The behaviour of wood crib fires under free burning and fire whirl conditions

The dynamics of wood crib fires were investigated under fire whirl (FW) and free burning (FB) conditions in a small-scale apparatus. For open-packed cribs, the burning rates and fire spread rates of the FB and FW cribs were almost identical. However, as the number of sticks per layer (n) increased from 3 to 7, the burning rate for FW experiments increased 1.0-1.3 times that of the FB cribs and the spread rate for FW experiments was 0.92-1.66 times that of the FB cribs for the same geometric configuration. Likewise, for open-packed cribs the average flame height of the FB and FW cribs were very similar, but as n increased the average flame height for FW tests increased from 1.0 to 1.69 times that of FB cribs for the same configuration, which was almost the same increase as that for the fire spread rates. Temperature measurements along the centreline above the crib showed distinctly different profiles for FB and FW crib fires. The ratio of the absolute temperature in the continuous flame region of a FW to that of a FB crib of the same configuration increased from 0.99 to 1.2 as n increased.