Armored 
Medical Research Laboratory 
Fort Knox, Kentucky 
PROJECT NO. 2 - OPERATIONS AT HIGH TEMPERATURES 
First Partial Report 
On 
Sub-Project No, 2-22, Determination of the Amount of Heat Transmitted 
to the Fighting Compartment of Tanks Under Field 
Conditions 
Project No. 2-22 
17 August 1943 ARMORED MEDICAL RESEARCH LABORATORY 
Fort Knox, Kentucky 
Project NTo. 2-22 
724-1 GNOML 
17 August 1943 
lo PROJECT: NOo 2 - Operations at High Temperatures * First Partial 
Report on: Sub-Project Mo, 2-22, Determination of the Amount of Heat Trans 
mitted to the Fighting Compartment of Tanks Under Field Conditions. 
Authority - Letter Commanding General, Headquarters Armored 
Force, Fort Knox, Kentucky, 400o112/6 GMOHD, dated September 24, 1942, 
b0 Purpose - To determine the adequacy, from the standpoint of 
heat dissipation by the crew members, of the limited rate of ventilation 
which is provided through the gas canister in a gas-protected tanko 
2o DISCUSSION: 
a® Owing to the space requirements of the gas canister and other 
equipment required in the conversion of the ventilating system in U4 tanks 
to the positive-pressure type for gas-protection, the rate of ventilation 
through the canister is limited. At the present time it appears that a 
rate of no more than 175 cfm is possible. 
b0 This limited rate of ventilation is in sharp contrast to the 
quantity of air flowing through the crew compartment of the standard M4 
tank (buttoned-up) which varies from 500 cfm'with engine idling to more 
than 2000 cfm when the engine is operating at cruising speed. Because of 
the great reduction in ventilation, the question is raised as to whether 
or not the air flow is sufficient to absorb and remove the heat released 
inside the tank and the moisture given off by the crew during the periods 
of continuous operation with the tank buttoned-up. 
c. Data with respect to the adequacy of the reduced ventilation 
from the standpoint of heat and moisture removal were obtained during actual 
driving tests on the range with a full crew in the tank. Details of "the 
test procedure and results are presented in the aopendix. 
3o CONCLUSIONS: 
ac A rate of ventilation of lr’5 cfm in the crew compartment of 
the experimental M4A3 tank (without special insulation of the transmission 
and final drive housing) does not remove the heat or the moisture at suf- 
ficient rates to maintain a tolerable atmospheric environment within the 
tank during a continuous period of buttoned-up driving, even on a moderately 
warm summer day. 
1 b0 If the anticipated combat conditions with respect to enemy 
uae of gas are such that the gas-protected tank must operate buttoned-up 
and be continuously prepared for attack by chemical warfare agents for 
prolonged periods in moderately warm areas (where, for example, the tem- 
perature and humidity exceed 85° F0 and 60 percent H0H0, respectively) 
then additional facilities for crew cooling will be required* 
4o RECOMMENDATION: 
That this report be distributed to the agencies concerned with 
the development of gas-protection of tanks0 
Prepared by: 
Lto Colo Theodore Fe Hatch, SnC 
Lto Robert Hc Walpole, SnC 
Lto Glasselle So Lawson, Info 
/ - s' / ' /' 
APPROVED . * c *' • s; 
Colonel, Medical Corps 
WILLARD VACHLE 
Commanding 
3 Incls. 
#1 - Appendix 
#2 - Tables 1 thru 3 
#3 - Figures 1 thru 6 
- 2 - APPENDIX 
In the standard series Ml Medium Tank the rate of ventilation through 
the crew compartment with the tank buttoned-up varies from 500 cfm at idl- 
ing engine speed* up to rates in excess of 2000 cfm with the engine operat- 
ing at cruising speed* In contrast to this, in the experimental gas-pro- 
tected tank (MlA3) described in a recent report from the Laborstory**, a 
rate of ventilation of only 175 cfm is provided through the gas canister. 
