Document RwOaMaBR0G2mrrgZr5NmjZxk

American Society of Heating and Ventilating Engineers Guide, 1932 toxic volatile matter in the expired air is now limited, in the light of numerous researches, to the much less dogmatic view that the presence of such a substance has not been demonstrated. The only fact that does appear certain is that expired and transpired air is odorous and offensive, and it is capable of producing headache, nausea, loss of appetite and a disinclination for physical activity. These reasons alone, whether aesthetic or physiological, are sufficient to warrant adequate air con ditioning. A certain part of the dissemination of disease which occurs in confined spaces is caused by the continuous emission of pathogenic bacteria from infected persons. Infections by droplets from coughing and sneezing constitute a limited mode of transmission in the immediate vicinity of the infected person. Experiments have shown that the mouth spray is a coarse rain which settles down quickly. The contamination is local and the problem is considered to be largely one of contact infection rather than air-borne infection. The primary factors in air conditioning work, in the absence of any specific contaminating source, are temperature, humidity and air move ment. As compared with these physical factors, the chemical factors are, as a general rule, of secondary importance. HEAT REGULATION IN MAN The importance of temperature, humidity and air movement arises from the profound influence which these factors exert upon body tem perature, comfort and health. Body temperature is a resultant of two factors, (1) heat production and (2) heat loss. The heat resulting from the combustion of food within the body maintains its temperature well above that of the surrounding air. At the same time, heat is constantly lost from the body by radiation, conduction and evaporation. Since, under ordinary conditions, the body temperature is maintained at its normal level of about 98.6 F, the heat production must be balanced by the heat loss. In healthy persons this takes place automatically by the action of the heat regulating mechanism. According to the general view, special areas in the skin are sensitive to temperature. Nerve courses carry the sense impressions to the brain and the response comes back over another set of nerves, the motor nerves, to the musculature and to all the active tissues in the body, including the endocrine glands. In this way, a two-sided mechanism controls the body temperature by (1) regulation of internal heat production (chemical regulation), and (2) regulation of heat loss by means of automatic varia tion in the rate of cutaneous circulation and the operation of the sweat glands (physical regulation). The mechanisms of adjustment are complex and little understood at the present time. Coordination of these dif ferent mechanisms seems to vary greatly with different air conditions. In reasonably warm environments (75 F to 80 F), metabolism, or internal heat production, is decreased to some extent, probably by an inhibitory action on heat producing organs, such as the liver. The blood capillaries in the skin become dilated by reflex action of the vasomotor nerves, allowing more blood to flow into the skin, and thus increase its temperature and consequently its heat loss. The increase in peripheral 388 Chapter 28--Air Conditioning in Relation to Comfort and Health circulation is at the expense of the internal organs. If this method of cooling is not in itself sufficient, the stimulus is extended to the sweat glands which allow water to pass through the surface of the skin, where it is evaporated. This method of cooling is the most effective of all, as long as the humidity of the'air is sufficiently low to allow for evaporation. In high humidities, equally good results may be obtained by increasing the air movement, and hence heat loss by conduction and evaporation. In cold environments, in order to keep the body warm there is an actual increase in metabolism brought about partly by voluntary muscular con tractions (shivering) and partly by an involuntary reflex upon the heat producing organs. The surface blood vessels become constricted and shrink further below the surface, thus increasing the insulating layer and decreasing heat loss. The blood supply to the skin is curtailed by vaso motor shifts to the internal organs, in order to conserve body heat. EFFECTS OF ADVERSE AIR CONDITIONS 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 heat regulating center fails, for instance, if 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, accele rated respiration and the like (see Table 1). In extreme conditions, the metabolic rate is markedly increased owing to the excessive rise in body temperature, 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 Table 1. Physiological Responses to Heat of Men at Rest and at Work3 Effective Temp. Actual Cheek , Tbmp. (Deo Fahr) Men at Rest Men at Work 90,000 ft-lb of Work pbb Hour Rise in Rectal Temp. (Deg Fahr per Hour) Increase in Pulse Rate (Beats per Min. 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 Min. per Hr.) Approximate Loss in Body Wt. by Per spiration (lb per Hr.) 60 70 0.0 6 80 96.1 0.0 0 85 96.6 0.1 i 90 97.0 0.3 4 95 97.6 0.9 15 100 99.6 2.2 40 105 104.7 4.0 83 110 5.9b 137> 6.2 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,(WO. 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 Laboratory. ^Computed value from exposures lasting less than one hour. 389