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Flanking and Backing Fire Behavior

The tables and nomographs produce good estimates of head fire behavior.

This nomograph uses effective windspeed to produce adjustment factors for both spread rate and flame length that can be applied to the head fire behavior outputs.

Backing and Flanking Nomograph

Procedure:

  1. Begin with the EWS at the base of the right-hand chart, draw vertical line to intersect desired spread direction and the axis at top to read the length to breadth ratio.
  2. Draw horizontal line from intersection at desired spread direction into and across the left-hand chart to intersect the left axis. Read the fraction from left axis and apply it to the headfire ROS to obtain the spread rate in the assumed direction.
  3. Draw vertical line down from where horizontal line intersected curve in left hand chart to bottom axis.  Read the fraction from this bottom axis and apply it to the headfire flame length estimate to obtain the flame length in the spread direction assumed.
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