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90 CHAPTER 7 I960 Guide tential source of disaster at some distance from the dusty operation. (See Chapter 52.) Intensity of a dust explosion depends upon: chemical and thermal properties of the dust; particle sue and shape; con* centration in air; proportion of inert dust in the air; moisture content and composition of the air; size and temperature of the ignition source; and degree of dispersion of the dust cloud. Investigations on the explosibility of dusts require determina tion of the maximum pressure developed during explosion of a known air concentration, as well as determination of the rate of pressure rise. Investigators frequently experience difficulty in obtaining dust suspensions of uniform dispersion, and this should be kept in mind when comparing results from several sources" Minimum explosive concentrations of airborne dusts al ready tested range from 0.01 to 03 oz per cubic foot, or 10 to $00 grams per cubic meter of air. Maximum pressures gen erated have been reported as high as 500 psig, although they are more likely to be of the order of 50 prig. Investigations on the flammable characteristics of dusts are currently made at 0.1 and 0.5 oz per cubic foot."'" ATMOSPHERIC POUEN Properties of pollen grains discharged by weeds, grasses, and trees and responsible for hay fever, are of special interest to designers of air cleaning equipment (see Allergic Dis orders in Chapter 8, and Air Owning, Chapter 24). Whole grains and fragments transported by the air range chiefly between 10 and 50 microns in site, but some have been meas ured as small as 5 microns, and others over 100 microns in diameter. Ragweed pollen grains are fairly uniform in size within the range of 15 to 25 microns. Pollen grains can be removed from the air more readily than the particles of dust prevalent in outdoor air or produced by dusty processes, since the latter predominate in the range of 0.1 to 10 microns in size. Most grains are quite hygroscopic and therefore vary in weight with the humidity. Illustrations and data on individ ual pollen grains are available in the botanical literature."1 " ** Geographical distribution of plants known to produce hay fever is also recorded."1" The quantity of pollen grains in the air is generally esti mated by exposing an adhesive-coated glass plate outdoors for 24 hr, and then counting calibrated areas under the micro scope. Methods are available for determining the number of grains in a measured volume of air,"1 01 * but their greater accuracy has not caused them to replace the more simple gravity slide method used for most pollen counts. Counting technics vary somewhat, but the daily pollen counts reported in local newspapers during the hay fever season usually repre sent the number of grains found on 13 sq cm of a 24-hr gravity slide. Hay fever sufferers may notice the first symptoms when the pollen count is 10 to 25, and in some localities the maxi mum figures for the seasonal peak may approach 1000 for a 24-hr period, depending upon the sampling and reporting methods of the laboratory. Translation of gravity counts by special formulas to a volumetric basis, or. the number of grains per cubic yard or per cubic foot of air, is unreliable because of the complexity of the modifying factors. When such information is important, it is best obtained directly by a volumetric instrument. The number of pollen grains per cubic yard of air evidently varies from 2 to 20 times the number found on 1 sq cm of a 24-hr gravity slide, depending on grain diameter, shape, specific gravity, wind velocity, humidity, and physical placement of the collecting plate.1 01 AIRBORNE BACTERIA Study of the occurrence and significance of micro-organisms in the atmospheres of the indoor world is absorbing the en ergies of a substantial number of physicians, bacteriologists, agrobiologists, physicists, public health workers, engineers, and hospital personnel. Some data are available on the types and quantities of bacteria found in a variety of spaces, but it is not possible at present to use this information as a con clusive index of the potential health hazard of a given en vironment. The reported number of airborne organisms may vary from 1 to 1000 per cubic foot of air, influenced some what by the method of testing." Many are attached to the dust particles present in the air. Where it seems advisable or desirable to control the bac terial content of rooms, public conveyances, or buildings, highly effective methods are available (see Chapter 8), and their extended use may do much to assist the workers in this field in accumulating the necessary mass of evidence