Development of a technique for establishing a pseudo tunnel length

Abstract

In the case of a tunnel fire, it is likely that the evacuation path of some of the tunnel users will be obstructed by the cloud of smoke that falls to the road surface of the tunnel. It is important to be able to predict the falling point of the ceiling jet smoke resulting from the fire for improving evacuation strategy. However, a considerably long tunnel is required for examining the distance traveled by the smoke generated in full and model scales fire experiments. It is often difficult to satisfy this requirement while performing fire experiments at laboratory scale. The objective of this study was to develop a new technique for examining the smoke falling phenomenon by using a model scale tunnel with insufficient length. In the new technique, a cooling apparatus was introduced to simulate heat transfer from smoke to tunnel walls. If the amount of convective heat absorbed by the cooling apparatus with length Lc is equivalent to the amount of convective heat lost by the heat transfer to the tunnel walls while the smoke flowed through the distance Ls under a tunnel ceiling, the cooling apparatus with length Lc can be equivalent of a tunnel length Ls. We denote the tunnel length simulated by the cooling apparatus by a pseudo tunnel length. A series of fire experiments were conducted using a 1:10 scale model tunnel with a length of 12 m. In this study, we assessed the effectiveness of the technique for simulating a pseudo tunnel. Experimental results showed that a tunnel with a length of 18.6 m can be simulated by a 12 m tunnel using the new technique proposed.