Armored Medical Research Laboratory Fort Knoxn Kentucky indexed Final Report On PROJECT NO. 35 - DETERMINATION OF THE OPTIMUM METHOD FOR PROTECTION OF TANK CREWS AGAINST CHEMICAL WARFARE AGENTS Project No. 35 13 September 1944 ARMORED MEDICAL RESEARCH LABORATORY Fort Knox, Kentucky Ireject Moa 35 File 470.7 SPliaA 13 September 1944 EFFECTS UPON TAM CREWS OF SEVERAL METHODS OF PROTECTION AGAINST CHEMICAL WARFARE AGENTS 1. PROJECT I Final Report on Project No, 35 - Determination of the Optimum Lethod for Protection of Tank Crews Against Chemical Warfare Agents, a. Authorityi Letter, Array Service Forces, Office of The Surgeon General, Washington, D. G., 8th Indorsement, File 700.2-1 (Fort Knox)N, 3FIDO, dated 24 April 1944. hm Purpose: To determine, by field test, the optimum method for the protection of tank crews against Chemical Warfare Agents from the standpoint of factors other than protection against the chemical agents themselves0 20 DISCUSSION Previous tests have shown that tank crews can be adequately protect- ed against Chemical Warfare Agents by three methods! (l) individual combat masks, (2) individual ventilated facepieces supplied with purified air from • central motor-blower-canister units and (3) collective protection of the entire tank with purified air under positive-pressure ventilation,. The first two methods require the crew to wear impregnated clothing at all times; the third method does not require impregnated clothing so long as the tank and protective system are intact. Accepting the fact that the three methods adequately protect against Chemical Warfare Agents, the relative merits of these methods were determined in a field test carried out for the purpose of determining the heat loads and limitations and advantages of the three methods in terms of physiologic effects upon the crew and upon their ability to discharge their duties. The heat load and the respiratory load appeared to impose the greatest stresses<> Impairment of vision, interference with the proper use of visual equipment (particularly fire control) and restriction of movement appeared to constitute the greatest limitations. A proper evaluation of these loads and limitations required that the tests be conducted in a tropical (hot, humid) climate, since heat and humidity accentuate the loads imposed by gas protective equipmento Gamp iolk, Louisi- ana was chosen for these tests since it was the hottest and most humid region in the United States where tanks were operating„ Unfortunately, the weather - 1 - at this camp proved to be hot temperate and not sufficiently humid to simulate the tropics. Therefore, the conclusions of this report must be accepted with this reservation and the understanding that in the tropics different effects on the crew may be obtained. 3. CONCLUSIONS: a* Tank crews can operate and discharge their duties efficiently in buttoned tanks for at least four (4) hours during the hottest part of the day in the hot climate. Longer periods of operation appear possible. This is true whether the crew is unprotected or is equipped with one of the follow- ing protective assemblies; (l) combat masks plus impregnated clothing, (2) individual ventilated facepieces and impregnated clothing, (3) collective protector for the entire tank (T23) plus impregnated clothing without the hood and gloves. b. Equal heat loads, only slightly greater than that of the unpro- tected control, are imposed by the three protective methods detailed above. Co Accuracy of fire and sensing were equally good without regard to the type of protection employed. d. From the standpoint of comfort, total protection with positive pressure ventilation and the ventilated facepiece (with air flow reduced to 3#5 c.f.xn.) were preferred to the combat mask. The ventilated facepiece with the prescribed rate of air flow of 6 c.f.m. was strongly disliked, the blast of hot air being barely tolerable. e. The individual combat mask is considered to be the most accept- able and practical means of protection now available for tank crews. It is not considered the optimum method of protection—its deficiencies, however, can be corrected by development and change. f. Despite its greater comfort, the individual ventilated facepiece system offers insufficient advantages over the combat mask and is not consider ed desirable for the following reasons: (l) does not reduce the heat load, (2) does not enable better gunnery ,when using current fire control equipment, (3) its use in the tank requires the provision of combat masks for use after evacuation of the tank, (4) creates a separate supply, installation, servicing and maintenance problem, ($) it is dependent upon the electrical supply and subject to failure on that account (two such failures occurred during test), (6) if the equipment fails several men rather than one are imperiled, (7) the problem of location of the canister is critical, and has not been solved; it is not clear that properly situated stowage space for this equipment is available, (8) plastic shields scratch easily and are of extremely short life, (9) it has not been established by test that the equipment will provide adequate protection against GWA, when the reduced air flow of 3.5 c.f.m. is used, (10) the hoses restrict movement,-cause interference and are easily damaged. g. Collective protection with positive-pressure ventilation presents a method with many inherent advantages, its further development is desirable. - 2 - The sole objection to this method (T23) was the heat in ’the turret, due to poor distribution of air. ho The assembly of impregnated clothing has the following disadvan- tage; the hood is too thick and does not fit well over the crash helmet, the jacket sleeves pull out of the glove wristlets and the jacket bottom out of the trousers. ; i. An estimated 50% to 9C$ of the protective ointment, M5, applied to the neck and face as a substitute for the hood and to the wrist and fore-* anas to protect the jacket-glove juncture, was rubbed off after four (4) hours of operation. 