Experimental study on collaborative longitudinal ventilation of smoke control for branched tunnel fires considering different branch angles

Abstract

For branched tunnel fires, the main tunnel and the branch should be collaboratively ventilated to keep the branch and upstream of the main tunnel free of smoke. In this paper, reduced scale experiments were conducted to study the collaborative longitudinal ventilation in branched tunnel fire, considering three branch angles (15°, 45°, and 60°) and five ethanol pool fire sizes. The fire source located at the intersection. The results show that the longitudinal controlling ventilation velocities in the main tunnel and branch are related to the critical ventilation velocity of branched tunnel fire when only the main tunnel is ventilated, vc,m. Two critical ventilation modes were proposed: (a) the values of ventilation velocities in the branch and the main tunnel are equal; (b) the ventilation velocity in the main tunnel equals to vc,m, and the ventilation velocity in the branch is smaller. Under ventilation mode A, when ventilation velocity is approximate 42 % of vc,m, the smoke can be controlled. Under ventilation B, when ventilation velocity in the main tunnel equals to vc,m, and the ventilation velocity in the branch is within 0.10 m/s–0.22 m/s, the smoke could be controlled. However, the heat release rates in ventilation mode A could be larger than that under mode B by 33 %—99 % regarding the same pan size. Hence, in practice, the collaborative ventilation modes, in which the ventilation velocities in the branch and the main tunnel are close, should be avoided. This work could help to guide the emergency rescue in relevant fire accidents.