Armored 
Medical Research Laboratory 
Fort Knox, Kentucky 
Report On 
CONTROL OF GUN FUMES IN M-4 SERIES MEDIUM TANKS 
Project Nos. 3-1, 3-3 
February 15, 1943 ARMORED FORCE MEDICAL RESEARCH LABORATORY 
Fort Knox, Kentucky 
Project Nos, 3-1 and 3-5 
File No. 724.41 
February 15, 1943 
CONTROL OF GUN FUMES IN 
M-4 SERIES MEDIUM TANKS 
10 PROJECT: Determination of the Characteristics and Effects Upon 
the Crew of Gun Fumes from Firing of the Weapons in Tanks of the M-4 
Medium Series and Development of Effective Control, 
a. Authority - Letter Commanding General, Headquarters Armored 
Force, Fort Knox, Kentucky, 400»112/6 GNOHD, dated September 24, 1942, 
b. Purpose - To determine the magnitude of the hazard resulting 
from the gun fumes in the M-4 series of medium tanks and the development 
of effective means for the control of the hazard. 
20 DISCUSSION: 
a. Methods - 
(1) Fire pattern0 The quantity of gas released inside the 
tanks in a given period of time increases with the rate of gun fire0 It 
is necessary, therefore, to employ a standard fire pattern in the evaluation 
of the hazard which approximates the maximum rate which may be encountered 
in combat. In the tests reported herewith, the following fire patterns were 
employed: 
75MM GUN 
The gun was fired in bursts of five rounds each with a time interval 
of five minutes between bursts and approximately ten seconds between rounds. 
Six bursts or a total of thirty rounds were fired in a complete test which 
extended over a period of thirty minutes. 
MACHINE GUN 
One belt of 250 rounds was fired in approximately four minutes at a 
rate of two rounds every two seconds. Four belts were fired in a total per- 
iod of twenty minutes to constitute a complete test. The average rate of 
fire was therefore 3000 rounds per hour. 
1 (2) Permissible gas concentrations. Of the gases produced 
by gun fire, carbon monoxide is the most important from the standpoint of 
toxicity. The maximum concentrations of this gas which may be breathed 
with safety varies with length of exposure. In these tests an average 
concentration of 0,05 percent was established as a maximum permissible 
value. For an exposure of one-half hour or less this atmospheric con- 
centration will produce no perceptible effect, and for an exposure of one 
hour only a slight headache. 
(3) Tank operation. The tank was completely buttoned-up and 
except in special tests the motor was operated at its normal idling speed. 
It was not possible to orient the tank with respect to wind direction, but 
in general the wind was from the rear. 
(4) Ami-irnitionc 75 mm: AP M-61 FHH and super TIE Machine 
gun: Calibre 30 ball. 
3. CONCLUSIONS: 
a.0 M-4 and K-4 A-l tanks. The concentrations of carbon monoxide 
produced by the 75mm gun and by the turret and bow machine guns were below 
the maximum permissible concentrations of 0,05 percent. There was, however, 
definite eye irritation resulting from ammonia produced by the 75 mm gun. 
b, L-4 A-2, N-4 A—3, and N-4 A-4 tanksu 
(1) The concentration of carbon monoxide in the turret result- 
ing from the firing of the ?5mm *un exceeded the maximum concentration of 
0,05 percent and is a very real hazard to tank personnel, 
(2) The concentration-of ammonia in the turret was such as to 
casue considerable eye irritation and watering. As a result, the commander 
and the gunner were frequently unable to see the target. This condition 
alone is serious enough to make necessary the installation of control meas- 
ures, 
(3) The concentration of oxides of nitrogen was within the 
perm! ssible .1 evel 0 
(U) There was no accumulation of curbon monoxide from one 
burst to another with repeated firing of bursts at five minute intervals. 
(5) The direction of air flow toward the rear of the tank 
prevents the passage of gun fumes from the turret into the bow. As 
a consequence, the driver and the assistant ‘driver are not exposed to ex- 
cessive concentrations of carbon monoxide from the gun. 
