Internal Fire Whirls in a Vertical Shaft

Abstract

Internal fire whirls induced by a pool fire in a vertical shaft of height 15 m with different ventilation conditions are studied experimentally. Ventilation is provided through a rectangular gap at the side wall with varying widths. Gasoline pool fires with diameters up to 0.46 m are set up at the center of the floor. Flame height and burning duration of the pool fire are measured. Average flame height ranged from 1 to 4.5 m when whirling is onsetted in the vertical shaft. Experimental studies indicate that air supply to the upper part of the shaft is a key factor for onsetting internal fire whirls. Oxygen is required to sustain combustion to generate heat for inducing whirling motions. Therefore, flame will not whirl without adequate oxygen supply. In this study, the flaming zone in a vertical shaft is divided into four stages: the initial stage, flame rising-up stage, stable flame, whirling stage and decay stage. Based on the flame height correlations for free burning pool fires, the fuel consumption rate of the pool fire in the shaft at each stage is estimated. Correlations of the whirling flame height with fuel mass and other key parameters are then derived. Computational fluid dynamics is applied to examine the validity of the derived correlation expressions.