Experimental Study on Smoke Backlayering Length and the Temperature Distribution of Parallel Dual‐Fire Scenarios in a Longitudinally Ventilated Horseshoe‐Shaped Tunnel

Highway tunnel fires caused by traffic accidents can lead to multiple simultaneous fires, which are more destructive and difficult to control compared to single fires. This study conducts a series of experimental tests to examine the smoke backlayering length, maximum gas temperature rise beneath the tunnel ceiling, and other critical parameters of dual source fires. The experiments were carried out in a 1:10 reduced‐scale model tunnel with longitudinal ventilation, varying burner separation distances and burner dimensions. The results indicate that the smoke backlayering length in dual source fires is influenced by the longitudinal ventilation speed, heat release rate, and burner separation distances, while the maximum temperature rise beneath the ceiling decreases with increasing burner separation distances. A function incorporating burner separation distance and burner dimensions was proposed to predict the smoke backlayering length, based on the prediction model for a single fire source and the experimental data for dual fire sources. Additionally, based on the single fire source theory, a prediction model for the maximum temperature rise beneath the ceiling with dual fire sources was established. These findings provide a theoretical basis for risk prevention in tunnel fires involving multiple fire sources.