(6) Concentrations of carbon monoxide generated by the turret 
and bow machine guns were below the permissible concentrations of 0*05 per- 
cent * 
2 £. Control of gan fumes. 
(1) Increasing the engine speed is an effective .method of 
control of fuiaes from the 75 l<M gun, 
(2) A high velocity jet blowing down across the breech was 
also effective in controlling the fumes„ 
(3) An exhaust system directly over the breech of the gun 
which removed the contamination through the turret ventilator was found 
to be effective with or without the tank engine operating,, 
(4) The rate of exhaust ventilation required was 130 cfm 
with a total resistance of 0,$5 inches, water gauge» 
(5) An exhaust system which meets the above specifications 
has been installed in an M4A3 tank and was found not to ILoit the depression 
of the gun or otherwise interfere with normal operations in the turret. The 
essential requirements of the system are shown in Figaro I accompanying this 
report. Power requirements and superiority of this method over others is 
discussed in Appendix III. The reasons for including the M4 and M4A1 .models 
in this recommendation ore also discussed in Appendix III. A pilot model is 
available at the Medical Research Laboratory. 
Ac RECCm'LEDATIOKS: 
a, Install a turret exhaust system, in all tanks of the M4 series 
to be shipped overseas, 
b0 Provide kits for the field installation of such an exhaust 
system in all *'4. tanks now overseas, 
£o The capacity of the exhaust system to be not less than 150 
cubic feet per minute-with the inlet located over the breech at recoil 
position. Hie essential requirements are shown in Figure 1 of the Appendix, 
Submitted By; 
Lt. Col. Hatch 
Captain Heison 
Captain Horvath 
Lieutenant Eichna 
Lieutenant Walpole 
approv ad u* w '4: & 
willard machle 
4 Inclso Lieut. Col.? Medical Corps 
jgrl - Appendix I, Sampling arid Analysis Commanding 
if2 ~ Figure I, Essential Hequireiaents of 
iixhaust System 
#3 - Appendix IIy Gun Fume Concentrations in M4 Series of Tanks, 
with Table.. I thru IVa and Figures 2 and 3 
#4 - Appendix III, Control of Gun Fumes in the M4 Series of Tanks, 
with Tables V th~u VII, and figures a thru 6 
3 APPENDIX I 
SAMPLING AND ANALYSIS 
1, Carbon Monoxide. 
a. Collection of air samples: Three methods were employed. 
(1) The Mine Safety Appliances continuous indicator. 
(2) Instantaneous samples in evacuated flasks for the 
determination of peak concentrations and clearance rates at the end of 
firing, 
(3) Continuous samples in evacuated flasks, sampling being 
continued at a constant rate throughout a given test in order to determine 
the average concentration for a given condition. Samples 'were collected 
in this manner at one or more crew positions. 
b. Blood samples for the determination of carbon monoxide con- 
tent v/ere obtained from the tank crew members in the standard manner be- 
fore and at the end of all complete tests. They were not obtained in 
exploratory tests, 
c. CC Analysis; Evacuated flask samples were analyzed by the 
iodine pentoxide method and blood samples by the Scholander-Roughten and 
Spectro Photometric methods. The MSA GO indicator was’checked at regular 
intervals against known air-CO mixtures. 
2, Concentrations of ammonia and oxides of nitrogen were determined 
in portions of the instantaneous flask samples, employing the Nessler and 
phenoldisulphonic acid procedures respectively. 
1 FAN TWISTED 
. it 
APPROX, /jf TO 
HAT C! 
~RECOIL GUARD RAIL 
CUTOUT 
OF GUN 
D/A. OF TURRET 
HATCH CUTOUT 
CUTOUT TO ACCOMMODATE 
OPERATING CRANK CAM 
EXISTING VENT OPENING 
LOCATION OF 
INLET 
w 
FAN CAPACITY• 150 CFM 
ARRANGED TO CLEAR GUN 
RECOIL 
GUN AT MAX. 
