How is my Fire Factor calculated?

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Learn how property-level fire risk is determined.

The First Street Foundation National Wildfire Model is a first-of-its-kind, nationwide, behavioral wildfire model that shows a specific location’s probabilistic risk of wildfire based on the vegetation, topography, and fire weather in the surrounding area. It builds off of decades of peer-reviewed research and forecasts how wildfire risks will change over time due to changes in the environment. Use Risk Factor™ to find property-specific wildfire risk assessments for any U.S. address.

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Property Fire Factors 

A property's Fire Factor® is an indicator of its comprehensive, aggregate thirty-year risk of exposure to wildfires. Properties are assigned a risk score, ranging from 1 (minimal risk) to 10 (extreme risk) based on the likelihood of direct wildfire impact or indirect exposure to embers from nearby wildfires.  Fire Factor also takes into account how wildfire risks will change over time with a hotter and drier climate over the next 30 years, which means even a property that hasn’t experienced wildfire in the recent past could still face risk today and into the future. Properties with higher Fire Factors are more likely to burn, meaning there is a higher likelihood that they will ignite in the event a wildfire occurs in that area.

Exposure to wildfires

A property’s Fire Factor reflects its exposure to wildfire, including both direct flames and embers blown by the wind. A home located on a property where a wildfire is likely to occur is exposed to wildfire risk. 

Direct exposure

Homes may be located in an area that is directly exposed to wildfire from nearby vegetation and fuel sources. For example, a home located adjacent to a densely wooded forest could experience impact from flames if that forest burns. Anything that can burn is fuel for a fire. This includes various plants such as grass, shrubs, trees, fallen trees, and dead leaves. As this vegetation piles up, the chance of it burning, or fueling a fire, increases. The type of fuel source impacts how intense a fire is and how quickly it can spread under different weather conditions. 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 ignite and cast embers several miles away.


The First Street Wildfire Model incorporates wildfire fuels, such as trees and other vegetation, based on the U.S. Forest Service’s national fuels dataset. Additionally, the First Street Foundation Wildfire Model uniquely considers properties, homes, and businesses within the Wildlands Urban Interface (WUI) to be a burnable fuel type. The WUI is an area of transition, where houses and wildland vegetation meets or intermingle and where wildfires are most pronounced - typically suburban areas that have been extended into and surrounded by wildlands.

The location and intensity of historic fires are used to determine the most likely potential ignition locations for future wildfires. The model also considers a wide variety of weather patterns that impact fuels by making them hotter and drier, as well as the weather conditions that help spread fires further such as high winds and low humidities.

Indirect exposure

Some homes are located in an area indirectly exposed to wildfire from embers. Embers are small pieces of material that remain after a fire and radiate a substantial amount of heat and are light enough to be carried by the wind for long distances without being extinguished. A property in an urban area with little vegetation can be indirectly exposed to distant wildfire from embers carried aloft by the wind.

Weather data from NOAA is used to determine where and how far wildfire embers will spread and when combined with climate forecasts,  considers how future weather conditions will change with a hotter and drier climate over the next 30 years.  

Fire Factor scores

In order to provide the most accurate current and future wildfire risk assessments, the Model simulates over 100 million wildfires each for the 2022 and 2052 simulations,  to see which of these wildfires grow and become damaging. It outputs over 8 million significant fires per simulation that are then used to calculate risk. Publicly available and 3rd party data is used to identify property boundaries and buildings. The building’s location is then used to determine the likelihood of the home being in a wildfire based on how many times the 8 million simulated fires reached the home

Properties with no risk of being in a wildfire based on our fire simulations and with no modeled exposure to embers are considered to have minimal risk or a Fire Factor of 1. The probability of a home being in a wildfire or its exposure to embers is used to determine the boundaries for each level of fire risk. These boundaries produce a set of rules that can be used to understand why one property may have a Fire Factor of 4 while another has a Fire Factor of 7. 

  • Fire Factors of 2 represent properties located in areas indirectly exposed to wildfires from embers or in an area with less than a 1% chance of burning over 30 years
  • Fire Factors of 3 represent properties with a 1-3% chance of burning over 30 years
  • Fire Factors of 4 represent properties with a 3-6% chance of burning over 30 years
  • Fire Factors of 5 represent properties with a 6-9% chance of burning over 30 years
  • Fire Factors of 6 represent properties with a 9-14% chance of burning over 30 years
  • Fire Factors of 7 represent properties with a 14-19% chance of burning over 30 years
  • Fire Factors of 8 represent properties with a 19-26% chance of burning over 30 years
  • Fire Factors of 9 represent properties with a 26-36% chance of burning over 30 years
  • Fire Factors of 10 represent properties with more than a 36% chance of burning over 30 years

How is my Fire Factor calculated - fire factor scoring system replacement screenshot.png

Like getting bloodwork to determine your risk for certain illnesses, Fire Factor should be viewed as a diagnostic tool that can help alert homeowners or buyers to the potential wildfire risk facing a property over the life of a 30-year mortgage. But just because something could happen, doesn’t mean that it will. 

Although unlikely, a home with an Extreme Fire Factor may never experience a wildfire, and a home with a Minimal Fire Factor could. Having that information allows you to then consult a specialist or local fire station, who can help you learn more, evaluate your risk, and help you find ways to protect yourself.

Ensuring scientific accuracy

The creation of the peer-reviewed First Street Foundation Wildfire Model required an unprecedented partnership with top climate scientists and modelers from leading organizations along with top data scientists and technologists to ensure the data is accessible, accurate, and actionable. 

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