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 a slope varies from 0 to 10%. Parameters such as ceiling temperature and airflow velocity are measured. The results indicate that the relationship between smoke back-layering length and tunnel slope can be described as an exponential function. The smoke temperature at the downstream exit first increased and then decreased with a higher slope. The airflow velocity at downstream outlet increased nonlinearity when tunnel slope was less than 8%. In the slope tunnel, the fire smoke spread process can be divided into three stages. Fire smoke spreads upstream to the peak distance, subsequently, the upstream smoke layer decreases gradually, the tunnel fire reaches a quasi-steady state. The backflow characteristics of smoke in sloped tunnels are coupled with the 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.