Effect of Wind on Fire Whirl Over a Line Fire

Abstract

Fire whirls are often reported to occur in wildland and urban fires due to the effect of ambient wind. This paper presents an experimental study on the fire whirls over a line fire with cross wind, focusing on the occurrence frequency of fire whirls. The experimental observations indicated that the fire whirls induced by a line fire may spread beyond the line fire region with the effect of wind. For the effect of cross wind, it is indicated that the cross wind basically increases the occurrence frequency, while the velocity components parallel or perpendicular to the line fire have competitive effects. A scaling law is presented for the critical wind speed inducing fire whirls based on the experimental data in this work and literature. A method is proposed to estimate the magnitude of the fire whirl height under the critical wind speed.