Owing to the limited space available in the tank for the canister and other 
parts of the ventilation equipment it does not appear that a higher rate of 
ventilation during gas protection can be anticipatedo 
Field observations and Laboratory measurements have shown that even 
with the high rate of ventilation provided in the standard tank, the solar 
heat absorbed and the heat given off by the transmission and final drive 
and the moisture released by the crew are sufficient-to raise the tempera- 
ture and moisture content of the air within the tank an appreciable amount. 
In view of this fact question may properly be raised as to the adequacy of 
the limited ventilation which would be available through the canister in a 
gas-protected tank, from the standpoint of heat and moisture removals 
TEST PROCEDURE 
Data collected under summer climatic conditions at Fort Knox are 
reported herewith. The tests consisted in operating the tank on the high- 
way and cross-country in accordance with the standard schedule shown in 
Table 1. This schedule, which may be referred to as a "standard tank day", 
is not necessarily representative of a typical day under actual field con- 
ditions but contains the elements of such a dayc In each test the tank was 
fully manned and at intervals throughout the day temperature readings were 
taken in the tank according to the schedule in Table 20 Observations on 
the crew included initial and final body weights and temperatures, the body 
temperature at the end of the lo5 hours of buttoned-up driving in the after- 
noon and a record of the water consumption and excretion during the dayc 
Tests were run on the experimental tank on 3 different days, one a moderately 
cool day with little sun, the second an average summer day with variable sun- 
shine and the third e day of moderately high temperature with substantially 
continuous sunshine* For comparative purposes, a similar test was carried 
out with a standard tank, also on a moderately warm day with fairly continuous 
sunshine* At half hour intervals during each day of test the following measure 
ments were taken at the Laboratory central weather station: (1) dry bulb 
♦ Approximately 500 cfm in the M4A2, liUAJ and MIA*; 1000 cfm in the M1A1. 
** Project No, 3° Toxic Gases in Armored Vehicles, Second Partial Report 
on Sub-Project No, 3~9 - Determination of Ventilation Requirements for 
Gas-Proofing Tanks of the Ml Series 0 23 June 1%3° 
- 1 - temperature in the shade, {2) wet bulb temperature in the shade, (3) wind 
velocity, (4) solar radiation on a horizontal surface„ The climatic data 
were taken at a point approximately 3 miles from the driving range but 
simultaneous check readings of temperature and humidity on the range re- 
vealed no differenceso Interior surface temperatures in the tank were 
determined by means of thermocouples attached to the metal under conven- 
iently located nuts0 Dry bulb temperatures at the various crew positions 
were measured by hanging thermometers and the moisture content of the air 
in the bow and turret was determined by means of an aspirating psychrometer 
which had been checked against the fan-operated psychrometer at the control 
station,. 
RESULTS 
The records of temperature and humidity within the experimental 
tank and in the standard vehicle are shown in Figures 1 to 4o The climatic 
data for the four days are also shown on the graphs„ 
ao Performance of experimental pressure tank compared with 
standard aank, Figures 1 and 2 give the surface and air temperatures and 
the humidity inside the standard and experimental tanks respectively, under 
closely comparable outside conditions» Although the tests were run on two 
different days, it will be observed that the outside dry and wet bulb tem- 
peratures and the solar radiation values were practically the same. The 
wind velocity was somewhat lower in test 2 with the pressure tank. Atmos- 
pheric conditions inside the two tanks, however, were strikingly different. 
The dry bulb temperatures did not differ gre tly but there was a general 
elevation of the wet bulb temperatures in the experimental tank as compared 
with the standard vehicle resulting from the increased moisture content of 
the air. This is shown clearly in Table 3 which gives the increase in 
raoisuire content of the tank air over outside air for both vehicles. At 
the end of the morning and afternoon periods of operation with the tanks 
buttoned-up, the moisture content of the air in the standard tank averaged 
approximately 30 percent in excess of that in the outside air* In the 
pressure tank, on the other hand, the excess moisture content averaged 
62 percent at the end of the morning period and 113 percent in the after- 
noon. These striking differences resulted from the fact that there was 
insufficient rate of air flow through the gas-protected vehicle to absorb 
the moisture given off by the crew members. As a result, rapid deteriora- 
tion of the atmosphere from the standpoint of crew comfort occurred. 