DEPRESSION 
TURRET EXHAUST SYSTEM FOR M4 MEDIUM TANKS 
SHOWING LOCATION IN RELATION TO VENTILATOR AND GUN 
Fig.I APPENDIX II 
GUN FUME CONCENTRATIONS IK M-4 SERIES OF TANKS 
The results of gun fume tests in the standard M-4 series of tanks, 
with normal ventilation, are tabulated in Tables I to 4 and are shown 
graphically in Figures 2 and 3. 
10 75Mm Gun. 
The average concentrations of carbon monoxide from the ?5Mm gun 
(Table I) were found to be in excess of the acceptable limit of 0„05 per- 
cent in the turret of the M-4 A-2, M-4 A-3 and M-4 A-4 tanks and somewhat 
below this value in the M-4 and M-4 A-l tanks. The more favorable con- 
centrations in the latter models result from the higher rates of ventil- 
ation which are provided. These- tanks are operated by air-cooled engines 
and have two oil-cooling radiators in the bulkhead whereas the other models 
have only one. As a consequence of the greater area of openings in the 
bulkhead, more air is drawn through the fighting compartment into the 
engine compartment, 
The concentration of CO'at the driver’s position in the bow of 
the li-4 A-3 tank was low, indicating that little of the contamination from 
the turret reaches this forward position in the tank. 
Concentrations of carbon monoxide in the blood of the crew members 
(Table II) were in approximate agreement with the atmospheric concentrations 
with the highest blood saturation values for the loader, and no significant 
increase in either of the two bow crew members. 
There was no evidence of accumulation of carbon monoxide from one 
burst to another. This is shown for the M-4 A-3 in Figure III and similar 
results were obtained in the other tanks, It must be noted, however, that 
with higher rates of fire removal of the contamination would not be complete 
between bursts and, as a consequence, the average concentration of carbon 
monoxide would be higher. With a two minute interval between bursts, for 
example, the average CO concentration would be more than 2-1/2 times higher 
than the values here reported. 
Ammonia was found to be troublesome in the turret and in certain 
tests was sufficiently strong to cause irritation of the nose and eyes with 
considerable watering cf the latter. Concentrations of ammonia immediately 
after the fifth round of a single burst ana the subjective symptoms of the 
turret crew members are given in Table III. It will be noted that the 
commander and even the gunner suffered some temporary loss of effective- 
vision as a result of tae irritation. This is obviously undesirable since 
it occurs at a critical time when these two crew members are in particular 
1 need for maximum vision. Quite apart from the more subtle action of 
carbon monoxi.de, this immediate effect is sufficiently serious to require 
effective control of gun fumes. 
Oxides of nitrogen were found to be present in the gun fumes but 
never in concentrations above 15ppm, which is well within the safe concen- 
tration for the period of exposure involved. Concentrations of methemoglobin 
in the blood of crew members were also found to be insignificant. Thus, the 
oxides of nitrogen may be considered unimportant, from the present findings. 
2. Machine Guns. 
Carbon monoxide concentrations resulting from operations of the 
turret and bow machine guns (Table IV) did not exceed 0.C5 percent in the 
M-4 A-3 tanks. Ammonia concentrations were also low (Table IVa) and no 
eye irritation was reported. 
Since the ventilation in this tank is no better, basically, than 
in the 1-4 A-2 and li-4 A-4 tanks the findings reported in Table IV may be 
considered representative of all three. In the case of the M-4 and M-4 A-l 
models, lower concentration undoubtedly would be found, as was the case with 
the 7gun. It is to be noted that little of the contamination from the 
turret machine gun reached the bow crew members, and conversely, the turret 
crew members were not affected by the operation of the bow machine gun. 
Blood concentrations of carbon monoxide for various crew members are given 
in Table IVa. It is evident from these findings that the bow and turret 
machine guns do not produce a hazard or unpleasant eye irritation when 
fired at a rate of 3000 rounds per hour. 
3. CONCLUSIONS. 
From the foregoing data, it is concluded that more effective re- 
moval of gun fumes from the 75Mm gun is required in the M-4 series of tanks. 
