Classifications Of Fuels
Fuel is basically any potentially burnable material. When considering the Wildland Urban Interface, the fuels that first come to mind are trees and the materials that make up the home. However, there are a great deal of potential fuels, both in the wilderness and in urban areas, that can feed a fire. We will go into both these categories in this introductory section.
Grass, shrubs, pine needles, fallen branches and leaf litter-- all of these are examples of wildland "surface fuels"; surface fuels are burnable materials found at lower, ground levels. Although the fires sustained by surface fuels may be of a lower intensity than full-blown canopy/crown fires, they often serve as a precursor for such higher intensity fires by burning into ladder fuels and extending into forest canopies. We will cover ladder fuels next.
Ladder fuels include tall brush, low branches, and other mid-level fuels that can carry fire from surface fuels up into the tops of trees (the crowns or canopies of trees, which we will cover next).
Crown fuels include the flammable tree tops and tall shrubs. Once a wildfire becomes a crown fire, it spreads rapidly and reaches extreme intensity. During a high-intensity wildfire, homes are far more likely to be threatened by firebrands (burning embers) that can be carried more than a mile by strong winds and start separate fires that lead right up to the home.
In the Urban Interface, homes are probably the most obvious fuel source. However, there are a number of other urban fuels that are often found in the wildland urban interface. For example, any wooden structure around the home, such as decking or wooden fencing, is a potential combustible. Wooden roofing, especially untreated shake roofing, is extremely prone to combustion.
Woodpiles, especially uncovered woodpiles within 30 feet of the home, are another extreme fire risk (in a wildfire scenario). Dry lawns, fire-prone landscaping vegetation (sagebrush, juniper), and flammable outdoor furniture are all examples of urban fuels that could seriously jeopardize the safety of your home (and your own personal safety).
Automobiles, lawnmowers, and fuel sheds are also examples of urban fuels found around the home. Extreme heat/flames can burn cars and ignite their fuel reservoirs. Open fuel sheds are extremely susceptible to fire brands/embers during a wildire. Fully enclose fuel storage areas, and always properly store fuel-soaked rags (in a sealed container-- or dispose of them at the proper disposal site.)
Now that you know the fuel elements that can endanger your home during a fire event, it's time to discuss some fuel mitigation strategies. The primary defense against wildland urban interface fires is creating Defensible Space with which to separate your dwelling from flames (and also provides space for firefighters to operate safely within). Click this "Defensible Space" link to learn more about what you can do to protect yourself.