Influence of transverse fire locations on hot smoke movement and critical driving force of bifurcated tunnel fire under forced ventilation

Fire hazard on both sides of tunnel is significantly higher than in the middle, and the tunnel walls and bifurcation areas significantly affect the flow of hot smoke and subsequent effective control, causing serious fire hazards. The smoke movement and critical ventilation threshold to prevent smoke backlayering in bifurcated tunnel fire are studied. The results show that when the fire occurs in the bifurcation area, the hot smoke generated is more difficult to be completely suppressed. When the distance between the fire and the side wall of the tunnel decreases from 9 m to 1 m, the slope k gradually decreases from 2.365 to 1.708 and V shows a "decreasing-increasing-decreasing". When the distance between the fire source and the side wall of the tunnel is 3 m, the maximum intercept b is -1.181. The hot smoke at H4 is more difficult to be completely suppressed. For smoke movement, the side wall of the main tunnel limits free diffusion and promotes smoke shock and asymmetric flow. As the fire gradually approaches the side wall, the dominant factor of smoke movement changes from bifurcation flow to the limiting and guiding effect of the side wall of the tunnel. Combined with the theoretical formula, the forced ventilation driving force to prevent smoke backlayering at different transverse fire locations is deduced. This study provides insights for tunnel fire prevention and control by examining hot smoke movement and management under realistic engineering conditions.