A thermally insulative inflatable garment designed specifically as a lightweight low storage volume emergency suit for subzero weather survival is reported. Testing confirms that the inflatable suit design satisfies the objectives for a subject standing at rest with environmental temperatures down to -450 F if the garment is inflated with Freon

Curtis, D. L.

English

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26 AN EMERGENCY SURVIVAL SUIT 
Daniel L. Curtis 
Mechanics Research, Inc. 
INTRODUCTION 
This paper describes a thermally insulative garment designed specifically as a lightweight, low 
stowage volume emergency suit for subzero weather survival. The insulating principal employed can 
be applied to many other thermal applications. 
The primary design objective was to construct a minimum weight, insulative garment capable of 
providing thermal protection for sedentary metabolic rates of 450 Btu/hr, with an environmental 
temperature of -40" F. It was intended that the garment be stored as a part of a survival kit, or as a 
piece of emergency cold weather gear for motorists in the northern portions of the country. 
DESIGN CONFIGURATION 
Testing confirmed that the inflating suit design satisfies the objectives for a subject standing at rest 
with environmental temperatures down to -45" F. The garment weighs 11 oz excluding the weight 
-. 
Figure 26.1 Emergency survival suit. 
of the inflating-gas source. Initially, the use of 
lung power or a small hand pump was planned 
for filling the suit walls. This would have 
resulted in an 11 ounce system with a stored 
voluem of approximately 30 cu in. However, 
a small, compressed-gas source was introduced 
to provide for rapid inflation. This addition 
increased the total system weight to about 
Figure 26.1 shows a photograph of the suit 
being worn for the cold room test. As shown, 
the garment is a form of superinsulator 
composcd of multilaycr, aluminizcd plastic. 
Specifically, the suit is constructed of three 
layers of aluminized polyethelyne with the 
edges sealed for suit-wall inflation. It is 
donned in the same manner as coveralls with a 
zipper down the front. The zipper serves both 
as the suit closure device and as the means of 
adjusting suit heat loss. The wearer simply 
opens the zipper if he becomes too warm. 
The suit completely covers the body, 
including the hands and the head. For 
simplicity, an extension of the sleeves 
2-1 /2 lb. 
347 
https://ntrs.nasa.gov/search.jsp?R=19720019482 2020-03-17T03:55:40+00:00Z
surroundsthe hands.A headcoveringandviewingvisor arealsoincluded.However,for future
models,the visorwill probablybe replacedwith an openslit in the coveringto preventinternal
fogging.
DESIGN CALCULATIONS
Figure 26.2 shows the suit wall model used for
radiation and conduction calculations. Boundary
condition temperatures were -40°F for the
exterior surface and 80 ° F for the interior surface.
Radiation heat transfer was computed using an EXTERNAL
emittance value of 0.2, characteristic of poly- f/WEAR RESISTANT
ethylene aluminized on only one surface. The UNDERGARMENT
surface area of the garment was estimated to be 20 FREON13BI .....•
ft 2. For these conditions, the heat loss by radiation THERMALBARRIERS "_-_
BODY
is approximately 210 Btu/hr. A lower value could (SHIRTSLEEVE)
be obtained by introducing double surface
aluminization of the polyethylene. A single surface 114 in .... 114 in
was used for the prototype suit, because this was _/e in .......
the only material available at that time. APPROX.
Heat loss also occurs by conduction through the
garment wall. In space, this term is quite small for Figure 26.2 Garment cross section.
a superinsulator because of the vacuum-inner-space between the aluminized surfaces. For the 1 atm
condition, however, it is necessary to fill the suit inner space with a gas, which increases wall
conduction. Convection is considered negligible because the close spacing of the suit walls prevents
appreciable gas circulation within.
Designing for air as the insulating gas with a suit conduction heat loss equal to one half the
total allowable (100 Btu/hr for the -40 ° F condition), requires an inflated suit thickness of about
1.1 in. Inflating the suit to this thickness is considered practical. However, a better alternative is the
use of another gas with better thermal insulative properties. This permits a thinner suit wall.
The gases that were considered are shown in figure 26.3, with thermal conductivities plotted as a
function of molecular weight. As a general rule, the greater the molecular weight, the lower the
