Over 46 million homes in 70,000 communities are at risk of Wildland-Urban Interface (WUI) fires, which has destroyed an average of 3000 structures annually over the last decade and is rapidly growing[1,2]. Within the last 100 years in the U.S., six of the top 10 most damaging single fire events involving structures were WUI fires. The WUI fire problem is a structure ignition problem. To reduce the risk of structural ignition, the technical basis for improved test standards and building codes are being developed. Post-fire damage assessment evidence suggests that firebrands (embers) are a major source of structural ignition in WUI fires. A unique experimental apparatus, known as the NIST Firebrand Generator (NIST Dragon), has been constructed to produce a controlled and repeatable firebrand attack. The experimental results generated from the marriage of the NIST Dragon to the Building Research Institute's (BRI) Fire Research Wind Tunnel Facility (FRWTF) in Japan are being used by standards organizations to guide the development of new standards and provide the scientific basis for new performance-based requirements with the intent to make structures more resistant to firebrand attack. The results of this research will allow improved fire-resistance of building components, structures and communities which will resilience of WUI communities.
Objective - To reduce the risk of structural ignition during a wildland-urban interface (WUI) fire by developing the technical basis for new and improved standard laboratory test methods and building codes considering WUI fire hazards, including wind-transported firebrands.
What is the new technical idea? While firebrand showers are responsible for a majority of structure ignitions in WUI fires (see any number of post-fire investigation reports over the past 60 years), there exist no scientifically-based standard laboratory test methods to evaluate individual building component's resistance to ignition from wind-driven firebrand showers. Without standard laboratory test methods, it is impossible to evaluate and compare the performance to different building elements ability to resist firebrand ignition. It cannot be over-stated that current understanding of building component type to WUI exposure is still mainly predicated on anecdotal evidence. As a result, the limited WUI building codes and standards in practice lack scientific rigor and, when implemented, it is not clear if these present any benefit to structures in the path of hazardous WUI exposures.
Before such test standards are developed, detailed full-scale experiments that systematically evaluate individual building component vulnerabilities to ignition to firebrand showers are required. It is critical to understand the full-scale assembly performance when exposed to firebrand showers since weak points in a given assembly can be investigated. In turn, this will lead to determining the necessary scale of building component mock-ups that can be used in standard laboratory test methods. As wind is a critical component required to transport firebrand showers observed in actual WUI fires, and wind plays a major role in whether ignition is observed, full-scale experiments must be able to consider the influence of an applied wind field to understand such ignition vulnerabilities.
This project will determine the vulnerabilities of structures to firebrand showers using the NIST Dragon coupled to a full-scale wind tunnel at the Building Research Institute (BRI) in Japan. The BRI facility is used since it is the only facility in the world to determine building component behavior under wind-driven firebrand showers. Most recently, the NIST Dragon technology was improved to allow for the generation of continuous firebrand showers, as opposed to the original batch-feed Dragon. With this technology, it is now possible to systematically ascertain building component vulnerability to wind-driven firebrand showers of any duration. The full-scale experiments will be targeted to address specific vulnerabilities observed during NIST's post-fire field studies of structures exposed to actual WUI fires.
What is the research plan? The basis for this research plan is to develop needed standards for building components, such as roofs, decks, fences, and walls. Field observations and experiments conducted at NIST and the BRI Fire Research Wind Tunnel Facility in Japan have identified firebrand flux as a key parameter contributing to the ignition of combustible materials and building assemblies. Full-scale experiments with an emphasis on firebrand flux are being used to guide the development of laboratory-scale standard test methods. The ignition behavior in reduced-scale is being compared with real-scale, matching not only the size/mass distribution of firebrands that arrive at the test specimen (e.g. section of deck, section of a fence), but also the wind speed. The physical understanding is acquired from full-scale experiments, which is then applied to develop reduced-scale test methods that will be able to adequately represent the full-scale experimental results.
Laboratory scale tests are being conducted at the National Research Institute of Fire and Disaster (NRIFD) under a new agreement drafted between NIST and NRIFD. NRIFD has the experimental facilities ideal for developing bench-scale test methods using the NIST bench-scale continuous feed Firebrand Generator in their wind facility. This effort directly supports the development of the NIST WUI Hazard Scale, since it will be possible to develop test methods for use by testing laboratories to expose mock-ups of building components to various exposures. The specific exposure ranges (e.g. duration and intensity of firebrand flux) are being determined as part of this effort.
To date only a very limited number of integrated firebrand flux measurements have been made, and the need remains for the quantification of firebrand deposition. A "firebrand catcher" system will be developed to enable quantification of the deposition of firebrands and the measurement of firebrand fluxes. The firebrand catching system will be designed to operate both indoors in a laboratory setting and in the field. Results from field experiments will inform test method development.
 U.S. Communities Dealing with WUI Fire Fact Sheet (ICC) 1.1.2011; Headwaters Economics, www.headwaterseconomics.org.
 WUI Fact Sheet, Communities Dealing with Wildland/Urban Interface Fire, International Code Council; www.iccsafe.org, and Natural Association of Resource Conservation & Development Councils.
 ASTM E1623-11 Standard Test Method for Determination of Fire and Thermal Parameters of Materials, Products, and Systems Using an Intermediate Scale Calorimeter (ICAL), ASTM International, West Conshohocken, PA, 2011.
Potential Research Impacts:
Realized Research Impacts:
Impact of Standards and Tools:
NIST's Firebrand Generator generates burning embers (or firebrands) that are major sources of ignition of house fires during blazes at the wildland-urban interface (WUI). Photo credit: NIST
Start Date:October 1, 2011
Lead Organizational Unit:el
Related Programs and Projects:
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