Analysis on Downwind Distribution of Firebrands Sourced from a Wildland Fire

Generation of firebrands from a wildland fire and their distribution downwind are studied using an analytical approach. The processes considered include emission of firebrands, wind-driven transport and the associated spot ignition. Emission of the firebrands from a fire front is treated as a stochastic process reflecting the interaction between gas flow plume and the burning fuel debris formed, with the emission rate being dominated by the rate of fuel consumption, emission factor and a function of firebrand sizes. Analogous to the random distribution of non-burning windborne particles, the transient distribution of firebrands downwind is described by a statistical pattern of Rayleigh form. Number and mass of firebrands landed downwind within the maximum travel distance are then determined by integration over the entire impact period during fire spread and burning-out processes. Application of the model to the bushfire occurred in Canberra, Australia in 2003 indicates that this model provides reasonable prediction in the distribution of firebrands downwind, and quantitatively exhibits the role of ember attack in massive destruction of houses at urban interface.