The Wildland-Urban Interface (WUI) is defined as the location where structures and communities meet or intermingle with undeveloped wildland. In the USA, over 46 million homes in over 70,000 communities have been built in the wildland-urban interface. Since 2000 in California alone, an average of over one thousand structures per year have been lost to WUI fires. An improved understanding of WUI fire dynamics and structure ignition mechanisms is critical to improving structure and community resistance to WUI fires. Post-fire data collection and analysis reveal how WUI fire behavior is driven by the interactions among fuel, weather, and terrain and the roles played by heat, embers, and direct flame impingement. This knowledge is organized through a WUI fire and ember exposure scale. Post-fire analysis also shows how fire behavior is modified by defensive actions, both active and passive. Building and community vulnerabilities identified through post-fire analysis, including fences and woodpiles, are further investigated through laboratory experiments. Field-scale experiments provide data for development and validation of the NIST's Fire Dynamic Simulator computer fire model. The increased understanding and data are 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 fire and firebrand attack. The results of this research will allow improved fire resistance of building components, structures and communities, which will improve the resilience of WUI communities.
Objective - To develop the measurement science needed to mitigate the effects of wildland-urban interface (WUI) fires by providing technical guidance on building components, landscaping elements, and community designs that resist ignition and limit the spread of WUI fires.
What is the new technical idea? The new technical idea is to address structure and community vulnerabilities to WUI fires through development of fire resistant design and advanced materials, based on reliable post-incident data, and promoted through incorporation into codes, standards, and best practices.
The WUI Fire Hazard Scale has been created to document and quantify the severity of WUI fire events. The ember and fire exposure scale provides a framework for characterizing the impact that the fuel (structural and vegetative), weather (wind, humidity), and terrain play in WUI structure fire spread. Since the scale is based on the exposure to flames and embers and not on specific vegetation or materials, the exposure scale will be broadly applicable across WUI communities. The exposure scale will guide future WUI fire research and provide a technical basis to organize the understanding of the vulnerability of building components, structures, and communities to WUI fire. It provides a basis for development of science-based performance metrics and representative test methodology for components, buildings, and communities, which will allow new materials, designs, and technologies to be evaluated under more realistic conditions. To realize these benefits, the scale must be populated with data linking fuel, weather, and terrain to potential fire exposure.
Post-fire analysis of WUI fires provides the knowledge to focus experiments and modeling on critical vulnerabilities of structure design and materials. Standard data collection methodologies, once implemented, will generate reliable post incident data for inclusion in NIST's Disaster and Failure Studies Repository. Documentation of defensive actions during WUI fire incidents is critical to the understanding of WUI structure survivability and the effectiveness of risk reduction methodologies. The new insights will be incorporated into design of new buildings and communities and retrofitting of existing buildings.
Fences, decks, and woodpiles have already been identified through post-fire analysis as vulnerabilities that may enhance the spread of fire from the wildland to structures during a WUI fire. Experiments under controlled conditions in the field and in a large wind test facility will provide data on ignition, ember generation, and fire spread involving these landscape elements. The results will be disseminated to homeowners through existing community outreach programs and incorporated into existing WUI fire and building codes.
There is a need to develop a better understanding of the relationship between the cost paid by a community for fire protection, the level of protection afforded, and the losses resulting from a WUI fire. Exposure to flames and embers must be considered in the development of metrics to assess the performance of individual structures and the community during a WUI fire. Statistical methods may be used to evaluate the relative contribution of various factors that affect structure ignitions (e.g., structural spacing, distance to wildland, topography, and fuel treatments) during WUI fires.
What is the research plan? The Research Plan proceeds from obtaining an understanding of the vulnerabilities of structures and communities, finding ways to address them, and disseminating the new knowledge. It includes the following components:
- Implementing the WUI Fire Hazard Scale – Filling in the Exposure MatrixA WUI exposure scale framework has been developed to provide a common scale for quantifying the assault on structures from embers and fire. The exposure scale can be used to improve building codes, standards, and best practices to meet the survivability requirements of structures in certain fire and ember exposure environments. The exposure scale needs to be populated based upon historical data, field data collected in coordination with state and local agencies, data provided through standardized data collection methodologies, NIST FDS model simulations, and targeted laboratory and field experiments. Particular attention will be paid to extreme fire events, in which high winds, rapid changes in wind direction, horizontal roll vortices, and interactions among fuel, weather, and topography lead to rapid and disastrous fire growth.
