TeActEG

SAMPLE GBCILLOGRAPE

Freure 3. Sample oscillograph tracing.

PROJECTED AREAS OF HUMAN SUBJECTS

Ficure 4. Projected areas of human subjects.


In any event it should not be inferred from
the above results that forces on the body due
to air movement can be readily calculated from
the DTMB data for all practical situations. Ac-
tually, such calculations only apply accurately
to conditions of uniform airspeed in a rela-
tively unconfined space. In such practical
situations as are discussed in this report in
connection with airplane decompression, it can-
not necessarily be assumed that such condi-
tions are approached. An extreme example of
a situation in which these calculations could
not be used would be the case where an open-
ing was completely occluded by a person. In
this case, the force on the body would be esti-
mated by multiplying static pressure by the
area of the body involved, However, except
for such an extreme case, the DTMB data can
be used to make order-of-magnitude estimates
which are helpful, for example, in designing
experiments to measure directly the magnitude
of force that air movement exerts on man in
particular situations.

APPENDIX

Calculation of Airloads on Man Standing Near
A Door During Decompression Due to Door
Failure

The values needed for calculating drag force
frdm the equation, D= (vH/S) x C. xq are
given below:

vi
—=071
rs 0.7

C= 11 (from the DTMB report)

NOTE: This is the value for a clothed indivi-
dual facing the door.

To obtain q, an estimate must be made of
the airspeed at the point where the subject
stood. The velocity at the door may be taken
as 886 ft/sec according to a previous estimate
for a pressure differential of 6.5 1b/in® (see
test). The effective cross-sectional area where

the subject stood can be taken as a first ap-
proximation to be equal to the width of the
door (37 in.) X the height of the chamber
(96 in.) or 3352 in. plus twice the length of a
quarter circle 30 in. in radius < the height of
the chamber or 9043 in*, which gives a total of
12,595 in? A 30 in. radius instead of a 24 in.
radius (the dista...: setween the frontal plane
of the subject and the door) is taken to allow
for the thickness of the body. In this approxi-
mation, the two quarters of the cylindrical sur-
face are visualized as being positioned at the
two sides of the door. The area of the doorway
is 2886 in* or 0.23 of the effective area, which
gives an estimated airspeed at this point of
0.23 x 886 or 204 ft/sec, and a q value of
47 1b/ft.

Substituting these values, we have

D=G71 X 11 X 47 = 367 1b

This value is considerably greater than the
166-174 1b (Table II) force found necessary
to displace a person standing with his back to
the wind. The explanation of this discrepancy
presumably is that the duration of airload in the
experiments facing the door was shorter than
the duration of airloads in which the forces
causing body displacement were measured. As
suggested in the text, considerable judgment
must be used in applying to a given situation
experimental data obtained under other condi-
tions, or in using drag coefficients to calcu-
late reliable estimates of forces.

REFERENCES

1. Swearingen, J. J., Protection of Passengers
and Air Crew from Air Blast Effects of Ex-
plosive Decompression. Report No. 1, Civil
Aeronautics Medical Research Laboratory, Pro-
ject No. 50-516, August 1950.

2. Schmitt, T. J., Wind Tunnel Investigations
of Air Loads on Human Beings. Report 892,
Aero 858, Navy Department, The David W.
Taylor Model Basin Aerodynamics Laboratory,
Washington 7, D.C., January 1954.

—8—

BS GOVERNMENT PRINTING OFFICE 1964 0—732-437


carriage mount, one end of which was linked
to a heavy steel spring to which strain gauges
were affixed for measurement of forces (Fig. 2).
Table I summarized the averages of five to
eight trials on each of five experimental
subjects. Eleven different body positions were
tested. It was expected that the forces acting
on the body would vary between subjects and
would be roughly related to body sizes,

The column “Projected Body Area” of Table
I represents the area of the silhouette of each
subject in each position assumed.

Measurements were also made of the forces
acting on a series of flat plates of various sizes
placed in the wind tunnel on the human subject
carriage. These are shown graphically in Fig. 5.
The third column of figures in Table I repre-
sents the flat plate area equivalent of the
force measured on the human subject. The
last column of Table I represents the ratio of
the equivalent flat plate area to the projected
area of the body.

290

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130

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POUNDS FORCE

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Figure 5.

Flat plate resistance to wind blast (33 cm

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AREA WN SO, FEET

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Taste If.
Summary of Force Data Obtained in Wind Blast Study (Phase 2).

