Using this output plus the firefighters own

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ematical fire models, fire behavior output is obtained. Using this output, plus the firefighter's own experience with this fire and with other fires, enables the firefighter to make the best predictions or estimations. Figure 10 delineates the process of using a fire behavior prediction system. First, we must assess the fire situation and determine the inputs essential to using the system. There are four: The fuel moisture content, primarily of fine fuels; second, physical descriptions of the fuels, which can be categorized into fuel models; third, the steepness of slope, measured in percent; and finally, wind speed and direction at points of calculations. These values are processed by entry into fire behavior models, which are now available for use in several forms. Fire behavior outputs are received from the models and recorded as follows: Rate of spread in chains per hour, fireline intensity in BTUs/foot/second, and flame length in feet. Area and perimeter, and probability of ignition, can also be obtained from simple tables. The last steps in figure 10 are to interpret those outputs for various points on the fire perimeter; to estimate spotting and crowning potential, and size and fire perimeter location at various times; and finally, to use these estimations to determine control force requirements for the fire. A mathematical model can never account for all of the many variable factors that govern wildfire behavior. In addition, it is very difficult to exactly assess all these factors on a specific fire and to determine exact inputs for the model. However we can do a reasonably good job, and can expect model answers that give better judgment aids than ever before in this inexact science. Personal experience, interpretation and feedback are essential to the fire predictions modeling process. On page 17, we want to take a closer look at the mathematical fire behavior prediction model. The model processes fuel and environmental conditions to give expected fire behavior. Methods of estimating the input values and interpreting the output values will be covered throughout the course. In the final unit of this course, Unit XI--Predicting Fire Behavior, you will go through the entire process of assigning input values, using the model in the form of tables and graphs to obtain output values, and interpreting these output values. An entire unit will be devoted to each of the following basic input values: Fuel bed description, fuel moisture, slope, and wind speed. These units will cover both the general information required for a firefighter to assess the fire situation and also the specific information that is required as input to the model. In order to express the many interactions that occur during a forest fire in mathematical terms, certain simplifying assumptions have been made. Among these are the following: The model describes fire behavior only at the leading edge of a 'free burning fire; the fuels are assumed to be continuous, uniform and in a single layer contiguous to the ground; wind, slope, and fuel moisture content all are constant for the time period of the calculation; the fire is not spreading by spotting or crowning; and firewhirls and other fire-induced atmospheric disturbances are not occurring.
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