The M-4 and M-4 A-l are included in this recommendation, in spite of their 
favorable showing with respect to carbon monoxide, because of the eye 
irritation noted in the turret crew members, and the fact that when used 
as pill-boxes with the tank motor not running, these tanks are no better 
than the others of the series. 
If the proposed changes in tank ventilation cannot be made in all 
tanks immediately it would be desirable to equip the M-4 A-2, M-4 A-3 and 
M-4 A-4 models first. 
2 TABLE I 
CARBON MONOXIDE CONCENTRATIONS FROM 75Mm GUN 
And 
CLEARANCE RATES IN SERIES M-4 TANKS 
Standard Conditions of Ventilation 
Tank 
Model 
No 
Average 
Concentration-Percent 
Average 
Peak Cone. 
Percent 
Loader 
Clearance * 
Rate 
of 
Bursts 
Loader 
by 
MSA 
Cent. Flask Samples 
Loader 
Commander 
Gunner 
Bow 
M4 
6 
0,039 
0.037 
0.029 
0.022 
0.247 
5 Sec. 
M4 A1 
2 
0.031 
0.243 
17 Sec, 
M4 A2 
2 
0.054 
0.125 
0,350 
33 Sec 0 
M4 A3 
6 
0.070 
0.099 
0.122 
0,016 
0.330 
32 Sec. 
M4 A4 
6 
1 
0.123 
0.330 
50 Sec. 
-a- Time to clear >0 percent after five rounds fired 
3 TABLE II 
BLOOD CONCENTRATIONS OF CARBON MONOXIDE IN CRM.. MEMBERS 
AFTER FIRING 6 BURSTS WITH 75Mrn GUN 
(30 Min. exp0 to cyclical CO cone, in Air) 
Tank 
Crew Lember 
CO Hemoglobin 
Percent Total Pigment 
Aver. CO. cone, in 
Air (Cont, Flask Sample) 
Before 
Exp. 
After 
Exp. 
Increase 
M4 
Loader 
0 
13.3 
13.3 
0.037 
75Mm 
Commander 
0 
4.5 
4.5 
0.029 
Gun 
Gunner 
0.5 
4.5 
4.0 
0.022 
U14 A3 
Loader 
0.1 
20.0 
19.9 
751m 
Commander 
0.0 
14.3 
14.3 
0.087 
Gun 
Gunner 
4o9 
15.0 
10.1 
0.108 
Driver 
5.0 
5.9 
0.9 
Asst. Driver 
1.4 
1.7 
0.3 
0.016 
M4 A4 
Loader 
0 
22 o 5 
22.5 
75Mm Gun 
Commander 
1.5 
14.7 
13.2 
0.123 
Gunner 
3.3 
8.8 
5.5 
Driver 
2,8 
4.3 
1.5 
Asst. Driver 
2.6 
4 TABLE III 
ALMONIA CONCENTRATIONS FROLI 75Mm GUN 
And 
REPORTED EYE EFFECT 
Tank 
Range in Ammonia 
Cone, - ppm * 
Effect Upon Eyes of Turre 
t Crew 
Loader 
Commander 
Gunner 
M4 
105 - 210 
Irritation 
Very little 
smarting 
Very little 
smarting 
M4 A2 
2A0 to 270 
Watering 
Watering 
Watering 
MA A3 
180 to A10 
Watering 
Watering 
Smarting 
MA Aa 
210 to 350 
Mod. Smarting 
Watering 
None 
Mod. Smarting 
Watering 
* At loader's position, approximately 10 seconds after 5th round of burst 
5 TABLE IV 
CARBON MONOXIDE AND AMMONIA CONCENTRATIONS 
FROM 
MACHINE GUNS 
Standard M-4 A-3 Tank 
No. 
