A comprehensive study of two fire sources in a road tunnel: Considering different arrangement of obstacles

This paper uses Fire Dynamics Simulator (FDS) to study various arrangements of different vehicles at upstream of two fire sources. In order to make a comprehensive study, the effects of two fire sources in both lateral and longitudinal directions are investigated. The results reveal that the behavior of two fire sources, in both perpendicular directions, is directly influenced by distance between them. For small vehicles, variations of the arrangement and distance between the vehicles and fire sources do not affect the calculated Critical Ventilation Velocity (CVV). However, the presence of medium vehicles strengthens the influence of inertia force rather than buoyant force of fire plume in the tunnel. Accordingly, when there is a short distance between fires and medium obstructions, less air ventilation is needed to prevent smoke back-layering. Eventually, far distance between the vehicles and the fires results in vanishing obstruction effects. Consequently, CVV is the same as the case in which there is no vehicle in the tunnel.