Armored Force 
Medical Research Laboratory 
Fort Knox, Kentucky 
PROJECT NO. 3 - TOXIC GASES IN ARMORED VEHICLES 
Final Report On 
Sub-Project No, 3-13 - Determination of the Characteristics 
and Effects Upon the Crew of Gun Fumes 
from Firing of the Weapons in the K? 
Tank 
Project No# 3-13 
Arpil B, 1943 ARMORED FORCE MEDICAL RESEARCH LABORATORY 
Fort Knox, Kentucky 
Project No. 3-13 
724.41 GNOML 
April d, 1943 
1* PROJECT: Noa 3 - Toxic Gases in Armored Vehicles. Final Report 
on: Sub-Project No. 3-13, Determination of the Characteristics and Effects 
Upon the Crew of Gun Fumes from Firing of the Weapons in the M? Tank. 
a, Authority - Letter Commanding General, Headquarters Armored 
Force, Fort Knox, Kentucky, File 400.112/6 GNOHD, dated September 21, 1942. 
b. Purpose - To determine the extent of the hazard from fumes 
released by firing of the weapons in the M? Tank. 
2. DISCUSSION: 
a. Methods and Conditions 
(1) Fire Pattern« 
(a) 75 nan gun; The weapon was fired at the rate of one 
round every 10 seconds in bursts of five—one burst being fired every five 
minutes, 
(b) Machine guns: One belt of one hundred rounds, fired 
in approximately 2 minutes. The interval between belts was approximately 
2 minutes; total, for each gun, 300 rounds, in 9 minutes, 20 seconds. 
(2) Ammunition. 75 mm; Super HE M48. Machine gun. Caliber 
.30 ball. 
(3) Tank Operation. Tank buttoned up and motor running at 
normal idling speed. Auxiliary generator vent to engine compartment open. 
Wind quartering from rear, 10 mph. Full crew in tank. Two tests were 
carried out with the 75 ram gun. In the first, all ventilating fans were 
on intake; in the second, the fans were exhausting air from the tank, 
(4) Analysts. Air samples were analyzed for carbon monoxide 
and ammonia by methods previously reported (Report on Projects No. 3-1, 3-5, 
February 15, 1943)* Analysis for nitrous fumes were not carried out, earlier 
studies with the same ammunition having indicated the absence of any signifi- 
cant amounts. Results of the tests are given in the Appendix0 2. CONCLUSIONS; 
a. 7$ mm Gun. 
(1) The average carbon monoxide concentration at the loader's 
position was with the ventilating fans on intake. Some improvement 
was obtained with the fans exhausting, but not enough to insure satisfactory 
conditions. 
(2) There was no accumulation of carbon monoxide in the tank 
air from one burst to another„ 
('3) Sufficient ammonia was “present in the turret during firing 
to cause eye and nose irritation., 
(h) Negligible amounts of fumes reached the bow members of the 
crews, 
(£) Improvement of the turret ventilation in the M7 tank is 
needed® 
b. Bow Machine Gun. 
(1) The average carbon monoxide concentration at the breathing 
zone of the bow gunner was 0.05>3f. 
(2) The blood of the bow gunner did not contain a serious 
accumulation of carbon monoxide. 
(3) Gunner did not believe fumes or ammonia, interfered with 
operation of weapon, 
(ii) Ventilation is adequate for operation of bow machine gun. 
c. Turret Machine Gun. 
(1) The average concentration of carbon monoxide at the loader’s 
position was 0.173$ and dropped only slightly below 0.1$ during re-loading. 
(2) The blood of each of the turret crew members showed dangerous 
accumulations of carbon monoxide. 
(3) Concentration of ammonia and other irritating fumes in 
turret were sufficiently intense to make operation of the weapon extremely 
difficult and unreliable. 
(U) The unsatisfactory performance of the turret machine gun 
resulted from the fact that the rauzsle does not extend outside the exterior 
shield. Thus, gases escaping from the muzzle are trapped between the shield 
and turret and are drawn into the turret by the inward air flow0 
► 
(£) Correction of this situation requires changes in the gun 
mount. h, RECOMMENDATIONS: 
a, That the present turret ventilation be modified to provide in- 
creased exhaust ventilation and the exhaust intake to be relocated for more 
efficient removal of fumes from the 7b mm gun, 
b» That the turret machine gun be remounted in such a manner as to 
prevent the entry of fumes from the gun muzzle into the turret. 
Submitted 3y; 
Captain Norton Nelson, SnC 
Captain Steven M. Horvath, SnC 
Lieutenant R. H. Walpole, SnC 
Lieutenant L. W. Eichna. MC 
APPROVED 
WILLARD MACHLE, 
Lieut. Colo, Medical Corps, 
Commanding,, 
1 Incl. 
Appendix I with 
Tables 1, 2, & 3 
Ficso 1, 2, 3, & h 
headquarters armored force 
Office of the Commanding General 
Fort Knox, Kentucky 
April 20, 19b3 
1, Recommendations are approved. However, due to limited number 
of vehicles scheduled for procurement, modifications are not warranted 
at this time. 
2. Accordingly, it is further recommended that existing vehicles 
and vehicles presently scheduled for procurement, be not modified and 
that this report be re-considered when necessitated by future designs. 