Aver* 
QARBOM MONO 
TIDE CCNCENTR\TIONS - 
Percent 
Belts 
Fired 
HSA 
Spot 
Flask 
Aver. Concentrations by 
Cont. Flask 
Gun 
Loader 
Turret 
Bow 
Loader 
Gunner 
Driver 
Asst, Driver 
Turret Mach- 
ine Gun 
4 
0*034* 
0.046 
0.018 
0.017 
Bow Machine 
Gun 
’4 
0.022** 
0.006 
0*015 
0.050 
Ammonia Cone, - ppm 
Spot Sampa.es at. End of Each Belt 
Turret Mach- 
ine Ch m 
4 
30* 
Bow Machine 
Gnn 
4 
42*~* 
* At Loader’s Position in Turret, Average of 3 Samples. 
*-> At Aset. Driver’s Position in Bow, Average of A Sampler. 
6 TABLE IVa 
BLOOD CONCENTRATIONS OF CARBON MONOXIDE 
IN CREW MEMBERS 
AFTER FIRING 4 BELTS IN TURRET AND BOW MACHINE GUNS 
(20 min. EXP.) 
Gun 
Crew Members 
CO Hemoglobin 
Percent Total Figment 
CO 
Average Cone, in 
Air (Cont0 Flask Sample) 
Before 
Expo 
After 
Exp. 
Increase 
M4 A3 
Loader 
4,8 
0,046 % 
Turret 
Gunner 
7o2 
0.018 
Gun 
Driver 
4c3 
0.017 
Asst.Driver 
2o6 
M4 A3 
Driver 
4.3 
3.9 
0.015/ 
Eow Gun 
Asst.Driver 
2.6 
6.2 
3.6 
0.050 
- 7 - Legend ■ 
Peak Cue 
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7Aver Cc/jc 
Couc. By MSA. 
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t • 
RBBCEAJT 
jsaaal 
M4A4 
M^AjI 
O.ZC 
A/CA/O/fOP 
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3 
0, 
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Tf i :E - /’/ ores 
5 o 
S o 
Cad.eo>i M Concentrations Rf /v,-c.,£ /C 
StMnl / re T/ • 
/ i Cr ISSk&HQ. 
Peak Conc. : 
— Die away Cohc. 
Ave Gong. 
- Comc br M.5.A. 
Rds. Fip:ed 
v t 
0.50 
PERCENT 
0.20 
mono xj'Df 
gunnJee 
Q.lO 
COMMANDER 
C A.RBC3N 
I ASS T 
'deivee 
0 
5 
10 
Ml. 
15 
20 
25 
50 
Carbon Monoxide Comc. Trpm Rfpeated p»f?e of Bursts of* Fsve Rf ;nds 75 MM Standard M 4A5 
Time 
Minuted 
Fig 3 APPENDIX III 
CONTROL OF GUN FUMES IN THE M-4 SERIES OF TAJIKS 
Ventilation of the fighting compartment of the M-4 Series of tanks is 
incidental to the engine ventilation. The engine-coo ling fan drav/s some 
of its air from the fighting compartment through one or two radiators and 
certain other openings in the bulkhead. The primary purpose of this air is 
to cool the transmission oil, and in the case of an air-cooled tank motor, 
the engine oil. Air gains entrance into the fighting compartment through 
four special ventilators in the hull and turret and through other cracks 
and joints in the structure, such as around the ?5Mm gun. 
The rate of ventilation through the fighting compartment is a function 
of the engine speed and is at a minimum when the tank is buttoned-up and 
the engine operating at its idling speed. It falls, of course, substantially 
to zero when the tank engine is not running. Since the guns are most commonly 
fired when the engine is idling it is clear that effective means for control 
of gun fumes must be provided when the rate of tank ventilation is at a 
minumum. 
The distribution of air flow through the fighting compartment is not 
uniform. It has been found, for example, that the rate of effective venti- 
lation in the turret is only one-quarter of the total rate of ventilation through 
the tanks. Thus, the concentration of gun fumes which builds up in the turret 
is four times higher than it would be if the ventilation were uniform through- 
out the tanks. In this connection, it may be noted that the special venti- 
lators, owing to their limited capacity, have little influence upon the dis- 
tribution of air flow. The flow through a single ventilator amounts to only 
9 percent of the total. 