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TABLE I.
Wind Blast Forces on the Human Body (Phase 1).

force (in Projected Equivalent
Body Fosition Subject lbs) average Body Area Flat Plate RE/aP
5.8 trials (Sq. Ft.) Area(Sq.Ft.)
s 177.3 6.38 4.35
i: “ 217.0 Tbk 5.23
see ee & 6.08 4.68
i blast 3 6.08 4.63
c 6.97 §.02
Ay, 6.59 4.88
[ seandine | s 6.38 £3 BB
x Tohd 4.93 :
Standing a 6.08 a5 4
blast 8B 6.08 4.35 +72
c 6.97 4678 .
av. 6.59 4,60
s 3.38 2.08 64
Standing y 4.63 2.83 61
side to rN 3.92 2.70 oa
3 B 3.9 2.65 .
Blase © isa 2.92 265
ay. 4.18 271
s 3.00 +70
Sitting * 3.23 265
back to a 2.88 69
blast. 8 351 282
& 3.49 75
av. 96.5 3.22
{ s 84.2 42? 2.97 +70
Sitting [——H 4 OH 107.8 49, 3.53 7
face to F— 2th 4 90.2 4619 3.13 +75
f—F_4 8 90.0 2.27 3.22 +B
pos jc 105.0 4.63 3.48 5
=v av, 95.4 hth 3.24
f —————]_ s 72.0 4,02 2.63 -65
... —- =e * 77.6 4.77 2.79 +58
Sitting Fy 8 84.6 3.83 2.42 63
side to F——~ Wi doa 7.2 3.92 2.75 :70
ble Fo oc 76.0 4.33 2.7% 63
i -—- 3 Av. 73.2 Al? 2.66
8 42.6 3.50 2.88 +54
. x 50. 3.88 1.98 51
ed —d a 45.6 2152 Lei v72
blast _——, a B 50.6 2.72 2.98 +73
c 53.8 3.61 2.08 258
av. 49.6 3.25 2.94
s ear 3.50 2.40 69
vei M102. 3.88 3.42 388
fete Qs 33.8 2.52 2.08 83
blast -—~ > yjoB . 2.72 x 2.02
}—— a Sg 72.8 3.6L 2.65 273
- ay. 73.9 3.25 2u
s 62.2 3.61 2.35 65
x 84.6 4.47 2.98 67
a TB 3.54 2.72 .
B 78.4 4.05 2.82 +78
c 7b 4.92 2.76 Ao)
ay. 369% R72
a 3:32 a %
j 3.52 La 50
Saugtedn =r a 3 2.45 1157 %6e
blat, aa 8 48 2.90 1.68 58
© 53.4 3.43 2.07 a
L av. 43.2 3.03 L72
$ 43-2 1.37 1073 2.26
A S 2.02 2.13 1,06
mre, Pose] 4 45.2 Lez iro las
Kees B 44.6 Lak Lv 1.23
c 55.2 1.72 2.13 1.24
av. 48.6 2.55 1.02



The drag coefficients (C,) which sre of more
immediate appl’cation to the purpose of the
present report are given in terms of the body
parameter vH/S which was selected from five
trial parameters as giving the least variation
in drag coefficients (v = volume of the body in
ft’; H = height in ft; S = body surface area in
ft’). The values of this parameter for the 16
subjects of these tests varied from 0.65 to 0.82
ft’, with a mean value for the group of 0.72 ft’.

Schmitt also reported dynamic pressures (q)
with corresponding airspeeds and Reynolds
numbers. These are reproduced in Table V.
Drag coefficients were found to be practically
independent of the Reynolds number within
the range of test, except below a Reynolds
number of 0.5 X 10°, where a sharp increase
in drag coefficient was found,

TABLE V

Summary of Test Dynamic Pressures with
Approximate Corresponding Airspeeds and
Reynolds Numbers

Vv
q

lb/ft fi/sec knots Rx i0~

10 30.1 17.8 0.17

9.0 90.2 53.4 0.51
26.0 153 90.8 0.87
37.0 183 108 1.04
43.0 195 116 1.44
50.0 212 126 L21
58.0 227 134 132
66.0 243 144 1.39

With the above information, drag force (D)
can be calculated from the determined coef-
ficients of drag using the equation, D = C,
x (vH/S) * q. This calculation, of course,
requires that the airspeed which is needed to
obtain values for q be known.

