Armored 
Medical Research Laboratory 
Fort Knox, Kentucky 
Final Report 
On 
PROJECT NO. T-2 - TEST OF HEAT LOAD IMPOSED BY PROTECTIVE CLOTHING 
Subject: Ventilation Reouirements of A Ventilated Suit 
Project No. T-2 
21 September 1945 ARMORED MEDICAL RESEARCH LABORATORY 
Fort Knox, Kentucky 
Project Noo T~2 
File SPMEA 727-2 
21 September 1945 
1 e PROJECT: NOo T-2 - Final Report on Project T-2, Test of Heat Los*d 
Imposed by Protective Clothing, Subject: Ventilation Requirements of a 
Ventilated Suit0 
a0 Authority: Letter, 1st x idorsement, Office of the Surgeon 
General, Washington, DoC0, dated 1 December 1944o 
bo Purpose: To determine the ventilation requirements of an impervi- 
ous ventilated suit for use in hot working environments0 
20 DISCUSSION: 
A positive pressure impervious ventilated suit for industrial purposes 
was submitted by Chemical Warfare Service for study by this laboratory0 This 
suit, made of nylon fabric impregnated with neoprene, was ventilated by positive 
distribution of air0 The study was undertaken to determine the volume, the 
temperature, and the water content of the ventilating air that would permit men 
to work in the suit with comfort in environments with dry bulb temperatures up 
to 120°Fo 
3o CONCLUSIONS: 
ac To maintain comfort for men working in environments with dry bulb 
temperatures up to 120°Fo and air movement up to 70 fpm. the following suit 
vehtilation characteristics were satisfactory: 
(1) Air flows from 1<>5 to 205 lbs, per minute0 
(2) Water content of the incoming air below 60 grains per pound 
of dry airP 
(3) If the air flow is 2o0 - 205 lbs0 per minute and the water 
content 45 grains or less, the temperature of the Incoming air 
may vary between 60°Fo and 130°Fo 
1 4o RECOMMENDATIONS: 
a0 That provision be made for a maximum air flow of approximately 
three (3) pounds per minute with lowest possible water content below 60 
grains per pound of dry air, 
bo That provision for individual adjustment of air flow for each 
suit be providedo 
Co That for further improvement of the suit additional studies be 
conducted to determine the best internal distribution of the ventilating air0 
APPROVED 
WILLARD MACHLE 
Colonel, Medical Corps 
Commanding 
Submitted by; 
Theodore F0 Hatch, Lt0 Col, SnC 
James W0 Gregg, P-/* 
Ludwig W. Eichna, Major, MC 
Steven M0 Horvath, Major, SnC 
Walter B0 Shelley, MC 
Charles R0 Park, Captain, MC 
3 Incl»o 
§\ - Appendix 
#2 - Photographs (2) 
#3 - Figure (l) 
2 APPENDIX 
lo DESCRIPTION OF THE VENTILATED SUIT: 
A ventilated suit for certain industrial uses was submitted by Chemical 
Warfare Service for study by this laboratory* The experiments were planned 
to determine the necessary ventilation characteristics© The suit offered for 
testing was not a final model© As such, it was to be studied also to secure 
data and information which would facilitate the construction of improved 
ventilated suits© 
The suit (Photographs Nos 1 and 2) weighed 19 pounds and was made from neo- 
prene impregnated nylon (0©5 mm thick)0 A heavy zipper ran transversely across the 
back to allow the men to enter and leave the suit® The ventilating air entered 
the suit in the back after passing through a seven-foot length of cloth covered 
rubber hose (l"ID)o The air was distributed internally by a spider of smooth 
bore flexible rubber tubing to the most distal parts of the suit (Fig0 1)® From 
the ends of the tubing, the air circulated over the body of the man to discharge 
through a single l£ inch opening in the back of the suit® Three other exit open- 
ings were available but were not used in this test because samples of the mixed 
outflow were desired® 
IIo METHOD: 
The studies were made on eight acclimatized men who walked for two-hour periods 
on a treadmill in a hot room wind tunnel® A complete list of the variables con- 
trolled in each experiment is given in Table 1 together with the range of values 
