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Abstract Smoldering combustion frequently occurs in the mined-out gobs of coal mines. This can act as an ignition source, triggering gas explosions and resulting in serious accidents. In this study, a smoldering test device was constructed, in which horizontal, vertical, forward and reverse smoldering combustion experiments were performed to explore the smoldering characteristics (dynamic development process, smoldering rate and temperature, etc.) of a coal pile. It is found that owing to the evaporation moisture present in the coal and its re-condensation on the coal ahead of the smoldering front, a constant temperature of approximately 70–90 °C is maintained during the spread of forward smoldering. In the initial stage of reverse smoldering, both the pyrolysis and oxidation fronts exist and propagate backward; meanwhile, in the later stage, the intensity of the endothermic pyrolysis reaction is greatly reduced, resulting that the maximum smoldering temperature of reverse smoldering is slightly higher than that of the forward smoldering. The vertical smoldering temperature is 1.5–2 times that of horizontal smoldering, owing to the poorer oxygen supply in the horizontal spread. The propagation of the oxidation front is extremely slow, and is in the order of 0.1 mm/min; this makes it difficult to characterize and detect the smoldering fire, especially in inaccessible mined-out gobs with complex environments. This study provides useful insights into the identification of smoldering fire and assesses its development stage. Highlights • A constant temperature process exists around 70–90 °C during forward smoldering. • The maximum temperature of reverse smoldering is higher than forward smoldering. • Vertical smoldering temperature is 1.5–2 times that of horizontal smoldering. • Propagation rate of coal pile smoldering is on the order of 0.1 mm/min. [ABSTRACT FROM AUTHOR]

Large-scale coalmine accidents have occurred occasionally with great impact on society. To assess the characteristics of large-scale coalmine accidents, a database involving 782 Chinese accidents from 1950 to 2016 was built and analysed. The historical change of large-scale coalmine accidents was divided into four stages according to the accident number per year. Explosions and fires were the primary causes and deemed to be thermodynamically driven accidents due to their identical thermochemical essence of combustion, interchangeability and producing similar gaseous hazards. By constructing an analysis framework, some useful features were derived from the database. About 55% of the gas explosions occurred in coalmines with low methane-gas emission rates. Coal dust explosions were responsible for about 59% of the fires and explosions with over 100 casualties. The interchangeability of fires and explosions led to 79% of the large-scale coalmine fires and explosions in recent years. As ignition sources, blasting work, self-heating and friction and impact caused 86% of the fires and explosions from 2007 to 2016. About 44% of fires and explosions happened in coalmines with central ventilation systems. About 85% of fires and explosions concentrated on the locations of coalface, heading face and roadway. [ABSTRACT FROM AUTHOR]