4. RH£Qm<£KD ATOMS: a* That the combat mask and impregnated clothing be considered the most practical method now available for field issue. b. The development and improvement of combat mask be pursued along following lines;' (1) Reduce the thickness of the attachment tabs of the head harness to the facepiece in order to eliminate localized areas of pressure under the crash helmet,, (2) Rearrange the head harness straps to avoid interference with the newij developed head phones (HS-16 ()/U) for tank crews. (3) Redesign the eyepieces of the mask to provide for a greater ? field of vision, give binocular vision at close range, and permit proper use of newer fire control equipment. Reduction of eye relief to a minimum can secure these aims. (4) Relocate the canister in a position interfering least with other tank equipment and the activities of tank crews. (5) Reduce canister resistance to the minimum compatible with adequate protection. c. Further development of collective protection by positive pres- sure ventilation be pursued. d. Improve the impregnated clothing assembly: (l) make hood of lighter material and of sufficient size to fit over crash helmet, (2) wrist- lets of gloves should reach midway to the elbow, (3) fasten rear and front of jacket to trousers. e. Protective ointment, be considered an inadequate substitute for the impregnated hood and glove wristlets until further tests demonstrate its protective value after prolonged use in closed tanks operating in hot climates. - 3 - f. Coordinate all development of protective equipment for use by Armored personnel with the Amo red Center. (NOTE: The conclusions and recommendations set forth above have been con- curred in by W. H. Nutter, Colonel, G.S.C., Chief of Staff, Head- quarters Armored Center and It. Col. G. Ae Douglass, Armored Board.) Submitted by: Lo W0 Eichna, Lajor, IUC0 R. H. Walpole, Captain,R: W. B. Shelley, 1st Lieut., M,C0 J. L. Whittenberger, 1st Lieut., M.G. (Chemical Warfare Service) IVa££&uJ •IJ-LLARD I-xvCH'IE Colonel, Medical Corps Commanding 3 Incls. §1 - Appendix #2 - Tables 1 thru 11 #3 - Charts 1 thru 8 - 4 - APPENDIX A0 EXPERIMENTAL CONDITIONS AND PROCEDURES lo Locale and Climate These tests were carried out at Camp Polk, Louisiana, from 10 July to 10 August 1944* The test area was located between 31° and 32° North Latitude and 93° and 94° West Longitude. The terrain was slightly rolling, moderately covered with second growth pine and largely free of undergrowth* During the test periods, shade was slight and spotty. The climate9 was hot temperate. Chart 1 indicates the daily maximum and minimum dry and wet bulb temperatures and relative humidities during the hours of test each day0 During the tests, the dry bulb temperature ranged from 88°F« to 103°F<> and the relative humidity from 27*5/*> to 64* 5$. Two cool days (DoB0 80°F.) were omitted from this study and are not considered here0 The averages of the daily maximum dry and wet bulb temperatures were 96o3°F* and 77*8°Fo respectively. Diurnal and daily variations in wet bulb tempera- ture were small; accordingly, the relative humidity changed indirectly with the dry bulb temperature. Rain was infrequent and did not occur during the test periods utilized in this report* Since the tes(t periods extended from 1100 hours to 1600 hours, the temperature during a test was not uniform but slowly rising throughout0 2* Subjects Sixteen enlisted men and four officers comprised fcmr tank crews and served as experimental subjects. One officer occupied the loader’s position in each tank. In addition to being a subject, he was the observer for his tank* The enlisted men were healthy, physically fit and had been training at Camp Polk at least since early spring* The officers were older and less fit than the enlisted men. The ages of the subjects ranged from 19 to 36 years, but only one enlisted man was over 21 years* The subjects lived in barracks on the post and subsisted on field ration A eaten at 0600, 1000 and 173° hours© 3o Protective Equipment Four tanks were equipped as follows: one (M4A3) with individual M5-11-7 combat masks with Mil canister (formerly E6-3-7 assault masks), another (M4A3) with the individual ventilated facepiece system (Protector, facepiece, E21R1), the third (electric drive tank, T23) with collective protection (canister 50) for the entire tank and positive pressure ventilation and the fourth tank (M4A3) served as a control* Initially, the air flow to each ventilated facepiece was approximately 6 c.f 0m. This air blast proved to be intolerably hot and the rate of flow was reduced to 3o5 Cofo.m0 per facepiece for the final tests* The T23 tank was sealed and supplied with .275 c.f.m. of purified air, producing a positive pressure of three-fourths inch© The four - 1 - Inclo #1 tanks were operated simultaneously each day with the crews rotating through them according to a randomized Latin Square* Each crew operated each tank for a day and at the end of four (U) days had experienced each of the three types of protection and the control,,. Regulation fatigue clothing (shorts, socks, 2 piece coverall, shoes and leggings) was worn in the control tanko In the three protected tanks, the men wore the following impregnated clothing: shorts, socks, trousers, jacket, hood and gloves and non-irapregnated shoes and leggings* The 1'5 protective ointment was substituted for the hood in special studies0 4o Work The test period consisted of 4 hours (between 1100 and 1600 hours) of buttoned-up driving over a 3o5 mile standardized, moderately rough trail, winding among the trees„ The tanks followed each other around the course in a staggered fashion, averaged 10 miles per hour and completed a circuit in 20 to 25 (usually 23) minutes0 Two circuits were made each hour (fast run). During the remaining 10 to 13 mirfutes, the tank was stationary and data was taken. In some tests, one circuit was made per hour with the tank stationary for the remaining 35 to 40 minutes, (slow run). During all stationary periods, the engine was idling. Only the driver worked during the test period, the remaining 4 men merely rode. Each man entered the tank with 3 canteens of water (2,700 c.c.) from which he was permitted to drink during the hourly halts for data taking. At these times, combat masks, ventilated facepieces and hoods were removed for 5-B minutes0 5 o a0 Weather During- the test period, the dry and wet bulb temperatures, wind velocity and direction, and condition of the sky (sunlight) were recorded every half hour* During the