Explosive dust

EXPLOSIVE DUST (EN: explosive dust; DE: Explosivstaub; FR: poussiere inflammable; ES: polvo inflamable; RU: взрывчатая пыль) is the dust, which, within the mixture with the air, is able to ignite spontaneously during the thermal and shock-wave impact.

At the enterprises of the mining industry, the explosive dust is formed from the coals of all the marks (except from the anthracites), from the petroleum shales, from sulfur and its compounds. The degree of the explosiveness of the dust depends on the type of the substance, which has formed the explosive dust, on the dispersive composition of the dust, on the emission of the volatile (combustible) substances during the heating of this dust, on the humidity, ash content, and so on. The explosiveness of the explosive dust grows with the increasing of the degree of the dispersivity; the fractions with the size of less than 0.075 millimetres are the major carriers of the explosive properties. The maximal size of the cross section of the particles of the explosive dust is 0.75-1 millimetres. The explosiveness of the explosive dust decreases with the decreasing of the yield of the volatile substances (the coal dust explodes in case of the yield of the volatile substances of at least 6%), with the increasing of the ash content (the limiting value of the ash content for the coal dust is 86-88%) and of the humidity. The temperature of the explosion of the explosive dust from the coals is 575-850 degrees Celsius.

The lower concentrational limit for the explosiveness of the coal dust (the minimal concentration for the dust-air mixture, in case of which the dust is yet able to explode), depending on the yield of the volatile substances, and on the ash content, varies from 12 to 45 grams per cubic metre and more; in case of the 1% content of the methane within the underground mine atmosphere, this limit decreases to 6-23 grams per cubic metre. The maximal effect of the explosiveness is achieved with the content of the coal dust of 300-400 grams within 1 cubic metre of the air, the further increasing of the concentration of the explosive dust to 900-1000 grams per cubic metre does not increase the explosiveness substantially. The upper concentrational limit for the explosiveness of the coal dust (the maximal concentration of the dust-air mixture, above which the dust is not able to explode already) is 2000-3000 grams per cubic metre. The explosive concentrations of the dust within the underground mines may emerge during the blasting works, and during the work of the combined cutting-loading mining machines (near the working tools), which are not equipped with the means for the dust suppression. There is dangerous not only the flying dust, but also the dust, which has been deposited onto the surface of the mine workings, because this dust may transition into the suspended state under the impact of the air push or other factors.

For the dust-explosion protection of the underground mines, which are developing the layers, which are dangerous because of the explosions of the dust, together with the comprehensive dedusting of the underground mine air, they perform the activities for the prevention and localization of the explosions of the dust, which are based on the usage of the water (the washing off the dust using the water, the whitewashing of the mine workings using the cement-lime mortar; the binding of the dust using the wetting-binding solution, and using the continuously working fog-forming curtains; the water curtains; the bulkheads of the louver type; the installation of the water barriers), of the inert dust (the facing of the mine workings using the schist; the installation of the schist barriers), or of the water and inert dust (the combined dust-explosion protection).