Armored 
Medical Research Laboratory 
Port Knox, Keinjtuckv 
PROJECT NO. 3 - TOXIC GASES IN ARMORED VEHICLES 
Partial Report 
On 
Sub-Project No. 3-9> Determination of the Ventilation Requirements 
for Gas-Proofing Tanks 
"SUBJECT: VENTILATION REQUIREMENTS FOR GAS-PROOFING 
TANKS OF THE U~U SERIES 
March 1, 1943 
Project No. 3-9 ARMORED FORCE MEDICAL RESEARCH LA30RAI ORY 
Fort Knox, Kentucky * 
Project No. 3-9 
File No. 72L.2 GWL 
March 1, 19U.3 
PARTIAL REPORT OP VENTILATION RSQT'TREME:!TS FOR 
GAS-PROOFING TALKS OF THE M-U SERIES 
1, PROJECT: 3-9 - Determination of the Ventilation Requirements for Gas- 
Proofing Tankso 
a. Authority - Letter, Commanding General, Headquarters Armored Force, 
Fort KnoxT Kentucky, 1*00.112/6 GNOKD, dated September 2h, l?h2, 
b. Purpose - To determine the important leakage areas in the series 
M-U tanks”and the amount of sealing required to maintain adequate pressure for 
gas-proofing the tank with ventilation equipment of practical size and power 
consumption. 
2. DISCUSSION: 
a„ Methods - The fighting compartment of an Mi;A2 tank was sealed as 
completely as possible and air delivered into it at measured rates by an external 
fan. For each rate of air flow, the corresponding static pressure within the 
tank was noted. Following this, various leakage areas were successively unsealed 
and new pressure volume curves obtained. The difference between any two suc- 
cessive areas represented the rate of leakage contributed by the particular area 
which was opened up. Pressure—volume curves obtained in this manner are shown, 
for the important sources of leakage, in the Appendix» 
3. CONGO! SIGNS: 
a. The 75 ram gun mount is the most important leakage area and the 
effective””sealing of this area is essential to the development of a gas-proof 
tank with a pressure ventilating system of practicable size and power consumption,, 
b. The turret hatch race contributes little to the leakage. 
c. The main turret ring was found, in these tesss, to contribute little 
leakage. "The air flow through it depends upon the amount of grease in the ring. 
do Leakage around hatches and periscopes is easily reduced to a 
minimum. 
e„ These tests indicate that with a practical degree ol sealing of 
present areas of leakage, a positive pressure can be maintained in the fighting compartment with a ventilating system of moderate capacity and power consumption, 
provided tae bulkhead between the fighting and engine compartments is completely 
sealedo Such a system, utilizing only space formerly wasted, has been installed 
in an h4A3 tank and is being studied to determine the internal pressure required 
for effective gas protection. 
4* HECQif iENDATION: 
That this report be transmitted to the agencies concerned with the gas- 
proofing of vehicles„ 
Submitted by; 
Major To F. Hatch 
1st Lt. R0 Ho Walpole 
APPFOVSD 
' WILLARD MACrfLE 
Lt. Colo, Medical Corps 
Commanding 
3 Inclso 
#1 - Appendix 
#2 - Table I 
#3 - Figure 1 APPENDIX 
Gas-proofing of the series M-U tanks requires that the fighting compartment 
be provided with a pressure system of ventilation so as to maintain an outward 
flow of air through cracks and other leakage openings. During operation in a gas- 
contaminated area, the air must be passed through a suitable conditioning canister 
for removal of the contaminating gas. The capacity of a practicable system is 
necessarily limited by the space requirements of the fan, motor, gas canister and 
other appurtenances. It must, however, be adequate to maintain a pressure in the 
tank sufficient to prevent the ingress of toxic material. For a given positive 
pressure, the required capacity of the system is determined by the total area of 
leakage openings in the hull and turret„ The bulkhead between the fighting and 
engine compartments must be sealed. 
The purpose of the present tests was to determine the magnitude of the leak- 
age through the tank as usually constructed and the practicability of sealing 
openings, particularly the more important leakage areas, to permit the use of a 
ventilating system of reasonable size. 
Air was delivered into the tank through an orifice meter at measured rates 
and the corresponding static pressures within the tank determined. A pressure- 
volume curve was first obtained with the tank sealed as tightly as possible. 
Following this, soecific leakage areas were unsealed and new pressure-volume curves 
obtained. The difference between two adjacent curves gave the pressure-flow curve 
for the leakage area in question. Because the work was done on a standard tank 
it was not possible to seal the bulkhead completely, and, as a consequence, an 
unknown quantity of air was constantly leaking through it. Since the flow through 
a given leakage area was obtained by difference. However, these measurements were 
not affected by the unknown leakage through the bulkhead. Pressure-volumes curves 
for the important leakage areas, obtained in this manner, are shown in Figure I. 
The internal pressure required to provide protection against outside gas is 
not known at this time. To counteract the pressure of a 20-mile per hour wind 
would require a pressure of one-half inch water while one inch pressure 
would be effective at 30 m.p.h. or more. At these pressures, the air flow through 
the more important leakage areas in the yluA2 tank are given in Table T. It wm.ll 
be noted that the most important area of leskage is the 75 mm gun mount. The 
problem of sealing this point of leakage is complicated by the movement required 
in elevating and depressing the gun. It is believed possible, however, to reduce 
the leakage by suitable gaskets without interfering with the movement of the pun. 
Other leakage areas such as the turret and bow hatches are easily sealed by proper 
packing. 
From these data it is concluded that the fighting compartment of the series 
M-ii tanks can be effectively sealed and maintained under a pressure of one-half 
inch water gauge, with a ventil ting system of a moderate capacity which will 
permit its installation in the tank in space now available. This requires that 
the ventilation of the crew compartment be separated entirely from the ventilation 
of the engine compartment and that the bulkhead be sealed. Further investigation of this problem is under way and an Ml|A3 tank has been 
equipped with a system of positive ventilation for determination of the internal 
pressure required for effective gas protection0 With only the bulkhead and 
ventilators sealed, an air flow of approximately pOO cfm has been found sufficient 
to produce an internal pressure of one-inch water gauge» With moderately effect- 
ive sealing of the gun mount and other leakage areas, the air flow requirements 
will be reduced considerably below 500 cfm. TABLE I 
AIR FLOW THRU IMPORTANT LEAKAGE ARSAS IN MR A 2 Tank 
AT AND 1” STATIC PRESSURES"" 
Air Flow 
- Cfm 
Leakage Area 
Static Pressure in Tank 
Water 
1" Water 
Turret Hatch Race 
12 
16 
Turret Hatch 
5U 
77 
Driver’s and Ass't. Driver's Hatches 
he 
62 
Periscopes (five) 
85 
120 
Gun Mount 
116 
165 
Thru 75 mm Gun, Breech Closed 
27 
38 
TOTAL 
■ 
O 
U78 
■ — AIR FLOW THRU IMPORTANT LEAKAGE AREAS IN M4A2 TANK IN 
RELATION TO TANK PRESSURE 
FIG. 1