other hours of daylight, the same determinations were made at hourly intervals 0 b0 Tank Hourly readings of the dry and wet bulb temperatures were made in the bow (bog) and turret (gunner) as soon as the tank haltedo At the same time, the temperatures of the final drive and of three locations on the hull (bow top, turret top, turret side) of two representative tanks were measured by thermo- couples 0 During slow runs, temperature readings were made on halting and at the end of resting period0 Co Subjects The oral temperature, the rectal temperature, and the weight (within 5 grams) of all crew members were determined before entering and after dismounting the tanks„ At these times, the men were naked and their urinary bladders empty0 During the hourly halts of the tank, the heart rates and oral temperatures were determinedc Continuous notes were made of rhe appearance of the men, their reactions and coiaplaints and the proficiency of the drivingo Incl. #1 - 2 - Both the water drunk during the four hour period and the urine excreted were measuredo 60 Typical Daily Schedule 0800 hours Tanks arrive at test area with crews• 0800 to 1000 hours Preparation of tanks and equipment for test run® Tanks "sitting" in sun, hatches open. 1000 to 1030 hours hunch 1030, 1045, 1100, 1115 hours The 4 crews, in order and successive- ly, have initial data taken* dress in designated clothing and equip- ment 0 1045* 1100, 111$, II30 hours The crews, in order and successive- ly, enter designated tanks and button up, motor idling0 1100, 1115, 1130, 114$ hours The 4 crews, in order and successive- ly, begin test runs over course, buttoned-up ® 1500, '1$1$, 1$30, 1$45 hours The 4 crews, in order and successive- ly, dismount tanks and have final data taken® 1545 to 164$ hours Collection and storing of test equip- ment, policing of area. 1700 hours Test area vacated. B® PHYSIOLOGIC CHANGES lo Thermal Load The thermal loads Imposed during the test period on the bow and turret crews of a standard tank and of an experimental (T23) electric drive tank are plotted in Charts 2 and 3 respectively® These charts also indicate the relationship of the air and hull temperatures of these tanks to the ambient air temperature® The plotted day was one of the hotter ones but the data is repre- sents tive« Both tanks operated simultaneously® In the M4A3 tanks, the bow air temperature generally exceeded the ambient temperature by 20°F„ for the dry bulb and 11°F® for the wet bulb (Table 1). The turret air increased less in temperature, 7°F® for the dry bulb temperature and $°F® for the wet bulb temp- erature (Table l). In the T23 tank, the bow air temperature exceeded the ambient temperature by 9°F. for the dry bulb and 6°F® for the wet bulb® Corres- Inclo #1 r 3 - ponding increases in the turret air ?/ere 6°F, D0B0 and 9°Fe W0B„ (Table 1)0 20 Fast and Slow Huns In cruising M4A3 tanks, the air flow varies from 1200 to 1500 c.f0m0 When stationary with engine idling the flow is only 300-400 c0fom0 Since the internal environment of the tank might deteriorate badly at the lower air flows, it became necessary to determine whether there were significant differ- ences in the tank environment and in the physiologic changes in the crew when the tank was largely on the move (fast run) and when largely stationary with engine idling (slow run). The relationship of the environment of a M4A3 tank to the ambient temperatures during a day of slow running is plotted in Chart 4 which should be compared with Chart 2, a plot of similar data during a fast run. A similar comparison is obtainable from Table 10 The combined data indicates the essential similarity of the tank environments during both types of runs. Table 2 indicates that the sweating rates, rectal temperatures and heart rates were somewhat higher during the slow than fast runs. The changes during both types of runs are still of the same order of magnitude and within the same physiologic range. The differences are at best small and not of practical importance0 This permits treatment of the data from fast and slow runs without differentiation, a course to be pursued henceforth. All tanks operated either fast or slow on the same day. Sinceithe ventilation rate of the T23 tank is fixed by the blower- canister system and is independent of the movement of the tank, the data on this tank will not be separated into fast and slow runs0 Chart 5 (slow run) and Chart 3 (fast run), together with Table 1, indicate the essential similarity of the environment within this tank during both types of operation0 3. Effect on Sweating. Rectal Temperature and Heart Rate Table 3 details the physiologic changes (sweating rate, rectal temp- erature and heart rate) at the end of 4 hours of closed operation in three tank crews, which rotated through the three methods of protection and the control0 The data on crew 3 have been excluded. This crew failed to coiiiplete 4 hours of operation with the facepiece system (mechanical failure) and did not wear the hood and gloves in the totally protected (T23) tank® In the M4A3 tanks, the physiologic changes are greatest in the bow crew (particularly the driver) and considerably smaller in the turret crew0 This was true for both the unprotected crew in regulation fatigue clothing and for the protected crew whether equipped with combat masks or ventilated face- pieces„ The bow men lose twice as much sweat (400 coc0 to 500 CoCcT/hour more) as the turret men, have rectal temperatures that are 1°FC to l05°Fo higher, and pulse rates that are 25 to 30 beats/rain0 faster (Table 3)» In the totally protected, positive pressure ventilated, tank (T23) the situation is greater changes occur in the turret crew (particularly in the loader and com- mander) than in the bow crew* The differences, however, are not so great as in the M4A3 tanksc The turret crew loses about one-third again as much sweat (200 c0c./hour more) as the bow crew, attains rectal temperatures that are 0o3OFo higher and pulse rates that are faster by 20 beats/minute^ Incl. #1 -4- On the assumption that the physiologic load can be evaluated by the changes in sweating rate, rectal temperature and heart rate. Table 3 and Charts 6, 7, and 8 indicate the loads imposed on tank crews by the various protective methods. It is at once apparent