Three methods of control of gun fumes were investigated 
1, Increasing Rate of Ventilation by Increasing Engine Speed. This 
method has the advantage of requiring no modification in the tanks or its 
parts and is immediately applicable to tanks in the field. Its disadvantages 
are that it requires coordination of function between the driver and gunner 
and is undesirable from the standpoint of engine maintenance. The vibration 
produced may also interfere with effective gunnery. 
2. Improving Distribution of Air Flow Within the Tanks. Since the 
rate of effective ventilation in the turret is only one-quarter of the over- 
all rate of tank ventilation, more complete internal air mixing would reduce 
the carbon monoxide concentration. The power required to increase the 
effective ventilation rate in the turret by this means should be less than 
that required to provide an actual increase in the flow of outside air through 
the turret. 
1 3o Removal of Gun Fumes by Exhaust Ventilation Through the 
Turret Roof Ventilator. This method contemplates the direct removal of 
fumes as they escape from the gun and before being dispersed into the 
surrounding atmosphere. It should be independent of the main tank ventil- 
ation and work effectively when the tank engine is not running. Limitations 
in this method are that the installation must not interfere with normal 
elevation and depression of the gun and the power requirements must not 
exceed the supply available. 
The three methods of control of fumes from the 75MM gun have been 
investigated, with the results reported below; 
1. Increasing Engine Speed. 
In these tests the engine speed was increased before firing 
started and was maintained at the higher RPM for two minutes during each 
burst. The resulting carbon monoxide concentrations in the turrets of 
the M-4 A-2 and M-4 A-3 tanks at increased engine speeds are compared with 
the results obtained ft normal idling speeds in Table V, and are represented 
graphically in Figure 4. The increased ventilation obtained by this means 
reduces the average CO concentration below the acceptable concentration of 
0.05 percent. It is of interest to note, that the peak concentrations 
immediately after the fifth round were not reduced. The rate of clearance 
however, was increased three-fold or more, and as a consequence, the aver- 
age concentration was reduced. It is evident that this is an effective 
method of controlling gun fumes. 
TABLE V 
CARBON MONOXIDE AND AMMONIA CONCENTRATIONS FROM 75MM GUN 
AND 
CLEARANCE RATES AT VARIOUS ENGINE SPEEDS 
Tank 
Model 
No 
of 
Bursts 
engine 
Speed 
RPtf 
CARBON MONOXIDE - 
PERCENT 
Peak 
Ammonia 
Cone. 
PPM 
Aver, Cone 
At Loader 
By MSA 
. Thru Burst 
s Position 
Cont. Flask 
Aver. Peak 
Cone. 
Loader 
Clear- 
ance 
Rate 
MA A2 
2 
300-A00 
0.05A 
0.125 
0.350 
33 Sec 
2A0-270 
MA A2 
2 
1130-1200 
0.012 
0,011 
0.165 
5 Sec 
MA A3 
6 
500 
0.070 
0.099 
0.330 
32 Sec 
P.80-A10 
MA A3 
2 
1000 
0o031 
0.032 
0.333 
12 Sec 
110-305 
MA A3 
1 
1300 
0.01? 
0.020 
0.6A9 
5 Sec 
3A0 
2 2, Internal Air Mixing0 
Several methods of increasing the rate of effective ventil- 
ation in the turret were investigated with the results shown in Table VI 
and in Figure 5. 
In the first test, a centrifugal fan with a capacity of 250 
cfm was placed on the turret floor and arranged to draw in relatively 
clean air and blow it upwards across the breech in order to increase the 
rate of ventilation in the upper zone of the turret. With this change in 
ventilation the commander and gunner were completely free from contamination. 
No improvement was noted, however, at the loader’s position. In spite of 
the greatly increased rate of ventilation, the gun fumes we re not dispersed 
and diluted in the air stream before reaching the loader’s breathing zone. 
A centrifugal fan mounted directly over the breech and dis- 
charging toward the floor improved conditions but there was considerable 
rebound of the contaminated air from the turret floor which carried the 
gas back through the breathing zone of the loader. 
