Full-scale experimental study on fire under vehicle operations in a sloped tunnel

Urban rail systems are developing rapidly, and due to the limited space of the metro tunnel, once a fire occurs will result in disastrous consequences. Full-scale fire experiment is an effective testing method for fire prevention of metro systems. Aiming at the characteristics of a long continuous downhill distance and large lifting height in the sloped metro tunnel, a full-scale fire experiment under vehicle operations was carried out on a metro line. By changing the operated speed and direction of the vehicle, the airflow velocity, ceiling temperature distribution, and smoke layer characteristics in the tunnel were studied. The results show that when a fire occurs in a sloped tunnel, the running vehicle will produce piston effect, and the airflow will be affected by the stack effect and the piston effect simultaneously, which will change the flow field in this area, and then affect the flame shape, ceiling temperature and smoke distribution. Through the dimensionless treatment of the ceiling temperature, a longitudinal attenuation distribution model of the ceiling temperature was established, which reveals the law of fire smoke migration and diffusion under different vehicle operating conditions. The conclusions of this study could technically support the smoke control design in such metro tunnel fire scenarios.