Burning Characteristics of Individual Douglas-Fir Trees in the Wildland/Urban Interface Public
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The Wildland/Urban Interface, in which homes are intermingled with forested areas, presents unique challenges to fire protection and fire prediction, owing to the different fuel loads, conditions, and terrain. Computer models that predict fire spread through such an area require data for multiple scales, from crown fire spread to the heat release rates and ignition conditions for individual trees, as well as an understanding of fire behavior and spread. This discussion investigates a means by which fire behavior for Douglas-fir trees can be determined from quantifiable characteristics, such as height and moisture content. Mass, flame height, peak heat release rate, and total energy can be estimated from these simple measurements. A time scale of 60 seconds, combined with a peak heat release rate estimated from tree size characteristics, provides an approximation of total energy that is within 11% of measured values. Pre-heating of trees with a low (2.5 kW/m2) radiant heat flux did not have a noticeable impact on the resulting heat release rate. In addition, fire spread between trees was highly dependent on the presence of ambient wind; in the absence of wind or wind-borne embers, the trees were very resistant to ignition even when in close proximity (3 spacing). With the addition of wind, the fire would spread, although the heat release rates were dramatically reduced for trees of sufficiently high moisture content (< 70%).
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