Fire safety investigation for road tunnel ventilation systems – An overview

In recent years, research activities about fire events in tunnel have received a significant impulse, especially after several accidents. The Computational Fluid Dynamic (CFD) has a fundamental role about. Researchers have spent resources on various topics involving numerical tools as the performance of a ventilation system, the influence of this on the air flow motion in the tunnel or the methods for fire schematization, fire-induced smoke characterization, turbulence models, etc. One of the main phenomena to consider for the safety when a fire occurs in a tunnel is the possibility of the fire-induced smoke to rise the tunnel (backlayering). A well-designed ventilation system shall provide almost a defined value of ventilation velocity (critical ventilation velocity) in order to avoid this phenomenon. The aim of this paper is to give an overview as complete as possible on numerical aspects about the cases of fire in road tunnel. Numerical strategies and schematization methods are presented for several cases, then a specific overview on the critical ventilation velocity formulations is proposed. Here, results show a variety of equations, each one slightly different from the others, aimed to relate the critical ventilation velocity to the main parameters able to influence it (e.g., heat release rate, tunnel geometry, etc.). This variety is mainly due to the wide range of factors that can influence the backlayering and the difficulty to keep them together in a single and “global” equation.