Smoke movement and stratification of tunnel fires under coupled effects of rainfall and ventilation

This study investigates the smoke movement and stratification characteristics of tunnel fires under coupled effects of rainfall and ventilation through a series of reduced-scale tests. Results show that the smoke movement is affected by both ventilation and rainfall-induced airflow. The smoke tends to move downstream of the dominant airflow. As the increase in ventilation velocity, the height of the downstream smoke layer decreases. Conversely, as the rainfall intensity increases, the height of the upstream smoke layer decreases. Forced shear airflow consistently disrupts the smoke stratification downstream of the flow, whether induced by ventilation or rainfall. Although strong ventilation is capable of controlling smoke downstream, it may destroy the downstream smoke stratification. Compared to critical velocity, the confinement velocity is more suitable for tunnel smoke control as it maintains the stability of downstream smoke and thus can be applied in the early stage of fires. The confinement velocity is found to be 0.73 times the critical velocity. A model of the confinement velocity under the effect of rainfall is established. Findings are helpful in emergency rescue and evacuation of tunnel fires under rainfall conditions.