Further indication of the effect of the limited ventilation is seen in 
Figure 5 which shows the increase in effective temperatures* in the two 
* The effective temperature scale combines in one reading the effects of 
temperature, humidity and air movement upon heat loss from the human 
body. An environment having a dry bulb temperature of 105° and a wet 
bulb of 85° F and zero air velocity, for example, has an effective tem- 
perature of 90° F, This is equivalent to a saturated atmosphere of 90°F 
and zero velocity. It is also equal to an atmosphere having a dry bulb 
temperature of 100°, wet bulb temperature of 90°, and an air velocity of 
* 200 fpia0 
2 vehicles in comparison with the effective temperature level for the outside 
air, assuming in the latter case the same air velocity as inside the tanks0 
Effective temperatures for the outside air were substantially the same during 
the two testso Inside the standard tank the effective temperature did not 
exceed 90°, whereas within the pressure tank and particularly in the bow. 
the effective temperature throughout most of the day was in excess of 90 , 
and at the end of the afternoon period of buttoned-up operation reached a 
level of 96*5°o There was a steady rise in effective temperature during 
the morning and afternoon periods of operation which indicates that even 
more serious deterioration of the inside atmosphere would have occurred had 
the period of buttoned-up operation been continued;, It should be noted that 
during these tests the temperature of the transmission in the pressure tank 
ran uniformly below the transmission temperature in the standard vehicle 
with a corresponding lesser radiation heat load which is net included in 
the effective temperature scale0 This improvement resulted, no doubt, from 
the relocation of the transmission oil cooler on the engine compartment deck 
where it was more effectively ventilated. Bow and turret skin temperatures 
did not differ markedly in the two tanksc 
Rapid deterioration of physiological function occurs when 
the effective temperature exceeds 90° and when it approaches body temperature 
(9808), this deterioration will lead to complete collapse if exposure is pro- 
longed. At 1430 hours, in the case of the experimental pressure tank, the 
body temperature of the driver and assistant driver had increased over 3c0°Fo 
In the standard tank, on the other hand, the increase in body temperature was 
less than lo0°Fo The total water loss throughout the day amounted to 603 
pounds per man (9=35 pounds for driver) in the pressure tank, and 4*1 pounds 
in the standard vehicle (603 pounds for driver)„ At the end of the after- 
noon period of buttoned-up operation, the crew in the pressure tank showed 
definite signs of heat exhaustion0 
b. Atmospheric conditions inside gas-proof tank in relation 
to outside thermal conditiona0 The atmospheric conditions within the gas- 
protected tank were found to vary with outside conditions, as would be ex- 
pected* In figures 2, 3 and 4, one notes progressive improvement in the 
thermal conditions within the vehicle as the outside temperature end amount 
of solar radiation decreased* Figure 6 shows the effective temperatures in 
the bow during the three days together with the average outside climatic 
conditions* In contrast to the serious deterioration in the tank atmosphere 
which was observed on a moderately warm day with continuous sunshine (Figo 
2), operation of the gas-protected tank on a cool day with low solar radiation 
did not produce unacceptable interior conditions (Fig. 4). The effective 
temperature reached a maximum of 87*5° arid there was no significant rise in 
body temperature* The total water loss throughout the day averaged 3<>5 
pounds per man. Attention should be called, however, to the fact that there 
was a significant rise in moisture content of the tank air at the end of the 
morning and afternoon periods of buttoned-up operation, the average increases 
being 50% and 70% respectivelye This again attests to the li.nlted capacity 
of the quantity of air flowing through the tank to take up moisture,, 
- 3 - On the intermediate day with irregular sunshine and 
average temperature (Fig0 3), effective tempenatures in excess of 90° 
were encountered during the afternoon period of buttoned-up operations 
only, with an increase in moisture content over outside air of 75%o The 
total water loss throughout the day was ?02 pounds per man* and the 
average rise in body temperature at 1430 hours was lo0° F0 
CONCLUSIONS 
aQ It is evident from the findings of these tests that a rate 
of ventilation of 175 cfra is insufficient to remove the heat and moisture 
from the tank when the outside temperature is of the order of 90° and 
higher and the relative humidity above 50% □ If the operation of the 
buttoned-up tank is prolonged the crew will suffer serious deterioration 
and collapse0 
b0 At outside temperatures between 80° and 90° F the deterioration 
in the tank atmosphere with prolonged buttoned-up operation, the crew will 
experience definite fatigue and loss of efficiency. 
