Bettelini: The Prediction of Smoke Propagation Due to Tunnel Fires

A new one-dimensional time-dependent model for analysing fire scenarios in tunnels with longitudinal ventilation is presented. An important feature of the model is its ability to handle the stack effect and gravity-driven smoke propagation due to the strong thermal stratification in the tunnel. The new model was implemented in the computer code ‘Rabbit’. The validation was based on results from the Memorial Tunnel Fire Ventilation Test Program [5]. ‘Rabbit ’ was able to reproduce in a qualitatively and quantitatively correct way the main experimental findings. It was concluded that the model is suitable for design and review work. The application to an existing tunnel, the Pierre Pertuis, illustrates the ability of the code to handle real-life situations. The results also demonstrate that for tunnel inclinations in excess of 1-2 % the stack effect plays a prominent role in case of fire. Only when this is properly accounted for can dangerous situations, such as flow reversal and smoke spread over halted vehicles and escaping persons, be analysed to the extent required by modern safety standards. Nomenclature A [m2] area cp [W/kgK] heat capacity cw [-] drag coefficient Dh [m] hydraulic diameter g [m/s2] gravity constant i [-] inclination k [-] wall loss factor of jet fan L [m] tunnel length n [-] number of ∆p [Pa] pressure difference Q [W] heat flux T [K] temperature t [s] time u [m/s] velocity x [m] axial distance α [W/m2K] heat conduction coefficient ε [-] emissivity λ [-] wall friction coefficient ρ [kg/m3] density of air σ [W/m2K4] Stefan-Boltzmann constant ζE [-] portal entry losses (=0.6) ζO [-] other discrete losse