Dust Explosions in Industrial Plants' By Hylton R. Brown Hr
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by the Ihrcnu of Clieinistry of the United States Department of Agriculture have shorn that practically all combustible dusts arid some dusts not gencrally considered combustible will explode with violence under favorable conditions, when mixed with the proper proportion of air and ignited by a flame, spark, or other source of ignition.$ Much laboratory work mnst still he done before the exa.ct conditions uiider which various dusts will or will not explode can be determined. The fineness of the dust, the ash aud moisture content, the presence in the dust of oxygen-carrying material, the uniformity of distribution through the air, and the temperature of the ignition source are among tho factors to be studied. It is known, however, that dust from practically any material whicli will burn or he readily oxidized when fine enough arid dry enough t o form a cloud or be thrown into suspension in the air will explode if it conies in contsct with a flame or spark sufficiently hot to ignite it. Some dust.8 will ignite when they come in contact with metal having a temperature as low as 540" C., whicli is well below dull red heat. For some of the more explosive materials 7 mg. of dust in a liter of air will form aii explosive mixture. No record of a spontaneons dust explosion has ever been obtained. A spark, fiame, or other source of ignition must he present to ignite the dust. The conditions necessary for an explosion are sufficiently common and occur often enough in manufacturing plauts to indicate to the management the necessity of giving serious conaideration to the dust explosioii hazard. Dust explosions have occurred in many industries and under different conditions. Manufacturers, however, do not yet realize the extent of this hazard and tlie importance of adoptiug preventive measures. Some feel that a plant manufacturing dusty material is immune from dust explosions simply because in their experience no du& explosions have ever occurred in their particular industry. Such a feeling of
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Received Mareh 2, 1925.
* Priee and Brown, "Dust Explorios," ~ o s t o n 1981. ,
Nolionol Firc Prolailivn Aisor.,
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safety is dangerous if for 110 other reason than because it breeds carelessness. There are in the United States at the present time approximately 22,OW)establishments manufacturing dusty products, such as starch, feed, cocoa, spice, and sugar, or producing dust during the manufact.ure of wooden ware, aluminium ware, corks, etc. The dust explosion hazard, present in these 22,ooO manufacturing plants, exists also, in snraller degree, in the thousands of warehouses, transfer stations, and similar establishments where large quantities of the dust or dusty material are handled either in bulk or package form. During the past year forty-five lives were lost, twenty-eight employees were injured, and approximately 53,000,000wortli of property was destroyed in dust explosions and resulting fires in the United States. These explosions and fires occurred in starch-manufacturing plants, wood-working establishments, leather-grindiug mills, feed-mixing plants, and grain elevators-iiidustries in which the dust explosion hazard is generally considered t,n he present. I n 1023, however, explosions of lignone, dye, aluminium bronze, dried rrood pulp, spice dust, paper dust, wood flour, powdered milk, cork dust., and hard rubber dust were reported. The protection against dust explosions needed in these industries means not only the eliminatioii of the hazards common to all plants and the application of the preventive measures dcveloped by tlie Bureau of Chemistry, but also a thorongh study of any individud hazards which may be present in any particular plant. It seems to be generally known that open lights, electric ares, matches, lighted cigars, cigarets, and pipes, sparks of static electricity, and the breaking of lighted electric lamps are sources of ignition sufficientto start a dust explosion when enough dust to form an explosive mixture is present in the air. Methods of eliminating or reducing the possibility of having present at tlie same time the two requisites of a dust explosion -a cloud of dust and a source of ignition-may not be so well known. Plants where consideration should be given to the elimination of the dust explosion hazard may be classified in
September, 1026
INDUSTRIAL S N D ENG)[NEERING CHEMISTRY
three groups: plants handling dusty or powdered material in packa.ge forni; plants handling such material in loose form; and plant,s manufacturing or producing exploaive dust. Plants Handling Dusty Material in Packages Where the material beiiig handled is in packages or bulk lots, with little clianee of a cloud of the dust being thrown into suspension, as in mrehouses or shipping rooms, the principal precaution necessary is general cleanliness. In a plaiit of this type it is easier to guard against dust explosions by preventing the forrn~tionof a dust cloud thau to remove all sources of ignition. This (:an be done by giviug proinpt attention to all spills or the hreaking open of packages nud preventing tho :~ci:uinulntionof loose dust where it could form a cloud of snfliaieiit density to propagate a flame. Special attention slionld be given to the elimination of dust accumulations overhead or where a jar or concussioii would throw the
