Document ppaJ76K33zrpYYJv4LEomG99E

102 CHAPTER 7 Table 1 .... Minimum Odor-free Air Requirements to Remove Objectionable Body Oder; Under Laboratory' Conditions1 Type at Occupants P*cl*Ha Oder-free Air Supply CFM per Pereoa 1965 Guide And Data Book healthy individuals.4Thereisstillmuchtobelearned aboutthe biological effects of air ionization, although the literature on the subject is quite extensive.* Ozone in amounts of 0.01 to 0.05 ppm of air is allowable in comfort air conditioning. Above this limit, there is a pun gent, unpleasant odor, and perhaps respiratory distress, de pression, and stupor.* Heating season with or without redradation. Air not conditioned. Sedentary- adults of average socio- 100 200 300 -500 25 16 12 :i PHYSICAL IMPURITIES IN AIR j -- Dust particles of almost any type can produce irritation of the mucous membranes of the nose and throat, if present in high concentrations. Certain dusts may be very harmful, * . but coal dust is well tolerated. Tbe effects of various indus Laborers.................................................. 200 Grade school children of average socio. 100 200 300 500 Grade school children of -lower socioeconomic status................................ Children attending private grade schools................................................. 200 100 23 :29 .-..17. 11 38 22 trial dusts, pollens, etc., are discussed in Chapter 11. A certain portion of the disseminationof disease in confined spaces may be due to pathogenic organisms floating 'in the air like dust particles. (See Chapter 10.) While, it may be possible in some instances, to reduce the physical impurities of the air by dilution from a non- contaminated source, such a source is rarely available. Fre-- quentiy, outdoor air contains a higher concentration of phys ical impurities than indoor air. Therefore, it is usually desirable to reduce the concentration of physical impurities by air cleaning methods. (See Chapter 36.) Heating Mason. Air humidified by meant of centrifugal bomMIfier. Water atomization rate 8 to 10 gph. Total air circulation 30 cfm per person. Sedentary adults.................................. 200 12 Summer teatoo. Air cooled anddehumldlfied by meant of a cpray 30 efra par penoti. .Sedentary adults.... ................ ............... j 200' j <4 THERMAL INTERCHANGES WITH ENVIRONMENT Body temperature depends upon the balance between heat production and heat loss. Heat resulting from oxidation of food elements in the body (metabolism) maintains the body temperature, well above that of the surrounding air in a cool or cold environment. At the same time, heat is constantly lost from the body by radiation, convection, and evapora tion. Since, .under ordinary resting conditions, the body from heating appliances). For such conditions,-the control of air temperature is the major consideration. - In more crowded rooms (large offices, large workrooms, auditoriums); where the cubic space per person is less, and it is usually impossible to admit untempered,outdoor air with out creating drafts, mechanical ventilation is essential. Freedom of movement, action, and thought, together with the variability of stimuli experienced by persons-under ideal conditions in the country,, mountains, or seashore,, un doubtedly has some stimulating effect. Various experimenters have attempted to duplicate the invigorating- qualities of outdoor air by the use of ionization, ozone, or- ultraviolet light.4 Air conditioning today provides control of most'of the climatological- environmental factors for- the'service and comfort of man There are; however, some less well known environmental factors not presently controlled - that may be of increasing importance to the engineer desiring to pro vide an artificial atmosphere equal in all respects to outdoor air having the most favorable qualities. Atmospheric elec tricity is one such factor. Under normal circumstances, the ion content of conditioned air may differ.from that of outdoor air. Such devices as mechanical filters, electrostatic precipitators, ultraviolet lamps, incandescent heaters, and spray or steamjet type humidifiers are knows to alter markedly the normal ion density. However, research to date has failed to show any significant effect of air ionization on the comfort of normal, temperature is maintained within its normal range of 97 to 99 F, the heat production must be balanced by the heat loss. During work, the body temperature may rise; afternoon temperatures of normal persons average 1 deg above the rest ing value of the morning, whether they are working or not. The fundamental thermodynamic proccses concerned in beat interchanges between the body and its environment may be described by the equation: M - S + ESC ' (1) where . M = rate of metabolism, heat produced.within the body. S = rate of storage, change in intrinsic body heat. E = rate of evaporative heat loss. " R -- rate of radiative heat loss or gun. C =* rate of convective heat kiss or gun. The rate of metabolism, Af, is always positive. The storage,' S, may be either positive or negative, depending upon whether heat is being stored or depleted, owing to a rise or fall in body temperature. Under ordinary circumstances (when the dew point of the air is below the body surface temperature), the evaporation loss, B, is always positive, that is, ;heat from metabolism supplies this loss. R mid C are positive when body surface temperature is above that of walls and air, and nega tive when it is below. ' DuBois,7 after careful calorimeter studies on a fasting, nude man, plotted the partition of body heat loss and heat pro duction as a function of temperature, fig. 1 shows some dis parity between heat production and heat loss. This disparity Physiological..Principles 103 ` S in Equation 1 In the central range of the experiments, . f was quitelow, and no increase in heat loss by vaporization - waWs aitphpinarteilnet., of 81-86 F air temperature, with still air, icre is, for a resting, nude man, a point at which his body - needs to no particular action in order to maintain its heat balance.