A numerical study on smoke behaviors in inclined tunnel fires under natural ventilation

To investigate the effect of tunnel slope on hot gas movement and smoke distribution in a slopping tunnel fire, a series of tunnel fire models are built by Fire Dynamics Simulator (FDS) with the slope varies from 0 to 10%. Parameters such as ceiling temperature and airflow velocity are measured. Results indicate that the relationship between smoke back-layering length and tunnel slope can be described by an exponential function. The smoke temperature at downstream exit increases first and then decreases with higher slope. The airflow velocity at downstream outlet increases nonlinearity when tunnel slope is less than 8%. In the slope tunnel, the process of fire smoke spread can be divided into three stages. Fire smoke spreads upstream to the peak distance, then the upstream smoke layer decreases gradually, the tunnel fire reaches a quasi-steady state. The backflow characteristics of smoke in sloped tunnels are coupled by downstream length and outlet smoke temperature. In the initial stage of a slope tunnel fire, smoke spreads upstream for a long distance, endangering human health.