that the major load is iraposed by the buttoned tank and that the various types of protective equipment impose only slight additional loads, which in themselves are not sufficient to produce changes significantly beyond the order of magnitude of the control. In the M4A3 tanks, this is exemplified by the driver, who withstands the greatest load (both thermal and work) and sustains the greatest changes. With protective equipment, his sweating rate averages 1 litre/hour, only 15C c.c, to 200 c.c„/hour more than in the control tank without protection; his rectal temperature ranges between 101°F. and 101.5°F., only 0o5°f,o to 0.75°F© higher than in the control and his heart rate of 110/min. to 120/rain. exceed his control rate by only 10 to 20 beats/min© In the other crew members, the loads were considerably less and physiologic disturbances more mildo In the totally protected (T23) tank, the changes were of the same order of magnitude as in the M4A3 tanks with protection, except that the greatest load fell on the turret crew with the loader and commander sustain- ing physiologic changes similar to those of the driver in the M4A3 tanks Table 3, Charts 6, 7, 8). The order of magnitude of the physiologic changes indicates that the loads imposed on the crew are moderately severe (driver in M4A3, loader and commander in T23), but still below the limits of tolerance0 There were indications that such limits of tolerance were at times closely approached© On four occasions during the month of operation, men (all drivers) were forced by disability to leave their tanks before the end of 4 hours© On two of these occasions, the failure to finish was attributed to an insuf- ficient water intake. On several other occasions, men forced themselves to finish the scheduled 4 hours of test in spite of severe synptoms and their obviously poor and inefficient condition. Employing the average of the sweating rates, rectal temperatures and heart rates for the five men of the crew as an index of the overall load of the protective systems, the totally protected tank (T23) with a ventila- tion rate of 275 c.f.m. imposes a slightly greater load than the individual combat mask or the ventilated facepiece system (Table 3)o The last two methods inpose equal loads© The differences between the three systems are not sufficiently great to permit a preference of one method over the other two on the basis of the physiologic changes induced. In the climate of this study, therefore, the preference for one method over the others would have to be decided on some basis other than the physiologic load© C© OPERATIONAL LOAD The evaluation of the operational loads imposed by the protective equipment was based on observations of driving and of target firing© - 5 - Incl© #1 1. Driving. The officer observer in each tank quickly learned to appraise the driving ability and characteristics of his driver. In spite of the subjectiveness of this evaluation, it is significant that on each occasion that drivers reached, or came close their limits of tolerance, a change in driving was noted by the officer observer. The driving became more rough and “slap-dash” with a tendency to take the bumps Mon the fly” and to hit trees. Usually the driving was excellent, carefully and well done. No change was noted when the drivers were subjected to the three types of* protective equipment. 2. Firing No ammunition was available for the 76mm gun of the totally pro- tected tank (T23). Therefore, the tests were limited to firing the 75 ram gun of the MAA3 tanks by crews equipped in rotation with combat masks, ventilated facepieces and no protection. a. Procedure Three tanks fired on each of three days. During the firing tests regular loaders replaced the officer observers heretofore in the loader*s position. In one tank, the crew was equipped with combat masks and impregnated clothing; in another with individual ventilated facepieces and impregnated clothing; in the third no protection and regulation fatigue clothing. The crews rotated from one tank to another daily until each crew had fired under each of the three above listed situations. The crews donned their designated equipment and entered the tanks at approximately 1130 hours, immediately buttoned completely, and thereafter remained completely buttoned until the end of the firing program (3j to 4 hours in all). After entering the tanks, the crews drove, completely buttoned, to the firing range. This required Ig to 2 hours. At the range, high explosive ammunition (73mm, flE, M48) fused on delay was fired at standard HE targets. Fifteen rounds in three bursts of 5 rounds per burst were fired at a far target (approximately 1,200 yards) and ten rounds in two bursts of 5 rounds per burst at a near target (approximately BOO yards). The tanks fired in rotation, one burst at a time, a tank be- ginning fire after another had ceased. Following each burst of 5 rounds, each tank elevated its gun and moved back 100 yards from the firing line and behind the crest of a hill0 Here it waited with idling engine until signalled to advance to the firing line and deliver another burst of 5 rounds. The far and near targets were engaged alternatelye Once on each day, each tank fired a burst at the far target and immediately thereafter a burst at the near target before moving back from the firing line. On all other occasions only one burst was fired on each trip to the firing line. Inclo #1 - 6 - In the observation tower, observers equipped with binoculars estimated the distance from the target of the burst,of each round and re- corded its location on a grid. The bow gunner of each crew (listening over the interphone) recorded the sensings and firing orders of his com- mander for each round. Prom a comparison of the two records, the correct- ness of the sensings and the degree 6f interference by the protective equipment was determined. In this study, the accuracy of sensings is limited to the gross classification of over and short. At the conclusion of the firing, the blast crater of each round was located and its distance from the target measured and recorded. Since deflection from the gun-target line was minimal, only the distances in front and behind the target were measured. From this data, the mean of the distances of the bursts