Document 9bzy02m9zwkkb28KdBzxxwE3

562 IRVING HARTMANN B. MINIMUM EXPLOSIVE CONCENTRATIONS There is probably greater variation in the values reported by different vestigators of minimum explosive concentrations of dust clouds than for an|, other explosibility factor, because the uniformity of the dust cloud, which varij| TABLE 5 Minimum Explosive Concentrations of Metal Powders Powder Aluminum, atomized Aluminum, stamped Antimony Dowmetal Iron, carbonyl Iron, hydrogen reduced Iron, carbon reduced Magnesium, atomized Magnesium, milled Magnesium, stamped Manganese Tin Minimum concentra- tion (mg./liter) 40 35 420 20 105 120 250 10 20 20 125 100 190 Powder Thorium Thorium hydride Titanium Titanium hydride Uranium Uranium hydride Vanadium Zinc Zirconium Zirconium hydride Ferrosilicon (88% Si) FeiTotitanium, low-carbon Magnesium-aluminum f50-50) MinimuilJ concenttf. (mg./U||| 75*ii 80*ii 45! rp 70 df 60*4 600$ 220 480 40-ijjg 85f| 425;H 140S soil TABLE 6 Minimum Explosive Concentrations of Dusts in Plastics Industry Powder Minimum concentration (mg./liter) Resins AUyl alcohol 35 Cellulose acetate Cellulose propionate Coumarone-indene 25 25 15 Lignin 40 " PEenoluT ............. 25---------- Pine-rosin base 55 Polyethylene 20 Polystyrene 15 Polyvinyl acetate 35 ------SHeUadrrosihrgum___________ 15 Urea Vinylbutyral Resin ingredients Hexamethylenetetramine Pentaerythritol Phthalio anhydride Rennet casein Resin stabilizer Powder Minim| concentratiqj (mg./lite|| . .Molding compositions . .no] Cellulose acetate Cellulose acetate butyrate 25,^ Ethyl oellulose Methyl methacrylate Phenolic 2qrj .30*S|i --Polystyrene------- ---------- ------ Rubber, .synthetic '1 Urea 755M . 'UWtsjks iSIl Fillers for molding compositions Ground alpha pulp Ground cotton flock Ground wood flour . HAZARDS OF COMBUSTIBLE DUST 563 according to the experimental procedure, is very important in the determination, and because different interpretations were placed on what constitutes a feeble ^explosion, such aB is obtained at these low concentrations. For aluminum powder jthe published values16 range from 7 to 432 mg. per liter and for sugar dust they range from 10.3 to 370 mg. per liter.8 A dust concentration of 1 mg. per liter is approximately equal to 1 oz. per 1,000 cubic feet. Tables 5, 6, and 7 list selected values of minimum explosive concentrations of metal, plastic, agricultural, and miscellaneous dusts and powders determined in TABLE 7 Minimum Explosive Concentrations of Agricultural and Other Dusts f Agricultural produots Minimum concentration (mg./liter) Miscellaneous dusts Minimum concentration (mg./liter) Alfalfa 'Almond flour Cellucotton Citrus peel, dehydrated plover seed ornstarch, ordinary Cornstarch, modified Corncob, ground, dried '-arlic, dehydrated Guar Beed . Himr/dehydrated....... * j;ea, dehydrated ~eanut cracklings `Rice oybean ugar ng kernels heat, cracked jyhieat flour 35 70 60 50 Aluminum stearate Bark dust, Douglas fir Coal, bituminous0 Coal-tar pitch Cork Dinitro-orthocresol Gilsonite Liver protein Napalm Phenothiazine -p^Gxybenzaldehyde Rubber, hard crude Soap Sulfur Thyroid, desiccated 15 30 50 35 35 25 20 45 20 15 20 25 45 35 60 "See Figure 1. She Bureau of Mines studies previously mentioned (see Figure 1 for data for coal |||iirrand ;in-oxygen), -In general,-these values are. determined by dispersing, vary- `Mfe quantities of dust samples in a cylindrical test vessel in which a high-voltage electric spark is formed across an approximately V4-inch gap. The top of the essel is closed by a filter-paper diaphragm, which ruptures upon ignition and -loaon, of,..a gpfficiently dense ,dust cloud (see Figure 6) . Recently' the lower plosive limits of several dusts have been determihed""aTso in h .flUntinUtiuS dust1- ij stream. For the most part, the results check the earlier data rather satisfacfjrily, but further refinements in the test procedure are being made. To date very little experimental work has been done on determination of jthe optimum concentrations and of the upper explosive. limits of dust clouds. The Y ' >ri! M R. B, Mason.and C. S. Taylor, Ind. Eng. Chem., 29, 626 (1937).