Document 2Jk5dn3ad78Z88VRxVOk0kz35

224 HEAT CHAPTER 12 1946 'Guide Increased Metabolism Failure to Sweat Derangement of Heat Regulatory Center HEAT STROKE INCREASED BODY TEMPERATURE Vasodilation AfcCLIMATIZATION - SWEATING Increased Ability to Sweat Salt Economy Increased Circulation to Skin Increased Pulse Rate Temporary Loss of Blood Volume Circulatory Insufficiency HEAT EXHAUSTION Decreased Metabolic Rate Maintenance of Normal Body Temperature Excess Water Loss SUPER DEHYDRATION Excess Salt Loss HEAT CRAMPS Fig. 2. Physical Effects of Overheating and Acclimatization and heat strokes 10. Heat exhaustion is due to circulatory failure; heat cramps to excessive loss of body chlorides and heat stroke to dn inade quacy of the heat dissipating mechanism which results in hyperthermia (high fever) (See Fig. 2). If the hyperthermia becomes excessive, the liver and the central nervous system may be seriously injured and this damage may prove fatal. The hazards of liigh temperature are not understood. It is difficult to say whether short exposures at high tem peratures are more harmful than longer exposures at lower temperatures. A new concept is evident from the observation of an increase in leucocytes (white cells) of the blood in workers subjected to high temperatures. These leucocytes are defensive factors which are increased when infection invades the body. A rise in temperature and leucocyte count indicates a mobilization of the body defenses. Since both' temperature and cell count are increased20, the question arises as to whether long exposures to very high-temperatures might not cause exhaustion of these defense mechanisms. A study was made recently at the: Armored Medical Research Lab oratory 21 to determine the upper limits of environmental conditions under' which a man can perform certain work. Thirteen enlisted men, who were first thoroughly acclimatized to the hot conditions, served as i Physiological Principles Table 3. Upper Limits of Environmental Conditions for Acclimatized, Healthy, Young Men in Military Service Environment Reactions at the end of 4 hr Rectal Temp F Pulse rate. Relatively Easy................................... Impossible............. ..... ...............--------- Below 101 101 to 102 Above 102 Below 130 130 to 145 Over 145 subjects. During each test, the subjects were required to march for 4 hr at the rate of 3 mph, carrying 20 lb packs. Tests were made under a wide range of environmental conditions, and these environments were rated in 3. zones as relatively easy, difficult, and impossible, on the basis of the physiological reactions of the subjects at the end of the 4 hr period as shown in Table 3. Fig. 3 shows the limits of the three environ mental zones. Recognition of the need of air conditioning for workers in hot indus tries is growing rapidly and this should become an important field for the air conditioning, engineer. The hot conditions may be remedied by any of the recognized comfort cooling applications. The choice of the type of system and cycle to be used in a given instance must be determined by the air conditioning engineer,after a study of surrounding conditions. In some hot industries where a small number of workers are engaged in spaces of large volumetric capacity the worker himself, rather than the Fig. 3. The Endurance of Environmental Conditions by Acclimatized Subjects Working at a Specific Rate From The Upper Limits of Environmental Heat and Humidity Tolerated by Acclimatized Men Work ing in' Hot Environments (Journal of Industrial Hygiene-and Toxicology, March, 1Q45, p. 70). Used by/ permission. .