Experimental study on maximum smoke temperature beneath the ceiling induced by carriage fire in a tunnel with ceiling smoke extraction

Tunnel fire is an important topic considering tunnel safety design and regulations, a process in which the high smoke temperature under the ceiling is the key parameter. This paper investigates experimentally the maximum temperature beneath the ceiling induced by carriage fire in a tunnel with ceiling smoke extraction, which have been studied in the past. A series of small scale experiments are conducted in a model tunnel, consisting of a carriage (with an opening) in a tunnel. A range of ceiling smoke extraction rates, and heat release rates are considered. The maximum temperature is measured, and shows different development trends with increasing ceiling smoke extraction rate. Maximum temperature measurement without ceiling smoke extraction shows some deviation with previous model predictions, which mainly can be explained by the effect of stack effect, induced by narrow channels, and wall entrainment restrictions. This study also revealed the variation characteristics of ceiling maximum temperature with different ceiling smoke extraction rates. A correlation was proposed to describe the maximum temperature beneath ceiling induced by carriage fire in a tunnel with ceiling smoke extraction, which is a piecewise function. These results and correlations are new and a significant improvement over previous results in the literature.