Our study analyzed the fire (pyric) environment (vegetation or fuels, meteorology, topography, suppression time) of the large forest fires (greater than 1,000 ha) that occurred in Greece during 1990-2003. Statistical analysis of 84 large fires (representing 0.37% of the total number of fires) revealed that they usually spread under moderately to low relative humidity (21-40%) in the presence of strong to moderate northern winds. Approximately one-fourth of all large fires occur during heat waves (i.e. air temperature higher than 30℃ and air relative humidity 21-40%). Large fires occur as both surface and crown fires and usually spread in dense vegetation with a continuous duff layer. Successful containment requires a combination of both ground and aerial fire suppression forces. Although large forest fires usually have short initial attack time (less than 30 minutes), the suppression time is variable. The main differences between the large fires and all the others lie in the prevailing wind speed (strong for large fires, moderate for smaller fires) and the mode of propagation (mixed surface and crown spread for large fires, only surface spread for smaller fires). However, no unique characteristics of large fires were found that would distinguish them from smaller fires. This supports the hypothesis that any fire may become large under certain circumstances. The results of this study could be useful in forest fire danger rating and presuppression alertness in the context of judicial fire prevention and suppression planning.
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