Commonly used vocabulary on Fire Factor

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Understand the meaning of commonly used terms on Fire Factor.

Wildfire Model: The First Street Foundation Wildfire Model is a nationwide, probabilistic wildfire risk assessment that includes comprehensive current and potential future wildfire risk data at the property level. The outputs of this model are used to determine a property’s Fire Factor® based on the likelihood of wildfire impact or exposure to embers. In addition to current risk, the model provides an analysis of how the changing environment will impact a property's wildfire risk over the next 30 years. Use Risk Factor™ to find property-specific wildfire risk assessments for any U.S. address.

Vegetation and fuel sources: Anything that can burn is fuel for a fire. This includes various plants such as grass, shrubs, trees, and dead leaves. As this vegetation piles up, the chance of it burning, or fueling a fire increases. The type of fuel can have an impact on how intense a fire can get and how quickly it can spread. While dry grass can catch fire and spread quickly with high winds, extremely intense fires tend to build more in dry dense vegetation areas where treetop canopies can cast embers miles away. The First Street Foundation Wildfire Model uniquely considers properties, homes, and businesses within the Wildlands Urban Interface (WUI) to be a burnable fuel type.

Embers: Small pieces of material that remain after a fire and radiate a substantial amount of heat. This can include twigs, branches, pine cones, or wood shingles torn from burning roofs. They are light enough to be carried by the wind for long distances without being extinguished and can cause properties to ignite if a wildfire is nearby. 

Possible ignition locations: Geographic areas where wildfires are likely to ignite. Historic wildfire data is used to determine where fires are more likely. Nationally, nearly 9 out of 10 wildfires are caused by humans. The main causes of human-ignited wildfires are campfires left unattended, debris burning, hot ashes and BBQ coals, and vehicles or equipment that throw sparks.

Likelihood of wildfire impact: The likelihood that a wildfire will occur in a specific area. A property’s burn probability refers to the likelihood that it will ignite in the event a wildfire occurs in its area. 

Controlled burn: Also known as prescribed burning, it involves setting planned fires to maintain the health of a forest by reducing overgrown or dead vegetation which can become fuel leading to more intense fires.

Vulnerability: The degree to which a property will be damaged if a wildfire occurs. The severity of the damage depends on the likelihood a home will be in a wildfire, the intensity of that fire, and the characteristics such as the slope, exterior wall materials, age, roofing materials, etc, associated with that property.  

Defensible Space: The cleared area between the home and surrounding vegetation such as grass, trees, shrubs, or any wildland area that surrounds it. This cleared area protects the home from catching fire by distancing it from vegetation and other fuel sources. 

Roof type: The material the roof of a building is made out of such as concrete, slate, gravel and rock, tile, and wood. A key factor for structure survival indicates a structure's ability to prevent ember or flame penetration. Roofs are rated for fire resistance from Class A to Class C with Class A providing the most protection from fire.

Slope: The steepness of a property. It refers to the number of feet the land rises, or falls, across a property. The slope is an important indicator of the ability of fire to reach a building.

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