## 1 Introduction
In recent years, a scholar [11] proposed that in order to prevent the massive accumulation of gas in the goaf from flooding into the working face in Sunjiawan Coal Mine, when the top coal is caved in layers under mining, pressure-equalization ventilation should be adopted to prevent the gas from flooding into the working face. Some scholars [12] implemented pressure equalization and fire prevention technology in the well when solving the problem of large-area CO leakages and achieved remarkable application effects. Some scholars [13] developed a complete automatic control pressure-balancing system based on pressure-balancing technology. A scholar [14] proposed that in order to prevent the emissions of toxic and harmful gases, such as CO, pressure-equalization ventilation measures should be adopted at the working face to make the pressure in the goaf lower than that at the working face, thus preventing harmful gases from entering the working face. A scholar [15] put forward that the main reason for the impact of support withdrawal due to the presence of a flammable caving face is that there are hidden dangers of spontaneous combustion in the goaf. The ventilation method of the working face adopts positive pressure ventilation and other anti-fire measures, such as nitrogen injection into the goaf, to eliminate hidden dangers of combustion in the goaf and ensure the safe withdrawal of the working face. A scholar [16] established an automatically controlled positive pressure ventilation system based on research on the principle of working face pressure-equalization ventilation technology. The system was applied in the field to ensure that the pressure-equalization area was 50 Pa and that the pressure in the pressure-equalization area was controlled. Some scholars [17; 18; 19], while researching the actual situations of Xiaokang Mine, Yangquan CoalMine, and Liyang Coal Mine, proposed that during the demolition and withdrawal of the working face, the problem of fire prevention during the withdrawal was solved by adopting methods of pressure-equalization ventilation and nitrogen injection in the goal. Some scholars [20; 21] put forward the method of pressure-balancing ventilation combined with nitrogen injection in the goal as well as plugging up and down the mine according to the abnormal CO emissions at the working face of Yunfei Mining and Longhua Coal mines, effectively preventing toxic and harmful gases from entering the working face. Based on the research by the above scholars, it was found that the local positive pressure ventilation technology of the coal mine's underground working face is mainly used to solve the abnormal emissions of toxic and harmful gases in the return airflow and upper corner of the working face, as well as the insufficient oxygen concentration. Measures such as nitrogen injection and grouting in the goal during working face withdrawal are used to prevent fire in the goal. Pressure-equalization technology can effectively prevent and control gas leakages in the goal of upper coal seams and reduce the air leakage in goats. But the equalizing technique has its own drawbacks. Pressure-equalizing technology relies too much on ventilation facilities, such as pressure-equalizing fans and wind windows, and once the relevant facilities fail, the pressure distribution of the working face will change abruptly. It causes the gas in the goaf of the upper coal seam to leak rapidly, which will easily produce unexpected consequences [22; 23; 24]. To sum up, traditional pressure-equalizing technology uses pressure-equalizing fan and air windows to increase the goaf's pressure in the lower coal seam and achieve the purpose of equalizing goaf pressure with that of the upper coal seam so as to avoid the goaf gas leakages in the upper coal seam.