Co At outside temperatures up to 80° F the tank atmosphere will 
be acceptable from the standpoint of crew efficiency and fatigue. 
do These findings are of considerable importance in connection 
with tile design and operation of so-called gas-protected tanks since the 
installation crew—cooling equipment would greatly complicate the problem0 
The need for such equipment depends upon two conditions: (l) climate in 
the combat area and (2) the conditions under which the tank must operate, 
that is to say, the length of time it must be driven completely buttoned- 
up. The latter depends upon the anticipated nature of attack by chemical 
agentso If, for example, the principal advantage of gas protection of the 
entire tank is to guard arainst ambush or other unexpected attacks then 
the tank must be prepared for attack at all times while in a combat area 
where the use of gas is expectedo If, at the same time, moderately high 
temperatures are encountered there will be a need for crew cooling0 These 
considerations must be kept in mind in the further study and development 
of gas protection by means of positive-pressure ventilation through a gas 
canister0 
* A different crew of higher average body weight were employed in this 
testo 
~ 4 - TABLE 1 
Operating Schedule During "Standard Tank Day" 
Legend of 
Opero Schedule 
In Figs. 1 to 5 
Time* 
Operation 
0900 to 1000 
Driving over highway to range, hatches 
openo 
1000 to 1030 
Tank stationary, hatches open, crew in 
tank* Fan operating in gas-proof tank; 
engine idling in standard tanK0 
1030 to 1130 
Cross-country driving, tank buttoned-up 
1130 to 1230 
Tank stationary, hatches open, engine 
dead, crew outside<> 
1230 to 1300 
Cross-country driving, hatches open0 
1300 to 1430 
Cross-country driving, tank buttoned- 
upo 
1430 to 1$00 
Tank stationary, hatches open, engine 
1500 to 1600 
Cross-country driving, hatches open. 
1600 to 1630 
Driving over highway to motor park, 
hatches open. 
* Schedule followed approximately. Time varied slightly in several tests0 TABLE 2 
Location and Schedule 
of 
Temperature Measurements in Tank 
1= Surface Temperatures (Contact thermocouple readings at beginning 
and end of every halting period) 
a« Bow; on front slope midway between two seats. 
b0 Turret; roof over gun and on rear wallo 
c. Transmission: front, next to final drive housing0 
20 Air Temperatures (Readings every one-half hour) 
ac Bow: four locations - driver's left at chest height; asst0 
driver*s right at chest height; over transmission, midway 
to roof (shielded)*; to rear of and above transmission next 
Co turret basket. 
