The ceiling temperature characteristics in a tunnel under different fire locations

Abstract

Current studies on tunnel fires mainly focus on central-axis fires, and the combined influence of fire elevation and transverse fire location has not been explored adequately. To address this gap, a 1:8 scale experimental campaign was conducted in an 8 m × 1 m × 1 m rectangular tunnel model with variations in fire elevation and transverse fire location. The maximum ceiling temperature rise was more than twice as responsive to the fire elevation as to the transverse fire location, highlighting the dominant role of thermal radiation feedback. Accordingly, the dimensionless temperature rise reaches an upper limit of approximately 3.2, from which a linear correlation between the dimensionless maximum ceiling temperature and heat release rate was established. By accounting for transverse fire location effects, the dimensionless model describing the maximum ceiling temperature rise was refined. Furthermore, the transverse temperature attenuation was governed primarily by the transverse fire location rather than the fire elevation, with near-to-far wall differences of up to 70 K. By incorporating a double exponential summation term into the classical single exponential attenuation model, a generalized dimensionless equation was developed to accurately predict the transverse temperature profiles for various fire locations. Comparison with existing correlations and experimental data revealed a maximum relative error below 20 %, confirming the reliability and stability of the new model.