Risk Assessment

Risk assessment

Risk is defined as the likelihood that a particular home or community will experience a fire in the foreseeable future (Long and Randall 2004). The assessment of risk helps establish priorities for: 1) guiding community development, 2) assisting landowners with their landscaping and home design, 3) planning fuel management, and 4) allocating fire suppression resources.

Regional and state level risk assessments

Remove Excess Fuels from Roadsides

The Southern Wildfire Risk Assessment (SWRA) is a regional effort commissioned by the Southern Group of State Foresters that allows agencies and organizations to assess the overall potential for wildfire and its associated problems (Southern Group of State Foresters 1998). The SWRA establishes a process to assess fire hazards and the values to be protected. The assessment provides managers with a strategic view of the region to improve public safety and protect homeowners from property losses. The SWRA uses Geographical Information Systems (GIS) to create data layers that are analyzed to classify and identify areas of relative danger from wildfire risk. The GIS layers include: population density, historic fire occurrence, values at risk, topography, fuel types, available suppression resources and response times, and structural density (Space Imaging 2003).

The Florida Division of Forestry’s Fire Risk Assessment System (FRAS) completed in 2003 is an information system that assists fire managers in prioritizing mitigation projects throughout the state and also functions as a planning tool for local fuel reduction efforts (McLellan and Brenner 2003). FRAS is composed of the following GIS layers: wildfire susceptibility, population density, land value, and fire response accessibility. These factors are weighed, ranked, and combined to develop levels of concern. FRAS is flexible to allow the adjustment of input values and can be run iteratively to produce new estimates of risk.

The Virginia Department of Forestry (VDOF) developed a similar GIS model that incorporates maps of wildfire risk with areas of moderate to high population, and forest cover. The wildfire risk map input layers include: slope, aspect, landcover, distance to railroads, distance to roads, population density, and historical fire occurrence. Synthesizing the spatial relationship of these and other features allows VDOF to concentrate their prevention education, resource allocation, and emergency response efforts where fire poses the greatest risk.

Risk assessment for communities

The most efficient and cost-effective time to make the preparations to protect the home from fire is during the initial development of a wildland property. Florida’s DOF distributes a helpful guide for home protection to developers and fire departments that suggests how to plan access routes, utilities and fuelbreak zones.

Standards and rating systems for the different factors that influence community susceptibility to a fire have been developed by the National Fire Protection Association (NFPA), the Firewise program, the U.S. Department of the Interior, the International Fire Code Institute, and a number of different states. Many community risk assessments developed by individual states or local governments follow the NFPA standards or have modified them to fit particular situations.

NFPA 1144 Standard for Protection of Life and Property from Wildfire was developed to provide minimum planning, construction, maintenance, fire education, and management elements for the protection of life, property, and other values that could be threatened by wildfire (NFPA 2002). NFPA 1144 recommends a numerical rating system to define the relative contributions to hazard severity of the following factors, listed by the possible score each individual factor can contribute to the severity rating with 0 being the lowest severity:

• 0 - 25 points each: roofing materials, vegetation (types and defensible space)

• 0 - 10 points each: slope, water sources, siding, and deck construction

• 0 - 7 points each: subdivision design (ingress, road width, grade, turnarounds, lot size, signs)

• 0 - 5 points each: special topographical and weather features; utility placement

Risk assessment for individual homes

Whether or not a wildfire ignites a home depends on the length of time it is exposed to high heat or firebrands, direct flames, and the home’s properties as a fuel (Long and Randall 2004). Firebrands that land on a roof, attached structure (e.g. deck) or vegetative fuels adjacent to a structure account for the majority of homes burned in the wildland urban interface (U.S. Department of Agriculture, Forest Service 2003).

Homeowners can assess and rank their individual levels of risk from an approaching wildfire by using one of several risk assessment programs. These programs focus on only those factors over which individual homeowners have control:

Reducing Fire Risks Around the Home

• The Wildfire Risk Assessment Guide for Homeowners in the Southern United States focuses on two sets of risk factors: the vegetative fuel component and the structural component. The fuel component includes ratings for the natural plant communities and defensible space around homes. The structural component includes ratings for firebrand ignition factors (i.e., wood shingles, wood deck); indirect ignition factors (i.e., slope, wood fence); and heat-related or direct ignition factors (i.e., wood siding, vinyl siding). A numeric score is determined for each factor and the total risk rating is related to four levels of fire risk (low to very high) (Long and Randall 2004).

• The USDA Forest Service’s Structure Ignition Assessment Model (SIAM) uses an analytical approach that relates the potential for sustained structure ignitions to the location (rather than the potential for structural survival) and characteristics of adjacent fires and the structure’s materials and design (Cohen 1995). The model is based on research and the principle that a homes characteristics and the 100 to 200 foot area immediately surrounding a home determine a homes ignition potential during a severe wildfire.

• The University of Florida developed a simple system in 1999 that allows landowners unfamiliar with risk assessment to determine the ignition risk to their home using a checklist of risk factors (Monroe and Long 1999). A home is then ranked as being at low, medium, or high risk of wildfire.

• The USDA Forest Service has also developed the NED DSS (Decision Support System) fire risk program for homeowners and landowners across the South to evaluate and mitigate their particular landholding. The NED DDS applies to both wildland urban interface and rural forest situations and is based on vegetation conditions, local topography, and structural characteristics.