From dynamic goaf formation to evolving spontaneous combustion and gas explosion hazard management

Coal spontaneous combustion and methane explosions persist as major hazards in longwall mining, posing serious threats to worker safety and operational continuity. However, most existing studies rely on static numerical models with fixed methane explosive thresholds, often overlooking the complex, dynamic nature of goaf development and evolving gas concentrations during longwall face retreat. To address these limitations, this research employs a three-dimensional computational fluid dynamics (CFD) model with a dynamic mesh, coupled with a colour-coded Coward’s triangle, to capture the spatio-temporal progression of spontaneous combustion, methane explosion risk, and synergistic hazards in an advancing longwall goaf. Results show methane concentrates centrally in the goaf, while oxygen dominates the goaf edges. Hazard zones expand preferentially near ventilation inlets, with synergistic risks spatially distinct from active mining areas. Proactive nitrogen injection reduces oxidation and explosive zone retention times by over 80 %, though low goaf permeability limits its spatial penetration at higher injection rates. Injection location minimally affects hazard volumes but influences retention durations, with distal placement extending explosive risks. The findings demonstrate the necessity of dynamic hazard modelling in longwall operations and provide actionable guidelines to optimize inertization strategies, targeting persistent risk zones during face retreat. This dynamic modelling advances proactive safety and contributes to safer and more sustainable longwall mining operations.