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The objective of the study was the development of an empirical model to predict when a surface fire may ignite the forest crown and become a crown fire. Through an extensive literature review candidate variables for inclusion in the model were identified. The importance of these variables and their relationships were examined experimentally. The effect of water stress on ignitability of tree branches was examined by exposing branches of water stressed and unstressed seedlings to a hot air convection column (513 °C) and measuring the time required for ignition. The data did not provide column air temperature and live needle moisture content on ignitability of tree branches was quantified by exposing branches of three conifer species to a hot air convection column, at temperatures between 400 and 640 °C, and measuring time-to-ignition. Three multiple regression equations for the prediction of time-to-ignition with temperature and moisture as the independent variables were developed. Experimental burns in a wind tunnel provided temperature profiles obtained by thermocouples at four different heights above the fuel beds. A series of regression equations were developed to predict time-temperature profiles at any height above moving fires. A crown fire initiation model was developed based on the equations from the last two experiments. It is based on calculation of an ignition score. The threshold value of the score above which ignition is predicted was determined experimentally through additional burns in the wind tunnel and in the field, by exposing tree branches and small trees to moving fires, obtaining temperature profiles at their bottom, and calculating the corresponding ignition score. © by the Society of American Foresters. Abstract reproduced by permission.
Cataloging Information
- air temperature
- bibliographies
- convection
- crown fires
- ignition
- moisture
- rate of spread
- seedlings
- temperature
- trees
- water
- wilderness fire management
- wildfires
- wind
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