- Case Studies and Post Incident Data RepositoryDetailed case studies are carried out on three major fires: the Witch Creek-Guejito fire (San Diego, CA, 2007), the Tanglewood Complex fire (Amarillo, TX, 2011), and the Waldo fire (Colorado, CO, 2012). A methodology is developed to collect, store, and analyze pre- and post-WUI fire data. Reports present the findings and recommendations from these studies, and the results are used to identify structure ignition vulnerabilities and guide hazard reduction research and solutions. Data collected from NIST WUI fire deployments can integraated into the NIST Disaster and Failure Studies Repository. The extensive data collection effort during and after the Witch Creek fire provided a testbed for a variety of hardware, software, and field methodologies. Rapid deployment deployment and data standardization and compatibility are necessary to ensure that critical data are not lost (e.g., due to recovery efforts). The data are analyzed to determine how structural construction and landscaping attributes affected structure fire performance during the fire, and the validity of the NFPA Firewise methodology for WUI fire community protection is assessed. Documenting only destroyed and damaged structures can result in erroneous assessments and misleading conclusions with respect to structural vulnerability. The recent instrumentation of the Trails community and surroundings with wind sensors allows wind flow in the absence of fire to be compared to evidence of wind direction during the Witch/Guejito fires. The comparison will highlight the relative importance of ambient wind in determining the fire path through the community. The data collection methodology was successfully utilized in response to the Amarillo and Waldo fires. The first Amarillo report, NIST TN 1708, outlines the deployment and data collection process, while the second report documents fire behavior, defensive actions, and event timeline and identifies structure and parcel level ignition vulnerabilities. For the Waldo fire, deployment and data collection were not initiated immediately after the fire due to limited resources. Researchers spent over 4000 hours collecting and analyzing fire behavior and defensive action data. The incident analysis focus was on interactions between fire behavior and first responders, providing for the first time an incident level detailed analysis on the interaction between fire behavior and defensive actions.
- WUI Data Collection PartnershipsThe NIST/USFS WUI data collection efforts in the three case studies (Witch Creek 2007, Tanglewood Complex 2011, and Waldo 2012) were accomplished through partnerships with the fire services of CA, TX and CO respectively. Establishment of a national WUI post-fire data collection team that assembles partners with complementary expertise would lead to significant gains in WUI knowledge. For example, the joint NIST/USFS team that responded to the Waldo brought together backgrounds in both structural and wildland fires that connected fuels to fire exposure to building vulnerabilities. Unfortunately, no further large scale deployments are planned with this team due to limited resources. Instead, the focus is shifted in FY16 to collecting data from VA, where WUI fires are smaller in size and logistically easier to respond to from NIST in Maryland. There is little information available on legacy WUI fires. An analysis of historical WUI data will be initiated in Texas, where the Texas Forest Service has an extensive incident documentation system. This data will be mined to extract WUI fire data, which will be cross-correlated with weather data from the National Weather System. This will begin the process of assessing the WUI fire data at a state level - an important task, as the incident level information collected from individual case studies offers little information on quantification of the WUI fire problem at the state and country levels. The information generated in Texas will enable the assessment of current data collections in the National Fire Incident Reporting System (NFIRS) and the National Interagency Fire Center (NIFC).
- Technology Transfer of the NIST WUI Data Collection Methodology.To date there has been no standardized approach to collect basic WUI community fire response data at a national level. Legacy data collected from past incidents are not uniform in content, amount, or type. The NIST WUI 1 data collection methodology has been designed to address this need. Widespread use of the WUI 1 methodology would generate a usable data set showing what structures are burning in the WUI. The NIST WUI data collection methodology was used to train the Texas Forest Service in October 2010 and was field tested during the initial reconnaissance deployment to the fires around Amarillo and Bastrop Fires in Texas in 2011. This methodology is being used to collect the VA statewide data described earlier. The VA methodology will be assessed for effectiveness and potential implementation in other states with similar-sized WUI issues (on the order of 100 homes destroyed per year.
