Fire Spread Between Vehicles in Tunnels: Effects of Tunnel Size, Longitudinal Ventilation and Vehicle Spacing

Abstract

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.

Critical ventilation velocity of two fire sources with different separating distances in road tunnel

“…24 For example, in the St. Gotthard fire accident in Switzerland, it involved two crashed vehicles and the nearest heavy goods vehicle (HGV) quickly caught on fire even though it was 30 m away from the initial fire source. 25 Under such conditions, the fire behaviors can be very different from those with single fire source, 26,27 while the critical ventilation velocity changes accordingly. This could be much dependent on the distance of these two fire sources, as the two fire plumes can interact with each other, resulting in different HRR s, temperature distribution, and smoke back-layering.…”

Handbook of Tunnel Fire Safety, 2nd edition

“…It has been found that the critical HRR (Q fc ) for spread in a tunnel similar in size to the Channel Tunnel increases with increasing ventilation velocity, but Q fc is considerably less when assuming flame impingement. However, it has also been found from a study that increasing velocity increases the probability of flame impingement (Carvel et al, 2005).…”

State of the Art of Tunnel Fire Research

“…Due to the lack of systematic experimental data, the authors declared early that when new data becomes available the results will be refined. This has also been done in publications such as references [42,43].…”