Unfortunately, airspeed values at various
points in an airplane or other pressurized vessel
undergoing decompression are not usually avail-
able. However, some estimate of airspeeds can
generally be made, For example, in the studies
on the physical displacement of man reported

in the previous section. the following ressoning
may be applied: (a; since the ratio of the
area of the ruptured window to the cross-
sectional area of the corridor or “wind tunnel”
was approximately 0.13. the airspeed in the
corridor was 0.13 of that at the window, (b)
the airspeed at the window may be estimated
at 886 ft/sec from the equation for the efflux
of gases (v = \/2ZP/p) and (c) the airspeed
in the unoccupied tunnel was about 0.13 x 886
= 118 ft/sec. Using this estimate of airspeed
and the mean value of 0.72 for vH/S, drag
forces are calculated from the DTMB data and
compared in Table VI with the data on clothed
subjects given in the section on the physical
displacement of man. Excepting the supine
position, there is agreement between the ob-

TABLE Vi

Comparing Calculated Drag Forces From
Wind Tunnel Tests With Observed Values
in Short Duration Blast Studies

Drag.
z Drag.
(Ditis —~—, Obs.
Posture Angle data) Cale. Obs. Cale,
Standing 0 120 136 162 12

90 5.0 57 % 13
180 HO 12 18 15

Sitting 0 78 88 95 1d
90 44 50 73 15

‘ 180 70 79 9% 12

Supine 0 15 17 49° 29

Squat No. 1 180 25 28 43°15
Squat No. 2 0 43 49 74 15
90 3.5 40 7% 19
180 3.0 34 50. 15

served and calculated values. More experience
in this relatively unexplored field is needed tc
judge how well calculated and observed results
might be expected to agree in such a situation.
For example, the method used to calculate air-
speed at the point of entry to the corridor
would have over-estimated this quantity. This
over-estimate may have approximately com-
pensated for the fact tha‘ the subjects occupied
an appreciable portion of the cross-sectional
area of the corridor.

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STUDIES OF AIR LOADS ON MAN

639

pai

FEDERAL AVIATION AGENCY
AVIATION MEDICAL SERVICE
AEROMEDICAL RESEARCH DIVISION
Cv AEROMEDICAL RESEARCH INSTITUTE
OKLAHOMA CITY, OKLAHOMA

DDC:IRA C



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Puase 2. Buast Forces Propucinc
Dison entation

Another series of fifty tests was made on
one subject (clothed) as an initial step in the
accumulation of data on the forces required
to disorient man from standing and seated
posture, and while walking with face, back and
side to the blast. In these tests repeat meas-
urements were made of the maximum forces
acting on the human body at successive incre-
ments of window pressure differential. These
pressure differentials on the window ranged
from 5.5 to 44.0 cm Hg, in 5.5 em Hg incre-
ments. After establishing these vaiues for the
single subject, he assumed the same positions
in the wind tunnel without attachment to
strain gauges or other force measuring devices.
The subject was secured by a safety belt and
slack cable to minimize the danger of bodily
injury. A series of trials was made increasing
the pressure differential in successive trials
until the subject was unable to maintain bal-
ance or to recover. The criteria for not being
able to recover his body position was falling
beyond a possible point of balance at the
extreme range of the safety harness, Table II
shows the effect of wind blast upon main-
tenance of body posture. Table III presents
force calibration measurements on the subject
at eight window pressure differentials,

TABLE 01

Changes of Wind Blast Forces (Ib) on the
Human Body Due to Changes of Pressure
Differential

Subject: A
Standing Sitting

Differential Back Face Side Back Face Side
pressure to to to to to to
inom Hg blast blast blast blast blast blast
5.5 21 12 2 0 7 6
110 69 «59 «(14 Hs 20
16.5 116 96 2 47 4 37
22.0 143 125 48 S58 68 55
27.5, 166 154 75 71 #77 63
33.0 174 172 «(TT & 82 75
38.5 179 180 85 88 86 80
44.0 184 182 82 92 91 85

Puase 3. Errects oF CLOTHING ON DraG
Forces

The final phase was concerned with the
effects of clothing on the drag of the human
body. To determine the component of the
drag forces presented in Phases 1 and 2 which
could be attributed to the clothing, additional
tests were made with subjects wearing shorts
and shoes. Results are reproduced in Table IV
and show that drag forces are 17-22 per cent
less for nude individuals. This difference in
drag for clothed and nude subjects has been
confirmed. in wind tunnel studies by Schmitt’
who found 17-20 per cent difference during
long exposures to constant air loads.

TABLE IV

Effects of Clothing on Drag Forces, Standing
Back to Blast, 33 cm Hg Diff.

With shirt,
trousers With shorts

and shoes and shoes Difference

Subject A W70lb 138.0Ib 39%b
177.3° —- 188.0

Subject B 177.0 140.0 37
162.6° 139.0

Subject C 210.0 173.0 37
193.3° 173.0

* Average of numerous trials in Phase 1.

AERODYNAMICS OF MAN

The experimental results reported in the
previous section were obtained during very
brief exposures to air loads. Because it was
desirable to know whether these results would
hold during long exposures and for related rea-
sons, the Aerodynamics Laboratory of the
David W. Taylor Model Basin was approached.
through the Navy Department and agreed to
make aerodynamic measurements on human
subjects in their wind tunnel, Schmitt’ re-
ported the findings obtained in tests done in
collaboration with FAA personnel. Drag co-
efficients and lift, side force and moments to
indicate relative trends of motion for each of
five body positicns (standing, sitting, supine
and two squat positions) were determined.

