Under the gob-side entry retaining mining mode with roof cutting and pressure relief (GERRC), the gob and retained roadway section are interconnected to create an open area. Owing to the increased airflow, the coal remnants in the gob are more prone to spontaneous combustion. This study aimed to investigate the distribution of oxygen concentration within a gob and identify optimal parameters for nitrogen injection. The engineering context was the "110 method" introduced in the 1201 working face of the South Five mining area at Daxing. Computational fluid dynamics simulation software was used to analyze the effects of various nitrogen injection treatment parameters on the overall performance of the gob, including their impact on oxygen distribution. The simulation results showed that air leakage within the gob primarily originates from the working face adjacent to the intake roadway, as well as gaps within the retained roadway. The increased air leakage causes the high O 2 concentration range in the gob to expand, and the retained roadway section is connected to an area with a high concentration of oxygen near the working face, which increases the risk of residual coal spontaneous combustion. The results show that the optimal nitrogen injection conditions for inerting and reducing the risk of spontaneous combustion within the gob require an injection quantity of 500 m 3 /h, with the injection point located at a depth of 60 m. With these parameters, the range of the oxidation zone was significantly reduced. To monitor the O 2 concentration and temperature change curves in the gob during the project implementation, a bundle tube monitoring system was used, considering the actual mining situation. By varying the nitrogen injection spacing and quantity, we found that injecting nitrogen at a spacing of 30 m and at a quantity of 500 m 3 /h effectively placed most areas of the gob in the suffocation zone, reducing the risk of spontaneous combustion of residual coal. The accuracy of the simulation was verified. The study offers valuable insights into improving safety in coal mines and reducing spontaneous combustion incidents, providing important reference significance for fire prevention and control.
To ensure the safe construction of prefabricated buildings and improve the efficiency of the safe evacuation of construction personnel after a fire caused by improper operation during construction, this study used the PyroSim software to numerically simulate a fire situation based on the size and volume of a prefabricated building construction site. The variation rules of smoke visibility, CO concentration, and ambient temperature in the construction site of prefabricated buildings were analyzed and the available safe evacuation time was determined. Moreover, the Pathfinder software was used for simulation in combination with the physical attributes of personnel, evacuation speed, and personnel proportions. The time required for safe evacuation was determined and the factors influencing the evacuation time, such as the quantity and location of stacked prefabricated components, machinery, and appliances, and the number of on-site construction personnel, were analyzed. The results reveal that the original layout of the prefabricated building construction site cannot facilitate the safe evacuation of all construction personnel. The bottleneck area for the evacuation of construction personnel is the indoor corridor and evacuation stairway. The quantity and location of stacked items at the construction site greatly influence the evacuation time. When the number of construction personnel on each floor reaches a certain value, restrictions should be imposed. The results obtained by this study can provide the theoretical basis for the rational planning of evacuation routes and construction site management.
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