Impact of sealing speeds on the mechanism of hot smoke propagation in tunnel fires under single-sided and double-sided sealing conditions

A series of small-scale tunnel fire experiments were conducted to investigate the effect of different sealing speeds on the temperature attenuation characteristics of hot smoke under single-sided and double-sided sealing conditions. The internal temperature fields for both sealing methods were measured and compared. The results indicate that, within the experimental range of this study, sealing the tunnel entrance causes smoke accumulation and temperature rise inside the tunnel. Under natural ventilation conditions with the same fire source power, the maximum temperature for single-sided sealing is slightly higher than that for double-sided sealing. The faster the sealing speed, the lower the maximum temperature at the ceiling, due to reduced smoke accumulation and increased entrainment of air. The longitudinal temperature attenuation of fire smoke in the entire spreading region shows similar variation characteristics for both sealing methods. The previously proposed longitudinal temperature distribution equation below the ceiling centerline for sealed tunnel fires was revised, and a functional relationship between sealing speed and distance was established. A comparison with existing model experiment results and previous experimental data verified that the proposed equation falls within an acceptable error range. This study can provide a reference for firefighters to assess the temperature distribution and attenuation characteristics of fire smoke in underground spaces.