Characteristics and Safety of CO₂ for the Fire Prevention Technology with Gob-Side Entry Retaining in Goaf

The mining technology of gob-side entry retaining without a coal pillar is gradually becoming a mature and increasingly important mining technology. As it maintains the roadway near goaf, the air leakage should be greater than a U-type ventilation system in goaf, so it is prone to cause coal spontaneous combustion problems. CO₂ is an inert gas, and it is usually used to prevent spontaneous combustion and extinguish coal fire. However, there is a lack of research on characteristics and safety of CO₂ for the mining technology of gob-side entry retaining without the coal pillar. In this paper, the indexes of influencing factors were proposed on gas, pipelines, and mining technical parameters. Using a three-dimensional physical model of coal stope, the gas migration law of CO₂, the relationship between gas injection rate and the oxidation zone area, and the safety of the CO₂ inerting technology were analyzed. The results indicate that the O₂ concentration is diluted between the working face and the injection port, especially in the air intake side. Furthermore, the CO₂ injection rate is an important parameter to the fire prevention and extinguishing technology. When the gas injection rate ranges from 240 to 720 m³/h, the oxidation zone area varies from 7380 to 14 760 m², and the gas injection rate grows exponentially with the area of the oxidation zone. Moreover, the redundant CO₂ gas flows to the retaining roadway, and it reduces the O₂ concentration, resulting in asphyxia accidents of miners. The research results are helpful to balance the relationship between inert gas injection and production safety and provide guidance for the practical application of the inert gas fire prevention technology.