For the Commanding General: 
/s/ C. M. Yfells 
C. M. TOLLS, 
Lieut. Colonel, A. G. D., 
Assistant Adjutant General APPENDIX I 
RESULTS 
a. 75 ram gun. 
The average concentration of carbon monoxide at the loader's breathing 
zone, with ventilating fans on intake was (Table 1 and Fig. 1) and 
with fans on exhaust, it dropped to 0.01*5. In both cases, however, there 
was noticeable eye and nasal irritation in the commander's and loader's 
positions. Negligible amounts of fumes reached the bow members of the 
crew and there was no evidence of accumulations of fumes from one burst of 
fire to another. 
In general, the conditions were' noT satisfactory and it is concluded 
that further improvement in the turret ventilation is required. While no 
tests have been made with a modified system of ventilation, it is believed 
that an exhaust system similar to that recommended for the M-J; medium tanks 
would effectively remove the fumes from the 75 ram gun. 
b. Turret machine gun. 
The average concentration of carbon monoxide at the loader's breath- 
ing zone was and failed to drop below O.V% during the period of 
reloading. (Fig. 3) During exposure to fumes from this .gun, the blood 
concentration of carbon monoxide for the turret crew members increased 
at an alarming rate, reaching concentrations of 16, IS, and 23% in only 
9 minutes (Table 3)« These results indicate clearly that a major carbon 
monoxide hazard results from the firing of the turret machine gun. In 
addition to the high carbon monoxide, concentrations of ammonia and other 
irritating fumes were sufficiently intense to make operation of the weapon 
extremely difficult and unreliable. 
The much higher concentrations of carbon monoxide found vdth this 
gun, in contrast to previous findings on machine guns result, for the most 
part, from its mounting. In contrast to the unobstructed gun muzzle in 
other instances, the muzzle in this case does not extend beyond the back 
of the gun shield and only a small hole is provided for the passage of 
bullets. Thus, the gases which escape at the muzzle are trapped behind 
the shield and are drawn into the turret by the inward flowing air. Since 
the inward leakage occurs around the mm gun as well as trie machine gun 
mounts, it is not practical to capture and remove the fumes 'ey exhaust 
ventilation. The best solution of the problem appears to be to extend trie 
muzzle through the shield, or, at least, to provide an opening through the 
shield to allow the gases to escape to the outside. Correction of this 
situation is essential because of the serious magnitude of the hazard which 
now exists. c. Bow machine gun. 
The average carbon monoxide concentration at the breathing zone of the 
bow gunner was (Fig, Ii) and during the test period the concentration 
of carbon monoxide in the bow gunner’s blood did not increase seriously. 
The gunner reported no discomfort or eye irritation during operation of the 
weapon. It is concluded that ventilation is adequate for operation of the 
bov.r machine gun. TABLE 1 
CONCENTRATIONS OF CARBON MONOXIDE AND AMMONIA 
From ?*> MM Gun 
Peak Concentrations 
at End of Burst 
Carbon Monoxide 
Ammonia 
Percent 
p.p.m 
After 1st Burst 
0.17? 
After 3rd Burst 
0.333 
130 
After Uth Burst 
0.565 
3?0 
Aver. Concentration by Cont. Sampling 
Loader 
0.036 
Asst. Driver 
0.01^ 
- 
Clearance Rate after last burst 
(Time for core, to decrease $0%) 
seconds 
TABLE ? 
CONCENTRATIONS OF CARSON MONOXIDE AND AMMONIA 
From Turret Machine Gun 
(Samples taken at Loader's Position) 
- - «■■■■■■ -■ ■ —' • — - — 
~ ► 
Peak Concentrations at vEnd of Belt 
Carbon Monoxide 
Percent 
Ammonia 
p.p.m 
After 2nd Belt 
After 3rd Belt 
0.330 
0.2^2 
115 
iUo 
• 
Aver. Concentration by MSA 
Loader 
0.173 TABLE 3 
BLOOD CONCENTRATIONS OF CARBON MONOXIDE IN CREW MEMBERS 
After Firing Three Belts in Turret and Bow Machine Guns 
(Approx. 12 Min« Exposure) 
Turret Machine Gun 
Carbon Monoxicfe 
Crew Member 
Hemoglobin 
% of Total Pigment 
Gunner 
23.3 
Commander 
16.3 
Loader 
13.1 
Bcw Machine Gun 
< 
Asst. Driver (Gunner) 
i_ 
7.3 CARBON MONOXIDE PERCENT 
CARBON MONOXIDE CONCENTRATION 
M7 TANK 75MM GUN 
FIG. I 
F1G.2 Fig.3 
CARBON MONOXIDE CONCENTRATION M7 TANK 
CAL. 30 MACHINE GUN BY M S. A. INDICATOR 
TURRET MOUNTED CAL. 30 MACHINE GUN 
CARBON MONOXIDE-PERCENT 
MINUTES 
Fig. 3 Fig. 4 
CARBON MONOXIDE CONCENTRATION M7 TANK 
CAL. 30 MACHINE GUN BY M. S. A. INDICATOR 
BOW MOUNTED CAL. 30 MACHINE GUN 
CARBON MONOXIDE-PERCENT 
MINUTES 
Fig. 4