Analysis of critical air velocity in a road tunnel fire

A critical air velocity analysis was performed using a numerical model adapted for the eastern tunnel tube of the Kastelec road tunnel in Slovenia. This allowed the efficiency of the fans to be tested, which is required to maintain appropriate traffic conditions and prescribed safety in the tunnel. At the critical air velocity, that is, at an air velocity lower than the prescribed one, where the spread of smoke can still be effectively controlled to ensure time for a safe evacuation of passengers from a fire-endangered tunnel tube, special attention was paid to the phenomena of smoke backlayering and layered spread of smoke under the tunnel ceiling (so-called “stratification”). Simulations of the longitudinal ventilation system with single point extractions were conducted.