Temperature characteristics in a double long-narrow space with different fire locations

Maximum smoke temperature beneath the tunnel ceiling is always one of determining factors of the safety assessment of a tunnel fire. Although many studies have been undertaken, the double long-narrow space fire, such as in a subway tunnel with a train on fire, has been rarely considered and investigated. To benefit the fire safety assessment, the smoke temperature characteristics beneath the tunnel ceiling under various fire sizes and locations were then investigated in this study both numerically and theoretically. A new parameter called dimensionless offset distance (d∗) was proposed to address the influences of fire locations on fire behaviors. It was then known, as the d∗ keeps increasing, the maximum temperature moves from above fire source to above the train end. The change of the maximum temperature along with d∗ can be divided into two regions, namely Region I (0≤d∗<0.46) and Region II (0.46≤d∗<1). A new empirical model was also developed to predict the maximum temperature rise considering fire size and fire location. The smoke temperature rise was found attributing to the increased level of smoke accumulation inside the train, which can be characterized by factor af. Critical af for the transition from Region I to II was found between 0.145 and 0.165. This study will provide a reference for the relevant detection, protection and fire rescue in tunnel fires.