Risk evaluation of coal spontaneous combustion from the statistical characteristics of index gases

In this study, a logistic model was used to fit the volumes of index gases produced according to the coal tem-perature to obtain four fitted parameters, which were then normalized according to statistical characteristics. Model equations describing the variation in the volumes of the index gases with coal temperature were then established and used to determine the temperatures at the first and second inflection points of CO and C2H4. Thus, the temperatures at which CO, C2H4, and C2H2 were initially formed were obtained based on the statistical method, and these characteristic temperatures allowed classifying the risk of the spontaneous combustion of coal into six levels: safe, low, medium, high, very high, and disaster. Finally, combining the four gas ratios with these characteristic temperatures allowed the determination and normalization of the warning critical gas ratios to provide a set of indicators having warning threshold values of: 1.7 for low risk, 1.1???1.7 for medium risk, 0.6???1.1 for high risk, 0.3???0.6 for very high risk, and < 0.3 for disaster.