FIRE GROWTH IN GRASSLAND FUELS

The development of grass fires originating from both point and line ig nitions and burning in both open grasslands and woodlands with a grass y understorey was studied using 487 periods of fire spread and associa ted fuel, weather and fire-shape observations. The largest fires trave lled more than 1000 m from the origin and the fastest 2-minute spread rate was over 2 m s(-1). Given continuous fuel of uniform moisture con tent, the rate of forward spread was related to both the wind speed an d the width of the head fire measured normal to the direction of fire travel. The head fire width required to achieve the potential quasi-st eady rate of forward spread for the prevailing conditions increased wi th increasing wind speeds. These findings have important implications for relating small-scale field or laboratory measurements of fire spre ad to predictions of wildfire spread. The time taken to reach the pote ntial quasi-steady rate of spread at any wind speed was highly variabl e. This time was strongly influenced by the frequency of changes in wi nd direction and the rate of development of a wide head fire.