Investigation of temperature and gas release in spontaneous fires at rock dumps

Losses of coal, allowed in the mining process, as well as the creation of conditions that promote the flow of air to the oxidizable combustible components, can result in self-ignition and spontaneous fires in coal and carbon-containing rock accumulations in places of mining operations and at the rock dumps. Spontaneous fires in underground mines are the most dangerous because people can be poisoned by toxic carbon oxidation products released into the mine air. Self-ignition foci can initiate explosions of the accomulated combustible gases and coal dust. Taking into account the danger of spontaneous fires for coal mines, extensive research on the process of coal self-ignition is underway. The article presents the results of measuring the temperature and concentration of emitted gases in a self-ignition focus, which developed inside the coal-bearing rocks at a dump. The temperature was measured in boreholes drilled to the depth of 2.5 meters. The boreholes were spaced 10 m apart. At the ambient air temperature of 0°C, the upper layer of the rocks above the self-ignition focus is heated from +5 to +14°C, which allows using thermal imaging cameras to detect the self-ignition foci. The studies showed a non-uniform heating of rocks, which can be explained by the different content of coal in the dump and different air inflow to the combustible components. Various patterns of increasing or vice versa decreasing temperature of the dump rocks up to the depth of 2.5 m were revealed, so the currently recommended methodology for detection and control the hazards of spontaneous fire at the rock dumps does not allow to determine the real dimensions of the focus. Hydrogen sulfide and sulfur dioxide were detected in some of the boreholes, which confirms that sulfur is involved in the process of waste dumps self-ignition. Carbon oxide was detected in almost all the boreholes, but no direct correlation between the rock temperature and the carbon oxide concentration has been detected.