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Unit 5: Fuel Moisture

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Natural Fuels   ::   Environmental Factors   ::   Timelag   ::   Dead Fuels   ::   Ignition & Combustion   ::  Exercises

Exercise 1

Environmental factors affecting drying of dead fuels

If fuels are saturated during a heavy rainfall, the rate at which they lose their moisture content depends on several environmental factors. How do each of these factors determine the rate of drying in fuels?
Match the factor with its corresponding effect.

Factor Effect
1. Relative humidity a. Air and fuel temperatures are raised, thus reducing relative humidity of the air and increasing the evaporation rate.
2. Wind b. Equilibrium moisture content can be reached faster by air circulating and carrying off moisture from the fuels.
3. Compactness c. Air circulation around the fuels dries them more rapidly when the fuel particles are loosely arranged.
4. Exposure to sun d. The greater the surface area to volume ratio, the faster the exchange of moisture between air and fuels.
5. Size and shape e. The lower the water vapor pressure of the air, the faster the drying process.
6. Height above ground f. Air temperature at or near the surface can be considerably higher than at 10 feet above due to air circulation and vegetative cover.

Exercise 2

Probability of ignition and moisture of extinction

Answer the following questions:

Question 1 : A change in which variable will cause the greatest change in probability of ignition?

  1. Fuel moisture
  2. Fuel temperature

Question 2 : Can a fire continue to spread in short grass (fuel model 1) when the dead fuel moisture content reaches 15%? Explain.

Question 3 : If live fuels are present within a fuel complex, describe the conditions under which they will be consumed by fire.

Copyright 2008, Michael Jenkins. Cite/attribute Resource . admin. (2005, November 07). Unit 5: Fuel Moisture. 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