_oo- conductivity value. Hydrogen and helium
?
E
to
G
?
o
m
×
10
o HYDROGEN(H 2)
o HELIUM (He)
o AIR
)/ARGON(A)
CARBONDIOXIDE(C02)
o BUTADIENE(O4H6)
o KRYPTON (Kr) & BENZENE (CEHe)
o FREON 13BI
I i i_._ i i ill I_
IO IOO IOOO
MOLECULAR, Wt
Figure 26.3 Thermal conductivity of various gases as a
function of molecular weight.
ALUMINIZED POLYETHYLENE
are also shown for comparison. The most
favorable gas was found to be Freon 13B1,
which is relatively inexpensive and is used
for fire fighting because of its inertness and
comparatively high density.
Compared to air, Freon 13B1 is more
than twice as good an insulator. In
addition, it has a liquification temperature
of -70 ° F, which provides an ample safety
margin for a system designed for a min-
imum environmental temperature of
-40 ° F. With Freon 13B1, the required
inflated suit wall thickness is 0.5 in. This
provides for a conduction heat loss of 240
Btu/hr. The total calculated heat loss is
348
then 450 Btu/hr for the conditionsgiven.Respiratoryheat lossis alsoincludedfor a total heat
balance.The sensibleheat loss resultingfrom breathing40° F air is about 40 Btu/hr for the
sedentarycondition. An additional30 Btu/hr is lost through the latent heatfor vaporizinglung
moisture.Carbondioxide wasalsoconsideredbecauseit is a better insulatorthan air, andit is
readilyavailablein small,highpressurevessels.
r
.30 i
.25
-_ .20
.__
m .15
v
.IO
.05 ---
200
AIR
_ CARBON
DIOXIDE
(CO2)
/ //- FREON 131B
/ _ _-_ (CF3Br)
/ f" ..-------KRYPTON
// .1.1-"I - (Kr)
:500 400 500 600
T~OK
Figure 26.4 shows a plot of thermal
conductivities for various gases as a
function of temperature. In the
temperature range from -40°F to
normal body temperatures, the
conductivity of the Freon is
approximately 0.05 Btu-in/hr-ft 2-°F.
TESTING
A cold room with a liquid nitrogen
cooling source was used for testing.
The test subject wore a short-sleeved
shirt, slacks, and socks without shoes.
He stood in a small insulated enclo-
sure approximately 3 X 3 X 6 ft with
Figure26.4 Thermal conductivity of various heavy gases and air.
a thick piece of foam plastic on the
floor. The foam simulated insulating
shoes that would be incorporated into the final design. The enclosure was cooled by a liquid
nitrogen baffle and a large air circulating fan mounted directly in front of the subject. During the
test, it was necessary to exhaust the cold, vaporized nitrogen directly into the cabinet to attain the
coldest air temperatures. The cabinet was inclosed to minimize heat loss to the lab environment,
with a fresh air duct used during the latter portion of the test to facilitate breathing. Air
temperature was measured with an iron-constantan thermocouple and a Leeds and Northrup
potentiometer. The thermocouple was placed in front of the fan next to the test subject.
The garment without Freon was found to be a satisfactory insulator down to about 10 ° F. At
approximately this air temperature, the test subject began to feel cold, and the Freon was
introduced. The coldness soon disappeared and test subject again began to feel comfortable. The
temperature was then lowered to - 20 ° F. The test subject was comfortable except for his hand that
was holding the air duct. Also, the elbow became somewhat cold because in the bent position it
created a thermal short through the radiation shields in the area of the bend. By alternately using
the other hand to hold the breathing duct, the previously cold region became warm as soon as the
insulation was restored.
The temperature was then lowered to -40 ° F and held for 15 min. Temperature was then
reduced to -45 ° F for an additional 15 min. At this temperature the test subject's hands and elbows
became quite cold where thermal shorts occurred. The subject noted that his toes were also cold, and
with shirt sleeves, that his bare arms were cool. He mentioned that a sweater would have made him
more comfortable. However, he reiterated that the rest of his body was comfortable. He felt the test
could have continued much longer, and perhaps indefinitely, had he been wearing shoes, and had he
not had to grip the breathing duct with his hands.
349
CONCLUSION
The test subject had been in an environment corresponding to a moderate wind at a temperature of
-20 ° F, or lower, for more than an hour with 0.5 hour of this time at or below -40 ° F. The test was
considered a success with the results showing the technical feasibility of the design approach.
350


An emergency survival suit

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