Influence of slope and external temperature on smoke stratification in case of fire in bi-directional road tunnel

Abstract

Jet fan ventilation strategy in case of fire in bi-directional road tunnels is focused on maintaining smoke stratification. There are several factors influencing stratification under specific conditions. In this paper smoke movement during a 5 MW fire in a 600 m long road tunnel is studied by computer simulation and the influence of slope and external temperature on smoke stratification is analysed. Calculations were performed on a high performance computer cluster using parallel version of Fire Dynamics Simulator. Smoke stratification upstream of the fire is maintained in every simulation scenario with the exception of declivous tunnel, in which buoyancy intensifies backlayering. The behaviour of the smoke movement downstream of the fire is more complex. In the case of horizontal tunnel the stratification is not maintained in the vicinity of the fire and region with untenable conditions expands downstream. In the tunnel with slope of -2° this expansion is accelerated, while in the tunnel with slope of 2° untenable conditions spread in opposite direction. The influence of exterior temperature higher than temperature inside the tunnel is relatively weak in horizontal tunnels; however, it becomes very important in sloping tunnels, especially downstream of the fire.