Development of a Graded Early Warning Index System and Identification of Critical Temperatures for Coal Spontaneous Combustion Using Composite Gas Characteristics.

Conventional single gas alarm method and coal spontaneous combustion three-stage alarm method have become increasingly inadequate to meet complex underground conditions. To address this issue, this study focuses on the coal in the goaf of the Z109 working face in the Donggucheng Mine as the research object. Through program-controlled heating experiments, the production of carbon monoxide and hydrocarbon gases during the coal oxidation process was determined, and the variation characteristics of gas ratios with temperature were further analyzed. The coal spontaneous combustion process was subdivided into seven small stages, and a quantitative composite parameter coal spontaneous combustion grading warning system was formulated. Based on its characteristics, measures to be taken under different warning levels were proposed, and it was determined that 120, 140, and 160 °C are the key temperatures for coal spontaneous combustion prevention and control in the Z109 working face of Donggucheng Mine. By using numerical simulation, the optimal nitrogen injection position for the working face was determined and the on-site fire prevention and extinguishing measures were optimized, providing insights into the establishment of a coal mine spontaneous combustion warning system.