Wildfires and the generation of fire whirls

The paper first reviews the mode of generation of fire whirls, their properties, and operational regimes, under well-controlled experimental conditions. The situation is different with wildfires. These are uncontrolled and less well understood. A modified analytical approach is described for these conditions. This is based on global energy levels, per unit ground area, for different fuels, and their associated rates of fire spread, under different conditions. These enable regimes of possible fire whirl generation in wildfires to be defined. The associated accuracy is not that of a laboratory flame, but it is probably practically sufficient. Only in two instances were atmospheric fires experimentally controlled. In the remainder, the rate of fire spread was a more meaningful parameter than a burning velocity, and the critical lateral velocity was seldom known accurately. Nevertheless, it was possible to relate it to the heat release rate, with both in dimensionless form.