from the target and the dispersion of the individual blasts about the mean were calculated0 b. Sensing In this analysis, a sensing was called wrong only when it was entirely incorrect, e.g., a short or over called target, a short called over, or vice versa0 No attempt was made to determine the precise accuracy of the sensing, e.g., an over called 200 yards over was considered correct even though it was actually only 50 yards over. Table 4 indicates the accuracy (rather the inaccuracy) of the sensings of the three commanders on the three days of test. Of the three crews, crew A and commander A tried most consistently on all days making their data the most reliable® Several facts emerge from the Table. The percentage of grossly wrong sensings is high, both for crews with and without the protective equipment. In buttoned tanks, sensing inaccuracy is of the same magnitude whether crews wear combat masks or ventilated face- pieces or no protective equipment (see Crew A, Table 4). An appreciable learning curve is present for each crew, but is indicated best by Crew A (40$ wrong first day, 24$ second day, 24$ third day)* Since the same range was used'on each day, the true improvement in sensing ability from a buttoned tank is not indicated by these data, A new range each day would be required to determine this point. a. Accuracy of Fire The accuracy of the fire for both targets was determined in two ways: (1) determination of the mean of the distances of the blasts from the target and the dispersion of blasts about the mean in terms of the standard deviation (Table 5)j (2) determination of the number of effective rounds; i*e., rounds bursting within the effective bursting radius of the ammunition for a horizontal target (20 3/ards short and 5 yards over) (Table 6)0 The scores for the near targets will be discounted. These targets were badly placed in a hollow behind an upward roll in the terrain. Hounds going slightly over the target became far over and attempts to shorten the range yielded far shorts on the crest of the roll® Incl® #1 - 7 - An analysis of both scoring methods (Tables 5 and 6) permits the following conclusions: (l) fire from a completely buttoned tank can be reason- ably accurate; (2) fire from a completely buttoned tank is of the same degree of accuracy whether crews wear combat masks or ventilated facepieces or use no protective equipment; (3) there is a decided learning curve in the laying of accurate fire from a buttoned tank (since the firing was on the same range each day, the true extent of this learning can not be indicated by this data)0 Again crew A gave the most consistent and reliable data0 Since fixed white targets were used for the firing tests, no attempt was made to determine the effect of the protective equipment on the commanders ability to spot and recognize more natural targets« Neither the physiologic nor operational load permitted a preference of one protective method over the other0 There remains then an evaluation of the comfort-discom- fort load of each system0 Do COMFORT-DISCOMFORT LOAD lo Questionnaire At the end of the test program and after they had become accustomed to the equipment through repeated use, each man was personally and individually questioned regarding his preference for the protective methods and his complaints for each item of the assemblies0 The results of this questionnaire (Table 7) indicated that the men were equally divided in their first choice between the ventilated facepiece system (only when air flow to each facepiece is reduced to 3*5 Cof0m0 and the totally protected tank (T23) with positive pressure ventila- tion (when hood and gloves of impregnated assembly are not worn). The combat mask was universally considered the least comfortable, chiefly due to the resistance to respiration0 At the same time, it was considered not to render the operation of the tank much more difficult, except for the gunners0 The canister on the left cheek markedly interfered with their use of the telescopic sight. Table 8 is a detailed breakdown of this expression of preference accord- ing to position in the tank and the strength of the choice0 2„ Complaints Table 9 details the complaints registered by the men against the protective equipment and requires very little comment,, Although the complaints against the. combat mask were numerous, they were usually not critical and most crew members agreed that interference with operation was not great. (Notes men frequently fell asleep while wearing the combat mask). The complaints against the ventilated facepiece system in this table are for the revised arrangement with the air flow to each facepiece reduced to 3<>5 CofoCio and the canister- motor-blower units placed in the coolest locations possible0 When submitted for test each facepiece received 6 c0f0rrio of air and the blast of this amount of hot air was extremely disagreeable» Under such conditions, the crews preferred the combat mask to the ventilated facepiece system,. The complaints against the totally protected positive pressure tank were entirely by the loader and commande- er* The other three crew members, located near the canister outlet, found this system very pleasant and desirable,. Wearing the full impregnated assembly - 8 - Inclo #1 rendered the loader and commander incapable of functioning and the tank inoperable, Removing the hood and gloves (but having them at hand) rendered the load on the loader and commander bearable and the tank operable0 3o Modification of Equipment During the testing period, the equipment of each method of pro- tection was modified from time to time to give greater comfort. There finally emerged s "final11 form for each method. The'‘final’combat mask system con- sisted of a fitted combat mask (several men required special facepieces) with the inner nose piece removed, plus the full assembly of impregnated clothing. In the "final" ventilated facepiece system, the air flow to each facepiece was reduced to 3.5 c.f.ra. and the crew wore the full assembly of impregnated clothing. In the totally protected tank (T23), the crew wore only the impregnated clothing, but with the gloves in their pockets and vdth the hoods thrown off the head and over the back (clothing in readiness for evacuation). These three "final" methods