Fire Size in Tunnels
Carvel, Ricky O
In recent years, a number of high profile accidental fires have occurred in several road and rail tunnels throughout the world. Many of these fires grew rapidly to catastrophic size and claimed many lives. The processes involved in the rapid growth and extremely severe of these fires are not adequately understood as yet. The introduction to this thesis reviews a number of these accidental fires and describes much of the previous experimental research which has brought about the current understanding of tunnel fire behaviour. A detailed review of the relevant parts of elementary fire dynamics is also presented. This thesis addresses two main questions: 1. What is the influence of longitudinal ventilation on fire size in tunnels? and 2. What is the influence of tunnel geometry on fire size? The answers to both these questions are determined using a probabilistic method called Bayes Theorem. This provides a method of answering the above two questions using the handful of experimental data which are available. It is found that the heat release rate (HRR) of a heavy goods vehicle (HGV) fire may be greatly increased in magnitude by longitudinal ventilation, for example by about a factor of 5 with a longitudinal ventilation velocity of 3ms-1. It is also found that longitudinal ventilation may cause a significant increase in the HRR of large pool fires, but may cause a decrease in the HRR of small pool fires and car fires. An equation is derived to predict the influence of tunnel geometry on HRR. It is found that HRR varies principally with the width of the tunnel and the width of the fire object. The HRR of a fire in a tunnel my be increased up to four times due to the geometry of the tunnel.