Fire Growth in Grassland Fuels

Abstract

The development of grass fires originating from both point and line ignitions and burning in both open grasslands and woodlands with a grassy understorey was studied using 487 periods of fire spread and associated fuel, weather and fire-shape observations. The largest fires travelled 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 content, the rate of forward spread was related to both the wind speed and the width of the head fire measured normal to the direction of fire travel. The head fire width required to achieve the potential quasi-steady rate of forward spread for the prevailing conditions increased with increasing wind speeds. These findings have important implications for relating small-scale field or laboratory measurements of fire spread to predictions of wildfire spread. The time taken to reach the potential quasi-steady rate of spread at any wind speed was highly variable. This time was strongly influenced by the frequency of changes in wind direction and the rate of development of a wide head fire.

Upscaling the estimation of surface-fire rate of spread in maritime pine (Pinus pinaster Ait.) forest

“…1 describes the spread rate of line-ignited, ~10-m wide fires propagating over a distance of ~10 m, which for radiation-driven fires under calm or weak winds is expected to mirror the spread rate of larger fires (Wotton et al 1999). Experimental burning programs in grassland, woodland and forest in Australia have shown that the potential rate of forward fire spread increases with head fire width (up to 50-300 m) until reaching an asymptote determined by wind speed (Cheney & Gould 1995, Gould et al 2003.…”

Instrumentation of wildland fire: Characterisation of a fire spreading through a Mediterranean shrub

“…The by [11]. Their experiments, which were conducted in grasslands, showed that a fire may developed in a step-wise pattern with increases rate of spread being associated with shifts in wind direction and with a wider effective head fire.…”

“…Hence, the most relevant data available in the literature for field experiments such as the fire front shape, curvature and width cannot be used to validate the simulation of such models. Cheney et al [10,11] have however identified fire front shape as a significant variable influencing fire spread, which must be taken into consideration when using experimental fires to validate models. Then, caution should be exercised when those models predict rate of spread since it highly depends on shape and size of the fire front under wind and slope conditions.…”

“…The need of accurate and relevant experimental data on fire spread and related phenomena, in order to check modelling hypothesis or to validate existing models is commonly felt among the scientific community. A lot of experimental fire have been conducted at the field scale by scientific and research teams [10,11,[14][15][16][17]. However, thermodynamics quantities allowing characterising fires in field experiments from a physical viewpoint were scarcely investigated by researchers [17,18].…”

A physical model for wildland fires

“…Case 10 -Cheney et al [27] performed some experiments with large grassland fires over several years in Australia. Assuming that each vegetal stratum was reasonably similar, we applied our models.…”