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Unit 9: Extreme Fire Behavior

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

Objectives:

Upon completion of this unit you will be expected to:

  • Give the four major common denominators of fire behavior on tragedy fires.
  • Describe how both spotting and crowning potentials are determined on a fire.
  • Give four factors that contribute most to long range spotting.
  • Explain the causes and effects of dust devils and fire whirls.
  • Give four factors which are most responsible for blowup fires.
  • Given certain environmental conditions on a fire, determine how they could contribute to erratic or extreme fire behavior.
  • Given several fireline situations which are potentially dangerous, describe safety precautions which should be taken by personnel.

Fire Behavior Terminology

Extreme Fire Behavior : It implies a level of wildfire behavior that ordinarily precludes methods of direct attack, predictability is difficult because such fires often exercise some degree of influence on their environment, behaving erratically, sometimes dangerously.

Characteristics of Extreme Fire Behavior

Erratic, severe, or extreme fire behavior usually has one or more of the following involved:

  1. Very high to extreme rates of spread.
  2. Prolific crowning and/or spotting.
  3. Presence of fire whirls.
  4. A tall, well developed convection column.

The terms erratic or severe fire behavior might be preferred by some to describe the levels of fire activity that will be discussed in this unit. To others, the terms are somewhat interchangeable. In any case, we are concerned with levels of fire activity that present serious control problems and can threaten lives and property.

Common Names for Extreme Fire Behavior

The most extreme fire situations are usually described as being one of the following:

  1. Blowup : A sudden increase in fire intensity or rate of spread sufficient to preclude direct control or to upset existing control plans. Often accompanied by violent convection and may have other characteristics of a fire storm.
  2. The term blowup is most used by firefighters to describe extreme fire conditions on any size wildfire. Even relatively small fires can reach the blowup stage when they suddenly reach intensity levels that defy all control actions and pose a threat to life and property.

  3. Fire storm : Violent convection caused by a large, continuous area of intense fire. Often characterized by destructive, very strong surface indrafts near and beyond the perimeter, and sometimes by tornado-like whirls.
  4. Fire storms and conflagration fires are usually associated with mass fire, which denotes both large size and high rates of energy release. Fire storms have occurred during wartime when many ignitions over a wide area quickly coalesce into a single fire. Fire storms can develop under light wind conditions but produce strong indrafts as the many fires burn together.

  5. Conflagration : A large, raging, destructive fire. Often used to denote such a fire with a moving front as distinguished from a fire storm.
  6. Conflagration fires have definite moving "heads" or fronts. They are strongly affected by wind and topography; thus the depth of the intense burning area is usually relatively narrow.

 

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_1.html. This work is licensed under a Creative Commons License Creative Commons License