that will decade the practical value of air sterilization for the con trol of communicable disease. It is now well established that ultra-violet radiation is feasible for the protection or preserva tion of pharmaceuticals, cosmetics, and food products. RADIOACTIVE AIR CONTAMINANTS" Radioactive air contaminants are physically similar to ordinary industrial and chemical plant contaminants. They differ from ordinary contaminants, however, in that they may be highly toxic when ingested and may present a direct radiation hazard when accumulated in appreciable quantities. Another factor which must be considered in the filtration of these materials is the possibility of their being concentrated in plant and animal life in the area of contamination. Con centrations resulting from absorptions by plants and sub sequent feeding of animals in the magnitude of several thou sand times, is not unusual. Tolerances for radioactive contaminants have been established and are under continu ing study and review. Guidance in regard to tolerance levels for discharge of contaminated air in different types of lo calities can best be had from the classified literature which is available through proper clearance procedures. REFERENCES *J. E. Ives et al: Atmospheric Pollution of American Cities for the Years 1291 to 1933 (US. Public Health Service Bulletin No. 224, March 1936). *J. M. DallaVaile: Micrometries, The Technology of Pine Particles (Pitman Publishing Corporation, New York, 1943). 'A. C. Stem: Atmospheric pollution due to smoke (Heatinp and Ventilating, Ms7 1945). A. C. Stem: Atmospheric pollu tion due to dust and cinders (Heating and Ventilating, July 1UA\ . r.vy. reujer; ooouau studies lor New York City (ASHVE Journal Section, Heating, Piping arid Air Condition ing, September 1945, p. 495). * A. C. Stern: The use of fuel consumption and equipment r ,n abatement of atmospheric pollution (ASHVE JotmNAi Section, Heating, Piping and Air Conditioning, August 1945, p. 447). * J. H. Shrader, M. H. Coblents, and F. A. Korff: Effects of atmospheric pollution upon incidence of solar ultra-violet light (American Journal of Public Health, Vol. 19, 1929, p. 7). ' J. E. Ives: Studies in llhmtnation 111: A Study of the Loss Air Contaminants of Light Due to Smoke on Manhattan Island (U. 8. Public Health Service Bulletin No. 197, June 1930). F. M. Stead: Study control of industrial atmospheric pollution nuisances (American Journal of Public Health, Vol. 35, May 1945, p. 491). J. M. PailaValle and H. C. Dudley: Evaluation of Odor Nui sance t the Manufacture of Kraft Paper (V. 8. Public Health Service Reprint No. 2022, Public Health Reports, Vol. 54, Janu ary 13, 1939, p. 35). Disposal of Refinery Wastes, Section II: Waste Gases, Va pors, Sludges and Dusts (American Petroleum Institute, 1938). "David Ronald: Offensive Trades (William Hodge and Go.. London, 1935). **C- P. McCord and W. N. Witberidge: Odors: Physiology and Control (McGraw-Hill Book Co, New York, 1949). ** C. P. Yaglou: ASHAE Research Repost No. 1524--Venti lation requirements for cigarette smoke (ASHAE Transactions, Vol. 81, 1955, p. 25). MW. F. Hopper: ASHAE Research Report No. 1698--A method of measuring the odor adsorption and retention proper ties of surfaces (ASHRAE Transactions, Vol 65, 1959, p. 735). "A. B. Hubbard: Winning the air conditioning odor fight (Heating, Piping and Air Conditioning, Vol. 31, No. 2, February 1959, p. 119). "Arthus D. Little. Inc. (sponsor): Flavor Research and Food Acceptance (Remhold Publishing Corp., New York, 1958, p. 71). "R. M. Hamer: An information theory of olfaction (ed. A. G. Emslie and Ada Jacobson, Armais of the Neto York Academy of Sciences, Vol. 58, Art. 2, March 24, 1954, p. 161). *F. H. Murikelt: Air purification and deodorization by use of activated carbon {Refrigerating Engineering Application Data No. ifi, American Soctctt op Refrigerating Engineers). UA. B. Hubbard, N. Deininger, and F. Sullivan: ASHAE Research Report No. 1547--Air conditioning coil odors (ASHAE Transactions, Vol. 61, 1955, p. 431). W. F. Ker&a and C. M. Humphreys: ASHAE Research Report No. 1587--Temperature and humidity effect on odor perception (ASHAE Transactions, Vol. 62, 1956, p. 531). aR. L. Kuehner: ASHAE Research Report No. 150--Hu midity effects on the odor problem (ASHAE Transactions, Vol. 62, 1956, p. 249). " G. W. Meek: Your place in the smart man's war (Heating, Piping and Air Conditioning, Vol. 14, No. 8, August 1942, p. 463). nC. S. Leopold: ASHVE Research Report No. 1277--To bacco smoke control--a preliminary study (ASHVE Trans actions, Vol. 51, 1945, p. 255). ** J. C. White, J. K. Mustek, M. H. Boyer, R. S. Hartman, W. H. Schecter, and