were compared in a simultaneous run on a single day. The physiologic effects induced yn the three crews are indicated in* Table 10 and these should be compared with similar ‘data in Table 3 (before institution of comfort changes). It is evident that although the comfort of the crew was increased, the physiologic disturbances remained of the same order of magnitude. It was later suggested that comfort in the turret of the totally pro- tected tank (T23) might be increased by better circulation of the air in the turret. A 200 c,f,m. fan was placed just above the canister and directed the air in 2 streams toward the turret. This arrangement increased markedly the comfort of the crew but produced only a slight reduction in the induced physiologic disturbances (Table 11), 4, Faults of Items of Protective Equipment Often synonymous with the above detailed complaints but not neces- sarily, nor always, identical are the following observed faults which should be corrected. a0 Combat Mask0 (l) The facepiece and harness do not fit com- fortably under the crash helmet. Elevated-attachment tabs of head harness to facepiece cause focal pressure points0 (2) Improper fit across forehead and under chin—greater variety of sizes,, (3) Canister - too heavy causing neck fatigue. - Canister on left cheek interferes with gunner’s use of telescopic sight0 - Lateral position endangers seal of mask on face0 (4) Inner nose cup too narrow, occludes nose and interferes with respiration0 (5) Eye- pieces too vridely separated, limiting central visual field and causing monocular vision at close range, (6) Metal clasps on adjusting straps cut into the back of the ears. b0 Ventilated Facepiece Systera0 (1) Flow of air to facepieces too hote (2) Air supply hoses in the way, too soft, collapse readily on external pressure, twist and kink on themselves0 ' (3) Plastic shields much too soft. Incl, #1 9 scratch easily and badly,becoming practically non transparent in several (3-4) days. (4) Facepiece does not fit well under crash helmet, all leakage over forehead blocked. (5) Chin leakage valves tend to become occluded by the hood. (6) Difficulties in proper placing of canister- motor-blower unit as to stowage and relatively cool location, particularly bow unit, (?) Drain on power resources of the tank. c0 Totally Protected Tank (T23)o (l) Difficulty in proper place- ment of the canister and blower leading to (a) excessive heat in turret; (b) inadequate air circulation in turret; (c) stowage difficulties0 do Impregnated Clothing Assembly,, (l) Hood® (a) Too thick and too heavy,, (b) Not designed to fit over crash helmet and around canister of combat mask,, (c) Buttons around neck not properly placede When fully buttoned, hood chokes around neck0 (d) Possible break in protection between hood and jacket where interphone and microphone cords pass* (2) Glovese Wristlets too short permitting sleeves of jacket to pull out of glove0 (3) Jacket* Jacket tends to pull out of trousers0 E. PROTECTIVE OINTMENT M5 It has been suggested that the M5 protective ointment can replace the hood when an ample layer of the ointment is applied over skin areas usually covered by the hood. Similarly, its use on the wrists and lower forearms is suggested to protect an area often made vulnerable by the pulling of the jacket sleeve out of the glove. Protective ointment M5 was applied to these skin areas of two tank crews wearing combat masks and the impregnated assembly except for the hood. After 4 hours of operation in closed tanks, 50$ to 90$ of the oint- ment had been rubbed off the different areas of the skin, most of it into the clothing. Large areas, particularly of the neck and wrists were com- pletely free of ointment with only small flecks remaining on the akin. Crew members subjected to the greatest movement (driver, loader) rubbed • most of the ointment from the skin. One loader sustained chafing of the skin of the side of both jaws leading to denudation of skin from these areaso It was estimated that the ointment remained on the skin in pro- tective quantities for not more than one hour. Unless some means is dis- covered to prevent the ointment from being rubbed off or to reapply it frequently, the ointment does not appear to be a substitute for any item of protective clothing. FINAL EVALUATION In the climate of this study the combat mask with impregnated clothing proved to be a simple and operable method of protection, which with further improvement can become a nearly optimum method. Such development should be 3hcl. #1 - 10 - energetically pursuedo Certainly the simplicity of the method, its personal nature and its lack of demands on stowage, power, and additional equipment make it a very desirable method® Although placed last in the preference ratings, the combat mask cannot be considered to impose a high discomfort load. Men frequently fell asleep in the tank while wearing the mask. The ventilated facepiece system and totally protected tank (T23) offered advantages over the combat mask solely from the standpoint of comfort. The chief objection to these methods is not in the methods themselves but in the ability of the men to do so well with the combat mask® This coupled with the consideration that all crew members will require combat masks and impregnated clothing for evacuation of tanks make it difficult to propose one of the other methods, in which one must take into consideration: (a) installation of new equipment, (b) supply of the equipment, (c) power requirement, (d) servic- ing of the equipment,- (e) maintenance of equipment with replacement parts, (f) possible failure of operation of equipment through negligence of one man or through mechanical failure endangers several men, not one; (g) the problem of stowage is critical and has not yet been solved, nor is it' decided that properly situated stowage space Is available; (h) availability of non scratching plastic shields for the facepieces is not yet assured, (i) Adequst protection against CWA by an air flow of 3«5 c0f.m0 per facepiece has yet to be established® Incl. #1 - 11 - TABLE I INCREASE IN DRY AND WET BULB TEMPERATURES OF BOW AND TURRET AIR OVER OUTSIDE AIR TEMPERATURE (Standard M4A3 Tank and a Totally Protected Experimental Tank (T23) * O MAXIMUM INCREASE IN TEMPSiATURE OVER