- If he is clothed, or if he is active, this point will naturally lie at a lower level. At this point, which may be . termed the neutral point for that individual, conditions are neither too hot nor too cold. If, through a fall in air temperatore or a rise in air movement, the rate of heat loss from the skin to the environment is increased, then the body must do something to counteract this heat loss. Over a certain range, the body can do this by decreasing the flow of blood through the ptin' This will result in some cooling of the skin and sub jacent tissues, but the temperature of the deep tissues will be The range of external conditions over which this may be achieved may be termed the zone of vaso-motor regulation against cold. Beyoad this range, the temperature of the superficial tissues will fall still further, and that of the deep .tissues, will fall as well, unless some other steps are toVon The body normally does react; it increases heat pro duction by increasing muscular tension, by shivering, or by. spontaneous-increase in activity.* As long as these reactions are adequate to meet the increased rate of heat loss to the environment,-a fall in deep body temperature may be pre vented. Such conditions may be said to lie in the zone of meta bolic regulation against cold. Beyond this point, the body enters the zone of inevitable body cooling. - It will be seen that, in man, deep body temperature is pre served over an important range of cold external conditions, at tiie expense of (1) a fall in the temperature of the periph eral tissues, .and (2) an increased expenditure of energy. In the first of these, the farther away superficial tissue lies from the central body mass, the more readily will its temperature fall' On the hot side of the neutral point, there exists a zone of vaso-motor regulation against heat, corresponding to that against.coM. The blood Bow through the skin is increased when the opportunities for heat loss to the environment are restricted.* This increase in blood flow may double or triple the conductance-of the superficial tissues over that charac teristic of the'neutral point, and the temperature of the skin surface may rise until it is only three degrees below that of the deep tissues. If this increase in blood flow is unable to balance the restriction in heat loss, the body has entered the next zone. Once again, the normal body takes steps to prevent a change in its deep temperature, but they are not the counter part of the steps taken when exposed to cold. There is, in fact, very little.change in heat production, beyond that resulting from a disinclination for exertion. The second line of defense is a powerful method of promoting heat loss, the provision of water, through the operation of the sweat glands, for evapora tive cooling. As long as evaporation is adequate to restore the desired heat Joss, the body is in the zone of evaporative regula tion against heat. When evaporation ceases to be adequate, the body is in the zone of inevitable body heating. The body enjoys les latitude in this zone than it did in the corresponding zone on the cold side, but when the deep temperature rises more than 4 F deg, it loses its efficiency, and body temperatures above 110 F may be lethal if endured for longer than a few minutes. All factors which affect the evaporation of water from the akin affect heat regulation in the zone of evaporative regulation. Atmospheric vapor pressure and air motion are the most important of these. With dry-bulb temperature above `Nonsd control, ookod, to colorimeter at temperatures from 72A to 94J F. Rnl column to cedi experiment npntnfi hast production as de termined by faxfired catarimotry, to* tecood column,.(wot efiatooffen- The portion marked with vertical Enas represent! vaporization; A* wnmaHced areo, radiation, cod convection. Tht skin temperature roprasoats A* aver age redding at 19 spots on Ao turfac*. fig. 1.... Heat Loss from Human 'Being by. Evaporation and by Radiation and Convection* body temperature, air motion facilitates evaporative heat loss by removing hot humid air from contact with the skin and replacing it with relatively drier air. ' Temperature regulation in man requires an intact set of sensory nerves, a normal sympathetic nerve supply to sweat glands and blood vessels, a great'many sweat glands, and a circulatory system capable of carrying heat from muscles and viscera to the skin by circulation of the blood. . Some of the phenomena of. body temperature control are shown graphically in Fig. 2. The dotted curves, from a study at the John B. Pierce- Laboratory of Hygiene,1* are for sub jects lightly clothed in a semi-reclining position, and give.the relation between the dry-bulb temperature of the environ-; ment (with about 45 percent relative humidity)- and the metabolic rate (heat production), the rate of heat dissipation by radiation and convection combined, and the latent heat kiss due to evaporation from the skin and the respiratory tractvThe smooth line curves from the work of the ASHRAE Research,Laboratory11 give the same relationships for healthy, male subjects (18 to 24 years of age), seated, at rest and dresed in customary winter indoor clothing. The Fierce Laboratory data for-the.semi-reclining subjects also include the rate of heat storage (either positive or negative) due to a rise or fall in body-.temperature. For the normally clothed subjects, a curve gives the total heat loss, that is,. the sum of the radiation, convection, and evaporative losses. Storage is given by the difference between the metabolism and total heat loss. .The small difference between the metabolic rates for the two groups of subjects may. be accounted, for by difference in activity. Heat exchange between the body and the environ ment by radiation and convection is. greater for the lightly clothed subject, both for cool conditions where there is. ex cessive heat loss, and for very warm conditions where-there is transfer, of heat from the atmosphere to the body. The .two curves for evaporative loss serve, to show how physiological control uses evaporation of sweat to maintain equilibrium at high temperatores. Below 75 F, for the normally clothed sub^