The influence of longitudinal ventilation systems on fires in tunnels

Abstract

Many tunnels are equipped with longitudinal ventilation systems to control smoke in the event of a fire. However, the influence of such ventilation on fire development and fire spread has rarely been considered. This paper presents the results of a study investigating the influence of forced longitudinal ventilation on car fires, pool fires and heavy goods vehicle fires in tunnels. A Bayesian probabilistic approach is used to refine estimates, made by a panel of experts, with data from experimental fire tests in tunnels. Results are presented and the implications are discussed. The influence of longitudinal ventilation on heavy goods vehicle fires is predicted to be much larger than the experts’ estimates, causing a fire to grow ten times larger than if natural ventilation was used. The effect of ventilation on a pool fire in a tunnel depends on the size of the pool; the heat release rate of small pool fires may be reduced by forced ventilation, whereas it may be enlarged for large pool fires. The size of a car fire is not expected to be greatly affected by forced ventilation at low ventilation velocities.