Document B8GbnwJ8dymv4jxLqaVgLGY5o

190 CHAPTER 10 _______________ - 1946 Guide or unfamiliar odors tend to receive-much-more attention from the neigh borhood than the customary odors generated by well known processes and raw materials. Methods of odor control currently in use include charcoal adsorption, scrubbing towers and air washers, chlorination, condensation, masking, passage of the odorous air through combustion chambers, and best of all, substitution of less offensive materials whenever possible * *10- u. The control of air quality within buildings ventilated for human occupancy is discussed in -Chapter 12. Tobacco smoke odors, cooking odors and body odors are air contaminants of the nuisance type which now command a decisive position in the standards of air quality for indoor comfort. However, the engineer will find, at times, that odors originating outside buildings in industrial or business districts may have an even greater bearing than indoor contamination on the kind and capacity of equipment he must provide for a, high quality air supply installation. INDUSTRIAL AIR CONTAMINANTS Many industrial processes are sources of contaminants. Their unde sirable effects are known to the public and their control is an important function of the ventilating or air conditioning engineer, because the atmosphere within buildings is the medium whereby such finely divided matter is dispersed and transported from the source to remote locations where it may cause property damage, nuisance, fire, explosion, diseaseand even death. Tables 3,- 4 and 5 give the maximum allowable concentrations for industrial air contaminants as currently accepted in most sections of the country. They apply to exposures of 8 hours per day, and refer to the quantities of contaminant permissible in the 'workers'. breathing zone. Some of these figures may be altered as the result of continuous research, -and some may differ from those in force in a few cities.or states. The prudent engineer will design equipment using these values as the upper limits of air contamination, and will incorporate a reasonable margin of safety in his estimates of ventilation capacity. Information on the properties and effects, with respect to health, of -specific industrial air contaminants has developed rapidly within the past decade into an extensive literature. Some of the more readily available publications are listed at the end of this chapter. FLAMMABLE GASES AND VAPORS Adequate ventilation is a primary requirement for eliminating or .minimizing.the hazard of fire or explosion due to gases and vapors. The need for good ventilation is not removed by the use of other precautions,. such as the elimination of known ignition sources, segregation of hazard ous operations,' adoption of safe building construction, and installation of automatic alarms. Some safety engineers regard overventilation of an operation employing flammable liquids as a legitimate 4operating charge for the privilege or necessity of using a dangerous process. However, it is ' not possible to apply a reasonable safety factor to the ventilation estimate without consideration of the concentrations of gases or vapors that ap proach the danger point. Safety engineers prefer to limit the concen tration to A or M of the lower explosive limit, and this fact should be given full weight'in determining the capacity and design of ventilating equipment. Rarely- should consideration be given to operation' above Air Contaminants "________ ' .. V*l_ " 1__________ _______ __ 191 Table 3. Physiological Response to. Gases and VAPORSa Concentrations in Parts of Substance per Million Parts of Air (ppm) Substance Amyl acetate.-------------------- Rapidly Fatal 2,000 5,000 250 Dangerous to Life . in H to 1 Hr Maximum Allow able Concentration for Daily Exposures 100 2,500 "200 10 1 100 400 '5 1 Benzene (benzol)--------------Butyl acetate........ :-- ------- Carbon monoxide.-------- r-- Carbon tetrachloride. ...... 20,000 500 Too'ooo 2,000 4,000 50,000 . 1,000 . 5,000 40 10,000 50,000 1,000 - 1,000 ... -- 500 100b 1 400 5,000 20b' 100b 100c ... 1 75 15 Ether (diethyl)-----------------Formaldehyde-------- ----------- 40,000 35.000 : 10.000 . 4,000 -- --------- 400 400 100 10b . 1,000 Hydrogen sulfide......... ....... 1,000 200 600 100 50 200 . Methyl bromide.--:---------- 20,000 150,000 ' '2,000 ` 20,000 Nitrobenzene.................... -- Phosphine............................. Styrene._________-................ Sulfur dioxide.------------------ Tetrachloroethylene.------ Trichloroethylene. --......... Turpentine...._________ ___ - ..... ........ 300 50 1,000 ` 400 : . 7,000 20,000 26:660 ;----------- 100 -5 ' 400,; . ......150 "57606' 5,000 10 . 20 .. 3. 20b 200b - 50 . 100 500 . 75 5 . 25b 1 1 400b . 10 . . 10.. 200 ' 200 200 200 200b Adapted from: Manual of Industrial Hygiene^-by W. M. Oafafer et al. U. S. Public Health Service (W. B. Saunders Co.. 1943); Analytical Chemistry of Industrial Poisons. Hazards and Solvents, by M.B. Jacobs (Interscience Publishers, 1941); Noxious Gases, by Henderson and Haggard (Remhold Publishing Co., N. Y.. 1943); and other authoritative sources.., ' bAdopted by the'American Standards Association (American Standard Z-37). 50 ppm recommended by the Detroit Bureau'of Industrial Hygiene. ,. the upper explosive limit in the open areas of buildings or rooms--even though unoccupied--because . the-;,-..danger-; of: temporary drop of.1 gas concentration to, a, point within the, explosive range is top great. The ability of -at.flammable liquidcto form explosive mixtures is. de termined largely by its vapor pressure; volatility, or rate of.evaporation;