Smoke flow in full-scale urban road tunnel fires with large cross-sectional vertical shafts

In this study, a series of full-scale fire tests are performed in a tunnel with large cross-sectional vertical shafts. The heat release rates and fire locations are considered, and the general smoke development, smoke flow pattern in the shaft, smoke temperature distribution, and smoke front velocity are analysed. It is found that complete plug-holing occurs in the tunnel with large cross-sectional vertical shafts. The smoke flows into the shaft from the bottom sides and spreads out along the shaft sidewalls. The smoke cannot fill the shaft cross-section, even at the shaft outlet. In the early and full-development stages of a fire, a well-stratified smoke layer exists, whereas in the decay stage and after burning out, the visibility significantly reduces. The smoke can be controlled within 80-125 m on each side of the fire source, and it takes approximately 10 min for the visibility to self-recover naturally for common car fires after burning out. The results of the full-scale experiment indicate that the shaft has acceptable performance in smoke control for the test scenario investigated. According to an analysis of the tunnel environment during a common car fire, as well as the evacuation movement, it can be concluded that the occupants can escape safely. The experimental results are used to verify the smoke control performance of the vertical shaft and provide guidance for the design of naturally ventilated tunnels with vertical shafts.