An experimental investigation on temperature profile of buoyant spill plume from under-ventilated compartment fires in a reduced pressure atmosphere at high altitude

Abstract

Buoyant fire plume over a building façade spilled from the window of an under-ventilated compartment fire poses a serious fire hazard of flame spread to upper floors, a process in which the high plume temperature is the key parameter. In order to specify its counteracting fire safety design and regulations, the façade plume temperature profiles have been studied and correlated in the past. However, those correlations are all specified at normal atmospheric pressure conditions at sea level, which is needed however to be extended for conditions at low pressure such as in high altitudes. To investigate the effect of low atmospheric pressure on temperature profile of buoyant spill plume, a knowledge which has never been revealed, scale model experiments were carried out correspondingly at two different altitudes (Hefei city: 50m, 1atm; Lhasa city: 3650m, 0.64atm). Both the lateral (in the direction normal to façade) and vertical (along facade) temperature profile of the spill plume are measured. It is found that the lateral decay of temperature in the reduced pressure atmosphere is much faster than that in the normal pressure condition, but they can be converged and correlated by a proposed non-dimensional equation. For a given total heat release rate, the temperature of the spill plume near the façade wall is much higher in the reduced pressure atmosphere than that in the normal pressure condition at the same height, suggesting that the fire safety regulations to counteract the vertical fire spread to upper floors need to be specified more rigorous in high altitude. Based on the correlation of vertical temperature profile, it is found that the air entrainment of the buoyant spill plume is weaker in the reduced pressure atmosphere, being about 0.8 times of that in the normal pressure condition. Finally, the vertical temperature profile is collapsed non-dimensionally with this entrainment change accounted for. These results and findings at low pressure provide a significant supplement over previous results in the literatures, as well as application of current fire protection measure settings to high altitude locations with considerably reduced atmospheric pressure.