Document Gm6YEJq0djvMzVLGjXe8Ba01v

204. CHAPTER 12 1948' Guide exhaustion may include fatigue, headache, dizziness when erect, loss of* appetite, nausea, abdominal distress, vomiting) shortness of breath, flush- " ing of face and neck, pulse rate above 150, fever well above 102 F, glazed eyes, and mental disturbances as apathy, poor judgment, irritability and which usually precede fainting (syncope) Recovery is usually prompt when the man is removed to a cool place and kept lying down for a time, unless he has some other illness such as heart disease. Heat cramps are painful muscle spasms in extremities, back and abdomen due, at least in part,'to excessive loss of salt in sweating. For-, merly common in hot industries, this manifestation of illness due to heat/ is. now greatly reduced by drinking water containing 0.1 per cent salt, or by proper use of salt tablets. Heat cramps are readily alleviated by administration of salt solution intravenously. Heat stroke or sun stroke is a serious effect of exposure to great heat. The body temperature climbs rapidly to excessive levels often above 105 F when for unknown reasons free sweating suddenly stops. At such high temperatures coma appears arid death may be irnminent. Emergency measures are required to reduce the excessive body temperature by cooling quickly to avoid, irreparable damage to. the brain IZ. "The deleterious-physiologic effects of high temperatures exert a powers ful influence upon . physical activity, accidents, sickness and mortality. Both laboratory and field data show that physical work in warm; atmos pheres is a great effort) and that production falls progressively as the temperature rises. ACCLIMATIZATION When men moye 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 arid salt, and can sleep each night, acclimatization may be. complete in 7 to 10 days. The acclimatized man works with a lower heart rate, lower sldn and rectal temperature, and more stable blood pressure than when unacclimatized. The process of acclimatization requires work in the heat ". In recent tests made at the A.S.H.V.E. Research Laboratory I4, subjects were required to perform light work under very hot conditions for a 4-hr period each day. ' It was found that the ability pf a new subject to endure these conditions showed daily improvement for a period of at least 2 weeks. However, after acclimatization was completed, a recess of several days had no effect on the endurance of the subject. Individuals differ widely in their capacity to acclimatize. Acclimatized men lose these capacities in a few weeks of temperate climate, even though they are vigorously active. Acclimatization to dry heat increases the capacity to sweat and conserves salt by secreting a dilute sweatls. Deterioration of performance and other ill effects of heat may'arise during prolonged exposure to heat when men cannot get sufficient rest and sleep each day.. Acclimatization to extreme conditions involves a strain upon the heat regulating system and interferes with the normal physiologic functions of- the human body. Thousands of years in the heat of Africa do not seem to have acclimatized the Negro to a tempera ture exceeding 80 F. The same holds true of northern races with respect to cold, although the effects are mitigated by artificial control.. Some persons regard the unnecessary endurance of cold as a virtue. They believe that the human organism can adapt itself to a wide range of air Physiological Principles 205 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 Below 101 101 to 102 Above, 102 Pulse rate Below 130 130 to 145 Over 145 ' conditions with no apparent discomfort or injury to health. In the light' of present knowledge of air conditioning these views are not justified. ' , ' The adaptive level changes somewhat with the season. There are also marked differences between the sexes. In the cold zone the,thickness :of thermal insulating tissues of women is almost double that of men, although the sensory responses to cold are similar. In the hot zone, the threshold pf sweating is higher for women. The thickness and insulating value of the clothing worn are also important factors in the determination of the coirifort level. UPPER LIMITS OF HEAT FOR MEN AT WORK In very hot conditions humidity is the limiting factor and the .wet-bulb temperature assumes great importance. In 1905 Haldane recognized that 88 F wet-bulb was the limit of endurance for coal miners and later observers have concurred. A study was made at the Armored Medical Research Laboratory " to determine the upper limits of environmental conditions under which a. man can perform certain work. Thirteen enlisted men, thoroughly acclimatized to the hot conditions, served as subjects. During each test, the subjects were required to march for 4 hr at the rate of 3 mph, carrying 20 lb packs under a wide range of environmerital conditions which were rated 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 and Fig. 3. Recognition of the need of air conditioning for workers in hot indus- in m'Aurinrr 1 '-ri--------rf Kvstpm to be used in Fig. 3.' Heat Endurance of Acclimatized Subjects Working at a Specific Rate1*