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An Experimental Study on the Effect of Slope on the Critical Velocity in Tunnel Fires

The present article deals with the experimental study to investigate the effects of tunnel slope on the critical velocity in the tunnel fires. The 1/20 reduced-scale model tunnel is adopted on the basis of Froude scaling law. The methanol, acetone, and n-heptane pool fires are used as fire sources with the heat release rate ranging from 1.11 to 1.85 kW, 3.13 to 5.21 kW, and 9.16 to 15.6 kW, respectively. The angle of tunnel slope is varied as five different degrees 0, 2, 4, 6, and 88. A load cell is used to measure the mass loss rate of the burning fuel. The location of smoke layer is determined on the basis of temperature variation measured at the tunnel ceiling by K-type thermocouples. The present experiments observe the effects of the tunnel slope, fire size, and ventilation velocity on the back-layering distance. The results showed that critical velocity increases with tunnel slope due to the stack effect. The correlation between the critical velocity and the angle of tunnel slope was obtained for the pool fires whose heat release rate was varied with the ventilation velocity.