Armored Force 
Medical Research Laboratory 
Fort Knox, Kentucky 
PROJECT NO. 2 - HIGH TEMPERATURES IN TANKS 
Final Report On 
Sub-Project Test of Truck, 3A Ton, Refrigerated 
'^'Ambulance 
Project No. 2-29 
May 1$, 191*3 AIM)RED FORCE MEDICAL RESEARCH LABORATORY 
Fort Knox, Kentucky 
Project NOo 2-29 
451.8 GNOML 
May 15, 1943 
1® PROJECT: No0 2 - High Temperatures in Tanks0 Final Report on: 
Sub-Project No0 2-29 - Test of Truck, 3/4 Ton, Refrigerated Ambulanceo 
a„ Authority - Letter Commanding General, Army Ground Forces, 
Washington, D.’C., 451.8/39 - GMRQT-8/34292, dated March 14, 1943, and 
1st Indorsement, Commanding General, Headquarters Armored Force, Fort 
Knox, 451.8 (3-14-43) GNOHD, dated March 17, 1943. (See Inclosure # l) 
b, Purpose - To determine the suitability of subject ambulance 
(Array Serial No0 77974) for use in hot climates0 
20 DISCUSSION; 
Methods: Subject ambulance was tested in the Laboratory Hot 
Room under two simulated climatic conditions: 
a„ Desert, with diurnal variation in radiant heat, provided 
by a bank of infrared lamps on the ceiling, and with temperature changes 
approximating an average day in the deserto 
b0 Jungle, with moderately high temperature and extreme moisture 
content of the air. but vfithout radiation,, 
Air temperatures were taken periodically inside and outside the 
vehicle, and surface temperatures were measured on the top and sides, both 
externally and internally0 
Details of procedures and results are given in the appendix0 
3o CONCLUSIONS; 
a0 The refrigerating system in subject ambulance possesses ade- 
quate cooling capacity for use in desert climatese 
b« Refrigerating system in this ambulance does not possess ade- 
quate cooling capacity for use in tropical climates0 
£0 For successful operation, rear doors and bulkhead doors 
separating driving compartment from patient compartment must remain closed 
Insulation of bulkhead doors would be desirable0 
1 do Operation of intake fan on roof of patient compartment is 
optional with occupants0 
e0 Control of window and cowl ventilator opening in driving 
compartment is optional with forward occupants and does not affect the 
coolingo 
Uo RECOMMENDATIONS; 
a. That subject vehicle be considered adequate for transportation 
of casualties in climates where ambient temperatures above 100 F with low 
humidity are encountered® 
b« Greater refrigeration capacity be provided for use in tropical 
climates where high relative humidities are encounteredo 
Prepared by; 
1st Lt0 Robert H0 Walpole, Sn-C 
APPROVED 
WILLARD MACHLS 
Colonel, Medical Corps 
Commanding 
2 Inclo 
# 1 - Letter of Authority 
# 2 - Appendix, with Tables 
1 & 2, and Charts 1, 
2 & 3 
2 HEADQUARTERS 
ARMY GROUND FORCES 
ARMY WAR COLLEGE 
Washington, D0 C0 
451 o 3/39-«I.'HQT-8/3/4292 
(2-22-43) 
Mar0 14, 1943« 
SUBJECT: Test of Truck, 3/4-Ton, Refrigerated Ambulance 
TO : Chief of the Armored Force, Fort Knox, Kentucky 
10 Inclosed herewith is a copy of the Desert Warfare Hoard 
report of test of the Truck, 3/4-Ton, Refrigerated Ambulance0 
20 Instructions have been issued to the President, Desert War- 
fare Board to ship the suoject vehicle to the Armored Force kedical 
Research Laboratory, Fort Knox, Kentucky and to inform your headquart- 
ers of date of shipment thereof0 
3o It is requested that the subject vehicle be tested through 
the facilities of the Armored Force Medical Research Laboratory to de- 
termine its suitability for use in hot climates, and upon completion 
of tests report thereof be submitted to tliis headquarters in sextupletG 
command of LT, GEN„ McNAIR: 
/s/ J0 R. Dryden 
Ja Ro DRYDEN, 
Lt0 CoXo , Ao Cro Do, 
Asst0 Ground Adj0 Gen0 
1 Inclo 
Rpt of tst of Truck, 3/4-Ton, 
Refrigerated Ambulance, P-61-2, 
dt»d 2-22-43o 
Inclo #1 
1 U51o$ (3-14-43) GNOHD 
1st Ind. 
HEADQUARTERS ARMORED FORCE, Fort Knox, Kentucky, March 17, 1943* 
To: Commanding Officer, Armored Force Medical Research Laboratory, 
Fort Knox, Kentucky. 
For compliance. 
