Experimental investigation on onsetting internal fire whirls in a vertical shaft

Internal fire whirls might be induced in tall buildings under fires. Hazards associated with such fire whirls should be assessed carefully. The physics behind is not clearly understood, even the conditions of onsetting internal fire whirls are unknown. It is important to observe the physical phenomenon carefully first, before carrying out theoretical analysis. In this article, internal fire whirls were studied with a small vertical shaft model under different ventilation conditions. A 1.6 kW propanol pool fire was placed in a rectangular vertical shaft of height 145 cm. Ventilation provisions at the bottom and side wall were arranged. The conditions of onsetting internal fire whirls were investigated in detail with support from some full-scale burning tests at Harbin, Heilongjiang, China. It is concluded that allowing a vertical gap of appropriate width and height at the side wall would onset internal fire whirls. Flame height would be stretched by several times the value for free burning. The burning rate of the pool fire would increase. Results are also confirmed by full-scale burning tests.