Document 99nK8gvbwmJQrDDp1MLr2Ep73

HEATING VENTILATING AIR CONDITIONING GUIDE 1942 occasionally the engineer is confronted with the problem of removing such material before the air in question is suitable for use in building venti lation. The physical properties of the particulate impurities of air are summar ized conveniently in the chart of Fig. 1. In the case of gases, the objectionable features are the injurious physiological effects and the danger from inflammability. (See Table 1.) Dust Concentrations It is customary to report dust concentrations as grains per 1000 cu ft or milligrams per cubic meter (except for dusts that may cause pneu moconiosis, which are reported as so many particles per cubic foot of air). Gas concentrations are commonly recorded as milligrams per cubic meter or as parts per million or as per cent by volume. Typical ranges in dust concentrations as now found in practical applications are given in Table 2. Table 2. Dust Concentration Ranges in Practical Applications3 Application Grains Per 1000 Cu Ft Mas Per Cu M Industrial districts....................................................... Dusty factories or mines______________ .. Explosive concentrations (as of flour or soft coal).. 0.2 to 0.4 0.4 to 0.8 0.8 to 1.5 4.0 to 80.0 4000 to 8000 0.4 to 0.8 0.9 to 1.8 1.8 to 3.5 10 to 200 10,000 to 20,000 *1 grains per 1000 cu ft = 2.3 mgs per cubic meter; 1 oz per cubic foot = 1 g per liter. The engineer frequently desires information regarding the effects of various concentrations of gases or dusts upon man, as the success of a particular installation may depend upon the maintenance of air which is adequately clean. At the present time there are several organi zations working on this problem all of them publishing literature of various kinds.1 References to books covering the. hygienic significance, determination and control of dust are listed at the end of this chapter. AIR POLLUTION AND HEALTH The prevention of various diseases which result from exposure to atmospheric impurities is an engineering problem. It is important for the engineer to insure, by proper ventilation, suitable environments for working or for general living. If the equipment used is to be successful, it must operate automatically as in the modern air conditioned theater or railroad train. In Table 3 are given data on permissible concentrations of various substances, gases and dusts, which occur in industry. The prudent engineer will design equipment using these bench marks as the upper limits of pollution. In general it is good practice to avoid recirculation of air which originally contains toxic substances. Obviously there may be 1Nationai Institute for Health. U. S. Public Health Service; Division of Labor Standards, U. S. Depart ment of Labor; University of Toronto Medical'School, Canada; Saranac Laboratories, Saranac Lake. N. Y.;-Industrial Hygiene Foundation, Inc., Pittsburgh, Pa.; Harvard School of Public Health, Boston. Mass.; Haskell Laboratory. Wilmington, Del.; and the Departments of Health and of'Labor in the United 'States and in various provinces of Canada. 564 CHAPTER 28. AIR POLLUTION exceptions to this rule, but it is one which is generally being followed in current practice. Affections of the respiratory tract are associated with exposure to thick dust, and may follow inhalation of practically any kind of insoluble and non-colloidal dust. Atmospheric dust in itself cannot be blamed for causing tuberculosis, but it may aggravate the disease once it has started.2 Table 3. Toxicity of Gases, Vapors, Dusts and Fumes3 Substance Rapidly Fatal Single Exposures Dangerous for from H to 1 Hour Max. Safe Concentration for H to l Hour Max. Allowable Average Concentration for Repeated Exposures (ppm) (ppm) Ammonia................. 5,000-10,000 Aniline...................... 2500 Arsine.................... 250....... Benzene............... 190 Carbon bisulfide........ 4800 Carbon dioxide... .. 80,000-100,000 3200-3850 Carbon monoxide.... Carbon tetrachloride 4000 10,000 1500-2000 Chlorine................. 900 Hydrogen cyanide.... 270 Hydrogen chloride.... 1250-1750 Hydrogen fluoride.... 660 Hydrogen sulfide... 1000-2000 Methyl bromide .. 20,000-40,000 Methyl chloride.... 150,000-300,000 Nitrobenzene........ 110-135 1000-1350 50-250 360-500 2000-4000 20,000-40,000 Oxides of nitrogen.... Phosgene............ Phosphine........... Sulfur dioxide.- Tetrachlorethane.-... Toluene and xylene.. 320-530 90 2000 400-500 7300 117-154 12.5 150-190 I richlorethylene... 7800 Dusts: Containing high percentages of free silica....... Containing 25 to 35 percentages of free silica Containing small percentages of free silica___ Cadmium..................... ................. .--................. Lead.................................................... ;.................. Mercury.................................................................. Manganese.-...... ......................................-............ Zinc....................................... (ppm) 300 105-160 6 31-47 960-1600 400 1000 3.5 45-54 40-90 10 200-300 1000 7000 200 100-200 50-100 3700 (ppm) 100 5 1 100 20 100 100 1 20 10 3 20 5 10 i 2 10 10 200 200 5 millionb 10-20 million!) 30 million!) 0.1<= 0.15c 0.1c 30c 15c bf-yncr;aJoCuersnsatlhafnIn1d0umstirciarolnHsy)gpieenrecaunbdicTioZxictooloigfyi, W 1940-.nd trhefr aouthiownt3t`V''3 "ioSrctaean.d` "-Milligrams per cubic meter of air. . ...puuiuus mines ana tarry matter in smoke are more dangerous than the carbon. In foggy weather the accumulation of these substances in the lower strata may be such as to cause irritation of the eyes, nose, and respiratory passages. The Meuse Valley fog disaster will probably become * Physiological Response -of the Peritoneal Tissue to Dusts Introduced as Foreign Bodies, by Miller and Sayers (U. S. Public Health Reports, 49:80, 1934). 565