AMBIENT (°F.) Ambient M4A3* 123T Air Tempo Turret Bow Turret Bow Q D.B, W.B. D.B. W.B. D.B. 1 W.B. D.B. W.B. D.B., W.B. FAST RUNS 10 99.5 74o5 6.5 5.5 19.5 8,5 5.0 9.0 8.0 6.0 11 100 76 6.7 5.7 21.3 12 o0 5.0 9.5 10.0 5.5 13 93.5 77.5 7.5 6.5 19.7 9.7 2.5 8.0 6.5 6.0 24 97.0 78o5 8.0 5.5 23.7 1202 7.0 8.5 11.0 7.0 32 93.0 76.0 7o0 4o0 17.0 12.0 9.0 9o0 9.0 6.0 Avg( 96,6 76.5 7.1 5.4 20.2 10 09 5.7 8.8 8,9 6,1 SLOW RUNS 12 99.0 77 9.3 6.3 22.7 11.0 11.0 9.0 19.0 5.5 17 92.5 76 9.8 5.5 14.2 10.3 8.5 8.0 10o5 5.0 18 .94.0 78 13.7 ' 8.7 21.4 10.0 10 o0 11.0 13.0 9.0 Avgo 95.2 77 I 9o3 6.8 19.4 10.4 9c8 9.3 14.2 6 = 5 of 3 tanks per day (one tank on day 32, two tanks on day 10) ‘/One tank only. Incl. #2 TABLE 2 COMPARISON OF PHYSIOLOGICAL CHANGES DURING FOUR HOUR FAST AND SLOW TANK OPERATION (Standard M4A3 Tank, Crew Equipped with Combat Masks and Full Impregnated Clothing Assembly) CREW POSITION SWEAT LOSS/HR. FINAL RECTAL TEMP, FINAL PULSE Crew Member Fast Slow Fast Slow Fast Slow Commander 3 4 360 365 602 377 99 »4 99.2 99.B 99*8 73 66 75 75 Gunner ■ 3 469 489 99*4 99*7 57 72 4 400 460 99*2 99.2 81 84 Loader 3 4 302 459 432 450 100 o3 100 oO 100,5 100 o3 102 99 87 96 Bog 3 759 902 100o6 101.3 76 120 4 463 513 99.B IOO06 99 105 Driver*' I 3-3' 4 - 4' 1065 698 1125 1010 IOI06 101.9 101c 6 99 144 96 144 Average 534 636 lOOoO 100 0 5 90 95 drivers on the two aays0 WEATHER DATA During the Four (4) Hours of Test Day Temperature (°F.) of rpA Dry Bulb Wet Bulb Relative Humidity ($) 1C9 w Min. Max. Avg. Min. Max. Avg. ... Min. Max. Avg. 6 95 97' 96.1 73 75 73.9 32 34.5 33.6 7 93 99 95.9 74 76 75.1 33 0 5 40 37 o7 Incl. #2 TABLE 3 COMPARISON OF SWEAT LOSSES, RECTAL TEMPERATURES AND PULSE RATES IN THREE (3) TANK CREWS EQUIPPED WITH DIFFERENT PROTECTIVE DEVICES (Four Hours of Buttoned Operation, Crews in Impregnated Clothing, except for Control) crew POSITION SWEAT LOSS (gms/hr.) FINAL RECTAL TEMP. (°F.) FINAL PULSE RATE (beats/mino) Crew Number Control Combat Mask Ventilated Facepiece* ?? (H Control1 Combat Mask Ventilated Facepiece* cr\ CM Control Combat Mask T) * G) 4) •P O cd 0) rH *H •■H O-, •P flj >• (a. cn OJ E-> Coradr. 1 367 319 431 1000 99o2 98,9 100.1 101.3 72 81 105 117 2 359 464 363 649 98,6 99.6 99.1 99.6 64 88 60 92 4 231 377 383 731 99.4 99.0 99o2 101 oO 63 60 66 75 Avg. 336 387 394 793 99.1 99.2 99 0 5 100,6 66 76 77 95 Gunner 1 335 404 488 769 99o0 9Bo8 99*5 100.2 72 75 84 96 2 333 399 350 445 98,8 99.4 98.9 99.6 ■ 72 76 68 80 4 267 438 387 732 99 oO 98o8 99.2 98.8 69 75 81 99 Avg. 312 414 408 649 98*9 99.0 99.2 99.5 71 75 78 92 Loader 1 363 376 578 864 99.2 99.0 100.1 100 c 6 72 75 93 108 2 395 547 413 1085 99.4 99.6 99*4 100 0 3 76 88 72 116 4 298 470 491 9?2 99.6 100.2 100.4 101.0 87 102 96 132 Avge 359 464 494 960 99o4 99.6 100.0 100.6 78 88 87 119 Bog 1 666 563 790 618 99.5 99,6 101.0 99.6 93 84 99 93 " 2 714 1215 662 608 IOO06 101.8 100.2 lOOcO. 108 124 104 60 4 430 837 696 706 100.1 100.3 101.0 100.0 81 99 108 78 : Avg. 620 872 716 644 100.1 100.6 100.7 99.9 94 102 104 77 Driver 1 693 912 975 612 99.8 99.9 101.4 100.0 84 93 102 75 2 1190 1139 1195 744 101,6 101.0 100.8 100.2 136 120 124 108 4 693 905 858 566 99,6 101.6 101.2 99.9 V ' 111 111 84 Avg. 859 985 1009 641 100o3 100.8 101.1 100.0 104 108 112 89 SUMMARY Bow Men 739 929 863 642 100,2 100,7 100.9 100 o0 99 105 108 83 Turret Men 335 422 432 801 99ol 99.3 99.5 100.3 72 80 81 102 Entire Crew -ML. 624 604 737 22A. 99.8 100.1 100.1 83 90 92 94 *Flow to Ventilated Facepieces, 6 c*f*m Inclo #2 TABLE 3 (Cont‘d.) WRATHm DATA During the Four (A) Hours of Test Day Of Test TEMPERATURE (°F.) RELATIVE HUMIDITY (%) Dry Bulb Wet Bulb Min, Max. Avs- Min. Max. _ Avg. Min. Max. Avgo 10 96 100 98 04 73.5 77 74.7 27.5 38 31.7 11 ‘ 95 100 98.4 75 77.5 76.1 29 45 35.2 12 93 102 97,9 76.5 78.5 77.4 32 47 39.6 13 90 97 93.6 75.5 80 78,2 43.5 59 50.4 SCHEMA OF TEST Day of Test CRM 1 CRM 2 CREW 3 OTE OF RUN 10 Control T23 Combat Mask Fast 11 T23 Control Ventilated Facepiece Fast 12 Ventilated Combat Mask T23 Slow Facepiece , 13 • Combat Mask Ventilated Facepiece Control Fast Incl. #Z TABLE 4 MAGNITUDE OF SRRDR IN THE GROSS SENSING OF FIRE FROM BUTTONED TANKS • GREtfS Y»ITH AND WITHOUT PROTECTIVE EQUIPMENT No Protection, Fatigue Clothing Combat Mask, Impregnated Clothing Ventilated Facepiece, Impregnated Clothing Day Crew % Wrong* Day Crew % Wrong* Day Crew % Wrong* 19 A 40 19 B 48 19 C 65 20 C 40 20 A 24 20 B 24 21 B 60 21 - C — 21 A 24 of total rounds incorrectly sensed. Includes both far and near target. Incl. #2 TABLE 5 ACCURACY OF FIRE FROM BUTTONED TANKS CREWS WITH AND WITHOUT PROTECTIVE EQUIPMENT c; •3 FAR TARGET NEAR TARGET p & Standard Devia- Standard Devia- -P Mean of Bursts** tion About Mean Mean of Bursts* tion About Mean t Day Crew Yards Yards Yards Yards hO 19 A + 3 yds. 33 o4 • -131 113 c 'Jf ' •H 20 C - 4.4 37.6 - 11.0 50 o rd o 21 B +10 o 7 27.3 + 10o0 24.5 © . Sj © -H C3 P o © Avg, + 3.1 - 33 •zz Ct, 1 Xi 19 B +10 64 - 3 71 © p cd 6 20 A - 9 35 - 37 96 • ’ © © S CL. bO 21 C 0 16.7 33.1 40.4 g CJ P H *H c9 JC P H P fi iH O Odd Avg, + 0o3 - 2.3 O £. O <10 . i if O P P 19 C + 8 88 - 14 19 c3 O tA P i—t 20 ' ' B +65 137 - 29 83 ° © ft, t3 P © 21 A 0 16.7 - 33.1 40 o 4 oj 4-> d »s P O (5C a © © © p * Avg, +24 - 25o4 > a a Far target, 15 rounds; near target, 10 rounds. *Mean of the distances of the bursts from the target. Inclo #2 TABLE 6 EFFECTIVENESS OF FIRE (H.E.) FROM BUTTONED TANKS BY CRMS WITH AND WITHOUT PROTECTIVE EQUIPMENT AGAINST CHEMICAL WARFARE AGENTS (Number of Rounds Bursting U'ithin Effective ftange. Horizontal Target.) FAR TARGET* NEAR TARGET* Protective Effective, Rounds Effective -.Rounds Equipment Day Crew lumber /* Number None. 19 A 7 47 o£ c Fatigue 20 C 2 13 4 ■ 40 Clothing 21 B 4 27 3 30 ..... Average 4 29 2 23 Combat 19 B 2 13 2 20 Mask 20 A 3 20 2 20 Impregnated Clothing 21 C 11 73. _ . 