Risk analysis of coal self-ignition in longwall gob: A modeling study on three-dimensional hazard zones

• An effective determination for coal self-ignition hazard zones in the longwall gob was obtained.
• A risk analysis method based on three-dimensional physical modeling was proposed.
• Effects of ventilation mode and working face dip on oxygen supply were analyzed.
• Both the possibility and the severity of coal self-ignition were analyzed.

Coal self-ignition in longwall gob (mined-out) areas has caused serious personal casualties and economic losses. Effective determination of coal self-ignition hazard zones in longwall gob areas can enable more targeted fire prevention. In this paper, the effects of ventilation mode and working face dip on the oxygen supply for coal self-ignition were studied. A three-dimensional dip-adjustable physical model of the longwall gob was developed to study the coal self-ignition hazard zones at different dip angles varying from −45° to +45° with respect to the horizontal plane. In addition, the coal self-ignition risk was analyzed through the position, width and space range of the hazard zones. The results demonstrate that the hazard zone features “S”-types both in the dip and the advanced directions of the working face, with a dip angle ranging from +5° to +15° the hazard zone primarily locates on the lower air intake side close to the middle when the angle exceeds +25°. With an angle ranging from −5° to −45°, the hazard zone scope is reduced along the direction from the upper side to the lower side and gradually concentrates at the lower air return side. Being different from the probability of coal self-ignition, the hazard severity may reduce with dip angle regardless of ventilation mode. A risk analysis method based on three-dimensional physical modeling is proposed and applied to analyze the coal self-ignition in the longwall gob. This analysis is of great significance for both fire safety and miners' health.