employed, the method of measurement, and the time of recording data® 
During each test period the man in the suit walked in the nude except for socks 
and low quarter shoes and a control subject walked behind him dressed in herring- 
bone twill fatigues® Interruptions were made to allow the recording of data 
detailed in Table 2® Analysis of this detailed data indicated such large internal 
variations that generalized equations of thermal exchanges between man and environ- 
ment could not be developed® Therefore, these demonstrated limitations of air 
calorimetry in impervious suits allowed only a qualitative evaluation-to be made of 
ventilation requirements® 
III. RESULTS AND DISCUSSION: 
a® Ventilated Suit Design 
Although the suit weighed 19 pounds, this was not considered excessive due 
to the lifting action of the ventilating air0 A free air space of 1 to 5 inches 
was maintained between the suit wall and the surface of the man except for small 
constant areas of contact at the shoulders and inconstant points of contact at 
elbows, knees, and hands0 The ballooning of the suit gave an appearance of greater 
clumsiness than was actually the case0 The subject could walk without difficulty© 
The gloves were satisfactory for grasping but would not permit any delicate manual 
operations© Vision was considerably restricted particularly to the sides and down- 
ward © Fogging of the glass facepiece was no problem© 
Inclo #1 
1 The dimensions of the suit were not adjustable and would not accommodate 
a man of more than 72 inches in height.. The shortness of the shoulder to 
crotch length limited the use of the suit and caused chafing of the skin of 
the groin in most Entering and leaving the suit was difficult des- 
pite the long zipper opening across the back and skin contact with the exterior 
of the suit would easily occur at these times, Assistance was always required 
and tearing at the seams took place on several occasionse The air and water 
tight zipper was not sufficiently durable and was replaced with a Crown type 
zipper which was not air tight„ 
The neoprene impregnation rendered the basic nylon fabric nearly impervi- 
ous to water at the pressure of 1 to 2 mm of mercury used in the suit„ However, 
leakage of sweat was noted on occasion and seepage of water could be made to 
occur either by increasing the pressure or by rubbing the outer surface of the 
fabrico 
Depending upon the volume of air inflow, the air pressure at the entrance 
to the spider ranged from 18 to 40 mm. of mercury0 Because of the low outlet 
resistance internal suit pressures did not exceed 2 mm at the highest flow rates 
(35 cfm) o There was a small change in the temperature of the air during its 
passage through the spider, However, a considerable temperature change occurred 
within a short distance of the outlets due to heat transfer from the body and 
the suite 
The design of this suit should not be considered optimal and several de- 
ficiencies have been indicated0 Because of the excellent protective qualities 
of the ventilating air against excessive heat load it appears likely that a 
simplification of suit and spider construction and particularly a reduction in 
the overall size of the suit would render it less clumsy and better adapted 
for practical use0 Such alterations would change the characteristics of the 
suit as presented here and possibly decrease the demand for cooling and de- 
humidifying the inflowing air0 It is likely that the distributing system with- 
in the suit is unnecessarily complex and offers too high resistance, since 
approximately 40 mm of mercury are required at the inlet to attain an air flow 
of 2o5 Ibs/mino The heat of compression of the air is a drawback under such 
circumstanceso 
bo Ventilation Requirements 
In external environments ranging from 70°Fo to 120°Fo, tolerable 
