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Unit 9: Extreme Fire Behavior

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Terminology   ::   Tragedy Fires   ::   Predicting Behavior   ::   Safety Precautions   ::  Exercises

Exercise 1

Processes contributing to extreme fire behavior

Match the terms with the definitions

Term Definition
1. Convection column a. The thermally-produced, ascending column of gases, smoke, and debris produced by a fire. On multiple-headed fires, more than one column may be present.
2. Crown fire b. A spinning, moving column of ascending air, rising from a vortex and carrying aloft smoke, debris and flames. These range from a foot or two in diameter to small tornadoes in size and intensity.
3. Fire whirl c. A fire that advances from top to top of trees or shrubs more or less independently of a surface fire.
4. Flashover d. Sparks or embers (firebrands) carried by lower level winds starting new fires beyond the zone of direct ignition by the main fire. The range is usually less than one quarter mile.
5. Short range spotting e. Rapid combustion of preheated fuels and unburned gasses trapped at some distance form the main fire front.
6. Long range spotting f. Large glowing firebrands carried high into the convection column, falling out down wind beyond the main fire. Firebrands easily land one quarter mile or more down wind.

Exercise 2

Predicting extreme fire behavior

Using the following fire situations and any materials presented in this unit, describe the changes in weather and fire behavior that may be expected on each fire.

  1. A 40-acre fire is burning on top of a flat plateau area. The following wind changes have been observed and recorded during the past three hours: 0900 - SE 10 mph, 1000 - S 14 mph, 1100 - SW 18 mph. Fire activity has increased during the morning with increased wind speeds and temperatures. Today's forecast is calling for 80 degree temperatures and 22% relative humidity.
  2. A fire in the upper portion of a canyon has been burning actively throughout the night, but has cooled down some during the early morning. Many fires appear to be smoldering over a large area with smoke barely drifting over the ridgetop. Today's forecast is for warm and dry weather. Today's predicted probability of ignition is 70.
  3. A slow burning surface fire passed through a stand of young conifers, but very little torching occurred. Firelines are secure and mop-up is starting. A new forecast is predicting 35 mph winds, 75 degree temperatures, and 28% relative humidity by late afternoon. The calculated probability of ignition for this afternoon is 50.
  4. A timber fire is burning at a moderately slow rate through heavy surface fuels, but is now within two hundred yards of a second, larger fire. The current temperature is 90 degrees, relative humidity is 18%, surface wind 4 mph, and probability of ignition is 50.
  5. The convection column from your controlled slash burn has built up to over 3000 feet as a result of the intense heat. Flame lengths are over 10 feet. Surface winds have been light but shifting in direction. You notice the top of the column has been sheared off and is being carried to the east.

Exercise 3

Safety precautions on hazardous fires

For each of the fire situations and their expected changes in fire behavior and weather on Test 2 in this unit, prepare a list of safety precautions which should be given to firefighters on these fires.

  1. A 40-acre fire on top of a flat plateau.
  2. A fire in the upper portion of a canyon.
  3. A slow burning surface fire in young conifers.
  4. A timber fire burning near a second, larger fire.
  5. A controlled slash burn.

Copyright 2008, Michael Jenkins. Cite/attribute Resource . admin. (2005, November 10). Unit 9: Extreme Fire Behavior. 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_9__Extreme_Fire_Behavior_8.html. This work is licensed under a Creative Commons License Creative Commons License