Fire spread between vehicles in tunnels: Effects of tunnel size, longitudinal ventilation and vehicle spacing

In a number of catastrophic tunnel fire incidents, the fire has often spread from vehicle to vehicle over large distances, occasionally hundreds of metres. Five possible means of fire spread are briefly discussed. The paper focuses on fire spread by flame impingement and investigates the conditions under which flame impingement will occur on a 4 m high HGV downstream of the initial fire. The study uses Bayesian methods to predict the probability of impingement at distances from 0 to 20 m downstream, based on experimental tunnel fire data. The influence of tunnel size, ventilation velocity and vehicle separation on the probability of impingement are discussed. In general it is shown that impingement on a downstream HGV is more likely in a smaller tunnel with a higher ventilation velocity. It is suggested that flames from a HGV fire in a tunnel will almost certainly impinge on a downstream HGV at distances of up to 20 m, and possibly much greater distances. © 2005 Springer Science + Business Media, Inc.