Critical shaft height for complete smoke exhaustion during fire at the worst longitudinal fire location in tunnels with natural ventilation

Abstract In this study, the smoke control for fire situations in tunnels with naturally ventilated shafts was studied based on a 1/20 reduced-scale tunnel model, and the effects of the longitudinal fire location, shaft settings, and heat release rate (HRR) on the smoke control were discussed. The experimental results show that a worst longitudinal fire location for smoke control exists. Moreover, the critical shaft height for complete smoke exhaustion was studied experimentally and theoretically. According to the experimental results, the critical shaft height is almost independent of the HRR. With increasing shaft length, the critical shaft height decreases first and then remains stable until it finally decreases to zero. Furthermore, it increases with increasing interval between two shafts. In addition, a theoretical model for predicting the critical shaft height was developed and validated. The research results can serve as a useful reference for the design of natural ventilation systems with vertical shafts for the control of tunnel fires.