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Unit 2: Fuels Classification

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Distribution & Behavior   ::   Characteristics   ::   Timelag & Life Cycle   ::  Availability  ::   Models   ::   Exercises

Fuel Availability

Available Fuels are those that will ignite and support combustion at the flaming front under specific burning conditions at a given time.

Consumption of Fuels by Fire


Do all the fuels burn during the passage of a fire? The answer is no. Ordinarily only a portion of them burn, depending on factors of fuels availability. In a cured grass stand, we might get nearly 100 percent of the fuels consumed by fire. These indeed have a very high degree of availability. A stand of brush is seldom completely burned, but perhaps 5 to 95 percent is consumed. The stumps, logs, and larger limbs of logging slash rarely are totally burned; thus, consumption in slash might be 10 to 70 percent. In timber, standing trees are only partially burned, and overall fire consumption might be 5 to 25 percent.


We'll discuss some other aspects of fuels availability. A major concern of the firefighter is; will fuels ignite if subjected to heat or burning firebrands? For example, he needs to be able to recognize fuel conditions that are receptive to spotting.
Fuels that ignite most readily from embers (spotting) are:

  1. Rotten wood in snags or on ground
  2. Dead foliage
  3. Moss and lichens in trees
  4. Slash compacted in a tight arrangement
  5. Needle or leaf accumulations on ground
  6. Cured grasses

Crown Fires

Before we leave fuels availability, we should examine the fuel conditions that influence the probability and character of crown fires.
Fuel conditions which influence the probability and character of crown fires are:

  1. Vertical positioning of fuels above surface
  2. Character and availability of surface fuels
  3. Presence of fine dry aerial fuels
  4. Continuity of aerial or canopy fuels

Copyright 2008, by the Contributing Authors. Cite/attribute Resource . admin. (2005, October 20). Unit 2: Fuels Classification. Retrieved January 07, 2011, from Free Online Course Materials — USU OpenCourseWare Web site: This work is licensed under a Creative Commons License Creative Commons License