Forecasting spontaneous combustion of coal in underground coal mines by index gases: A review

Spontaneous combustion of coal in underground coal mine is a long-standing thermal dynamic hazard. The hazard is harmful in diverse aspects: causing loss of coal resource, raising safety concerns, and giving off noxious/greenhouse effect gases. Detection and trending analysis of a few particular gaseous products liberated during coal oxidation is the most fundamental spontaneous combustion forecasting technique in practice. This study mainly reviewed the mechanism and practical knowledge by using such technique to forecast spontaneous combustion. To give more insights in emerging order of fire gas, this study critically reviewed and analysed the detailed production sequences of these key gaseous products. It was indicated production of carbon oxide, hydrogen, methylene and some other hydrocarbon gases can be used to forecast early heating of coal. This study also summarised and discussed the interpretation of the index gases through absolute concentration of key gas indicators and composite ratios. Six common gas monitoring techniques (i.e. tube bundle system, telemetric system, portable system, gas chromatography, infrared spectroscopy, and tunable diode laser adsorption spectroscopy) are discussed in terms of their advantages and limitations in this study. Lastly, a practically demonstrated spontaneous combustion hazard management plan (i.e. TARP) is introduced. TARP uses different gas ratios in various locations to indicate escalating levels of severity of a heating event.