Document G6b85zaX5mY8ebVypkxnJ6YR4

TABLE 15 Relative Flammabilities of Dusts Relative flammability (%) Powder In In furnace spark test teBt Metals Aluminum, atomized Aluminum, stamped Antimony Cadmium Chromium Copper Dowmetal Iron, hydrogen reduced Iron, carbon reduced Iron carbonyl Magnesium, stamped Magnesium, milled 10 60 65 18 0 3 90 90+ 90+ 85 90+ 90+ 78 80 18 0 0 0 90 65 43 60 90+ 90 Lead, stamped Manganese Silicon Tin Titanium Titanium hydride Zinc Zirconium.... ...... Zirconium hydride Miscellaneous dusts 20 0 40 25 0 33 10 30 90 85 80 70 35 45 90+-... -90+ 85 80 Corn starch Peat moss 90+ 90+ 90 80 Volatile ratio Anthracite Low-volatile coa Medium-volatile (%) 5.0 18.5 0 60 O 0 coal 27.2 High-volatile coal 85 40 (Pittsburgh ' Beam')' Subbituminous 40:7 90 65 coil; Lignite Coal-tar pitch, 42.8 47.3 90 90 --"hard------------- Coal-tar pitch, soft Water gas-tar 60.1 -- pitch Petroleum pitch 49.0 66.3 -- -- Relative flammability,) (%) Powder In furnace test Resins Cellulose acetate 90+ Cellulose acetate butyrate 90+ Chlorinated paraffin 0 Coumarone-indene 90+ Lignin Phenolio 90+ 90+ Polystyrene Polyvinyl acetate Shellac, rosin, gum Urea 90+ 90+ 90+ . 85 Vinylbutyral 90+ Molding compositions Cellulose acetate 90+ Cellulose acetate butyrate 90+ Ethyl cellulose 90+ Methyl methacrylate Phenolio Polystyrene 90+ 90+ 90+ Rubber, synthetic 90+ -Urea--------------------- ..... 90+ Vinyl chloride-vinyl ace- tate Resin ingredients 5 Hexamethylenetetramine 90+ Pentaerythritol 90+ Phthalic anhydride 90+ Rennet casein 90 Fillers for molding eomposi- tions Ground alpha pulp 90+ Ground cotton flock Ground wood flour 90+ 90+ 570 HAZARDS OF COMBUSTIBLE DUST 571 Considerably greater than for the same materials in bulk. In general the dusts |nite at lower temperatures, they burn more rapidly, and the fires are more ||fficult to extinguish than for larger pieces. The ignition temperatures of undispersed layers of dusts (see Tables 1 and 2 Kid Figure 1) are one index of the potential fire hazard. Another index is the Minimum spark energy required for ignition of dust layers (see Table 8). This IsKcrws that fires in dusts might be started by weak electric sparks or arcs, includ ing static sparks, as well as by heating from hot surfaces, by glowing particles, gntional sparks, open flames, or other causes. Under ordinary circumstances of handling and storage, most dusts oxidize so ifowly that the heat of oxidation does not produce an appreciable rise in the temjsrature of the dust. However, there are some dusts, including certain agricultural pjpducts, activated carbonaceous materials, and some metal powders, that oxidize papidly and heat to the point of ignition under suitable conditions. Heating is in fluenced by the exposed surface, the density and depth of the stored dust, the temperature of the surroundings, air flow, heat losses from dust, time between Reparation of dust and its storage, moisture content, etc. Some metal powders - act with moisture, especially at elevated temperatures, to form hydrogen, which Hfjiuces the protective oxide film on the metal particles, facilitating their ignition. Recent experiments in England indicate that many dusts are capable of pro nged, often undetected, smoldering, even in thin dust deposits. The smoldering n' be initiated by very small sources, such as a glowing cigarette end, and under flight conditions it can result in a delayed, severe fire. The opinion is expressed fat many fires, formerly thought to have originated by" spontaneous" heating, tight have started in this manner. A. PREVENTION OF DUST EXPLOSIONS AND FIRES W.L . ` ijfc-The problem of preventing dust explosions is of such great importance in igmciustrial plants that considerable effort has been devoted to its solution. To this Jffijjp}6cthe- Dust Explosion Hazards Committee of the-* National Fire Protection association through its subcommittees has formulated a.series of safety codes170 Ht embody detailed recommendations for a number of industries; much of the fchnical information in these was derived from the experiments "to-which refer- gfgijhas been made here. The reader is referred to these oodes as a helpful guide l^rdesign^n"d?nbliitnic{ion'5TbuildiHge'atid''e'quipm'ent"'Sn'd iti'regaTd- to~safe prating procedures. The subject is also being considered by the'Research Comlt|ee of the President's Conference tin Occupational Safety,'by the National !||fjty Council, and by other groups concerned with reduction''o^feiStitits.'S^'far lisb-evplfision -codes have -been-prepared -for the -followinaoperatic>ns>.-and rations: 1. Aluminum-bronze powder manufacture (No. 651) ... 2. Magnesium powder or dust (No. 652) . mg'rThe National Fire Codes, Vol. II, Combustible Solids, Dusts, Chemicals, atf-Bgipfegyuo*. Il'Fire Protect. Assoc., Boston, 1956. W'x&gir' s JVty. >