Experimental and Theoretical Studies of the Effects of Fire Location on the Smoke Temperature Distribution in a Branched Tunnel

Most previous work concentrated on the thermal smoke temperature distribution in traditional single tunnel fires. However, few investigations have studied the effects of branch tunnel and longitudinal fire source location on thermal smoke temperature beneath the ceiling. In this paper, a series of experiments were performed in a 1:10 reduced scale branched tunnel to investigate the longitudinal fire location effects on the thermal smoke temperature distribution beneath the ceiling. Thirteen longitudinal fire locations and three heat release rates were considered. The main conclusions are summarized as follows: The thermal smoke temperature near the fire source is obviously different for various longitudinal fire locations, while the temperature in the area far from the fire source is basically the same. The dimensionless longitudinal thermal smoke temperature beyond 0.75 m downstream from the fire source in the main tunnel is not obviously affected by the longitudinal fire location, which can be well predicted by Li’s model. However, the attenuation coefficient is obviously larger than that in traditional single tunnel due to the existence of branch tunnel. Moreover, when the fire source moves away from the intersection region to upstream or downstream, the thermal smoke temperature in the branch tunnel shows a decrease. A modified model is proposed to describe the longitudinal temperature decay in branch tunnel taking the longitudinal fire location into account, which is reasonably well fitting with experimental results. The results in this paper are essential for better understanding of thermal smoke temperature in branched tunnel and providing references for fire safety design of branched tunnels.