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Unit 1: The Changing Fire Environment

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Radiation

Radiation : the transmission of heat energy by rays passing from a heat source to an absorbing material.

Radiant heat transfer

Radiant heat decreases inversely with the square of the distance from a point source. For example, if 100 heat units are received at 1 foot ahead of the source, only 25 heat units will be received at 2 feet. If we double the distance from 2 to 4 feet, the heat units received are reduced to one-sixteenth that of the 1 foot level, or 6.25. At 10 feet, the heat units have been reduced to only one one-hundredth of the radiated value at 1 foot. You can see how rapidly radiant heat drops off with distance.
It should be emphasized that, in fireline work, a point source is rarely encountered. Here, the source is better described as a wall, and radiant energy from it obeys somewhat more complicated physical laws. In this course, however, we will deal only with the basic point source relationships.

Radiant heat is increased when:

  • Fuels are upslope from fire
    Fuel upslope from fire
  • Flames are bent by the wind
    Flames bent by the wind
  • Fuels are concentrated
    Concentrated fuels
Copyright 2008, by the Contributing Authors. Cite/attribute Resource . admin. (2005, September 27). Unit 1: The Changing Fire Environment. 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_1__The_Changing_Fire_Environment_4.html. This work is licensed under a Creative Commons License Creative Commons License