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Unit 11: Fire Behavior Prediction Systems

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Systems Pt. 1   ::  Worksheet & Field Guide  ::   Practice   ::   Systems Pt. 2   ::   Estimating   ::   Exercises

Using the Worksheet and Field Guide

To assist you in performing the necessary calculations, a worksheet is provided above. The worksheet for predicting fire behavior has 36 lines for entries. Two columns allow two sets of calculations on the same sheet. The first portion of the worksheet requires site and other input data needed for calculations. The second portion takes you through the fire behavior calculations and gives you the output values. References or instructions are made to field guide sections, tables, calculations, or repeat entries. The sequence of entries was designed to permit forward progression through the field guide when completing the worksheet. One column of the worksheet is filled out to provide an example of entries to be made. Refer to the example entries on this page as we go through the next portions of the workbook.

Step 1: Determine Primary Input Values

  1. See units 1– 10 and/or field guide sections 1 – 5. (Enter values on worksheet lines 1 – 14, 16)

Step 2: Determine Effective Windspeed Factor

  1. Enter fuel model and midflame windspeed into table. Read wind factor at intersection. (Worksheet lines 15 and 18)
  2. Enter fuel model and slope percent into table. Read slope factor at intersection. (Worksheet line 17)
  3. Calculate the effective windspeed factor. (Worksheet line 19)
    Effective windspeed factor = wind factor + slope factor

Step 3: Determine Fire Behavior Values for No Wind or Slope

  1. Select the proper fire behavior tables for fuel model.
  2. Enter dead fuel moisture and live fuel moisture into table. Read rate of spread in chains/hour at intersection.
  3. Enter dead fuel moisture and live fuel moisture into table. Read fireline intensity in BTUs/Ft/S at intersection.

Step 4: Calculate Adjusted Fire Behavior Values

  1.  
  2. Adjusted rate of spread = ROS x (WF + SF + 1)
      = 2.6 x (1.0 + 10 + 1)
      = 2.6 x 12 = 31.2 chains/hour

    (Worksheet lines 22 through 24)

  3.  
  4. Adjusted fireline intensity = FI x (WF + SF + 1)
      = 26 x (1.0 + 10 + 1)
      = 26 x 12 = 312 BTUs/Ft/S

    (Worksheet lines 25 through 27)

Step 5: Determine Other Fire Behavior Values

  1. Enter adjusted fireline intensity into table. Read flame length to the closest foot. (Worksheet line 28)
  2. Enter percent shading, temperature, and dead fuel moisture into table. Read percent probability of ignition at intersection. (Worksheet line 29)

Step 6: Determine Fire Size For Point Source Fire

  1. Calculate forward spread distance. (Worksheet lines 30 - 32)
  2. Spread distance = adjusted rate of spread x projection time
      = 31.2 chains/hour x 2 hours = 62.4 chains
  3. Enter fuel model and the effective winspeed factor into table. Read effective windspeed at the intersection. Interpolate as necessary. (Worksheet line 34)
  4. Enter spread distance and effective windspeed into table. Read area in acres at intersection. Interpolate as necessary. (Worksheet line 35)
  5. Enter spread distance and effective windspeed into table; read perimeter in chains at intersection. Interpolate as necessary. (Worksheet line 36)

Copyright 2008, by the Contributing Authors. Cite/attribute Resource . admin. (2005, November 16). Unit 11: Fire Behavior Prediction Systems. Retrieved January 07, 2011, from Free Online Course Materials — USU OpenCourseWare Web site: http://ocw.usu.edu/Forest__Range__and_Wildlife_Sciences/Wildland_Fire_Management_and_Planning/Unit_11__Fire_Behavior_Prediction_Systems_3.html. This work is licensed under a Creative Commons License Creative Commons License