b. Turret: four locations - at chest height at each crew position 
(gunner, conuaander, loader); center of turret directly under 
gun0 
3« Moisture content (wet bulb temperature readings every one-half hour) 
aQ Bow: to rear of an above transmission next to turret basketo 
b. Turret: center, directly under guno 
* Always higher than other bow temperatures„ Mot included in obtaining 
average bow temperature0 TABLE 3 
Rise in Moisture Content 
of 
Tank Air in Experimental and Standard M4A3 Tanks 
Time 
Moisture Content 
- Crains 
Per Lbo Dry Air 
Experimental Tank 
Standard Tank 
Outside 
Bow 
Percent 
Increase 
Turret 
Percent 
Increase 
Outside 
Bow 
Percent 
Increase 
Turret 
Percent 
Increase 
0830 
— 
— 
— 
— 
— 
129 
134 
4 
135 
5 
0900 
118 
132 
12 
132 
12 
0930 
— 
— 
— 
— 
— 
124 
134 
8 
144 
16 
1000 
119 
143 
20 
139 
17 
119 
132 
11 
134 
13 
1030 
121 
150 
24 
141 
17 
119 
125 
5 
126 
6 
1130* 
128 
214 
62 
202 
12 
112 
112 
M 
in 
12 
1230 
120 
152 
27 
154 
28 
no 
140 
27 
135 
23 
1300 
115 
173 
50 
156 
35 
111 
n5 
8 
131 
18 
1330 
112 
197 
76 
200 
79 
no 
143 
30 
133 
21 
1400 
108 
215 
99 
204 
89 
118 
151 
28' 
140 
19 
1430* 
105 
220 
-119 
218 
108 
112 
i41 
22 
m 
ii 
1500 
106 
153 
44 
169 
60 
108 
133 
23 
136 
26 
1530 
106 
146 
38 
155 
46 
103 
127 
23 
129 
25 
1600 
105 
170 
62 
155 
47 
103 
135 
31 
142 
38 
1630 
105 
137 
30 
140 
33 
— 
— 
— 
— 
— 
* End of period of buttoned-up driving,, Fig, I 
TEMPERATURES IN STANDARD M4A3 TANK 
MODERATELY HOT DAY 
SOLAR RADIATION ~ BTU/SQ FT/HR . 
od ro 
WIND VELOCITY - M P H, 
TEMPERATURE °F 
Fig. 1 Fig 2 
TEMPERATURES IN EXPERIMENTAL M4A3 TANK ( 175 CFM) 
MODERATELY HOT DAY 
SOLAR RADIATION - BTU/SO.FT/HR 
co rv> 
WIND VELOCITY ~MPH. 
TEMPERATURE ° F 
Fig. 2 Fig. 3 
TEMPERATURES IN EXPERIMENTAL M4A3 TANK (175 CFM) 
AVERAGE WARM DAY 
SOLAR RADIATION - BID / SO FT /HR 
cp £ 
MND VELOCITY-M R H 
TEMPERATURES °F 
TIME - HOURS 
Fig. 3 Fig. 4 
TEMPERATURES IN EXPERIMENTAL M4A3 TANk(|75CFm) 
COOL DAY 
SOLAR RADIATION - BTU/SQ FT/HR 
-C- OD 
WIND VELOCITY - M. P H 
TEMPERATURE °F 
Fig. 4 Fig. 5 
EFFECTIVE TEMPERATURES IN TURRET AND BOW OF EXPERIMENTAL 
M4A3 TANK (175 CFM) 
AS COMPARED WITH STANDARD M4A3 TANK, SHOWING EFFECT OF LIMITED 
VENTILATION. MODERATELY HOT DAY WITH CONTINUOUS SUNSHINE. 
EFFECTIVE TEMPERATURE ° F 
Fig 5 Fig. 6 
EFFECTIVE TEMPERATURES IN BOW OF EXPERIMENTAL M4A3 TANK 
(175 CFM) 
ON COOL, WARM AND MODERATELY HOT DAYS 
EFFECTIVE TEMPERATURE °F 
TIME - HOURS 
AVERAGE CLIMATIC CONDITIONS 
TEST td tw WIND VELOCITY SOLAR RAD. 
I 07.0 75.5 3.6 230 
II 81.5 74 0 5.4 145 
HI 75.5 68 6 4.5 130 
FIG. 6