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Appendix


the restraint function of a seat belt and can
seriously compromise the entire restraint system.

Third, and most important, there is a signifi-
cant difference between the complete restraint
system (shoulder harness and seat belts) and a
system restraining only with a seat belt. These
differences can be recognized easily by compar-
ing the head kinematic patterns in Figure 4
with those shown in Figures 5 through 12.

In conclusion, these tests have clearly demon-
strated and reaffirmed the fact that the protec-
tive function provided by a complete restraint
system is significantly superior to the incomplete
system restraining only with a seat belt. It is
the opinion of this investigator that restraint
selection criteria should not be based exclusively
on (1) a particular configuration simply because

it may present more desirable features or (2) a
superior configuration, which, in actual usage,
could result in a severely compromised restraint
function. Although some differences are indi-
cated in the restraining characteristics between
the eight tested systems, these differences for
certain specific applications may not impair the
primary function of achieving adequate body
restraint. Therefore, restraint selection should
result in a complete system that can best be ac-
commodated by the particular vehicle design to
assure a proper restraint function. Additional
studies of this type and other various experi-
mental designs should be undertaken to test
other restraint configurations and provide the
designer with more complete data to evaluate
design concepts.



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APPENDIX

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Appendix



AM 67-13

A FUNCTIONAL COMPARISON OF BASIC
RESTRAINT SYSTEMS

Joseph W. Young, A.M.

Approved by Released by
Blt Rte (USagel 10
J. Rosert Diniz, M.D. P. V. Smern, M.D.
Curer, Civ AEROMEDICAL Feperat Arr Surezon

InstiTuTe
June 1967

FEDERAL AVIATION ADMINISTRATION
Office of Aviation Medicine



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Appendix


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Appendix


appear in this report. The italicized words
above are used to designate attachment methods.

Type of
Figure Shoulder Methods of Attachment
Number Harness Upper End Lower End
5 Single diagonal Fixed Fixed
6 Single diagonal Fixed Continuous
7 Single diagonal Self-adjusting Fixed
8 Single diagonal Self-adjusting Continuous
9 Double parallel Fixed Fixed
10 Double parallel Fixed Continuous
nu Double parallel Self-adjusting Fixed
12 Double parallel Self-adjusting Continuous

In addition to this series of tests for complete
systems, three other tests were conducted using
a seat belt as the only restraint. For each test
the seat belt was attached along the platform
(floor) surface at points (1) intersecting a ver-
tically projected seat back plane (Figure 2), (2)
eight inches forward of the seat back plane
(Figure 1), and (3) twelve inches aft of the
seat back plane (Figure 3).

These tests were included to demonstrate the
significant differences in the effectiveness of re-
straining characteristics of different types of
seat belts. Their function is, in part, dependent
on the angle formed by the seat belt as deter-
mined by the location of its attachment points.

Facilities provided for these dynamic tests
included an indoor acceleration track and ve-
hicle. The vehicle platform had a surface area
4 feet wide and 1014 feet long, to which the seat
was secured for the dummy subject. The 180-
pound dummy subject had a sitting height of
38 inches, representative of the Air Force 95th
percentile. Recording instrumentation for the
tests included an electric timer to record plat-
form velocity prior to impact, platform and
dummy mounted accelerometers to record the
magnitude of deceleration loads, and high speed
photography (3000 frames/second) to record
the dummy kinematics. The velocities of the
acceleration platform prior to impact ranged
from 40.6 to 41.3 ft/sec for all tests.

II. Discussion and Conclusions.

In Figures 1 through 12 the patterns of head
kinematics are graphically recorded to relate
dimensionally the head-face position and orienta-
tion to a seat reference point. The numbers
along the figure grid lines, vertical and hori-

zontal, are in inches. The seat reference point
is established by the intersecting planes that
represent the inferior surface of the legs and
buttocks (sitting surface) and the posterior sur-
face of the dummy back.

Patterns shown in the figure illustrations rep-
resent a composite average of at least three
duplicate test runs for each restraint combina-
tion. Certain restraint systems in this test series
demonstrated, as expected, that significant dif-
ferences between kinematic patterns can result
in any system from variations in restraint-body-
seat relationships and restraint adjustments.
Examples of the undesirable “submarining” ac-
tion by the restrained subject were specifically
noted in those configurations (arrangements)
using (1) fixed upper and lower attachments
and (2) a fixed upper attachment with the lower
end continuous as a part of the seat belt. These
same configurations have, however, produced
“non-submarining” patterns (Figures 5, 9, and
6, 10) that may be considered as potentially
acceptable systems.