-6—


to reproduce closely the conditions of a window
failure in flight, so the precise limits of distance
for safety in various practical situations in air-
craft remain unknown.

Subsequent experiments simulating failure
of a large opening such as a door in a pres-
surized aircraft were also made using one
subject.

The subject, wearing a safety hamess at-
tached to a slack cable, stood 24 in. in front
of and facing a 75 in. by 37 in. opening
covered by a diaphram pressurized to 6.5 !b/in*.
The forces were surprisingly low despite the
distance, relative sizes, and pressure differential
involved. He was not blown from his feet
but maintained balance by stepping forward.
This might suggest that personnel working near
pressurized doors could be protected by a
simple restraining cable, if a need for this arose.
The peak force in this experiment was found
to be about 170 Ib.

In chambers of larger size than the one used
{1350 ft*), air loads would last longer and
thereby have a greater tendency to displace
the body, For continuous air loads equal to
the magnitude of the maximum experienced in
a decompression from a sea level equivalent to
a pressure 6.5 Ib/in® lower, the magnitude of
the air load is estimated in Appendix I to be
about twice that experienced here.

PHYSICAL DISPLACEMENT OF MAN
BY AIR BLAST

One of the purposes of this series of experi-
ments was to determine the magnitude of short
duration air loads that would cause the subjects
to lose their balance or to be otherwise physi-
cally displaced. The experiments were con-
ducted in a space similar to corridor areas in
aircraft as shown in Fig. 2. The duration of
these forces was several tenths of a second.
Figure 3 gives a sample oscillograph tracing.
The various body positions studied are illustra-
ted in Fig. 4. Note in Fig, 4 that shadographs
were made of nude (shorts and shoes) subjects
in order to obtain a sharp outline for area
determinations.

Puase 1. MeasureMenr oF Drac Forces

This study included measurement of maxi-
mum forces acting on the clothed human body
(shirt, trousers and shoes) during equalizatiou
of a pressure difference of 6.5 Ib/in® following
puncture of a membrane separating a partially
evacuated low-pressure chamber and a “wind
tunnel” or collar at sea level pressure. The sub-
jects assumed an upright or other position in
the rectangular “wind tunnel” with the body
oriented in various directions in relation to the
air blast. The subject was supported upon a

Ficure 2 Mockup for measuring forces of wind blast on human subjects.

—~2—


STUDIES ON AIR LOADS ON MAN

JOHN J. SWEARINGEN and ERNEST B. McFADDEN

ABSTRACT

Data obtained in three different studies related to measurement of forces on the body
due to air movement are summarized. The effects of short duration blast forces on
personnel seated or standing at various distances from openings during pressure loss, blast
forces necessary to disorient the body from numerous positions, effect of clothing on the
drag forces, and measurements of forces and moments on the body during wind tunnel

tests are discussed and compared.

INTRODUCTION

The purpose of this report is to summarize the
findings of our laboratory on the effects of
air loads (wind forces) on man. These find-
ings are discussed in relation to the sudden
failure of a small area in a pressure envelope,
the physical displacement of man in corridor-
like areas and the aerodynamics of man,

PRESSURE ENVELOPE FAILURE

Experiments by Swearingen’ simulated fail-
ure of a window in a pressurized aircraft. The

order of magnitude of safe distances of the
occupant from the point of failure, ie. the
distance beyond which physical ejection or
serious-to-fatal head injuries from impact are
unlikely to occur, were shown, The tests in-
volved rupturing a membrane in the window
of a low pressure chamber (1350 ft* capacity),
maintained from 2 to 7.5 Ib/in’ below atmos-
pheric pressure with an articulated dummy
seated near windows of various dimensions.
Minimal safe distances for a pressure differen-
tial of 6 Ib/in* are reproduced in Fig, 1. It
was not possible with the facilities available

MINIMAL SAFE DISTANCES FOR PROTECTION AGAINST THE
WIND BLAST EFFECTS OF EXPLOSIVE DECOMPRESSION



STUDIES OF AIR LOADS ON MAN

JOHN J. SWEARINGEN, M. S.
Chief, Protection and Survival Branch

ERNEST B. McFADDEN, M. S.
Chief, Survival Equipment Section
Protection and Survival Branch

FEDERAL AVIATION AGENCY
AVIATION MEDICAL SERVICE
AEROMEDICAL RESEARCH DIVISION
CIVIL AEROMEDICAL RESEARCH INSTITUTE
OKLAHOMA CITY, OKLAHOMA
MAY 1963