The long and destructive 2000 wildland fire season ended, for the most part, with a spate of large fires in Georgia, Kentucky, Mississippi and Virginia with smaller fires were burning in several other states during late October into November. Photo by Robert M. Winston For a...
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Fuel moisture content is one of the most important factors in both ignition and how intensely a particular fuel will burn. As fuel moisture DECREASES, fire behavior INCREASES.
Fuel moisture will vary depending on the size and type of fuels; whether the fuels are live or dead; and on weather conditions. Moisture content can range from 2% to 30% in dead fuels, and 30% to over 300% in live fuels. (According to Bill Teie, author of the textbook, Fire Officer's Handbook on Wildland Firefighting, "Fresh new foliage, growing annual grasses, very green in color can hold 300% of fuel moisture. The cells are saturated with water.")
On the Cave Gulch Fire in the Helena National Forest in Montana, the fuel moisture in large-diameter live trees was measured in the single digits. Kiln-dried lumber is said to have a fuel moisture content of 12% to 15%. This dramatically low fuel moisture content of living trees gave an indicator of how serious the fire danger was in that part of Montana. I saw a large live pine tree that was cut down and ran my hand across the cut. I could feel no moisture and little or no tree sap was evident. Fuels in that forest were in severe stress from drought conditions and were drier than kiln-dried lumber.
Robert M. Winston
Robert M. Winston, a Firehouse® contributing editor, is a district fire chief in the Boston Fire Department with 31 years of structural and wildland fire experience. He is a Red Carded qualified Structure Protection Specialist and instructor for wildland/urban interface fire protection. Winston holds a degree in fire science and is a member of the National Fire Academy Alumni Association. He can be contacted via e-mail at firstname.lastname@example.org or at 781-834-9413.