Modelling Fire in Tunnels: A Large Scale Validated Two-Step Modelling Method

: Fire is a quite common phenomenon in tunnel and being able to model its consequences with a good precision is crucial to design adapted safety measures. Modelling the fire behaviour in tunnel is quite challenging. Managing large-scale experiment for all the possible configurations is however economically unrealistic. This paper presents an experimental real scale fire test that was used not only for demonstrating the fire behaviour but also for evaluating the capabilities of the FDS (fire dynamics simulator) fire code to model fire consequences too. It enables highlighting the importance of wall and inlet boundary condition treatment. Keeping in mind that predicting fire development using a CFD (computational fluid dynamics) code is quite impossible, a two-level approach is discussed with an analytical model to predict the fire curve and a CFD model for predicting smoke propagation, temperature and toxic gases distribution inside the tunnel. The comparisons show a good agreement between experimental fire test and CFD modelling but also let appear requirements when using CFD.