Document QgyE4Mxn1wJNgywknNZ2X2Yj6

104 CHAPTER 7 1965 Guide And Data Boot ject, and below 85 F for the lightly clothed subject, evapora tion loss is minimal and constant. Burch1 has shown that this * insensible perspiration reflects the permeability of the skin to the moisture of the body. Above these temperatures, con trol is obtained by the availability of sweat for evaporation. The difference in the curves above 75 F is probably largely determined by the difference in clothing and activity. . ^ LOW TEMPERATURE HAZARDS Human performance in extreme cold depends ultimately on the maintenance of physiological thermal balance.' This" ability to do so depends, in turn, primarily on extent of`cold exposure, heat production (inducting;level of activity), and heat conservation (including insulation and'clothing). From' a practical standpoint --30 F is probably the lower limit for efficient prolonged outdoor operations. At --60 F many kinds of outdoor activities become exceedingly difficult, but by no means impossible." ' Knowledge' of both the magnitude" (including eh-1 vironmental low temperature radiation exchanges as well as air movement and water vapor content) and duration of eh* vironmental exposure is essential in evaluating the psycho-' logical and physiological adjustments of man-to cold: Man may become habituated'to cold; i-e.,' learn how to survive during cold periods,17 and he may also become acclimatised,1 Le., physiological changes may be produced in the man'so'as to make him more tolerant'to coId^'Available information indicates that'man habituates, rather 'than -acclimatizes/ to cold. '- There are few, if any, specific evidences of large physio- logical changes indicating acclimatization in man,11 even in groups of`people habitually exposed to cold environmental such as the Eskimos and Indians in Alaska/Recent studies of primitive peoples, such as the Australian aborigines, have found that these people allow excessive body cooling during. sleep (2-4 F deg)' which may be interpreted as representing true physiological acclimatization to cold.0 However, physP ological changes in man. resulting from prolonged cold ex posure are small, compared with the importance of factors such as accustomiration experience, training, fitness, etc. The maintenance of high skin temperature and'blood flow of the face and hands during extreme cold exposure in cold-acclima tized -individuals1' -is another example of beneficial physio logical change which allows sacrifice of body beat to preserve important body parts from frost-bite -The'caloric requirement of man in the Arctic or in the' Antarctic is not appreciably different from that of mao living in the temperate climate* The slight difference observed11** is oo more than'what'could be accounted-for by the added caloric requirement caused by the hobbling effect of the winter clothing and the greater energy expenditure required bymovement through snow, etc. However,,prolonged cold exposure of nude men to cold was far more severe than that encountered in normal Arctic living;- and-produced changes in' hormonal' balance,' and. dietary intake. Continuous exposure of nude men to an'am bient temperature of 8 F for 3 to 9 days, caused a two-fold1 increase in metabolic rate, a significant increase in'pulse rate, and marked^toes in body protein which persisted several days after--the subject had returned to normal room tempera ture.*1 Under-three conditions, food intake is most important. A* reduction in calories from 3000 to 1500 per day caused a marked reduction in-physical work capacity, as judged by an all-out treadmill test'.0 On the other band, no appreciable de terioration-1occurred in physical work capacity when 3000 calories and-70 g protein were given daily for 9 days at 8 F. Cold injury occurred in the feet of these subjects, but was most pronounced in the subjects receiving a diet deficient both in calories and protein. - V HiGH TEMPERATURE HAZARDS 'Exposure of men to extreme high temperature is limited by two different physiological responses: (1) elevated skin tem perature resulting in pain and tissue damage, and (2) elevated body temperature and the asociated syndromes of heat exhaustjbn, heat cramps, and heat stroke. The first of these imitationsis most easily observed when the skin temperature is raised rapidly to levels of 113 F (45 C) or higher, by means of infrared'radiation or by contact with hot.liquids, or solids.. The second effect is that most commonly associated with working conditions in hot climates or in industrial and military situations requiring work in hot, humid spaces. TRANSITIONAL REWON . min limit 1 itchuoolimit . - I 1- I I' I Rg. 3 . Tolerance Tunes and Temperature limits of Un protected Subjects Exposed to Fast Heat Pulses with ah Approximate Definition', of the Transitional Region'between ' Pain limited and Body Heat Storage limits0 ' 105 Iphprolbgical-Prindples - -Experiments have been carried out on human volunteers ^weed'loude*in: