Abstract
Full-scale experiments in a bifurcated tunnel in a hydropower station with a fire source at the junction area were conducted to investigate fire-induced smoke spread characteristics in connected regions. The spread and descent of smoke in each tunnel were studied by analyzing the temperature profiles and smoke layer heights coupled with on-site observations. The results show that the slope and ventilation strongly affect the smoke risks in each tunnel with the smoke temperature steadily decreasing with distinct stratification upwind of the fire source. The smoke and fresh air mixture flow disrupted the smoke stratification and caused the smoke level to lower in the tunnel with the vertical temperature distribution becoming more uniform. Moreover, the aggravation of smoke deposition in the uphill direction in tunnel 2# increased the smoke temperature in the longitudinal direction below 3 m. The different fire risks in different tunnel sections should be carefully considered in smoke control designs. For the present fire heat release rate, the smoke layer height remained at 4.2 m in the upstream tunnel, while the downstream tunnels faced higher risks that the smoke layer descending below 1.5 m. The uphill slope in tunnel 2# increased the smoke descent with the smoke height decreasing to 0.8 m after 2 min, which should be considered in smoke control designs and fire emergency.
