Effect of bypass duct size on the opening pressure of fire doors in an escape tunnel

Emergency escape tunnel is increasingly being incorporated into urban transportation networks to ensure timely evacuation in the event of a tunnel fire. Pressure control within the escape tunnel is critical for ensuring safe evacuation and preventing smoke infiltration. This study investigated the effects of supply air pressure on various aspects of ventilation system performance, specifically focusing on supply airflow rate, bypass duct outlet pressure, and static pressure difference across fire door (SPFD). Numerical simulations were conducted to evaluate the relationship between supply air pressure and airflow rate, showing that differences in performance between cases with different bypass duct sizes became apparent when the bypass duct was opened. The study further examined the impact of supply air pressure on bypass duct outlet pressure and found that when the supply air pressure exceeded the opening threshold (i.e., 50 Pa), differences between cases became evident. The relationship between supply air pressure and SPFD was also explored, and the results showed that bypass duct size significantly influenced SPFD, with larger ducts providing better pressure regulation and maintaining SPFD below the critical opening pressure. Finally, the study explored how bypass duct size impacts pressure regulation at a supply air velocity of 7 m/s. The results indicated that increasing the bypass duct size enhanced pressure stability up to a certain threshold of 2.6 m², beyond which further increases had diminishing effects. The findings highlight the importance of optimizing bypass duct dimensions to ensure efficient pressure control without incurring unnecessary costs. A mathematical relationship between bypass duct area and SPFD was derived, which supports the design of ventilation systems that maintain safety and stability in emergency conditions.