Objective As metro interval tunnels are long and narrow confined spaces, in the event of a fire, human life safety can be extremely severely threatened. Therefore, it is imperative to conduct fire tests to summarize the longitudinal and vertical smoke temperature distribution patterns beneath the tunnel ceiling, and to clarify the characteristics of smoke diffusion and settlement.

Method With a 1:20 scaled-down tunnel model, the smoke temperature distribution in the tunnel central cross-section under different fire conditions is measured through varying the fire source elevation height and fire intensity. The variation patterns of the maximum smoke temperature beneath the tunnel ceiling, the longitudinal attenuation of smoke temperature, and the vertical temperature distribution with the fire source elevation height and fire intensity are investigated.

Result & Conclusion  The derived dimensionless formula for the maximum smoke temperature rise beneath the ceiling, and the fitted formula for the longitudinal attenuation of smoke temperature rise are accurate and widely applicable, which can be used to predict the longitudinal smoke temperature distribution beneath the ceiling in metro interval tunnels. Taking the thermal Gaussian layer thickness and the maximum smoke temperature as the characteristic smoke layer height and characteristic temperature rise, a dimensionless analysis of more than 540 temperature data from 10 test cases shows that the vertical smoke temperature variation follows the same smooth curve, independent from the horizontal position of the fire source, fire intensity, and fire source elevation height. This indicates that the vertical smoke temperature distribution in the tunnel follows a self-similarity law. The experimental data are in good agreement with the vertical smoke temperature distributions reported in other literature, confirming the self-similarity of the vertical temperature distribution. The dimensionless fitted formula for the vertical smoke temperature distribution is accurate and widely applicable.