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NIST and Forest Service team on wildfire risk assessment tool
Earthquakes have the Richter Scale. Hurricanes have the Saffir-Simpson Scale. Devastating wildfires could soon have their own grim measurement tool – the WUI Hazard Scale – to gauge their possible intensity and propensity for damage.
Spurred by the recent record wildfire seasons in western states, the U.S. Forest Service and the National Institute of Standards and Technology (NIST) have created a proposed system that links accurate assessments of risk from wildland fires to improved building codes, standards and practices.
The agencies said in a joint announcement on Dec. 5 that the new capabilities will help communities better resist the threats from wildfire disasters. The proposed Wildland Urban Interface (WUI) Hazard Scale framework addresses fires that occur where developed and undeveloped areas meet, they said.
"Structures in areas susceptible to other natural hazards, such as earthquakes, hurricanes and tornados, can be built to address the potential risks from these disasters because we have measurement scales that define that risk—the Richter for quakes, the Saffir-Simpson for hurricanes and the Enhanced Fujita for tornados," says NIST's Alexander Maranghides, who created the new wildfire hazard assessment tool with William Mell of the USFS. "Now, we have proposed a scale specifically for wildland fires that will allow us to link exposure to improved codes and standards, and as a result, save lives, property and dollars."
WUI fires, particularly in the western and southern regions of the U.S., have been growing more prevalent as housing developments push into wilderness areas, said the agencies. According to the Bureau of Land Management's National Interagency Fire Center (NIFC), they said, the 10 years since 2002 saw an annual average of nearly 71,000 WUI fires recorded and 1.9 million hectares (4.7 million acres) burned. Through the end of October 2012, the number of WUI fires for the year is below the average at slightly more than 54,000, but the amount of damage is nearly double with 3.7 million hectares (9.1 million acres) having burned—approximately 1,000 times the total area of Rhode Island. The NIFC estimates federal agencies spend an average of $1.2 billion per year on WUI fire suppression alone, with state and local agencies contributing millions more.
NIST and USFS said they have developed a proactive approach that could one day provide buildings and the communities in which they reside with increased resistance to WUI fires. The WUI Hazard Scale is designed to consistently measure the expected risks from fire and embers during a WUI fire event for individual locations within a community, taking into account the ever-changing nature of those hazards.
"Wildfires are among the few natural disasters in which risk levels can rapidly change as the event progresses and the threat doesn't weaken with distance away from a well-defined epicenter, as in a tornado," said Mell. "For example, if your home is nestled deep within a neighborhood away from the leading edge of a fire, you might not be at risk early on. However, the danger to your home dramatically increases if a neighboring house, the surrounding landscape or a nearby vehicle catches on fire."
Fire behavior in wildlands and the wildland urban interface is a function of fuel (both vegetation and structures), topography and local weather, said NIST and the Forest Service. The WUI Hazard Scale accounts for local and transient variations in these factors so each specific location can be rated as to its susceptibility to both fire and embers. The range of ratings can then be used to create a map of the different levels of risk throughout a community and pinpoint where protective measures or "hardening" of structures are most needed, they said.
According to the agencies’ statement, once the overall exposure risk in a particular zone is determined, researchers say they can predict the likely response of individual structures and even components of those structures (such as whether or not a wooden deck is treated with a fire retardant) to embers and fire.
The WUI Hazard Scale, they said, currently considers fire and ember exposure from a single source, wildland fuels. The researchers designed the scale to easily accommodate additional threats and plan to include exposure from three other sources associated with WUI fires—burning structures, ornamental vegetation and vehicles—at a later date, using the same methodology.
According to Maranghides, now that now that the hazard scale proposes a framework for addressing the WUI fire problem, the next step is to collect the appropriate data to make it viable. NIST and USFS, he said, will do field evaluations of exposure characteristics in a wide variety of communities and surveys of areas that have recently experienced WUI fires. The two agencies said they will also be working with various public and private stakeholder groups toward acceptance and implementation of the proposed scale and building construction classes with the goal of improving standards, codes and practices.