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In the fire fighting business accepted wisdom has been that
established fires of any size will move forward at the same pace, which will
vary with wind speed. But researchers from the CSIRO Division of Forestry have
found that wind speed is not the only factor. The width of the fire front also
is important. In experiments in open grasslands and woodlands in the Northern
Territory, researchers lit fires simultaneously at a single point and along
lines 100 metres and 200 metres wide. The widest fires always spread the
fastest. “If you had a sudden wind shift that increased the width of the fire,
it immediately went faster,” says Phil Cheney who was involved with the
experiments. The research confirms the value of attacking fires on the flank. By
narrowing the head of the fire, the spread can be kept below its potential rate
of spread. The findings also underscore the need for care when lighting lines of
fire along a break.