Elecrical ignitions and use of flameproof enclosures in coal-dust and methane atmospheres

摘要

In recent regulations of the European Unionconcerned with mine atmospheres the classification of anexplosive atmosphere was extended to include dusts. It isdemonstrated that, in the context of electrical equipment used inmines, coal-dust atmospheres present no risk in excess of thatfrom methane (firedamp) atmospheres. Current knowledge on thetransmission of coal dust and coal dust-methane combustionthrough safe gaps is reviewed and some experimental work onelectrical ignition of coal-dust atmospheres is described.Four main conclusions are drawn. First, it is unlikely thatcombustion of coal deposits will propagate through a gap of1mm or less in width and 3mm in length, and gaps designed tomethane flameproof standards are unlikely to permit propagationof coal-dust deposit combustion from inside the enclosure tooutside. Second, gaps of 2 mm in width or less are unlikely topermit external ignition by way of individual heated particles;gaps designed to methane flameproof standards are unlikely topermit external ignition of dust clouds or hybrid mixtures in thisway. Third, coal dust and coal dust-methane mixtures have safegaps designed to methane flameproof standard are unlikely topermit external ignition of coal dust or coal dust or coal dust-methane hybrid atmospheres by direct explosion transmission.Fourth, coal dust and coal dust-methane mixtures do not ignite atignition energy levels below that required.