One-Hour Fuel (dry weeds and grass)

“One-hour fuel” is the name that fire prevention workers have termed dry weeds and grass. In West Texas—where there is plenty of dry grass, for example—the grass can burn as quickly as one hour after it rains. Many areas of West Texas are fire hazards, especially during a drought.
 
The term “one-hour fuel” has been used since at least 2002.
 
     
California Forest Stewardship Program
What is “Fire Hazard”?
David M. Soho
Modified: 7/29/02
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Fuel Condition
Fuel condition is a combination of fuel size, quantity, arrangement, and dead:live ratio. Fuel characteristics help determine how a wildfire burns. The fuel condition determined for an area makes up fuel hazard which is not to be confused with fire risk.
 
Fuel size is measured by the number of hours it takes the fuel to reach equilibrium with the relative humidity in the air. One hour fuels dampen or dry quickly. Dead grass is a one hour fuel. Very small twigs and branches are examples of 10-hour fuels. Branches between 1/4 and 3” in diameter are usually considered 100-hour fuels. Larger branches, logs, and stumps over 3” in diameter are 1000-hour fuels because it takes so long for them to dry out each summer.
 
Sierra Sun (Truckee, CA)
Season’s a changin’, so are fire hazards 
Friday, April 2, 2004
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Another problem we will encounter is directly related to those pine needles that are showing. Pine needles on the ground are what we call a “one-hour fuel.” What that means is they are dead and while sitting around outside they will always try to reach equilibrium with the environment around them, primarily the moisture in the air. If the air is very dry like the last two weeks, they will burn. They will reach equilibrium with the air in one hour, hence the term one-hour fuel.
 
17 March 2006, Gettysburg (PA) Times, “Pennsylvania Wildland Fire Prevention week set for March 19.25,” pg. A11, col. 3:
Weeds and grass are considered a one-hour fuel. What that means is that if it is sunny outside, the material can burn one-hour after it rains.
     
KUNM-FM (Albuquerque, NM)
Santa Fe National Forest Moisture Levels: “Bone Dry”
Airdate: Wed., 21 Jun. 2006
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Williams: Indeed, as in the previous 43 years, Velasco, a fire behavior specialist, will take these samples back to his office, where he now bakes them in a little oven on his desk. The goal is to determine how much water content there is in the wood. Researchers have developed an entire measurement scale based on the size of the wood. The straw and twigs are “one-hour fuel”, meaning it takes one hour to remove sixty-six percent of the moisture from these little pieces:
 
Clark Fork Chronicle (Superior, MT)
Wednesday, August 22 2007 @ 12:35 PM MDT
Different fuel types pose different dangers to firefighters
by Glenda Wallace
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Hartman refers to grass as one-hour fuel. “In one hour, they can burn after a significant rain. Right now, we’ve had rain in the last couple days, but it’s going to kick-up as soon as the first sun gets to those one-hour fuels. Now the big logs, the 100-hour fuels…first of all, they dry out the slowest and burn the longest. The rain didn’t even dampen those fuels.”
 
Hartman hails from the Midwest and knows of what she speaks. Several years ago, grass fires in Oklahoma and Texas destroyed homes, even when made out of brick. Firewise principles teach that it’s “the little things” that destroy homes, such as debris on roofs and/or in nooks and crannies of decks and attached outbuildings—any place where a spark or ember could land and linger.
   
Mount Pleasant (TX) Daily Tribune
Last modified: Saturday, December 29, 2007 3:02 PM CST
Moisture prevented burn ban this year
By CASEY BUECHEL - Tribune Staff Writer
In 2006, with burn bans in place, Mount Pleasant and the county’s volunteer fire departments fought 185 brush fires. In 2007, with no burn bans in effect, that number dropped to 80 brush fires as of Friday, Dec. 28.
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McRae explained that dead grass, like that found in drought conditions or even in winter, is a “one hour fuel.”
 
“If it rains, and then the sun comes out and the wind increases, within one hour, that grass can burn,” he said.
   
Google Books
Trees, Truffles, and Beasts:
How Forests Function
By Chris Maser, Andrew W. Claridge and James M. Trappe
Published by Rutgers University Press
2008
Pg. 121:
(A one-hour fuel is a twig small enough to dry out to be combustible within an hour, while a 10-hour fuel is a piece of wood that requires ten hours to become dry enough to burn. The scale of combustibility then goes to 100-hour fuelds, 1,000-hour fuels, and 10,000-hour fuels, which are the trunks of huge fallen trees or cut logs.)     
   
KWES NewsWest 9 (Midland, Odessa, Big Spring, TX)
Wildfire Danger Remains High Across The Basin
15 March 2009
Staff Report
NewsWest 9
PERMIAN BASIN - Rain over the last few days didn’t drown out the fire danger.
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“So people need to be aware that the fire danger and drought are still here. And it’s not going to be over with for a while, I am afraid,” Sandra Taylor with the Texas Forest Service, said.
 
The grass here in West Texas is called one hour fuel, because even an hour after the wind blows a spark, it can cause a raging fire.