Brand Propagation From Large-Scale Fires

Abstract

This paper is one of a series on brand lofting and propagation. Here, spherical brand propagation in a constant ambient wind is addressed. Maximum propagation distances are calculated for wooden brands with diameters up to 0.18 m, which are lofted above axisymmetric pool fires with heat release rates, Q_o, between 1 MW and 3 GW. Winds of 1.8 m/s ≤ U_w ≤ 92 m/s are considered. A maximum propagation distance equation is developed as a function of Q_o, U_w and wood type, or β. Cedar brands (β = 1), lofted by fires with Q_o = 1 MW, 50 MW and 1 GW, travel a maximum of 49 m, 290 m and 1100 m, respectively, in 10 m/s winds before landing at burn out. Brands between a "collapse" diameter, d_col = 0.49 Q₀ ^0.269 β^0.782, and a maximum loftable diameter, d_o,max = 0.454 β Q₀ ^0.04, propagate the same maximum distance, since the larger brands move slower and therefore have more time to combust. Hence, only brands with 0 ≤ d ≤ d _col need be studied for given Q_o, Uw and β.