R. R. MUleo: Experimental Control of CO, and Oxygen Concentration Aboard the USS Sailflsh (Naval Research Laboratory, P-2665,T945). " Warren Viessman: Air conditioning for protective shelters (Heating, Piping and Air Conditioning, Vol. 28, No. 12, Decem ber 1954, p. 84). ** Warren Viesman: Cooling subterranean atomic attack shelters (Refrigerating Bngvneermg, Vol. 59/No. 12, December 1951, p. 1175). "H. Sleik and A. Turk: Air Conservation Engineering (Con nor Engineering Corp, 1953). **H. L. Baraebey: ASHAE Research Report No. 1646-- Activated charcoal for air purification (ASHAE Transactions, Vol. 64,1958, p. 481). " J. Von Bergen: Industrial odor control (Chemical Engineer ing, August 1957, p. 239). " Clean it Up (Industrial Bulletin No. Stt, Arthur D. Little, Inc., July 1955). ** C. L&moreaux: Stack effluent reodorixed (Plant Engineer ing, July 1955, p. 96). "Killing an unpleasant smell (Factory Management and Maintenance, Vol. 114, No. 4. April 1956, p. 87). "B. K. Tremaine: Industrial reodorants (Air Conditioning, Heating and Ventilating, February 1955, p. 83). "H. F. Coward and G. W. Jones: Limits of Inflammability of Gases and Vapors (U. S. Bureau of Mines Bulletin No. 279, 1939). 91 " G. W. Jones: Inflammation limits and their practical ap plication in hazardous industrial operations (Chemical Review$, Vol. 22, February 1938). **H. R. Brown: Private communication (U. S. Bureau of Mines). "P. W. Edwards and L. R. Leinbach: Explosibility of Ag ricultural and Other Dusts as Indicated by Maximum Pressure and Rates of Pressure Rise (U. S. Department of Agriculture Technical Bulletin No. 490, October 1905). "H. R. Brown: Dust Explosion Hazards m Plants Produc ing or Handling Aluminum, Magnesium, or Zinc Powder (U. S. Bureau of Mines Information Circular No. 7148, March 1941). "I. Hartman, J. Nagy, and H. R. Brown: Inflammability and ExplostbUHy of Meted Powders ((/, S. Bureau of Mines Report of Investigation No. 3722, October 1943). "I. Hartman, and /. Nagy: Inflammability and Explosibility of Powders Used in the Plasties Industry (U. S. Bureau of Mines Report of Investigation No. 3751, May 1944). "E.R. Brown: Industrial Dust Explosions (U. S. Bureau of Mines Information Circular No. 7309, January 1945). "Proposed Code for the Prevention of Dust Explosions m the Plastics Industry (National Fire Protection Aooci&tion, May 1945). 0 National Fire Codes for the Prevention of Dust Explosions (National Fire Protection Asociation, 1944). Contains codes for aluminum, magnesium, coal, pulverized fuel, flour, spice, starch, sugar, cocoa, sulfur, and wood. MG. Etdtman: An Introduction to Pollen Analysis (Chronica Botanica Co., Waltham, Massachusetts, 1943). "R. P. Wodehouae: PoUan Grains (McGraw-Hill Book Co., New York, 1935). " R. P. Wodebouse: Atmospheric pollen (Aerobiology, Pub lication No. 17, 1942, p. 8). R. P. Wodehouae: Hayfever Plants (Chronica Botanica Con Waltham, Massachusetts, 1945). " Hay Fever: A Geographical and Botanical Survey (E. R. Squibb and Sons, New York, 1937). ** Techniques for appraising air-borne populations of micro organisms, pollen and msetes (Phytopathology, Vol. 31, March 1941, p. 201). "B. J. Cody1, W. F. Kinney and N. A. Kerstein: Apparatus for Determining the Pollen Concentration of the Atmosphere (Research Department, Detroit Edison Company, Detroit). B0. C. Durham: The volumetric incidence of atmospheric allergens (Journal of Allergy, Vol. 14, September 1943, p. 455). "0. C. Durham: The volumetric incidence of atmospheric allergens, II: Simultaneous measurements by volumetric and gravity slide methods (Journal.of Allergy, Vol. 15, May 1944, p. 226). 0. C. Durham; Air-borne fungus spores as allergens (Aero biology, Publication No. 17, 1942, p. 32). M H. G. DuBuy and A. Hollaender: Sampling devices (Ameri can Journal of Medical Science, Vol. 209, February 1945, p. 172). 0 W. W. McIntosh: Ventilation Problems in Safe Handling of Radioactive Materials (Paper presented at ASME Spring Meeting, March 1952). BIBLIOGRAPHY Monthly, annual, and special abstracts and bulletins (Indus- ^ trial Hygiene Foundation, Inc.). ' Aerobiology (Publication No. 17, 1942). American Industrial Hygiene Association Quarterly. M. B. Jacobs: Analytical Chemistry of Industrial Poisons, Hazards and Solvents (Interscience Publishers, Inc., New York, 1941). Bibliography of Industrial Hygiene, 1900-1943 (U. 8. Public Health Service Bulletin No. 289, 1945). W. E. Gibbs: Cloud* and Smokes (P. Blakiston's Son A Co., Philadelphia, 1924). Bloomfield and DallaVatlc1. Determination and Control of Industrial Dust (U. 8. Public Health Service Bulletin No. 217, 1935). S. C. Blacktin: Dust (The Sherwood Pres, Cleveland, 1934).