Impact Airflow Evolution Induced by Hard Roof Collapse in Contiguous Seams and the Forced Ventilation Technology

In contiguous seam mining, the sudden large-scale collapse of a hard roof in an overlying goaf generates violent impact airflow, driving hazardous gases into the underlying working face and seriously threatening production safety. However, quantitative analysis of airflow responses under such transient impacts is rare for conventional exhaust ventilation systems, and proactive control strategies remain lacking. This study hypothesized that replacing exhaust ventilation with a forced ventilation system builds a sufficient counter-pressure gradient across the working face to block the downward migration of hazardous gases. Taking the Longhua Coal Mine as the engineering background, this study combines a theoretical velocity model of roof-collapse-induced impact airflow with numerical simulations and subsequently implements a forced ventilation system on site. Results show that under exhaust ventilation, roof collapse greatly intensifies air leakage in the goaf, causing the CO concentration at the return corner to spike to 5000 ppm within only 0.2 s. In contrast, the field-deployed forced ventilation system effectively suppresses this impact: by keeping the pressure difference across the air regulator within 338–417 Pa, the CO concentration drops from 36 ppm to below 15 ppm. Complemented by a real-time monitoring system for goaf pressure surges and hazardous gases, this strategy successfully shifts disaster control from passive ventilation to active aerodynamic suppression. This study provides a robust theoretical foundation and practical engineering reference for disaster prevention in contiguous seam mining.