Longitudinal temperature profiles beneath tunnel ceilings induced by lateral fire sources in a horseshoe-shaped tunnel

This study investigates ceiling temperature distributions induced by lateral fire sources in asymmetric tunnel fires. Using a 1:10 scaled horseshoe-shaped tunnel, experiments systematically examined effects of heat release rate (HRR), fire height, and longitudinal ventilation velocity. Longitudinal ceiling temperature measurements reveal: Fire height inversely correlates with maximum ceiling temperatures and accelerates downstream decay rates; HRR and ventilation velocity significantly modulate temperature profiles. A modified effective ceiling height model incorporating lateral fire position is proposed through dimensionless analysis. Validated under varying ventilation conditions, the model accurately predicts temperature distributions. The findings provide critical guidance for tunnel safety, particularly in the design of ventilation systems, the planning of evacuation routes, and the layout of fire detection devices. Overall, this work highlights the importance of explicitly considering lateral fire sources in tunnel fire safety design.