# Rate of spread which is the upper solid line is very

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Rate of spread, which is the upper solid line, is very much influenced by wind speed, which is the lower dashed line. The minimum rate of spread is predicted to occur about 0600 hours and is 0 chains per hour. The maximum rate of spread is predicted to occur about 1700 hours, and is 57 chains per hour. The dot-dashed line above represents flame length. It, too, is influenced by windspeed, but fuel moisture content has a very strong effect on flame length. Note the opposite curves of flame length on top and fuel moisture content below. The minimum flame length will occur about 0600 hours at 0 feet, and the maximum at 1700 hours at 9 feet. The points at which manual and mechanical forces are limited are also noted on the chart. Calculations for both flame length and rate of spread indicate 0 values at 0600. Does this mean that the fire will go out? Well, obviously not, but the fire will stop spreading and for the most part burn only in the larger fuels that have lower fuel moistures at this time of morning. The third output value, probability of ignition, is noted for certain hours only but can be estimated for any hour of the day. Note that the highest probability of ignition is 100 at 1700 hours. Probability of ignition figures can be used to help predict spotting. This chart can be valuable when a fire lasts several days, and especially when the weather pattern is persistent. It can be used to plan burnout operations and to position various control forces. Take a few moments to study the chart in more detail; then move on to exercise S on page 24. In this exercise, you will be interpreting information from the fire activity planning chart. This is a very important exercise, as it demonstrates_ the uses of various fire behavior input and output values that have been described in earlier units.

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When you have finished this exercise, check your answers; then review the entire unit and prepare yourself for the unit test.
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• Spring '04
• MIchealJenkins
• Combustion, fuel, Wildfire, fireline, firelines

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