Experimental study on ceiling temperature distribution under fire conditions at diverging points of underground branching roads

This study investigates fire scenarios at diverging sections of urban tunnels, with a focus on the fire environment characteristics under natural ventilation condition. A combination of theoretical analysis and scaled experiments was employed to analyze the temperature distribution of fire-induced smoke within the tunnel. Five fire sources with heat release rates of 1.71 kW, 3.43 kW, 5.13 kW, and 6.85 kW respectively were utilized to examine the influence of lateral fire source position on the maximum ceiling temperature rise in the near-fire zone. Result show that as the fire source moves closer to the sidewall, the maximum temperature increases. The results provide valuable insights for tunnel operation authorities to make emergency response strategies and improve technical standards for the operation of urban tunnels.