A NEW DIMENSION TO STUDIES OF SPONTANEOUS COMBUSTION OF COAL

Spontaneous combustion of coal is a hazard frequently encountered in coal mining. It has been researched extensively but the actual mechanism by which it occurs is not completely understood. Under suitable conditions, the spontaneous combustion hazard manifests itself in all major aspects of coal mining, namely, underground coal mining, surface mining, stockpiling of coal at the pithead, power stations and ports, during sea-borne transport and stacking of reject material. In underground coal mining, the most difficult situation occurs when spontaneous combustion takes place in the presence of an inherently explosive atmosphere which may promote a local spontaneous combustion incident into an explosion hazard involving the entire mine. Such an incident at the Moura mine in Central Queensland resulted in greater pressure on mine operators for the safe management of spontaneous combustion in their underground coal mines than ever before. As not all coal mines are equally liable to spontaneous combustion due to the different propensities of different coals to self-oxidation, the risk assessment for spontaneous combustion is a primary requirement for the development of a spontaneous combustion management plan for a mine. Once the coal seam has been classified into various categories of spontaneous combustion risk, it is necessary to determine a fire ladder for the coal seam. This should be followed by detailed planning of the mine layout including the mine ventilation system and a spontaneous combustion monitoring program before devising a spontaneous combustion management plan as required by the Coal Mines Underground Regulations 1999. In this paper, a case history is presented which includes the development of a spontaneous combustion management plan for a high-risk coal seam in a greenfield site, from the risk assessment stage to the outbreak stage of a spontaneous combustion incident. It is concluded that the risk assessment, evaluation of the fire ladder, comprehensive monitoring by a tube bundle system and trending of carbon monoxide/oxygen deficiency ratio (Graham's ratio) and CO levels were the main elements in an effective spontaneous combustion control system for the mine.