Best results were obtained by means of a six inch propellor 
fan mounted over the gun and arranged to blow down against the breech 
mechanism rather than directly across the breech. The result was to 
create a downward air movement after deflection off of the gun. The "slug” 
of contamination was broken up as it emerged from the gun and there was 
little rebounding of the contaminated air. As shown in Figure r, the car- 
bon monoxide concentration at the loader’s position was well below the 
acceptable maximum of 0oC5 percent. 
Another method of internal mixing which gave satisfactory 
results was to blow a small volume of air at high velocity downward across 
the breech at an angle toward the rear of the turret. The purpose of the 
high velocity jet was to break up the "slug" of contamination issuing from 
the gun, and mix it with the veltilating air stream and the low rate of 
air flow was employed so as to minimize icebound into the upper zone of the 
turret. Of the several methods of internal mixing, this has the greatest 
practical value owing to the fact that it requires only a small air supply 
tube mounted on the gun while the low-capacity fan can be located at a 
convenient remote spot. In contrast, a fan mounted directly over the gun 
would interfere with the normal depression of the gun. 
3 TABLE VI 
CARBON MONOXIDE CONCENTRATIONS FROM 75Mm GUN 
AND CLEARANCE RATES 
INTERNAL AIR MIXING IN TURRET 
CO Cone. - 
Percent 
Tank 
Loader 
Average 
Model 
Mixing Arrangement 
By 
MSA 
By 
Cont. 
Flask 
Peak 
Cone 
Loader 
Clearance 
Rate 
M4 A2 
Centrifugal Fan on Floor Blow: 
Toward Breech at 250 CFM 
Lng 
0.06? 
0.105 
0.365 
30 
Sec« 
M4 A3 
Centrifugal Fan Over Breech 
Blowing D0wn Velocity at 
Breech - 1000 FPM 
0.056 
0.070 
0.400 
30 
Sec 0 
M4 A3 
Centrifugal Fan Over Breech 
Blov/ing Down Velocity at 
Breech - 250 FPM 
0.048 
0.061 
0.170 
40 
Sec, 
M4 A3 
6" Prop. Fan Over Breech 
Mechanism and Blowing Down 
0o015 
0.013* 
0.103 
M4 A3 
High Velocity Jet Blowing 
Down at Angle Toward Breech 
Air Vol-50cfm. Velocity at 
Breech - 5900 fpm 
0.021 
0.021* 
0.076 
* Estimated from MSA readings 
4 3. Local Exhaust Ventilation. 
The practical application of this method of control is de- 
termined by the space requirements of the apparatus (intake duct, fan 
and motor), the rate of exhaust ventilation required and the amount of 
power needed to force the air out through the restricted opening of the 
ventilator. The purpose of the test here reported was to determine the 
minimum rate of exhaust ventilation and the power requirements of an 
effective system. Results are shown in Table VII and Figure 6. 
In the first test air was exhausted through the turret ven- 
tilator without any intake duct. There was considerable improvement in 
the turret atmosphere but owing to the distance from the gun breech to 
the ventilator the removal of gases was not complete. In subsequent tests 
an intake duct was carried from the ventilator along the roof to a point 
directly over the breech of the gun. Two tests were conducted with rates 
of air flow of 130 and 90 cfm respectively. The CO concentrations with 
the lower rate of air flow were below the limit of 0,05 percent but there 
was noticeable eye irritation. It is concluded, therefore, that the higher 
value of 130 cfm represents the minimum effective rate of exhaust ventilation. 
Of great practical importance is the fact that the exhaust 
system gave satisfactory control of gun fumes without any general ventil- 
ation of the fighting compartment, that is, with the tank engine not run- 
ning. No eye irritation was reported with the exhaust system in operation. 
■ The overall resistance of the exhaust system with 130 cfm was 
0.55 inches, water gauge. Thus, the theoretical power required to operate 
the system is less than 10 watts. Owing to the restricted space over the 
gun, however, and the limited area of opening into the ventilator, the 
conditions are not favorable for the installation of a highly efficient 
fan. In fact, a fan of special design is required if high fan speed is to 
be avoided. An efficiency of 30 to 40 percent would increase the power 
requirement to 30-40 watts. 
