by the passen-
gers in the next seat behind; yet in present day
seat testing, only the loads imposed by the Seat
and its occupants are considered, , a
so-called 12 g seat is probably net good for
more than 3 g (horizontally) under the con-
ditions cited above.

e

+

The deceleration factors of 285 g for the head
and 218 g for the legs are based on a 1-inch
deceleration distance during head-seat-back im-
pact, and %-inch deceleration distance for the
legs against the rigid lower cross member in
the basic seat frame. While it is known from
studies of individuals falling from high build-
ings that the human head and legs can, (if
properly supported), sustain such high decel-
erations without fracture, one would expect
that forces less than those demonstrated here
theoretically would result in fractures of these
body parts due to striking the rigid tubular
structures of present day seats. Preliminary
results of a current study being conducted in
our laboratories to determine the fracture forces
of the lower leg during dynamic load applica-
tion indicate that the tibia fails at approximately
100 g when impacted against a cylindrical
structure one inch in diameter. Since the
weight of the lower leg and shoe varies from
7 pounds, for a 100-pound woman, to 15 pounds
for a 200-pound man, each leg can be expected
to exert an impact force of between 700 and
1,400 pounds for a total of between 2,800 and
5,600 pounds for four legs.

Delethalization, based only on spreading
head and leg impact loads over larger areas—
without use of energy dissipating materials or
devices—will substantially increase these loads
on the seat due to prevention of leg fracture at
the above mentioned loads.

In any event, as shown here, a seat designed
to resist horizontal and vertical decelerations of
12 g and 6 g respectively could be severely
overloaded by as much as an average of 291
per cent when struck by the occupants of the
seat directly behind, in the crash landing con-
ditiohs cited above. This would indicate,
therefore, that currently accepted testing pro-
cedures—as well as. seat design parameters—do
not provide a realistic approach to crash-
worthy* seat design, and that consideration
should be given, to these “strike” loads imposed
on the rear of the seat.

’ fe A
‘ "4

\





=>

cleerenee

Ficune 10. '. </

FORCES OF BODY IMPACT '

In studying the range of possible body move-,
ment in transport seating environments during
euish decelerations, it becomes obvious that a
passenger restrained only by a seat belt in a
forward facing seat will strike the seat directly

‘ahead. Impact of head, upper torso, arms and
legs against a seat must tesult in some force

a a nl

being imposed on that seat, If the “strike”
loads imposed by the Occupant on the seat
ahead are of high magnitude, it is possible that
these forces may be responsible for seat-anchor-
age-floor failure in accidents in which the air-
craft deceleration imposes loads that are well
below design load requirements. Current de-
sign requirements are based on tests which
consider .anly the’weight of the seats and oc-
cupants. This may explain to some degree
why seat tie-down failure has been observed to
occur in apparently haphazard patterns in some
survivable transport accidents. It may also
provide an answer to why the rear-most row
of occupied seats sometimes remains secured to
the floor while the occupied seats ahead break
free—such as occurred in a Convair 240 accident
at Springfield, Missouri, and in the Boston and
LaGuardia Electra accidents, Hence, it would
seem desirable to determine the magnitude of
these body impacts,

An evaluation was made of the possible ef-
fects of body strike loads, in a hypothetical
crash landing condition, in which the opera-
tional flight parameters, as well as the decelera-
tions acting on the aircraft were considered to
be within realistic proportions—as related to
current turbo-jet transport operation.

The crash landing condition chosen assumes
an early “flare out” in which the aircraft's rate
of descent increases rapidly, resulting in failure
of the landing gear and application of reason-
ably “heavy” crash loads to the belly structure.
The aircraft, with a horizontal impact velocity
of 172 ft./sec., decelerating to 106 ft./sec., in
about 24 feet in .17 second, would experience a
12 g horizontal deceleration; assuming a 33 ft./
sec. vertical velocity and 2.8 feet crumpling of
the belly structure during the same interval,
the aircraft would sustain a 6 g vertical
deceleration.

Evidence indicates that these decelerations
(12 g horizontal and 6 g vertical) are represen-
tative of the worst conditions which most of the
latest domestic passenger seats can be expected
to resist without failure.

