On smoke layer thickness in short naturally ventilated tunnels with arched roof

Understanding the characteristics of smoke layer thickness is vital for accurate fire detection, efficient smoke exhaust and safe evacuation in tunnel fire. Nevertheless, smoke flow in tunnels with arched ceiling may show different characteristics from the tunnels with flat roof which is usually studied. Theoretical analysis was conducted on the smoke flow characteristics and thickness under the curved roof of natural ventilation tunnel, and further, numerical simulations were performed to elucidate and verify the mechanism. The results show that smoke mass flow rate is positively correlated with heat release rate(HRR) and section radius. However, the smoke layer thickness is not significantly affected by HRR, and is positively related to the section radius. Based on the mass conservation, a practical prediction model for smoke layer thickness under arched ceiling was derived, and an empirical equation for estimating the total smoke mass flow rate was also proposed. The results presented fairly good agreement with simulations and experimental data from previous works.