Coal-dust, explosibility

Whereas an explosion from methane tends to be localized, it may start coal dust explosions resulting in more widespread injury and loss of life. AH coal breaking operations result in formation of fine coal particles some are controlled with water during the mining operation. Breakage associated with hauling disperses dust, and dust accumulations can be made safe by rockdusting. Powdered limestone is spread over the mine surfaces to cover the dust. 

Powder Explosions. See under Coal Dust Explosion Hazards from its Uses in Vol 3, C359-R Dust Explosions in Vol 5, D1578-R and Powder-Air Explosions and Detonations in this Vol... 

From a safety point of view, one is also interested in grain elevator and coal dust explosions. Such explosions are not analyzed in this text, and the reader... 

Explosion of coal dusts in mines is described in Vol 3 of Encycl, pp C358 C359 under "Coal Dust and Its Uses and "Coal Dust Explosion Hazards from Its Uses . 

Suppression of firedamp and coal dust explosions, in high humidity coal mines, by stone dusting is affected by humidity. Agglomeration of moisture content of the dusting material influenced its effectiveness as explosion suppressor. Salt dusts become ineffective above 80% relative humidity because they dissolve (Ref 7)... 

S. Shaw D. Woodhead, Igniters for Experimental Coal Dust Explosions, a review of the use of gaseous solid initiators, gunpowder cannon low-concussion igniters (22 refs). Ministry of Fuel Power, Safety in Mines... 

D. Rae, Safety in Mines Res Estab, Res Rept 253 (1967) CA 69, 1140 (1968). The main characteristics of slow coal-dust explosions and their relation to the testing of barriers. The main characteristics of slow coal-dust explosions in the new gallery at Buxton are a const initial flame front acceleration from... 

See Coal Dust Explosion Hazards from Its Uses on p C359 R of Vol 3... 

K. Fischer, Ablauf von Kohlenstaub-explosionen (The process of coal dust explosions), pp 635—92... 

Gas and Coal Dust Explosion. Title of a series of papers published by K. Mat sumo to in J Minin gins t Japan 68, 260—5 379—82 (1952) 8t CA 48, 3691 (1954). The papers include adsorption of mine gases by the coal dusts heat of adsorption of mine gases by coal dusts and ignition temperature of the coal dusts... 

Meanwhile, in 1906, a terrible coal-dust explosion occurred at Courriere in France, in which about 1100 men lost their lives. The mine at Courriere had no methane at all and was considered to be safe, but as it turned out, it contained coal which in dust form produced a very dangerous suspension. The vast extent of this disaster aroused public indignation. It became obvious that the explosion of coal-dust may extend over a large area under ground and that this is much more dangerous than the explosion of methane which is usually localized within a small area. 

The permitted explosives are tested in experimental galleries in the presence of methane and coal-dust (explosives of groups (III) and (IV)), or in the presence of sulphur dust (explosives of group (V)). The explosives intended for use in oil fields are tested for safety towards petroleum vapours. 

J. Siebel, ... Vermiculite for Prevention of Fire-Damp and Coal-Dust Explosions in Hard or Brown-Coal Mining , GerP 1241393 (1967) CA 67,83762 (1967) 3) I.I. Strizhevskii et... 

Hartmann and associates (24G-28G) have conducted a great deal of experimental work on the combustion of dust dispersions. Explosions can be caused by particles as large as 700 microns. Many different dusts, including rosins, metal powders, and coal, have been investigated. Zirconium powder is the most explosive. Coal dust explosibility is closely associated with its volatile combustible content. Representative pressure rises as high as 75 pounds per square inch in an enclosed volume are reported. In all cases this maximum pressure is attained at mixture strengths well beyond stoichiometric. 

Water stemming of explosive-blasted boreholes consists of waterfilled cartridges made of plastic material, which give some protection against firedamp and coal dust explosions. 

The state of subdivision of a solid is important to the rate of its reaction. When a solid reacts with a liquid or a gas, contact between the two reactants occurs only at the surface of the solid. The more surface area per unit mass, the faster the reaction can occur (Figure 18.1). Thus, finely divided sohds tend to react more rapidly than the same solids in particles of larger sizes. An alarming illustration of this effect is a coal dust explosion in a mine. The finely divided coal, set off by a spark, can react almost instantaneously with oxygen. Coal in lump form bums slowly and quiedy and may have to be ignited with kindling to get it started in the first place. 

The main characteristics of slow coal-dust explosions in the new gallery at Buxton are a const initial flame front acceleration from... 

From a safety point of view, one is also interested in grain elevator and coal dust explosions. Such explosions are not analyzed in this text, and the reader is referred to the 1 iterature [17]. However, many of the thermal concepts discussed for homogeneous gas-phase ignition will be fruitful in understanding the phenomena that control dust ignition and explosions. 

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