Fire Safety Science Digital Archive

Fire whirls were frequently reported in forest and urban fires with devastating damages to life and property. This work conducted experiments by medium-scale facility to study the formation mechanism, as well as the vertical velocity and radiative heat transfer of fire whirl. Heptane was used as fuel in experiments. It was found that the drag force on the root of flame plays an important role in the formation and decay of fire whirl, as evidenced by the variations of burning rate data versus time. Analyses show that the pressure difference due to whirling, characterized by circulation Gama, affects the vertical centerline velocity remarkably. The variation of the vertical centerline velocity is correlated by Vz~z^0.14Gama^0.24 in the flaming zone and Vz~z^-1Gama in the plume zone. The radiation analysis results show that the heat flux in the vertical direction reaches maximum at z/H~0.4 for fire whirls, and variation of radiative heat flux in the radial direction can be correlated by q''(r)~r^-m with the exponent of nearly 1.1 for both fire whirls and general pool fires. It is also found that the radiative fraction of fire whirls is nearly 42%, 1.4 times as large as that for general pool fires. Radiative heat feedback is shown playing an increasing role in the burning rate with pool diameter, similarly as general pool fires.