- Simulation of WUI windWind, topography, and fuel are the main attributes that affect WUI fire behavior. The focus of this effort is to develop wind predictive capabilities at landscape, parcel, and community scales. This will be accomplished through coupled experimental and modeling work. Prescribed burns conducted near Bastrop, TX by the Texas Forest Service in collaboration with federal agencies, academics, and contractors generated a unique set of fire behavior data that can be used to develop and test FDS. The Trails community has been instrumented to collect wind data over rough terrain for comparison with data from the Witch Creek fire in 2007 and from modeling results. Challenges include integration of data from multiple instruments, such as aerial wind sensors, fixed sensors, and SODAR; incorporation of terrain and fuel information into model input files; and visualization of the time-dependent, three-dimensional wind field. Validation cases will be prepared for the FDS repository to confirm model integrity in WUI settings during the development of the model and the associated Smokeview visualization tool. NIST has led the world in development of UAVs for wildland fire data. Using metrology and operational methodologies developed by NIST and its contractors, the NIST UAVs successfully collected field data from the prescribed burns in Bastrop, TX. Despite their demonstrated usefulness for identification of community vulnerabilities and model validation, resources to fund field operations and FAA certification requirements are not currently available. UAV operations for WUI use have therefore been suspended. The U.S. Geological Survey (USGS) is borrowing the UAVs to support USGS field experiments.
- Ignition and Fire Spread Behavior of Structures Adjoining HomesAnalysis of post-fire data has identified some key vulnerabilities of buildings to wildfires, including fences, woodpiles, mulch, landscape borders, and ornamental vegetation. Research is required on ignition and flame spread along these structures and materials adjoining homes, as well as the role that they play in the ignition of buildings. A series of experiments will quantify the fire and ember exposures generated by detached combustibles under a variety of wind conditions. This complements ember studies being carried out under the project on Reduced Ignition of Building Components in Wildland Urban Interface Fires. A number of the experiments will be conducted in technical partnership with the Insurance Institute for Business and Home Safety (IBHS). The first stage of experiments is focused on fences. Future detached combustibles of interest include woodpiles, landscaping timbers, and ornamental vegetation. The results will be used to develop technically sound codes, standards, and best practices for homeowners and communities.
- Evaluate the relative contribution of different fire exposure elements and assess the effectiveness of fire protection strategiesMeasuring the fire resiliency of WUI communities requires:
- Understanding the relative contribution of fuel package configuration, weather, and terrain
- Quantifying the cost of providing the current level of fire protection,
- Understanding the losses resulting from WUI fires, and
- Using performance metrics to assess the effectiveness of current designs, materials, and technologies.
The research plan is to begin to understand the relative contribution of these different elements. This effort will link economic outcomes with mitigation actions, and thereby provide performance metrics to assess the effectiveness of community fire protection strategies.
 For example, at The Trails community in San Diego, CA, the Witch/Guejito fires in 2007 destroyed 74 homes and damaged 16. Out of the 74 destroyed homes 12 had wood shake roofs (of varying ages and treatments), while 37 had Spanish tile roofs (with and without bird stops), 24 had composite roofs and there was one metal roof. The wood shake roofs were present in 16% of the destroyed structures, while the Spanish tile roofs were present in 50% of structures. There were 245 structures within the fire line at the Trails. For the performance of roofs within the fireline 100% of wood shake roofs exposed were destroyed while only 24% of Spanish tile roofs were destroyed. By documenting all structures within the fire line, the relatively high (all other factors being equal) vulnerability of wood shake roofs stands out. While quantifying structure survivability is a complex process that involves construction particulars and measures of fire and ember exposure, the above example illustrates how misleading partial information can be.
 FAA requires that a site specific COA be obtained before an application can be filed for a statewide COA.
 Prescribed burns will be conducted by the US Forest Service and/or the Texas Forest Service.
- WUI Exposure Scale: A Technical Framework for Reducing Losses at the Wildland Urban Interface, Maranghides, A., and Mell, W.E., submitted to Journal of Wildland Fire
- A case study of a community affected by the Witch and Guejito wildland fires
- The Wildland-Urban Interface Fire Problem –Current Approaches and Research Needs, Mell, W.E., Manzello, S.L., Maranghides, A., Butry, D., and Rehm, R.G., International Journal of Wildland Fire 2010, 19,238-251 (FY2010)
Provided foundation for mitigation WUI fire losses.
Impact of Standards and Tools
- WUI Hazard Scale FY2012 Framework for Addressing the National Wildland Urban Interface Fire Problem – Determining Fire and Ember Exposure Zones Using a WUI Hazard Scale, Maranghides, A., and Mell, W.E., NIST Technical Note 1748, July 2012.
- Standardized post-fire data collection methods to be incorporated into standard practice by the CALFIRE and the Texas Forest Service (FY2012)
A member of a joint NIST-Texas Forest Service study team collects data on a Amarillo, Texas, building damaged by wildfires in February 2011. Photo credit: NIST.
October 1, 2011
Lead Organizational Unit:
Related Programs and Projects: