Description

This paper contains some theoretical speculations on the possible heating effect of flame radiation in front of forest fires. Flame variables used are rate of advance, length, angle of tilt and radiant intensity. Taking a simplified case, an expression is derived for the total radiation received by a fuel element before engulfment. This quantity is equated to the energy required to raise the fuel to ignition temperature, and an expression obtained for the ratio of flame length to rate of advance. By using published formulae linking flame length to a fractional power of the fire's energy output per unit length of front, the rate of advance can then be estimated. The final expression links rate of advance, fuel moisture content and flame angle in a way that corresponds roughly to the observed behaviour of surface fires of moderate intensity.