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Wildland Fire Fuels

Learn the basics of Wildland Fire and Urban Fire interface fuels.

Whether you are involved in a Wildland or Urban fire situation, being aware of the combustible fuels surrounding the area or in the fire's path is critical. Having this knowledge can help you make educated predictions on the fire's behavior and help you take effective actions that slow or suppress a moving fire.

When referring to ‘fuel’, this is anything that burns (combustible). Some fuels burn quickly while others burn long and slow. When looking at a fire triangle, we can see that fuel plays a very critical part. A fire must have all 3 components (Fuel, Oxygen, and Heat) in order to ignite.

Types of Forest Wildland Fuels

When listing wildfire fuel types, it's important to note that it comes in all forms from natural fuels to man-made fuels. For example, natural fuels include dry grass, pine needles, shrubbery, and trees whilst man-made fuels include, decks, patio furniture, fences, vehicles, homes, sheds, and more. Wildland fuel characteristics can vary greatly so knowing which fuels will ignite and which won't is important. This is broken into 2 main characteristics, surface fuel, and aerial fuel.

  • Surface Fuel: This is any combustible material on the surface such as pine needles and brush. There are 2 ways in which surface fuels are burnt, firstly as flash fuels which ignite and burn quickly when dry. Secondly, there are ladder fuels that allow the fire to climb to the top of higher vegetation.

  • Arial Fuels: This is any living or dead vegetation in the forest canopy which is above surface fuels. When a fire reaches this area it's known as a crown fire. These normally spread quickly along the tops of the vegetation by gusts of wind.

According to the National Fire Danger Rating System (NFDRS), there are 4 broad fuel types:

  • Light (grasses, forbs, sawgrasses, and tundra)

  • Medium (light brush and small trees)

  • Heavy (dense brush, timber, and hardwoods)

  • Slash (timber harvesting residue)

Wildfire Combustion Process

Combustion is a process by which a fire is started. This process can be broken into 3 actions:

  • Radiation - when heat energy is transferred through the air to ignite new fuels. No flames or sparks reach the new fuel but the heat energy is enough to ignite it. The fuel will reach 400-700 degrees F in order to ignite.

  • Convection - The most common way a wildfire spreads. This is when the flames, embers, or sparks reach a new fuel and ignite it.

  • Conduction - when the heat energy prolongs for a duration of time to burn 2 or more objects. This isn't as common in wildland fires since the materials found in forests are often poor conductors of heat. This is more common with urban structure fires where man-made fuels are present.

Managing Forest Fuels

The question is often asked, ‘What can be done to prevent wildfires in the future?’

The answer to this question is simple. Whilst some wildfires are started by mother nature (for example, lightning strikes), many are started by humans whether that is accidentally or deliberately. Between 1992 and 2013, humans started 84% of wildfire in the United States.

In order to limit the number of fires from natural forces, forest management has proven to be an effective method. On the other hand with fires started by humans, this simply requires greater education so people are aware of their actions and the consequences.

Forest management helps prevent the start and spread of wildland fire. The forest fuel management programs have the overriding focus to manage vegetation, restore ecosystems, reduce hazards, and maintain forest health. This includes forest thinning, controlled burns (prescribed burn), maintaining fire access roads, planting new trees, fuel reduction by removing slash, and so on. Whilst we are aware of what is needed, it's a challenge to execute it everywhere due to the vast mass of wildland that covers many parts of America. Since it's not possible to physically manage all of our forests, a focus is put on those that are closer to urban areas.

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