Although these variations do exist, some valid
generalizations concerning the restraining quali-
ties of the tested systems are offered for consid-
eration. First, it has been established that the
double parallel shoulder harness system, prop-
erly used, can provide a better restraint function
than the single diagonal system for at least two
reasons: (1) the distribution of applied loads to
two belts is greater than the same loads applied
to a single belt, therefore, less belt stretch results
in a greater restriction of forward movement,
and (2) certain combinations of omni-directional
forces have a tendency to cause a body torquing
action with a single diagonal restraint that may
result in a less efficient restraint function. In
all composite patterns the greatest restraining
function (considering both the vertical and hori-
zontal displacement) is achieved by the four
double parallel systems, although a single diago-
nal system in some. instances presents a better
restraint function in one direction.

Second, the relative position of a seat belt tie-
down which ultimately establishes the seat belt
angle, is a significant factor in achieving effec-
tive restraint. In Figures 1, 2, and 3 a compari-
son can be made to establish the fact that a
greater forward location of a tie-down decreases


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Appendix



A FUNCTIONAL COMPARISON OF BASIC RESTRAINT SYSTEMS

I, Introduction.

Concern for the inherent safety problems in
public and private transportation systems is
supported and well documented by the increas-
ing numbers and rate of serious injuries. Al-
though essential efforts have been and are being
made to study the nature of these problems, the
available information necessary to provide realis-
tic solutions for reducing personal injuries is
incomplete and inadequate.

It would appear unlikely, if not impossible,
to eliminate the cause of injury situations when
the primary contributing factors of the accident
are considered: human error and/or mechanical
failure. The problem of reduction or possible
elimination of personal injuries must then be
approached from the standpoint of providing
some means of effective protection for the occu-
pant throughout the duration of the accident
event. Realistically, any feasible solution to
these problems is a matter of selecting the best
available method to reduce at least the degree
of injury.

It is a well noted circumstance that, among
all possible types of injury occurring in poten-
tially survivable accidents, those most frequently
occurring result from the partially restrained
or wholly unrestrained occupant’s striking sur-
rounding structures. Potentially survivable ac-
cidents are defined as those occurring under con-
ditions in which the vehicle structure surround-
ing the occupant remains intact and human
tolerance levels are not exceeded. A great num-
ber of serious fatal injuries occur specifically
when upper body areas (head, neck and chest)
impact, or are penetrated by, rigid, uneven struc-
tural surfaces. These observations leave no
doubt that, in order to achieve the safest environ-
ment possible, the occupant must be adequately
restrained during accident impact, thus prevent-
ing or reducing the chances of interaction with
the structure.

It is the purpose of this study to define and
compare, in part, the functional (dynamic)
characteristics of basic restraint configurations

‘to assist further safety design efforts.

II. Methods.

Valid comparisons of the functional charac-
teristics of restraint systems necessarily involve
a comparison of each complete system (seat belt
and shoulder harness) assembled from all pos-
sible combinations and arrangements of com-
ponent parts and methods of attachment.

Two basic shoulder harness configurations
were selected for this study and are typical of
those now in use: the single diagonal belt and
the double parallel belts. A total of eight com-
plete restraint systems based on various combi-
nations of the two shoulder harness configura-
tions was used, with three primary methods of
harness attachments. Each system is identified
by the following criteria: (1) the harness con-
figuration, (2) upper harness attachment, (3)
lower end harness attachment. The upper at-
tachment methods include a direct fiwed (inde-
pendent) tie-down that is locked in place with
a snap ring, or, indirectly, as an integral part
of a self-adjusting inertia reel system. Lower
attachments were limited either to the fied tie-
down that was not functionally integrated with
a sea belt, or to the continuous, functioning part
of the seat belt. For single diagonal systems,
the lower end of the chest belt is continuous as
one half of the seat belt sliding freely through
a D-ring. Similarly, in the double parallel sys-
tem, both ends, threaded through dual D-rings,
unite to form the complete seat belt. Tests, in
which the occupant was restrained only by a
seat belt with typical seat attachments, were
conducted to provide a basic comparison.

The eight complete systems selected for test-
ing are listed below by figure numbers (all fig-
ures, 1 through 12, are in the Appendix) as they



ACKNOWLEDGEMENT

The personal assistance of John J. Swearingen and the technical support
of this laboratory is gratefully acknowledged. The author also wishes to
express his sincere appreciation to Sheila M. Mueller who, under a difficult
situation of arranging work schedules and timely deadlines, was responsible
for the design and production of these excellent illustrations.

Qualified requesters may obtain Aviation Medical Reports from Defense Documentation
Center. The general public may purchase from Clearinghouse for Federal Scientific and
Technical Information, U.S. Dept. of Commerce, Springfield, Va. 22151


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Appendix