Critical longitudinal ventilation velocity for smoke control in a tunnel induced by two nearby fires of various distances: Experiments and a revisited model

Abstract

Fire smoke in a tunnel fire is a key factor causing casualties, thus the critical longitudinal ventilation velocity is a key parameter in tunnel fire safety ventilation design. The correlation of critical longitudinal ventilation velocity for smoke control in a tunnel induced by two nearby fires has rarely been studied experimentally and quantified before, despite the fact that this scenario exists in practice. In this paper, the critical longitudinal ventilation velocities for smoke control in the tunnel, induced by two nearby fires were experimentally quantified, involving various separation distances between the two fires of both axi-symmetrical and linear sources of various heat release rates, with a total of 72 test conditions. Results show that the effect of separation distance between the two fires on the critical longitudinal ventilation velocity, decreases with the increase of fire heat release rates. The critical longitudinal ventilation velocities are found to firstly decrease with increasing separation distance between the two fires, and then remain unchanged when the separation distance between two fires beyond a critical value. A new modified model, involving two fires of various separation distances, is proposed. The model is shown to well represent the experimental results.