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162 CHAPTER 8 1953 Guii Table 6. Approximate Limits of Flammability of Single Gases and Vapo In Air at Ordinary Temperatures and Pressures* Gas ob Vapor , Acetyldehyde.. Acetone'........... Acetylene......... Allyl alcohol. .... Ammonia./....... Amyl alcohol.... Amyl chloride. ... Amylene................ Benzene (benzol) . Benzyl chloride ... Butane................... Butyl acetate....... Butyl alcohol........ Butylene Carbon disulfide.. Carbon monoxide. Crotonaldehyde___ Cyclohexane........... Cyclopropane.......... Decane..................... Dichloroethylene (1, 2) . Diethyl selenide. . ....... Dioxane............................ Ethane.............................. Ether (diethyl)............... Ethyl acetate.................. Ethyl alcohol.................. Ethyl bromide................ Ethyl cellosolve............... Ethyl chloride................. Ethylene.................... Ethylene dichloride. Ethyl formate. . ___ Ethyl nitrite.............. Ethylene oxide:......... Furfural (125 C). ... Gasoline (variable) . Heptane.................... Hexane...................... Hydrogen cyanide*.. Hydrogen......................... Hydrogen sulfide V Illuminating gas (coal gas) Isobutyl alcohol.............. Isopentane............. Isopropyl acetate'. . Isopropyl alcohol. . Methane............. Methyl acetate....... Methyl alcohol....... Methyl bromide........ Methyl butyl ketone. Methyl chloride........ Methyl cyclohexane-. Methyl ethyl ether... Methyl ethyl ketone ... Methyl formate___ Methyl propyl ketone!. Natural gas (variable) . Naphtha (benzine) . ... Naphthalene.. Nonane........... Octane....___ Paraldehyde.. Pentane........... Lower Limit Percent by /Volume ":. 4.0 2.5 ' 2.5 . 2.5 15.5 ; 1.2 ' 1.6 1.6 1.3 1.1 ' 1.4 1.7 2.0 1.2 12.5 2.1 1.3 2.4 0.67 9.7 2.5 2.0 3.1 1.8 2.2 3.3 6.7 2.6 4.0 2.7 6.2 2.7 3.0 3.0 2.1 1.4-1.5 1.0 1.2 5.6 4.0 4.3 5.3 1.7 1.3 1.8 . 2.0 5.0 3.1 6.7 13.5 1.2 8.2 1.1 2.0 1.8 5.0 1.5 . 4.3 ,1.1 0.9 0.83 0.95 .1-3 : 1.4 ,Uppeb Limit Percent by Volume ' 57 12.8 7.7 ` 6.8 8:4 15.0 9.7, . . 50 74.2 15.5 8.4 10.5 2.6 12.8 22.2 12.5 36.5 11.5 19.0 11.3 15.7 14.8 28.6 15.9 16.5 50 80 7.4-7.6 " 6.0 6.9 40.0 74.2 45.5 33.0 7.8 15.0 15.5 36.5 14.5 8.0 18.7 io!i 9.5 22.7 8.2 .13.5 6.0 2.9 3.2 7.8 Closed Ci*p^ Flash Point' Fahrenheit -17 0 NBFU. CLAssrpi cation* ' .1 1 12 140 *84 -22 55 1 iis 57 * 54 -49 28 54 104 - -58 56 -31 140 --50 25 -15 82 43 53 52 25 -35 30 -2 20-110 176 88 56 Air Contaminants 163 Table 6. Approximate Limits of. Flammability of Single Gases and Vapors In Air at Ordinary Temperatures and Pressures* (Concluded) Gas or Vapor Lower Limit Percent by , Volume Upper Limit . Percent by Volume Closed Cupb' - Flash Point . Fahrenheit NBFU classifi cation* Propane................................... Propyl acetate ........................ Propyl alcohol....................... Propylene................................. Propylene dichloride............. Propylene oxide...................... Pyridine............. .. -:............. Toluene (toluol)..................... Turpentine........ ................... Vinyl ether.............................. Vinyl chloride . ................. Water Kas (variable)............. Xylene (xylol)......................... 2.1 1.8 2.1 2.0 3.4 2.0 1.8 , 1.3 0.8 1.7 : 4.0 6.0 1.0 10.1 13.5 11.1 14.5 22.0 12.4 7.0 .27.6 :, 21.7 70 6.0 - 58 59 ' 60 74 : .40 95 63 3 2 3 * Adapted from: Fire and Explosion Hazards'of Combustible Gases and Vapors, by G. W. Jones; Chapter 13, Industrial Hygiene and Toxicology, edited by F. A. Patty (Interscience Publishers, 1948); Properties of Flammable Liquids, Gases and.Solids (Associated) Factory Mutual Fire Ins. Cos., January (1940); and National Fire Codes for Flammable Liquids, Gases, Chemicals and Explosives-* 1945 (National Fire Protec tion Association). '' b Closed cup refers to the equipment used in Hash point determinations. c From Standards for Storage, Handling and Use of Flammable Liquids (National Board of Fire Un derwriters, Pamphlet No. 2, April 1952). of uniform dispersion, and this should be kept in mind when comparing results from several sources.14. Minimum explosive concentrations of airborne dusts already tested range from 0.01 to 0.5 oz per cubic foot, or 10 to 500 grams pier cubic meter of air. Maximum pressures generated have been reported as high as 500 psi, although they are more likely to be of the order of 50 psi, Investiga tions on the flammable characteristics of dusts are currently made at 0.1 and 0.5 oz. per cubic foot.15-*1 ATMOSPHERIC POLLEN 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 Disorders in Chapter 7, and Air Cleaning, Chap ter 34). Whole grains and fragments transported by the air range chiefly between 10 and 50 microns in size, but some have been measured 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 individual pollen grains are available in the botanical literature.22 , 23 24 Geographical distribution of plants known to produce hay fever is also recorded.25,26 The quantity of pollen grains in the air is generally estimated by exposing an adhesive-coated glass plate outdoors for 24 hr, and then counting cali brated areas under the microscope. Methods are available for determin ing the number of grains in a measured volume of air,25, 27 28 but their greater accuracy has not caused them to replace the more simple gravity slide method used for most pollen counts. Counting technics vary some what, but the daily pollen counts reported in local newspapers during the