Experimental investigation on carriage fires hazards in the longitudinal ventilated tunnels: Assessment of the smoke stratification features

In tunnel fires, toxic and harmful smoke is more likely to cause many casualties. The smoke stratification is an important parameter for the smoke control in tunnel fires, which has practical significance for the personal emergency escape in the early stage of tunnel fire. This work focused on the stratification stability of the smoke layer induced by carriage fires in the longitudinal ventilation tunnel. The experiment is carried out in a model tunnel with a size of 22 m (length) x 1.2 m (width) x 0.8 m (height). In this experiment, the anemometers were used to measure to flow shear velocity of the upper smoke layer and the lower layer of cold air. In addition, vertical temperatures of different heights were measured using vertically arranged thermocouple trees. The laser sheet is used to show the buoyant smoke flow, and many methods are used to calculate and compared the thickness of the smoke layer under different longitudinal velocities conditions. Finally, it was found that the buoyant stratification pattern was divided into three regimes, stable stratification, stable stratification but with some vortexes existing and unstable stratification where a strong mixing existed between the upper buoyant smoke flow and the lower air flow. This work is a significant supplement to the buoyant stratification of smoke layer from previous results.