3 30. Average 5 35 2 23 Ventilated ,19 C 4 27 2 20 Facepiece • 20 B 4 27 2 20 Impregnated Clothing 21 A 8 53 ' 7 70 |Average 5 * 36 4 37 fired per crew per day - far target (1,200 yards) - 15 rounds near target (800 yards) - 10 rounds in poor site. Incl. #2 TABLE 7 TYPE OF PROTECTION CONSIDERED FIRST CHOICE BY TANK CRMS ON THE BASIS OF COMFORT Number of Men Type of Protection Strong Preference Mild Preference TOTAL Combat Mask, full impreg- nated assembly 0 1 1 Ventilated Facepiece Systera*(3.5 c.f.m.), full impregnated assembly 6 ' h 10 Totally protected, oositive pressure tank (T23), im- pregnated assembly with- out gloves or hood. 6 3 9 Second choice of Men who considered T23 first choice: Ventilated Facepiece System 7 Combat Mask 2 *With an air flow of 6 c.f.m. to each facepiece, the ventilated facepiece system was considered intolerable by most men. Incl. #2 TABLE 8 PREFERENCE FOR TYPES OF PROTECTIVE EQUIPMENT ON THE BASIS OF COMFORT BY CREW POSITION Tj NUMBER OF MEN rpe of Protection First Choice Second Choice Third Choice Strong i Mild t Strong Mild , Strong i Mild 03 U 0) TJ g 1 Combat Mask Ventilated Facepiece* Total Protection 2 1 1 1 2 1 1 3 Gunners Combat Mask Ventilated Facepiece* Total Protection 1 1 2 1 2 1 3 1 Loaders Combat Mask Ventilated Facepiec# Total Protection 1 1 2 2 1 1 3 1 Drivers Combat Mask Ventilated Facepiece* Total Protection 2 1 1 1 1 2 3 1 Bow Gunners Combat Mask Ventilated Facepiece* Total Protection 1 3 1 2 1 4 Combat Mask =s combat mask, plus full Impregnated assembly. Ventilated Facepiece = collective protector with individual ventilated facepieces (flow reduced to 3»5 c*fom9) plus full impregnated assembly 0 Total Protection - totally protected tank (T23) with positive-pressure ventilation (2?5 c0f,ra.) plus impregnated assembly without hood or glovss. *Ventilated Facepiece System with 6 cef.m. per facepiece was strongly disliked. Incl. #2 TABLE 9 COMPLAINTS EXPRESSED AGAINST THE PROTECTIVE EQUIPMENT I. COMBAT MASK a. Discomfort 1, Headache or distress from pressure on temple 2o Pressure on forehead due to» pressure of crash helmet on projection of mask, 3* Discomfort from head harness pressure 4. Pressure of eyepieces 5. Uncomfortable chin pressure 6. Breathing difficulty 7. Neck fatigue 8. Irritation of skin 9. Annoyance from perspiration 10o Obstruction to breathing by .inner nosepiece b. Limitation of Vision 1. Inadequate field of vision 2. iijyepieces too far apart (central blind spot) 3. Fogging of lens 4. Scratching of lens Co Interference with Operation lo Canister on left cheek interferes with gunner's use of telescopic sight 2. One driver felt mask "cramped" his driving ability. II. VENTILATED FACEPIECES AT REDUCED FLOW (3.5 c.f.m.) ag Discomfort 1. Excessive warning of face \ 2. Irritation of eyes 3. Drying of nose or throat 4. Induction of drowsiness 5. Poor fit under crash helmet b. Interference with Operation 1. Reduced vision (scratching of eye shields) 2, Hose-pieces in way III. TOTALLY PROTECTED, POSITIVE-PRESSURE VENTILATION (T23) (Men not wearing hood or gloves) a. Discomfort 1. Hot and stuffy 2. Nausea Inolo #2 TABLE 10 COMPARISON OF THE THREE MODIFIED (FINAL) ASSEMBLIES OF GAS PROTECTIVE EQUIPMENT FROM STANDPOINT OF THE PHYSIOLOGIC CHANGES INDUCE, IN THE GREW Position SWEAT LOSS (gms/hr.) i FINAL RECTAL TEMP. (°F) FINAL PULSE P (beats/min. l|TE • Combat Mask Ventilated Facepiece ” I-'’.-, ' . CM IH Combat Mask Ventilated Facepiece c^\ CM £~* -_i Combat Mask 0 0 •P 0 03 03 H •H 5 8 %% J> C*< CM E-< Commander 367 395 738 99 o4 99.7 100.2 72 60 72 Gunner 415 367 707 98 o9 99.6 99.0 81 84 78 Loader 364 339 820 99*2 100 a 101.0 78 96 119 Bog 827 756 471 100.2 100.4 99.8 87 96 81 Driver 904 1433 464 100.4 /101.2 100.0 96 120 84 Average 575 65a 640 99.6 100.2 100.0 83 91 87 During Four (4) Hours of Test WEATHER DATA AIR TEMPERATURE °F • RELATIVE Dry Bulb Wet Bulb HUMIDITY % Min. Max. Avg, Min. 1 Max. Ayg. Min. Max. Avg. 93 98 • 95=8 77.3 79 78.2 39V $4 sO 45.7 Inol. #2 TABLE 11 COMPARISON OF THE SWEAT LOSS, RECTAL TEMPERATURE AND PULSE RATE OF CREWS OF THE TOTALLY PROTECTED, POSITIVE PRESSURE VENTILATED TANK (T23) WITH AND .'WITHOUT ADDITIONAL CIRCULATION OF THE AIR OF THE TURRET Position SWEAT LOSS (gr/hr.) FINAL RECTAL TEMP. (°F.) FINAL PULSI (beats/mj S RATE in.) T23 T23 , T23 T23 T23 T23 No fan Fan No fan Fan No fan Fan Commander 386 355 100 e0 99.2 72 64 Gunner 280 284 99.7 99.1 84 68 Loader 574 404 99.6 99.6 76 72 •*' >■ r*-; ■ .* -_y.;,. j Bog 266 332 99.6 ■ ■ „■,! 4". 99.6 68 60 Driver 390 341 99.6 99.2 84 92 Average 379 343 99o7 99.3 76.8 71.2 WEATHER DATA During Four (4) Hours of Test Day of AIR mjPERATUPwE (°F.) RELATIVE HUMIDITY {%) dry Bulb Wet Bulb Test Min. M|x. Avg. Min. ' Max. ' Avg. Kin. Max. Avg. 31 89.5 95.5 92.6 78 80 78o7 46.5 63 54.7 32 88 96 92.3 75 t 76.5 75.8 39 56 47 Inc lo #2 CHART 1 DAILY MAXIMUM AND MINIMUM DRY AND WET BULB TEMPERATURES 8 RELATIVE HUMIDITY OF AMBIENT AIR AT TIME OF DAY WHEN TESTS WERE RUN DAY AMBIENT AIR TEMPERATURE (°F) RELATIVE HUMIDITY (%) JULY AUGUST ■ DRIVING 4 HOURS BUTTONED Incl. //: CHART I CHART 2 RELATIONSHIP OF THE HULL AND AIR TEMPERATURES OF A STANDARD M4A3 TANK TO THE EXTERNAL AIR TEMPERATURE DURING 4 HOURS OF BUTTONED OPERATION (FAST RUN) u. o, LU or ZD I— < or LU Q_ LU I- HOURS Incl. #3 ■ TANK MOVING EN "INF IDLING CHART 2 CHART 3 RELATIONSHIP OF THE HULL AND AIR TEMPERATURES OF TANK (T 23 ) TO THE EXTERNAL AIR TEMPERATURE DURING 4 HOURS OF BUTTONED OPERATION (FAST RUN) METAL TEMPERATURES, HULL AIR TEMPERATURES, DRY BULP AIR TEMPERATURES, WET BULB u_ o LU CC => cr LU CL LU h- TANK MOVING CHART 3 ENGINE IDLING Incl. ft3 RELATIONSHIP OF THE HULL AND AIR TEMPERATURES OF A STANDARD M4A3 TANK TO THE EXTERNAL AIR TEMPERATURE DURING 4 HOURS OF BUTTONED OPERATION (SLOW RUN) CHART 4 METAL TEMPERATURES, HULL AIR TEMPERATURES, DRY BULB AIR TEMPERATURES, WET BULB TEMPERATURE °F Incl. #3 TANK MOVING ENGINE IDLING CHART 4 RELATIONSHIP OF THE HULL AND AIR TEMPERATURES OF TANK (T 23 ) TO THE EXTERNAL AIR TEMPERATURE DURING 4 HOURS OF BUTTONED OPERATION (SLOW RUN) CHART 5 METAL TEMPERATURES , HULL AIR TEMPERATURES, DRY BULB AIR TEMPERATURES, WET BULB TEMPERATURE °F Incl. //3 TANK MOVING ENGINE IDLING CHART 5 CHART 6 WEIGHT (SWEAT) LOST PER HOUR BY TANK CREW MEMBERS EQUIPPED WITH VARIOUS METHODS FOR PROTECTION AGAINST CHEMICAL WARFARE AGENTS WEIGHT (SWEAT) LOSS (GRAMS/HR.) WEIGHT (SWEAT) LOSS (6RAMS/HR.) CONTROL COMBAT MASK VENTILATED FACEPIECE TOTALLY PROTECTED TANK{T23) (EACH SYMBOL OF EACH LOCATION = AVERAGE OF 3 MEN) CHART 6 Incl. //3 CHART 7 RECTAL TEMPERATURE AT THE END OF 4HOURS OF BUTTONED OPERATION IN TANK CREWS EQUIPPED WITH VARIOUS METHODS FOR PROTECTION AGAINST CHEMICAL WARFARE AGENTS UJ cr ID h- < cr lx) CL UJ •“ u_