WUI Building and Fire Codes and Standards Project

Summary

Although over 46 million residential structures in the United States are in areas of risk of wildfires, building and fire codes and standards do not provide the same resiliency for structures in wildland-urban interface (WUI) communities as provided in urban communities. Projects within the Fire Risk Reduction in Communities Program seek (through laboratory experiments, field measurements, and computer modeling) to improve our understanding of WUI fire dynamics and structure ignition mechanisms. This measurement science will support standard test methods for building materials and assemblies, guidelines for structural design and residential landscaping, and guidelines for community planning. This project will improve WUI building and fire standards and codes using the results of the science-based WUI projects, including adoption by model building and fire codes. As these results are incorporated into improved building and fire codes, the resiliency or "hardness" of each of the 70,000 communities that are at risk of wildland-urban interface fire will be improved.

Description

Objective: By 2014, assess and integrate the current state-of-the-art risk reduction tools and practices into model building codes and standards for fires at the wildland-urban interface.

What is the new technical idea? The new technical idea is to develop a national codes and standards strategy based on mapping zones of fire exposure severity within a WUI community. The fire exposure severity zoning system or exposure scale framework considers flame impingement, thermal radiative flux, and ember exposures and provides a basis for development of science-based performance metrics and representative test methodology for components, buildings, and communities. Since the fire severity 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. More representative metrics and test methods will allow new materials, designs, and technologies to be evaluated under more realistic conditions. As building codes and standards incorporate a fire exposure mapping system, the fire resistance of WUI communities will increase in a manner analogous to the use of the Richter Scale for increasing the earthquake resistance of buildings and communities. Construction in each fire exposure zone will meet the appropriate codes and standards. Established communities in each fire exposure zone would need to consider building retrofit and community and parcel^[1] landscaping guidance developed by NIST to address WUI fire hazards.

There is also a need to develop a better understanding of the relationship between the cost a community pays for fire protection, the level of protection afforded, and the losses resulting from a WUI fire. For example, if a community were to require a 30 m spacing between structures, what is the economic cost to the community? How much additional protection does a 30 m spacing provide? In the case of a fire spreading by thermal radiation, 30 m rather than 10 m spacing may increase the resistance to fire spread by a factor of 10. On the other hand, in the case of fire spread by ember ignition, 30 m spacing may provide little additional fire protection. 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.

Currently doing a cost/benefit analysis is hampered by the lack of understanding as to the relative contributions of the factors such as structural spacing, distance to wildland, topography, and fuel treatments. A second new technical idea is to use statistical methods to evaluate the relative contribution of various factors that affect structure ignitions during WUI fires. These findings will aid in the prioritization of research to assess the influence of exposure conditions and mitigation approaches on structure risk during WUI fire incidents.

What is the research plan? The primary focus of the research effort will be the development of a national strategy for WUI codes and standards, including model building codes to reduce losses in WUI fires. The foundation of the approach will be a nationally applicable WUI community fire-exposure zoning system, WUI performance metrics, and building and fire codes.

WUI Technical Solution Implementation Guide 
A WUI technical solution implementation guide will be developed for existing and new communities. The WUI fire-exposure zone concept will form the basis of the guide. The first generation of the WUI Technical Solution Implementation Guide will be based on existing expert knowledge. A science-based approach will improve subsequent versions by incorporating lab-scale and field-scale experiments, post-fire data collection, and fire spread and economic models.

The guide will serve two purposes. First, the guide will provide a centralized repository of all WUI fire research technical findings. Secondly, the guide will establish a framework that will identify the gaps in WUI hazard reduction solutions that are implementable and relevant to the WUI problem. The guide will be revised every two years. The results of experiments, analysis, modeling, and post-fire data collection and analysis will be essential to the development of this guide.

Suppression of Wildland Fires versus Hardening WUI Communities
The traditional approach to preventing WUI fires has been to focus resources and efforts on suppressing fire in the wildland. If all wildland fires were successfully extinguished then there would be no fires to spread from the wildland to the community. This suppression approach has focused most of the effort and resources on wildfire suppression to the exclusion of improving the fire resistance of communities. Increasing the fire resistance or hardening the communities involves making it more difficult to ignite structures and if ignition occurs, limiting the fire spread. WUI building codes and standards need to shift the research emphasis to hardening the community through less ignition-prone materials, more fire resistant designs, and new technologies to prevent fire spread within communities with less emphasis on wildland fuels management and suppression.

