The influence of vehicles on smoke propagation in transversely ventilated tunnels

We present an experimental study to assess the influence of realistic traffic conditions on the ventilation required to confine the smoke produced by a tunnel fire. The experiments are performed on a reduced-scale tunnel, with hot smoke modeled by a buoyant helium–air release. The tunnel is ventilated by two extraction vents placed on both sides of the source to confine the smoke, and a longitudinal flow is induced by a longitudinal pressure gradient. The traffic condition is simulated by arranging cubic blocks, representing vehicles, of two different sizes inside the tunnel. For each block size and various tunnel configurations (different damper geometries and positions, and the presence or absence of vertical barriers downstream of the vents), experiments are performed with and without longitudinal flow. The presence of vehicles can lead to outcomes that differ from the well-established results in the literature obtained in their absence, i.e., in an empty tunnel. Specifically, the performance of rectangular dampers becomes equivalent to that of squared-centered dampers unless vertical barriers are used. Furthermore, when barriers are employed, the geometry and position of the dampers become irrelevant to ventilation efficiency. Obstacles primarily affect ventilation efficiency when they interact with the buoyant smoke and change its stratification regime. • The presence of vehicles strongly affects the transverse ventilation of road tunnels. • Vehicles can be responsible for the destratification of the confined smoke. • Vertical barriers downstream the extraction improve the ventilation efficiency.