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Heating VentiiiAting Air Conditioning Guide 1939 EFFECTS OF HEAT Although the human organism is capable of adapting itself to variations in environmental conditions, its ability to maintain heat equilibrium is limited. The upper limit of effective temperature to which the human organism is capable of adapting itself without serious discomfort or injury to health is 90 deg ET for men at rest and between 80 and 90 deg ET for men at work depending upon the rate of work. Within these limits a new equilibrium is established at a higher body temperature level through a chain of physiological adjustments. The heat regulating center fails, when the external temperature is so abnormally high that bodily heat cannot be eliminated as fast as it is produced. , Part of it is retained in the body, causing a rise in skin and deep tissue temperature, an increase in the heart rate, and accelerated respiration. (See Table 1). In extreme Table 1. Physiological Responses to Heat of Men at Rest and at Works Emcnvs Temp Actual Cbsek Temp (Deg Fjhs) 60 70 80 96.1 85 96.6 90 97.0 95 97.6 100 99.6 105 104.7 no Men at Rest Men at Wonx 90,000 ft-lb or Work per Hour Rise io Rectal Temp (Deg Fahr per Hour) Increase in Pube Rate (Beats per Mio per Hour) Approximate Loss in Body Weight by Perspiration (Lb per Hr) Total Work Accomplished (Ft-Lb) Rise in Body Temp (Deg Fahr per Hr) Increase in Pulse Rate (Beats per Mio per Hr) Approximate Loss io Body Wt by Per spiration (Lb per Hr) 0.0 0.0 0.1 0.3 0.9 2.2 4.0 5.9>> 0 0 1 4 15 40 83 137b 0.2 0.3 0.4 0.5 0.9 1.7 2.7 4.0b 225,000 225,000 209,000 190,000 153,000 102,000 67,000 49,000 37,000 0.0 0.1 0.3 0.6 1.2 2.3 4.0 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 2.7 3.5b 4.4b Data by A.S.H.V.E. Research I-aboratory. ^Computed value from exposures lasting less than one hour. heat, the metabolic rate is markedly increased owing to the excessive rise in body temperature8, and a vicious cycle results which may eventually lead to serious physiologic damage. Examples of this are met with in unusually hot summer weather and in hot industries where the radiant heat from hot objects renders heat loss from the body by radiation and convection impossible. Consequently, the workers depend entirely on evaporation for the elimination of body heat. They stream with perspiration and drink liquids abundantly to replace the loss. One of the deleterious effects of high temperatures is that 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 anddiscomfort experienced is due in part to the anaemic condition of the brain. The stomach loses some of its power to act upon the food, owing to a A.S.H-V.E. Research Report No. 719--Basal Metabolism Before and After Exposure to High Tem peratures and Various Humidities, by W. J. McConnell. C. P. Yaglou and W. B. Fulton (A.S.H.V.E. Transactions. Vol. 31. 1925. p. 123). 52 Chapter 3. Physical & Physiological Principles or Air Conditioning 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 tract9. These are considered to be the potent factors in the increased susceptibility to gastro-intestinal disorders in hot summer weather. The victim may lose appetite and suffer from indiges tion, headache and general enervation, which may eventually lead to a premature old age. In warm atmospheres, particularly during physical work, a considerable amount of chloride is lost from the system through sweating. The loss of this substance may lead to attacks of cramps, unless the salts are replaced in the drinking water. In order to relieve both cramps and fatigue, Moss10 recommends the addition of 6 grams of sodium chloride and 4 grams of potassium chloride to a gallon of water. 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 clearly that physical work in warm atmospheres is a great effort, and that production falls progressively as the temperature 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 the temperature rises. EFFECTS OF COLD AND TEMPERATURE CHANGES The action of cold on human beings is not well known. Cold affects the human organism in two ways: (1) through its action on the body as a whole, and (2) through its action on the mucous membranes of the upper respiratory tract. Little exact information is available on the latter. On exposure to cold, the loss of heat is increased considerably and only within certain limits is compensation possible by increased heat produc tion and decreased peripheral circulation. The rectal temperature often rises upon exposure to cold but the pulse rate and skin temperature fall. The biood pressure increases, owing to constriction in the peripheral vessels. Just how cold affects health is not well understood. It imposes an extra load upon the heat-producing organs to maintain body tempera ture. The strain falls largely upon digestion, metabolism, blood circu lation, and the kidneys, and indirectly upon the nervous system11. Although the seasonal increase in morbidity and mortality sets in with the approach of cold weather and subsides in the warm summer months, little is known of the specific causative factors and their mechanism of action. Over-crowding of buildings, overheated rooms, lack of venti lation, and close personal contacts are frequently held responsible for our winter ills, but the evidence is not conclusive. In extremely cold atmospheres compensation by increased metabolism becomes inadequate. The body temperature falls and the reflex irritability ol the spinal cord is markedly affected. The organism may finally pass into an unconscious state which ends in death. Brody (Proceedings Society VofId. "Loc. Cit. Note 5. Bio/. Afed/i Vol. 24,1927. p.832}. ^^lntesunal lract' UPOn the Miner-. by K- N- MoSS 53 0/