Document yrQxMmOOXNXokgn78Qxe3p9n3

m T. F. HATCH abnormal rise in body temperature. For the clothed, resting man, not especial! acclimatized, the maximum endurable condition for sustained exposure was 88 Ti for still air saturated with moisture. Higher air temperatures were found only when the moisture content was lowered to increase evaporative cooling anr1 thus offset the hotter air. Haldane demonstrated the benefits of air movement;, reporting that with 170 f.p.m. air velocity instead of still air, the endurable-tdnil perature of saturated air was raised from 88 to 93 F. A moderate work rate: wja found to lower the acceptable level 10 to 78 F. for saturated air. Reasoning that the wet surface of the body and clothing would act like the wet-bulb tli mometer, Haldane suggested that environments with varying dry-bulb tempeiiiV, tures but having the same wet-bulb temperature would be thermally and physic| logically equivalent. Thus, to maintain heat balance without abnormal rise<f. body temperature, Haldane recommended the following maximum temperatufjl for clothed men not especially acclimatized: (1) resting, in still air--88 F., wet| bulb temperature; (2) resting, 170 f.p.m. air velocity--93 F., wet-bulb tempi -i ture; (S) moderate work, still air--78 F., wet-bulb temperature. B. EXPOSURE LIMITS IN TERMS 0 EFFECTIVE TEMPERATURE Later, with the development of the ASHAE Effective Temperature (*sca (Chapter VIII), it was found that physiological limits to prevent abnormal rise^ body temperature could be expressed, for different levels of activity, in termt|c this scale, which combines temperature, humidity, and air motion into a rsi thermal index. The rate of increase in temperature and in pulse rate rose sjia in the resting man when the effective temperature, ET, was above 90 F., break occurred at a lower ET level for the working man. In still, saturated air!t` ET is the same as the wet-bulb temperature, so that a recommended ET piffle agrees well with Haldane's earlier suggestion of 88 F., wet-bulb, for a reati man. For sedentary work (500 B.t.u./hr.) an ET of 85 was found accepta whereas for heavy work (1800 B.t.u./hr.) the ET of the environment shoui" .''(;Ag3p exceed 80 F.4 Within these limits body temperature remains below 101 K), the heart rate less than 125 beats per minute over a normal working day. ; C. PHYSIOLOGICAL LIMITS BASED ON PERFORMANCE ABILITY . ...AtJhe.ArrQargd...Msdkal,,ReSfiflcch_LahoJ:ato}L.Eichna..and_assaciB;|e tained more extensive, data on the upper limit of tolerance to heat. Ob||^ were limited to young men in good physical condition and well acclimatj^ heat. Tests involved 4 hours' exposure (nude) walking at 3 m.p.h., eqpiyal(eif| 300-400 Lp.m. air velocity, carrying a 20 pound pack (about 1200 B-t.u./hrflii `C. P. Yaglou (Chairman, APHA Committee on Atmospheric Control), Then arda in industry, Am. Public Health Assoc. Yearbook, 1949-50, pp. 131-143. 6 L. W. Eichna, W. B. Bean, and W. B. Shell, The upper limits of environmentaThr humidity tolerated by acclimatized men working in hot environments, J. Ini. Hyg:- 27, 59 (1945). -t HEAT CONTROL IN THE HOT INDUSTRIES 793 ^demonstrated ability or inability to complete the assigned task during the 4-hour '^period was used as the criterion of tolerance. "Relatively easy" environments fell salong line No. 1 on the psychrometric chart shown in Figure 2. The .work in these {'environments was easily accomplished without great effort or complaint and with .all subjects alert at the completion of the work period and seemingly capable of ^.continuing indefinitely. "Difficult" environments, in which all subjects completed jthe work, but only with great effort and with evidence of approaching exhaustion, /are shown on a parallel line, No. 2, in Figure 2. A third parallel line defines "Im- Figure 2. Lines of maximum physiological tolerance and calculated line of thermal balance, plotted on psychometric chart. Air and wall temperatures equal; air velocity, 400 if.pAn.; metabolic rate, 1100 B.t.u./hr. possible" environments, in which the work could be carried on only with real Hunger to health. The narrow differences in moisture content of the.air. between |asy, difficult, and impossible environments are especially to be. noted, ft? __ D. MAXIMUM PERMISSIBLE SWEAT RATE V?'^lere are practical objections to defining limits to heat exposure in terms pf AfeSB^Rt^telLtoa-aill^^-sipne-iaAiffeEent-Standard.jstreq.uired^fqjr-eaoh^jyork.i. ei ill.* liave proposed using the sweat rate as, a single, inciejf. of heat j|t|,e8s to include both the work load and the external heat load. Tliey recommend ^ ^ers output in four hours as the maximum permissible rate-'consisteht with jggplijyfflological well-being for repeated exposures to heat for,,acclimatised:'.yp.ung ** McArdle, W. Dunham, H. E. Boiling, W. S. S. Ladell, J. W. Scott,iM.,L; Thompson, Prediction of the Physiological Effects of Warm, arid ffot/Environments. Navy Personnel Research Committee, Med. Research Council, H. M. Stationefcy^Oflfee, *}j^Epndon, October, 1947. /.*