Ey command of Lieutenant General DSVERS; 
/a/ C0 Mo Wells 
C. M. WELLS 
Lieut. Colonel, A. 0. D„, 
Assistant Adjutant Generalo 
1 IncIs 
n/c 
In do #1 
2 APPENDIX 
TEST CONDITIONS: 
lo Test I to itf, inclusive; Dry desert atmosphere, with variation 
in radiant heat approximating the solar heat load (See Fige 1) and changes 
in air temperature simulating the average diurnal temperature curve for 
the California desert0 
Radiation was provided by a bank of heat lamps mounted below the 
ceiling of the hot room and the diurnal cycle was obtained by hourly 
changes in the number of lamps in operation„ The intensity of radiant 
heat reached a maximum of 320 Btu per sq0 ftfa per hour, which corresponds 
closely to the intensity of solar radiation at midday on July 21st at 
latitude 30°No Relative humidity was approximately 2$$. 
Test I - Test vehicle with cooling equipment not operatingo No 
outside air movement and no mechanical ventilation of vehicle0 Purpose 
of test; To compare the insulation of subject vehicle with that of a 
standard ambulance„ 
Test II - A standard ambulance tested under the same conditions 
as vehicle in Test I, 
Test III - Test vehicle with refrigeration system in operation., 
No outside air movement0 
Test IV - Test vehicle with refrigeration system in operation 
Outside air velocity approximately 10 mph to simulate wind or movement 
of the vehicleo 
20 Test V - Continual application of radiant heat equal to the max- 
imum solar radiation at noon, with correspondingly high maximum temperaturec 
Test vehicle with refrigerating system in Outside air movement 
of approximately 10 raphc Five “patients” in ambulance0 Purpose of test: 
to determine capacity of refrigerating system in relation to the mainten- 
ance of comfortable atmospheric conditions inside vehicle with maximum heat 
load and with relatively dry air0 
3» Test VI - Continual exposure of vehicle to an atmosphere sim- 
ulating extreme jungle conditions, with high relative humidity0 Test vehicle 
with refrigerating system in operation Five "patients” in ambulance0 
Purpose of test: to determine capacity of refrigerating system in relation 
to comfort of patients when the moisture content of the outside air is high. 
RESULTS: 
&c The relative degree of insulation of test vehicle as compared with 
standard ambulances is shown by the comparative temperature-rise curves of 
Tncle ff-Z 
1 inside air when the two vehicles were subjected to the same outside 
air temperatures and equal radiant heat loads (Fig0 2). In the test 
vehicle the inside temperature rose to a maximum of 22°F above that 
of the outside temperature whereas in the standard ambulance9 the 
maximum inside temperature was more than 40°F above that of the out- 
side air0 
b0 Refrigerating effect. The cooling capacity of the refrigera- 
ting system is also shown in Figo 20 Under the same test conditions 
as above but with the refrigerating system in operation (.Test III) 
the inside air temperature ros e to a maximum of 88°F while the outside 
temperature increased to 105°Fo By means of the cooling system the 
air temperature within the ambulance was maintained at least 20°F be- 
low the outside Conditions were even more favorable with 
outside air movement,, The effect of this was to increase the heat loss 
from the hot surfaces of the vehicle to the outside air and, as a con- 
sequence, the load upon the refrigerating system was reduced,, As a 
result, the inside air temperature was maintained at a lower level than 
with still outside air0 The beneficial effect of the cooling system is 
further emphasized by the marked drop in temperature when the refrig- 
eration system was turned on. During the first hour no cooling was 
provided and the inside air temperature rose to a level of 7° above 
outside temperature., Within an hour after starting the refrigerating 
apparatus, however, the temperature within the ambulance had dropped 
22° Fo 
Outside surface temperatures are tabulated for Test I to IV in 
Table 10 The beneficial effect of outside air movement is seen by com- 
paring the values for Test IV with the others 0 The maximum skin tem- 
perature was 124°F, whereas with still air the temperature rose to 170°. 
Co Comparative performance of refrigerating system in desert and 
jungle atmospheres. The performance of the refrigerated ambulance in 
the desert atmosphere with continued exposure to maximum solar radiation 
and air temperature is shown in Fig0 3o Five "patients" remained in the 
vehicle for five hours ,0 During this period the outside temperature 
averaged 114°F while the surface temperature was H0-150°Fo The air 
temperature within the vehicle was reduced to 86° after approximately 
one hour of operation of the cooler and the relative humidity was main- 
tained at about U0%o The "patients" were comfortable throughout the 
testo 
In comparison with the foregoing, conditions were not comfortable 
during continuous exposure to jungle heatc Atmospheric conditions with- 
in the ambulance are given in Table 2„ With an outside dry bulb tempera- 
ture of approximately 110°F, wet bulb temperature of 103°F and 80/4 
relative humidity, the inside atmosphere averaged 100° dry bulb, 94° 
wet bulb and relative humidity0 The test conditions were in excess 
Incl• #2 
2 of those encountered in jungles but the results, in comparison with 
those obtained with desert conditions, illustrate the important point 
that a greater refrigerating capacity is required in the jungle than 
in the desert in spite of the higher dry bulb temperature in the latter 
situation,, The explanation is that the total heat of the air is measured 
by the wet bulb rather than the dry bulb temperature„ In the jungle, 
wet bulb temperatures above 85° may be encountered whereas in a hot 
arid climate the wet bulb temperature rarely exceeds 80°„ Furthermore, 
in the latter case, the evaporation of sweat aids in cooling the body 
so that a higher dry bulb temperature can be toleratedo 
Mechanical features and durability of the refrigerating system 
were not considered in these tests, the purpose being only to determine 
cooling capacity in relation to simulated desert and-jungle conditions,, 
Incl* if2 
3 TABLE 1 
AVERAGE EXTERNAL SURFACE TEMPERATURE OF 
REFRIGERATED AMBULANCE (J779hh) AND STANDARD AMBULANCE (#71101*8) 
TESTS X, II, TIT, IV 
Simulated Sun 
Time, Hours 
Test I 
SURFACE TEMPERATT 
Test II 
RES, DEG, Fo 
Test III 
i 
Test IV 
0730 
V 
85.7 
75.7 
30,6 
07)45 
93,7 
' 111 
105 0 3 
93o7 
0300 
10l; 
115.3 
106.7 
96.3 
0815 
105.3 
171 
110 0 7 
9? 