An exhaust system with intake duct, special fan and motor is 
now being built which will fit into the allowable space and not interfere 
with the depression of the gun. The system is shown diagramatically in 
Figure I, 
5 TABLE VII 
CARBON MONOXIDE CONCENTRATIONS FROM 75Mm GUI: 
AND CLEARANCE RATES 
EXHAUST VENTILATION IN TURRET 
CO COKC. - PERCENT 
Loader 
Average 
Peak 
Tank 
Model 
Exhaust Arrangement 
% 
MSA 
By 
Cont, 
Flask 
Peak 
Cone. 
Loader 
Clear- 
ance 
Rate 
Ammonia 
Cone. 
PPM 
V4 A3 
Exhaust at 130 Cfm Thru Turret 
Vent. No Inlet Duct 
0.037 
0o051 
0,206 
125 
M4 A3 
Exhaust at 90 Cfm Inlet Duct 
Opening Over Breech 
0.036 
0.043* 
Mi, A3 
Exhaust at 130 CFM Inlet Duct 
Opening Over Breech 
0.020 
0.016 
0.119 
16 Sec. 
65 
M4 A3 
Exhaust at 130 CFM Inlet Duct 
Opening Over Breech. Engine 
Not Running 
0o031 
0.014 
0.109 
25 Sec. 
80-140 
* Estimated from MSA 
6 o.Zd 
{ 0,335 
.C.44-9 
M~4A-2 
££g£p 
t/So e,f?H 
, 
£ajg/k/£ srssp 
tooo £.5M. { 
M- 4 A-3 ; 
£a/0/a/£ 3p££0 
\ / 500 e. 5M. ! 
Ca bboaJ //lOKtoxfoS' r 
LcOFfQ 
10.20 
PrA& C6A/4. 
- P‘PAWA Y C&^C. 
A V4T- £c>aSC, 
~Coa/c. 3r' /vfSA 
II £2PS. £/C£p 
o.to 
0 
5 O 
50 
5 
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Op five ~75mm at_ H/gh £/xo/k'£ S/Qc^ds 
F/&. 4 0,50 
i I 
M-4 A-3 - | 
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AT 250 F.F/F. 
I M~4 A-3 
6 ' a’FoP. Fa a Bov'S 
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OA/ ro B/2££CH 
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£?££/. EC T/a/G GOA/ 
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Aceoss B&eEcM. Jej 
\ZScoc/ry at 3e£€&s~ 
5900 /T f?M, 
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— \A/A Y COA/6. 
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COa/c. OY M3 A 
bmi FoS. Fe£p 
a/c 
0 
5 0 
5 0 
S 
T/A/IE - A4//JOTF5 
CA&Bo/J MO/JOK/DS CoSo 7FA T/OA/ FjeoM OOJFST OF F//CF OF F/OS 
&CUA/OS 75mm Wjtj± /A/rzeASAL. M/a/a/g Cfz. A/& A/ Fuf/ff T 
//<?. 5 0.50 
■ I I i 
EL4A3 
£xh. vent * tie c/TH 
Mo Intake Duct 
Eng Idling soo npn 
i 
i, i 
Dxh Vent -- /SO CDM. 
With intake Duct 
Eng Idling 500 k PM 
maaA 
Exh Vent • 150 CFM. 
With Intake Duct 
Eng. Not Runn/hC 
■ 
0.20 
~ 
Peak Conc. 
O/fa way Cone. 
A vf Cone 
Cone. 1/ M 3 A. 
Pros. FtfZFO 
Carbon Mon ox /or -/ bfcrnt 
0.10 
5 
o 
s 
o 
0 
Time minutes 
Carbon Monokidf Coa/cfnfrat/on From Burst of F/re of Five /Founds 
7S M.M. With Exhaust Ventilation /n Torrl&t 
F/&.G