small chamber lined with quartz tube rfti-tia&ors: Measurements-were made of mean, wall tempera^ tu_ ^ temperature, akin temperature, body temperature, and-time of exposure to unbearable pain. Slowly and rapidly rising radiation pulses'were used, and the beat flux to the skin to both rases was about half radiative and half convective, with total heat fluxes to-the skin between 1000 arid 3000 Kcal/(tn7)(hr).ls Otherexperiments carried out at lower opera tive temperatures were limited by the elevation of deep body temperature Ti between 105 and 125 C (221-257 F). Fig. 3 diows the relationship of the limiting exposure time at very high wall temperature to the pain limit and body heat storage limit up to 50 minutes. In the transition region, both pain and heat1 storage may -be factors limiting the exposure time, but sufficientinformationin this' area is lacking. The high infrared radiation or wall-temperatures in these experiments must be considered a dangerous situation for a man, and clear-cut end points for exposure Htniis may not be available for every individual. Any covering of the exposed skin serves to protect the- individual,: >and thicker, highly reflecting' `garments offer additional- protection. However, only well ventilated, neck, pulse rate above 150, glazed eyes, and. mental disturb ances, such as apathy, poor judgment,- and irritability, which usually precede fainting (syncope). Unless the man has another illness, such as heart disease, he .will usually recover promptly if he is removed to a cool place and is permitted to heavy garments can prevent elevation of body temperature. Fig. 4 :indicates the-degree of protection that has been ob tained for various types of clothing in the pain limiting range of high"intensity infrared heating. An important oonsidera- turn in exposures of this type is the diffuse reflecting power of BeHdeoawtncfroaxmapstimaree.painful muscle spasms in the extremities, back, and abdomen, due, at least in part, to excessive loss of salt in sweating. Formerly common in hot industries, this manifestation of illness due to heat is now greatly reduced the skio. Fig. 5 shows a composite ofdata from many authors for the reflection in the visible and near infrared regions for a fair, blonde type ekin, and for a dark, negro skin. The majordifferencesin reflectingpower are in the visible and near infrared because for wavelengths longer than 3n, the human dun is essentially''black (reflecting power 1-1.5 percent), regWarhdelersesvoerf pSig(mEeqnutaattiioonn. 1) becomes strongly positive^,and body temperature rises progressively, men can continue to work until body temperature reaches 102-105 F.** When these by drinking water containing 0.1 percent salt, or by proper use of salt tablets. Heat cramps are readily alleviated by in travenous administration of salt solution. Heat stroke is a serious effect of exposure to great heat. The body temperature climbs rapidly to excessivelevels, often above 105 F, .when, for unknown reasons, free sweating suddenly stops. At such high temperatures, coma occurs, .and death may be imminent. Under these'circumstances, emer gency measures which quickly reduce .body temperatures are necessary, in order to avoid irreparable damage to the body temperatures are exceeded, men work with declining efficiency and may be subject to heat stroke. Heat exhaustion is a circulatory failure in which the venous return to the heart is reduced so that fainting results.0 -Early symptoms of heat exhaustion may include fatigue, headache, braTinh.*e deleterious physiologic effects of high temperatures exert a powerful influence upon physical activity, accidents, sickness, and mortality. Both laboratory and field data show that physical work in warm atmospheres is a great effort,' dizziness when erect^ loss of appetite, nausea, abdominal 'dis and that production falls progressively as the temperature tress, vomiting, shortness of breath, flushing of face and . rises. .: . - .;5 HEAT ACCUMATlZX'riON : 'T ._____c Limits to O .SloW ' -When men move to deserts or to jungles, some adaptation to the climate takes place. If work is gradually increased day by day, and if the men can get plenty of.water and salt, and can deep each night, acclimatization may be complete in17 to 10 days. The acclimatized man works with a lower-heart rate, lower akin and rectal temperature, and more' stable blood pressure than when unacclimatized. The process"of ao^ climatization requires work in the heat.0 During the recent war, white troops lived and did hard physical work'for'Tohg periods in tropical conditions, when disease hazards were con trolled. - In work tests made at the ASHRAE Research Laboratory,0 subjects were required to perform light work under very hot conditions for a 4-hr period each day. It was found'that the ability of a new subject to endure these conditions"showed daily improvement for a period of at least 2 weeks. However, ~~.i;^0f;Mtinn was completed,"several days without a.