‘ Figure 11 shows that the loads which dould
be applied to seat No. 1 by its occupants were
computed to be 3,708 pounds horizontal force,
6,448 pounds compression on the front legs of
the seat and 4,600 pounds tension on the rear
leg attachménts. These computations exclude

ol
cr

ot
ac

ge
se
an
so-
me

dit


FLAILING AREAS

To investigate the three-dimensional envelope
within which the body is free to move during
actual crash impacts, simulated tests were con-
ducted, in which one hundred male subjects
were accelerated forward and to the side over
a two-inch safety belt by a weight-dropping
mechanism. The orbits of motion of the body
were recorded with reference to the midpoint
of the line of intersection of the back cushion
and undepressed seat cushion (which served as
the reference point). The reference point was
intentionally located on the undepressed seat
to facilitate measurement to lethal structures
while the seat was unoccupied, The results
presented here are for subjects sitting on a
cushion depressed two inches below the refer-
ence point before the test and 3 inches during
the deceleration. These curves should be ad-
justed to the depression depth of other seat
cushions which may be used.

Two suitable techniques were developed for
recording the very rapid body motions whose
duration was approximately 0.5 second. The
photographic technique shown in Figure 1

,

- utilized a crude focal plane shutter consisting

of two opaque window blinds synchronized
with the falling weights and with a camera time
exposure of 0.5 second to photograph the sub-
ject’s shadow on the screen. To eliminate the
tediousness of reading shadowgrams from 4 by
5 inch negatives, a direct recording electrical
contact technique was also developed (Fig. 2).
The electrical contacts on the very light alu-
minum framework activated writing pens on a
moving tape to record vertical and horizontal
displacement of the subject.

Because of the low force (approximately 1.g)
used to displace the body, the measurements
presented here must be considered as minimal
“strike” distances. In a crash situation, the
greater forces involved—as well as the practice
of passengers to wear their lap belts more
loosely adjusted than the standard required for
these tests—will permit larger magnitudes of
body movement. It is interesting to note, at
this point, that the tangential velocity of the
head during these tests exceeded 12 ft./sec., as
calculated from the horizontal and vertical ac-
celerometers shown in Figure 2.

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KINEMATIC BEHAVIOR OF THE HUMAN BODY
DURING DECELERATION

J. J. SWEARINGEN, MS., A. H. HASBROOK, R. G. SNYDER, PH.D., and
E. B. McFADDEN, M.S.

ABSTRACT

The geometry of motion of the head, trunk and appendages was established for one
hundred male subjects restrained by a safety belt during forward and side dynamic loadings.

Lethal structures of present aircraft

seating and cockpit arrangements are revealed by cor-

relating crash injuries with these kinematic data. In addition an analysis of the forces created
by body Kinematics during forward deceleration sheds new light on seat anchorage problems.

INTRODUCTION

For the past twenty years, dedicated re-
search men have subjected themselves to
deceleration tests, often suffering extreme dis-
comforts and irreparable injuries in the process.
Hundreds of animals have been sacrificed and
millions of dollars spent in research to deter-
mine human tolerance to deceleratiox. Some
scientists have concentrated their efforts in at-
tempts to determine the forces necessary to
fracture cadaver skulls, vertefrae, or other bony
structures, or to investigate the forces and
mechanisms of btain concussion. Othersjhave
searched for means of preventing injyty by

delethalization of structural componghts, or .

studied injuries and human tolerance’ in acci-
dental falls and suicide leaps; still others have
investigated body measurement relationships,
pnd so on, infinitum. The monumental body
of data resulting from these research programs
— published in Rundreds of scientific reports —
consistently underlines one important fact con-
cerning human impact. survival; the human
‘body can tolerate unbelievable g forces while

-1-

striking relatively large flat surfaces that can
absorb energy by giving a few inches, but it
is more fragile than china when impaled
against narrow rigid tubes, protruding knobs,
sharp edges and angles.

In order to obtain an appreciation of the
average “habitat” of the aircraft occupant in
small planes and transports, a study was initi-
ated by the Protection and Survival Branch of
the Federal Aviation Agency’s Civil Aero-
medical Research Institute.

It is the purpose of this paper to describe the
results of this: study by (1) presenting a de-
tailed description of the areas which may be
traversed by the human head, trunk, and ap-
pendages during flailing motions in crashes
with safety belt restraint only, (2) relating
present aircraft cockpit and seating arrange-
ments with these areas of motion, (3) present-
ing an analysis of aircraft injuries, and finally
(4) discussing some of the body impact forces
which may be involved in a typical survivable
transport ¢rash,


KINEMATIC BEHAVIOR OF THE HUMAN BODY
DURING DECELERATION

J. J. SWEARINGEN, M.S., A. H. HASBROOK, R. G. SNYDER, Ph.D.,
and E. B. McCFADDEN, M.S.

62-13

‘

FEDERAL AVIATION AGENCY |; ,
? AVIATION MEDICAL SERVICE:
AEROMEDICAL RESEARCH DIVISION!
CIVIL AEROMEDICAL RESEARCH INSTITUTE
PROTECTION AND SURVIVAL BRANCH
OKLAHOMA CITY, OKLAHOMA |

JUNE 1962