Paper Title
The Influence Of The Fire Source Location On Critical Velocity And Backlayering Length

Abstract
Critical ventilation velocity and backlayering length have been studied quite extensively in the field of tunnel _re. However, in previous studies, the fire source was investigated at the centre point of the tunnel, with the same distance to the left/right of tunnel exit. A tunnel is a special, long but narrow structure, where fire can occur at any location, with varying longitudinal distance to the downstream/upstream opening of the tunnel. A thermal buoyancy-driven smoke flow that moves in a reverse direction (backlayering flow) is dangerous during passenger evacuation process. This paper investigates the effect of different longitudinal _relocations on critical velocity and smoke backlayering flow length beneath the ceiling in a tunnel. A set of small-scale experiments are conducted in a reduced-scale tunnel [3 m (length) X 0.6 m (width) X 0.96 m (height)]. n-Heptane placed in rectangular pools are used as the heat source. Based on the experimental results, critical ventilation velocity has an inverse relationship with the distance between the _re source and the origin of the tunnel (from 0 to 102 mm). Furthermore, backlayering length decreases with the distance between the fire source and the left end side. A new model is experimentally deduced to estimate critical velocity and smoke backlayering length including the factor of the longitudinal fire source location. Keywords - Critical ventilation velocity; Backlayering length; Longitudinal fire locations