The effect of forced ventilation by using two movable fans on thermal smoke movement in a tunnel fire

In this work, tests were conducted to investigate the propagation characteristics of buoyancy-driven thermal smoke for different multiple movable fan layouts in a full-scale road tunnel. The temperatures along the longitudinal direction of the tunnel ceiling upstream and downstream of the fire source were measured and the thermal smoke development was recorded using the laser sheet visualization technique. The spread velocity and descent velocity were derived based on the longitudinal and vertical temperature distributions in order to analyze the differences in thermal smoke propagation for various movable fan layouts. The results showed that the best configuration, which gives the highest reduction of maximum temperature and enhanced propagation of thermal smoke, is to install one fan downstream of the fire source rather than installing both of fans upstream. However, this configuration also increases the descent velocity of the thermal smoke. In addition, there may be a critical range for the distance between the fire source and fan installed downstream of the fire source because the conclusions above are no longer valid if this range is exceeded.