Response of Free-Burning Fires to Nonsteady Wind

Abstract

A speculative, phenomenological model is formulated for the time-varying intensity and spread rate of a free-burning fire under the influence of nonsteady wind. The model is linearized by approximations and explicit solutions derived for the amplitude response of spread rate and intensity as a function of the frequency of windspeed variations. Stylistic descriptions of typical wildland fuels are used to generate examples. The responses predicted for these fuels are intuitively satisfactory. The only directly observable feature of fire behavior predicted by the model is an inferred periodicity for the issuance of billows of smoke as the fire alternately races and pauses in response to the low-frequency variations (<0.05 Hz) in windspeed.

Keywords:

• free-burning fire
• fire dynamics
• nonsteady fire behavior
• wind-aided fire spread.