Piezoelectric effect and ignition properties of coal mine roof sandstone deformation and fracture

•The electric spark owing to the piezoelectric effect would ignite the premixed gas-air.•An instantaneous high voltage formed when the roof sandstone was broken.•Electric spark generated by roof rupture broke down and ionised the premixed gas-air. The spatial characteristics of goaf are conducive to causing gas explosions. Understanding the source of ignition is helpful in preventing and controlling this hazard. A high number of accident cases show that it is difficult for spontaneous combustion of coal or rock friction collision to become ignition sources. Therefore, this paper proposes that electric sparks generated by the piezoelectric effect of a coal seam roof ignites goaf gas to cause disasters. Through theoretical analysis and experimental research, it was determined that the piezoelectric effect of the roof was generated by quartz, which is the main component of roof sandstone. An instantaneous high voltage formed when the roof sandstone was broken, related not only to the quartz content but also the compressive strength of the rock. In the process of roof sandstone rupture, instantaneous discharge formed owing to the piezoelectric effect, which could break through the air. Considering the Babao coal mine gas explosion accident, the high quartz content of the roof rock reached a certain compressive strength and experienced simultaneous stress mutation, exhibiting instantaneous roof rupture and generating an electric spark. The premixed gas-air broke down and ionised, ignited the gas and led to the gas explosion.