working conditions in the suit could be maintained over a wide range of inlet 
air temperatureso When the moisture content was kept at less than 45 grains 
per poundp a range of inlet air temperatures from 60°Fo to 130°Fo was accept- 
able o However, optimal comfort* was provided by the use of the lower inlet air 
* Optimal comfort of the subject was associated with the following physiological 
conditions: sweat loss of less than 500 grams per hour and a rectal temperature 
of less than 100°Fo at cessation of a two hour work period,(A work rate of 250 to 
300 cal/hrj 
Inclo #1 
2 temperatures (70° to 80°) 0 An increase in the ventilation rate improved 
the comfort of the subjects and resulted in a lowering of sweat loss and 
final rectal temperatures0 Conditions leading to optimal comfort are 
desirable for maximal efficiency0 Since they vary from individual to 
individual, it is suggested that provision be made enabling each man to 
regulate the volume of air flowing into his suit to meet his specific 
needs for comfort„ 
Precise psychrometric control of the ventilating air is not important0 
The three critical variables controlling heat lose-volumc,,temperature, and 
moisture content-can compensate for one another to a considerable extent0 
Standard air conditioning apparatus having the following characteristics 
will meet the requirements: capacity - up to 3 lbs0 per minute per suit, 
and adjustable by the man; moisture content - down to 45 grains per pound 
of air; temperature of air delivered to the suit - down to 70°Fo (precise 
control not required)0 
3 
Inclo #1 TABLE 1 
Variables Controlled During Each Experimental Period 
Variable 
Range 
Employed 
Method of Measurement 
Time of 
Measurement 
Wind Tunnel DBT 
70°- 121°Fo 
Mercury stem thermometer 
Every 15 mins 
Wind Tunnel WBT 
5a0- 90°Fo 
Mercury stem thermometer 
Motor driven 
psychrometer 
Every 15 mins 
Tunnel Wind 
Velocity 
70 f 20 ft/rain 
Hot wire anemometer 
Velometer 
Every 15 mine 
Suit inlet DBT 
59° - 1340ro 
Mercury stem thermometer 
Every 15 mins 
Suit inlet mois- 
ture content 
41 - SB grs/lb 
Air washer dewpoint 
Automatic 
Constant Ad- 
justment 
Suit inlet air- 
flow 
l«l-2o8 lb«/min 
(15 - 35 cfm) 
Sharp edged pipe 
orifice meter 
Every 15 mins 
Treadmill Speed 
(3o036 Grade) 
2o3-2o4 mph 
Stopwatch 
Initial 
4 
Inclo #1 Variable 
Method of Measurement 
Time of Measurement 
A. Subject in Suits 
Rectal Temp,°F. 
Clinical Thermometer 
At start, 90 mins, & finish 
Skin Temp, °F. 
Copper-constantan Thermocouples (5) 
Every 10 mins 
Sweat Loss* - gms/hr 
Beam balance 
At start, 90 mins, & finish 
Oxygen consumption (Cals/hr) 
Tissot spirometer (12 min collec- 
tion) and Haldane analysis 
At 45 and 75 mins 
B, Control Subject: 
Rectal Temp, °F. 
As above 
At start, 90 mins, & finish 
Sweat Loss - gms/hr 
As above 
At start and finish 
Oxygen consumption (Cals/hr) 
As above 
At 15 mins and 105 fldns 
C, Environmental; 
Suit wall Temp, °F. 
Copper-constantan thermocouples (5) 
Every 10 mins 
Suit air Temp, °F* 
Copper-ccnstantan thermocouples (5) 
Every 10 mins 
Suit air pressure mm Hg 
Mercury manometer 
Every 15 mins 
Suit outlet DBT °F. 
Mercury stem thermometer 
Every 15 mins 
Suit outlet WBT °F. 
Mercury stem ,V.B. thermometer 
Every 15 mins 
Tunnel wall radiation Temp. °F. 
Radiometer 
At start and finish 
TABLE NO. 2 
Variables Observed During Each Experimental Period 
Inclo #1 View of men on treadmill 
showing sorre of test apparatus. 
ARMORED MEDICAL RESEARCH LABORATORY 
FORT KNOX, KY. 
Protect No. T-2 
IThotorrapn No, 1 Back View of Ventilated Suit 
showing apparatus used in the test runs 
ARMORED MEDICAL RESEARCH LABORATORY 
FORT KNOX, KY. 
Photograph #2 
Project No. T-2 FIGURE 1 
SKETCH OF AIR DISTRIBUTION SYSTEM 
WITHIN VENTILATED SUIT 
SPIDER MADE OF NONPERFORATED RUBBER TUBING OF 0.5" I.D. 
(EXCEPT CENTRAL BELT WHICH IS 0.75” I.D.) 
Incl, #3 
FIGURE 1