Document 2JYdVOnV9zLOVBRkxL7x35r06

286 W. N. WITHERIDGE I. Human Ventilation Requirements Ventilation of residential, commercial, and office spaces is now understo be necessary to control body odorB, tobacco smoke, cooking odors, and odorous impurities, rather than to maintain the required amount of oxyge remove the carbon dioxide produced by respiration. This is true becau standard construction of buildings for human occupancy cannot prevent-, infiltration and exfiltration of substantial amounts of air, even when all wi) door, roof, or mechanical-ventilation openings are closed. Published dat. the amounts of outdoor air normally available by natural ventilation or;in': tion indicate that suffocation by deficiency of oxygen or excess of carbon' di as a result of human respiration, is virtually impossible in buildings const:; above ground. - if In view -of the fact that industrial hygienists are called upon to justi| position to those who are not aware of the background of research and exqe upon which present ventilation standards are based, a brief review of the^'i of respiration on atmospheric air is in order at this point. A. AIR COMPOSITION The approximate composition of air under three conditions is given in' 1. Simple calculations will demonstrate that human beings do not requffi than a few hundred cubic feet of air per hour to satisfy their demand fdr| Component Inert gases (nitrogen, argon, etc.) Oxygen Water vapor Carbon, dioxide Total TABLE 1 Composition of Air (Volume per cent) Outdoor air, dry 79.00 20.97 0.00 0.03 100.00 Indoor air, 70 F. (RH 50) 78.00 20.69 1.25 0.06 100.00 and to dilute to a harmless concentration the carbon dioxide produced , !jb evenn- at-heavy work, breathes only about 40 liters (1.4.cu. ft.) of.....aaiirr==Ep^^j J3$p conssuummeess about two liters (0.07 cu. ft.) of oxygen, and produces about^l gf (0.06 cu. ft.) of carbon dioxide. 1 Heating, Ventilating, Air Conditioning Guide, 1957. American Society bf'He|lj|ft Air-Conditioning Engineers, New York, 1957, ch. 11. VENTILATION 287 lljllja;'ckey2 offered an interesting hypothesis on the physical and chemical spurring in indoor air as a result of human occupancy. His analysis was las follows (modified after communication with Mackey): at rest uses in one minute about 20 cubic inches of oxygen and produces about *^all^es car*-l0n dioxide. At 70 F., he loses in one hour about 300 Btu of sensible 'about 0.1 pound of water vapor. Assuming for simplicity that these rates remain YjS^iai'jShich they would not do in fact), if such an adult were confined in on airtight, a" ulated space of 1000 cubic feet, initially at 70 F. (ignoring humidity), the dryEftW=iuture would increase to 100 F. in less than two hours, while about 75 hours would ItfMSSQi toi rediuce the oxygen to 16 per cent and increase the carbon dioxide to 5 per cent. Extreme case, the physical change is seen to be much more dangerous than the rt* Jr^HVilllON DIOXIDE AS AN INDEX OF VENTILATION REQUIREMENTS MS.|,i^;ement of carbon dioxide concentrations in spaces occupied by human &. been standard procedure among ventilating engineers for many j|Yaglou, Riley, and Coggins3 reported in 1936 their results from a ggwa^eriments on ventilation requirements. They concluded that the carbon 7|||pentration "in the air of occupied rooms proved to be an unreliable entilation, from the standpoint of both outdoor air supply and odor suggested that "a great deal of unjustified effort would be saved |||uing the usual measurements of CO2 in ordinary ventilation work, ||>s in instances in which the air flow is well under 10 c.f.m. per person." research workers and writers during the .present century have recog^xistence of 0.10 to 0.50 per cent CO2 in spaces occupied by human |bf itself dangerous. Some still express the belief, however, that such gAoarbon dioxide, from a normal outdoor level of 0.03 to 0.04 per cent, ^presence of unhealthful constituents as a result of vitiation 0} air ggpiration. This question has not been settled to the satisfaction of the gburrent use of odors as indexes of ventilation requirements is still Some as neglect of a fundamental hazard to life and health. Neverk| health workers and ventilation engineers are now generally conlrygen and carbon dioxide concentrations in air at normal barometric r'j^sslhot of concern to health in the absence of more substantial dis&' -jmSgir composition, as might be caused by. industrial processes that l|g|8 or generate carbon dioxide. ^^gOjOnded use of odor-controlling processes for air conditioning will bring i'ui^n^r^eyisions in the standards of quantities of outdoor ,jur per capita MSbadfe or oorafprt.* In some situations it may be possible to approvi ni of 100 per cent recirculation of indoor air, on the strength ... 4>r Conditioning Principles. International Textbook, Scranton, 1941. SgsijfVSifigfou, E. C. Riley, and D. I. Coggins, Trans. ASHVE, 42, 133 (1936). wSiRwiilo'd and W. N. Witheridge, Odors: Physiology and Control. McGraw-Hill; ^144# " /* * tl *.