People evacuation in tunnel fires : a cross evaluation of two methodologies
Résumé
In France, safety assessment of tunnels is mainly based on a risk analysis called the specific hazard investigation. One of the key issues of these studies consists in modeling people evacuation. The commonly used method for computing the people evacuation consists in evaluating their displacement velocity based on smoke opacity. However, it is obvious that other fire consequences parameters, thermal effects and toxicity, will affect people displacement. To evaluate whether considering those effects is relevant and could modify conclusions of specific hazard investigations in tunnels or not, two approaches were used in a comparative manner. The first approach is based on currently used method and considers only the smoke opacity. The second innovative approach introduces thermal and toxic consequences on the displacement velocity. It enables considering the toxic dose impact on human being during the evacuation process and the thermal effect together with the visibility. This new approach also introduces a new method for the evaluation of lethality and user evacuation which are managed with thresholds in the current method. This difference was also considered in the comparison. Those two approaches were applied on many fire scenarios to compare the conclusions in terms of people trapped or killed by the fire. For each of those scenarios, consequences were evaluated based on a CFD model, for different tunnel geometries, design fires and ventilation strategies. The two most relevant of those scenarios are presented in the present paper. This comparison shows only minor differences for the specific case of tunnel fire safety. One way to consider the effect of the new methodology should consist in keeping the existing method but modifying the corresponding thresholds for the different quantities relative to fire consequences.
Domaines
Ingénierie de l'environnement
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