WUI Fire Data in the Disaster and Failure Studies (DFS) Data Repository
WUI field experimental and post-fire data is being collected as part of the WUI Fire Data Collection and Exposure Modeling Project and is being incorporated into the DFS Data Repository. However, while this data is currently used to develop WUI fire spread models and performance metrics, it can also be exploited to document the effectiveness of current building codes and standards and to establish a baseline to track improvement. The findings of post-fire analysis such as the ignition of wood decks will be used to assess whether specific modifications to the wood deck code provisions actually reduced the number of wood deck fires and subsequent spread to homes. Data will also be valuable as the DFS Data Repository is used to examine trends and common factors influencing the impact of WUI fires.

Evaluate the relative contribution of different fire exposure elements
Measuring the fire resiliency of wildland-urban interface (WUI) communities requires: 1) understanding the relative contribution of fuel package configuration, weather, and terrain, 2) quantifying the cost of providing the current level of fire protection, 3) understanding the losses resulting from WUI fires, and 4) using performance metrics to assess the effectiveness of current designs, materials, and technologies. The research plan is to begin understanding 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.

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[1] Section of contiguous land with its structures, driveways, and vegetation; may be single home or group of adjoining homes.

Major Accomplishments

Recent Results:

Workshop:

A WUI Fire Research Needs Workshop was conducted on August 15-16, 2012 in Boulder, CO. Participants included International Code Council, National Fire Protection Association, US Forest Service, Insurance Institute for Building and Home Safety, US Fire Administration, California Department of Forestry and Fire Prevention (CALFIRE) International Association of Fire Fighters (IAFF), International Association of Fire Chiefs (IAFC), National Wildfire Coordinating Group (NWCG), industry, fire service, authorities having jurisdiction (AHJ), and San Diego State University. 

Outputs:

Maranghides, A., and Mell, W., "Creating a Framework for Addressing the National Wildland Urban Interface Problem Using the E-Scale," to be submitted to Fire Engineering (in WERB review, June 2011).

Thomas, D.S., and D.T. Butry. 2012."Wildland Fires^[2]within Municipal Jurisdictions." Journal of Forestry 110(1): 34-41.

Developed framework^[3] for assessing community scale fire risk. Bryner and Johnsson, "Framework For Assessing Community-Scale Fire Risk," NIST Technical Note, 2012, in preparation.

Butry, D.T., J.P. Prestemon, K.L. Abt, and R. Sutphen. 2010. "Economic Optimization of Wildfire Intervention Activities." International Journal of Wildland Fire 19: 659-672.

Butry, D.T., D.S. Thomas, G.H. Donovan, and P. Lavappa. "The Role of Building Density in Wildland-Urban Interface Fires." (in Review).

Thomas, D.S., and D.T. Butry. "High Fire-Frequency Wildland-Urban Interface Areas." Journal of Forestry, 2012. (in Review).

Economic model of community-based mitigation accounting for the spatial spillover of individual homeowner mitigation efforts, and construction of a GIS data library to facilitate WUI community wildland fire risk analysis (Butry, Thomas, & Lavappa).

Standards and Codes: 

This project will focus on hardening communities that are exposed to WUI fires by incorporating the exposure scale into building codes and standards including 2012 International Wildland-Urban Interface Code (ICC), 2009 Wildland Urban Building Code, California Chapter 7A Building Code, 2013 Standard for Reducing Structure Ignition Hazards from Wildland Fire (NFPA 1144). Researchers are members of and participate on Fire/Performance/Wildland-Urban Interface Committee, FI PC WU –ICC (Bryner) and Technical Committee on Forest and Rural Fire Protection (Maranghides), Quantification of Exterior Fire Exposures, ASTM E05.14 (Manzello). The economic model will be incorporated into NFPA 1144 Committee on Forest and Rural Fire Protection to implement the use of the economic decision support tool as a standard method facilitating community risk assessment and disaster planning. The strategic roadmap^[4] and workshop proceedings also provide documentation of the WUI codes and standards strategy.^[5]

 

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[2] WUI fires is not univesally used to describe fire in wildland-urban interface communities. This reference uses wildland fire within municipal jurisdictions instead of WUI fires.

[3] Approach used Risk f(Vulnerability x Loss or Consequences x Threat) and Framework incorporates three components: 1) Exposure to Hazard, 2) Response of Structure/Community, and 3) Designs to Mitigate Risk

[4] "Reduced Risk of Fire in Buildings and Communities: A Strategic Roadmap to Prioritize and Guide Research," NIST Special Publication 1130, April 2012.

[5] NIST Workshop on Wildland-Urban Interface Fire Research Needs, August 15-16, 2012, Boulder, CO, Draft Proceeding 9/2012.