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Title: Deliverable 2.3-4 Fire behaviour in several fuel types: final achievements
Subject: [FIRE PARADOX Deliverables, Fire Paradox Modules, Module 2 - Physical mechanisms, WP2.3 - Policies and practices assessment]
Description: Fire experiments have been conducted in different surface fuels, both in laboratory and in the field. These experiments aim at understanding fire behaviour and producing data for testing of fire behaviour models. Indoor laboratory fires were carried out in three different pine needle fuel beds (Pinus pinaster, P. halepensis and P. pinea) in a low speed wind tunnel. Variations of rate of spread, flame height and flame angle with wind velocity, as well as profiles of temperatures with time, are analysed in these tests. Correlations between these variables are found to be close to earlier published correlations and the observed behaviour is interpreted as a result of a balance between wind forces and buoyant forces. Outdoor laboratory fires were carried out in a wind tunnel in a shrubland fuel, to study the vertical propagation of fire. Indeed it is important to determine which variables condition capability of a shrubland to sustain a high fire intensity burning the whole surface fuel layer. Fires were conducted with and with no pine dead needle fuel bed underneath the shrub layer and with and with no discontinuity between the needle layer and the shrub layer above. Under the wind conditions of these experiments (no wind and weak wind) fire does not propagate if there is no needle layer below the shrub layer. When there is a needle layer, the success of vertical propagation to the shrub layer was found to correlate with the maximum temperature measured in the lower part of the shrub layer. It is unclear however whether the temperature level determines the vertical propagation or is a consequence of this vertical propagation. Other variables, namely fuel discontinuity, wind or fuel moisture content, are not found to be explanatory of the vertical propagation in the statistical analysis. Four field experimental fires were conducted in 16 m diameter hexagonal plots selected in a uniform shrubland fuel type (Quercus coccifera garrigue) under 4-6 m/s wind speeds, in the South of France. In addition to rate of spread and fuel consumption, temperatures were measured within the plots at the top of the vegetation layer and radiant heat fluxes were measured outside the plots. Analysis of these data suggests that convective heating plays a dominant role in the propagation of these fires. Although two fires were conducted under low shrub moisture content and two under high shrub moisture content, the effect of fuel moisture on the rate of spread is found to be small with respect to the effect of fuel moisture on the heat of fuel ignition. Two hypothesis are proposed to explain this result. Two sets of six fires each in 30 x 30 m plots were conducted in two grassland fuel types in the Chaco region in Argentina. Fire spread about 30 % faster in the first grassland type, while wind speed was two times lower and fuel bulk density was two times higher. This effect is attributed to the fine fuel load, which was more than two times higher in the first grassland type. This result is an addition to the contradictory results on fuel load effect existing in the literature. It is also suggested that differences in plant architecture could explain the rate of spread variation.
Language: English
Creator: INRA
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Audience: public
Download: Deliverable 2.3-4 Fire behaviour in several fuel types: final achievements