0830 . 
106 
ll3o3 
112 0 3 
97 0 7 
081*5 
113 
121.3 
13:"'. 7 
99.3 
0900 
113 
171* 
11*0 
10? 
0915 
1 20,3 
125.3 
133.7 
106 
0930 
122,7 
123.3 
136.7 
105 
09u5 
ll*Oo? 
H3.3 
109 
1000 
131*.? 
1)46.7 
351-3 
110 
1015 
139 
113 0 3 
lay 
111 
1030 
151.3 
151.7 
153 
111,7 
113.3 
low 
11*7 
153 
155.7 
1100 
150.3 
160.3 
156.7 
116,7 
1115 
— 
161 
160 
116,3 
1130 
155.3 
166,7 
161 
122 
111,45 
— 
166,3 
123c. 7 
165 
1700 
1610 3 
172o 3 
160,3 
123.7 
1715 
159 0 ? 
173o3 
163o3 
122,7 
1230 
155.7 
177 
162,3 
121.7 
1?55 
157 
169.3 
161.7 
119 
1300 
— 
169.3 
161.7 
119 
1315 
156.7 
169 
157.3 
116,7 
1330 
U47.3 
171.3 
115 
156.7 
Incl, #2 
4 TABLE 2 
WET BULB, DRY BULB, RELATIVE HUMIDITIES, BOTH 
INSIDE AND OUTSIDE,'FOR TROPICAL TEST OF 
REFRIGERATED AMBULANCE 
Time 
Patient Compartment 
Outside Room Air 
In Minutes 
DoBo 
Wo Bo 
% RoH0 
DoBo 
Wo Bo 
% Ro Ho 
0 
104 
99 
84 
103 o 6 
103 o 6 
94 
5 
101 
94 
77 
10 • 
100 
94 
79 o 5 
15 
100 
94 
79 o 5 
20 
100 
95 
63 
108o8 . 
102 o 7 
82 
25 
100 o 5 
95 
81 
30 
100 o 7 
94o7 
80 
35 
101 o 6 
96 
81 
40 
101 
94 
76.5 
Hlo7 
104 o 3 
78 
45 
100o5 
94 
78 
50 
100o5 
94 o 5 
80 
55 
100o5 
94o5 
80 
60 
100c 5 
95 
81 
110o2 
104o7 
85 
inci. n 
5 INTENSITY OF SOLAR RADIATION , BTU/SQ FT./hR 
SUN T'ME - HCl IT 
SOLAR RADIATION IMPINGING AGAINST A HORIZON' L _ SURFACE FOR 30 DEGREE LATITUDE 
JULY ? 
ACTUAL AND SIMUl VT 'ONDITIONS 
FiC I 
-SIMULATED 
ACTUAL 
Irscl. f* 
Fig. I AIR TEMPERATURES 
GROUP ONE 
TEST NO. I n HI EC 
TEST’ U 
RADIATION 
COOL ING SYSf EV TURNED ON 
INTENSITY OF SOLAR RADIATION, BT.U./SO. FT./HR. 
TEST I 
TEMPERATURE, °F 
ROOM AIR TEMPERATURE 
TEST nr 
TEST m 
SUN TIME, HOURS 
Incl. §2 
Fig. 2 Fig. 3 
GROUP 2 
TEST OF REFRIGERATED AMBULANCE WITH DESERT CONDITIONS 
AND FIVE PATIENTS IN COMPARTMENT 
AVERAGE OUTSIDE SURFACE 
TEMPERATURE 
ROOM AIR TEMPERATURE 
TEMPERATURE °F 
PATIENT COMPARTMENT 
AIR TEMPERATURE 
REFRIGERATION SYSTEM AND 
INTAKE FAN STARTED OPERATION 
PERCENT RELATIVE HUMIDITY 
5 PATIENTS ENTER 
COMPARTMENT 
INSIDE 
RELATIVE HUMIDITY 
TEST TIME, HOURS 
r.ncl. #2 
Fig. 3