Document Rr4GE3QBbV8j62bwMgBXnjLX

222 CHAPTER 12 1946 Guide .. of the fingers and that this low temperature of the fingers-persisted for. one hour after the ice pack was removed: ADAPTATION TO ENVIRONMENTAt CONDITIONS As stated previously, the optimum environmental conditions for com fort are those under which the body can maintain complete thermal equilibrium with only minor adjustments in blood, distribution. As conditions depart from the optimum, more drastic adjustments are made by the body in its attempt to maintain equilibrium, and the sensation of comfort gives way to one of.increasing discomfort. If conditions.are too severe, adequate adjustments may be impossible, and prolonged exposure may result in serious injury or death. In a cold environment the blood vessels leading, to the surface are constricted, thus decreasing the flow of blood and heat to the skin, and reducing the radiation and convection losses from it. If this adjustment is insufficient, an involuntary muscular activity (shivering) takes place which increases the metabolism. The range over which these physiologi cal controls are effective is rather narrow, and .man's existence in cold climates is dependent upon his-ability to provide himself with heated living quarters and warm clothes. During the last few years extensive research has been carried on by and for the armed services of the United Nations to determine the proper types and amounts of clothing for a wide range of conditions. The results of these studies are now being released and should add greatly to our knowledge on the subject. As man's environment changes from cool or comfortable to warm, the ' body first attempts to adjust to the new conditions-by a redistribution of the blood circulation. Blood capillaries near the surface become dilated, . allowing more blood to flow to the skin, thus raising the skin temperature and increasing the radiation and convection losses from the body. If this correction proves inadequate, the stimulus is extended to the sweat glands which cause progressively greater portions of the body area to become moist or wet as conditions become more severe. The evaporation of this . moisture from the body surface provides the body with its most effective method of cooling, but even this fails when the dew-point temperature of the air becomes so high that rapid evaporation is no longer possible. Although -the body is able, by evaporative cooling, to maintain complete thermal balance under conditions of moderate excess, it does so only at the cost of considerable discomfort. \ . Studies at the John B. Pierce laboratory of Hygiene 13 have indicated the relation!between discomfort and the degree of wetting of the body surface by perspiration for lightly clothed subjects in a semi-reclining position, and the investigators there have designated this as the zone of evaporative regulation. The relation between sensible perspiration and the atmospheric environment for normal persons at rest and at workhas-been determined at the A.S.H.V.E. Research Laboratory 10. HIGH TEMPERATURE HAZARDS Studies at the A.S.H.V.E. Research Laboratory 14 and elsewhere15 during the past two decades have made available a mass of information dealing.with the physiological effects of, hot atmospheres on workers.and . means of alleviating the distress and hazards associated-therewith. This Physiological Principles- 223 interest has been termed air conditioning in industry, or the effects of hot atmospheres in industrial hygiene, and is a growing factor in air conditioning applications. Table 2 gives some of the,physiological responses of men at rest and at work, to hot environments. Physiological studies 16 indicated that frequent and continued exposure of workers to hot environments results in physiological derangement affecting the leucocyte count of the blood, and other factors dealing with man's mechanism of defense against infection. In hot environments the blood is diverted from the internal'organs to the surface capillaries, in order to serve in the process of cooling. This affects the stomach, heart, lungs and other.vital organs, and it is suggested that the feeling of lassitude and discomfort experienced is due in part to the anaemic condition of the brain. The stomach loses some of its power Table 2. Physiological Responses to Heat of,Men at Rest and at Work3 Effective Trap 60 70 80 85 90 . 95 too 105 110 Actual Cheek Trap (PtRR Deo) . Men at Rest i Men at Wore 90.000 ft-lb or Wore per Hour Rise in Rectal Temp . (Fahr Deg per Hr) Increase io Pulse Rate . (Beats pa Min pa Hr) Approximate Loss is Body Weigbtby ' Perspiration (Lb per Hr) Total Work Accomplished j (Ft-Lb) Rise in Body Temp (Fahr Deg . pa Hr) Increase io Pulse Rate (Beats pa Min pa Hr) Approximate Loss in Body. Wt by Pa* spiration (Lb pa Hr) - 96.1 96.6 97.0 97.6 99.6 104.7 :--------- 0.0 0.0 0.1 0.3 0.9 2.2 4.0 5!9l> -6 0 1 4 15 40 83 137*> o'! 0.3 0.4 0.5 0.9 1.7 2.7 4.o> '225.000225.000 209.000 - 190.000 153.000 102.000 67.000 49.000 - 37.000 0.0 . 0.1 0.3 - 0.6 1.2 2.3 4.0b 6.0b 8.5b 6' .7 11 17 31 61 103b 158b 237b 0.5 0.6 0.8 1.1 1.5 .2.0. 2.7b 3.5b 4.4b Data by A.S.H.V.E. Research Laboratory. ^Computed value from exposures lasting-less than one hour. to act upon the food, owing to a diminished secretion.of gastric juice, and there is a corresponding'loss in'the antiseptic and antifermentive action which'favors, the growth'of bacteria in the'intestinal tract17. These are considered to be the potent factors in: the increased suscepti bility to gastro-intestinal disorders in hot summer weather. . In warm atmospheres, particularly during physical,work, a considerable amount of chloride is lost fromthe system through:sweating. . The loss of this substance may cause excessive fatigue,ror.may lead to attacks of cramps, unless the salts are replaced.. 'In order to.'relieve both cramps and fatigue, it is recommended that salt tablets be taken, or that sufficient salt be added, to the drinking water to provide a'*/i* of 1 per cent saline solution18. ' , ....... " . , ; . . - . The deleterious physiologic effects of high temperatures exert a power-' 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 tem perature rises. The incidence of industrial accidents reaches a minimum at about 68 F, increasing above and below that temperature. Sickness and mortality rates increase progressively as ithe temperature rises. Diseases due to heat are now classified as heat exhaustion, heat cramps, S