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Improving WUI Community Fire Protection- Fire Resistant Building Design and Materials

Summary

The Wildland-Urban Interface (WUI) is defined as the location where structures and communities meet or intermingle with undeveloped wildland. In the U.S., over 46 million homes in over 70,000 communities have been built in the WUI. Since 2000 over 38,000 homes have been lost to WUI fires. The goal is to develop fire resistant building components, new fire resistant community construction design, and advanced materials that resist ignition and limit the spread of fire. Wildfires may behave erratically, and there are fuel, weather, and terrain conditions that are not well understood that result in explosive growth in size and intensity.  Understanding the interaction between fuel package, weather, and terrain is critical to exploiting fire resistant materials and design. Initial efforts will focus on building and community vulnerabilities identified by post-fire analysis of actual fire incidents. Issues already identified include fences (Waldo Canyon, CO), structural embers (Witch Creek, CA), raised foundations (Amarillo, TX), and horizontal roll vortices (Bastrop, TX). The increased understanding of these issues will be consolidated into WUI Exposure Scale matrix developed at NIST. In addition, the new insight and data will be transferred to standards organizations to guide the development of new code and standards, 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 improve the resilience of WUI communities.

Description

fire

Objective - To develop fire resistant building components, new fire resistant community construction design, and advanced materials that resist ignition and limit the spread of wildland-urban interface (WUI) fires.

What is the new technical idea? Address structure and community vulnerabilities to WUI fires through development of fire resistant design and advanced materials. Use post-fire analysis of WUI fires to identify vulnerabilities and then focus experiments and modeling to provide understanding of structure design and materials with WUI fuels, weather, and terrain. Incorporate new insight into design of new buildings and communities and retrofitting of existing buildings.

What is the research plan? Wildfires may behave erratically, and there are fuel, weather, and terrain conditions that are not well understood that result in explosive growth in size and intensity. Understanding the interaction between fuel package, weather, and terrain is critical to exploiting fire resistant materials and design. Initial efforts will focus on building and community vulnerabilities identified by post-fire analysis of actual fire incidents. Issues already identified include fences (Waldo Canyon, CO), structural embers (Witch Creek, CA), raised foundations (Amarillo, TX), and horizontal roll vortices (Bastrop, TX). Phase I of this project will focus on the built environment and gaining additional understanding as to underlying mechanisms for ignition and subsequent fire spread. . The increased understanding of these issues will be incorporated into the  into WUI Exposure Scale matrix developed at NIST.  There is a need to develop test methodologies that provide realistic exposures of thermal flux/flame contact to building components and assemblies of components. In addition, the new insight and data will be transferred to standards organizations to guide the development of new code and standards, 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 improve the resilience of WUI communities.

Built Environment: The spread of fire and embers will be studied, from the WUI interface to flammable outdoor structures (e.g. fences, woodpiles, decks) to residential structures within the community. The study begins with a set of experiments on fire spread along fences to follow-up the preliminary series of experiments performed during FY14. The experiments will take place outdoors under controlled wind conditions ranging up to 70 mph, complementing ember studies being carried out under the Reduced Ignition of Building Components in WUI Interface Fire Project in a wind tunnel, which is limited to 20 mph. As part of this study, an ignition target will be defined such that a distinction among the fences can be clearly identified. A method will be established to quantify the flux of embers emitted from the source (fence) and reaching the target. Finally, the methodology developed during the fence study will be applied to woodpiles and decks.

The experiments will be documented to provide guidance to improve codes and standards. This includes the quantification of the exposure hazard from fences, woodpiles, and decks.

WUI Incident Data Assessments: Data from post-fire analysis is of critical importance in determining the exposure and vulnerabilities of building components, structures, and communities to WUI fire. However, legacy data collected from past incidents are not uniform in content, amount, or type.  Data from WUI incidents has been collected by a wide range of local, municipal, fire service, state, and federal entities, and the information content ranges from the simple number of houses burned to detailed local information on fuel, topography, weather, defensive actions, and timeline. Typically, as the amount and type of data becomes more detailed, the usefulness of the data increases, but so do the required resources in cost, personnel, and training and analysis time. Conclusions from coarse data need to be drawn carefully or they may be misleading. For example, a simple comparison of destroyed and intact houses after a WUI incident may attribute the outcome to structural design or landscaping when the real reason for survival was active suppression of spot fires at a critical time during the event.  

Large Scale Extreme Fire Events: Large scale extreme fire events that highlight the interaction between fuels, terrain, and weather. Understanding this type of interaction is critical to characterizing the exposure conditions, both flame and embers, that occur during a WUI event. Cohen [1] indicated that when residential development is exposed to extreme wildfire conditions, numerous houses can ignition and burn simultaneously, overwhelming fire fighters and reducing fire protection effectiveness. High winds of extreme fire events resulted in fires igniting between 1 and 4 houses per minute, Laguna Fire, CA and Painted Cave Fire (CA). In recent fire seasons, extreme fire events have include high winds (Santa Ana) of up to 80 mph (36 m/s) have accelerated fire spread through communities, rapid wind direction change (Yarnell, AZ) contributed to the loss of 19 fire fighters (Yarnell, AZ), and horizontal roll vortices influenced the rapid fire spread through communities (Bastrop, TX). Since large scale extreme fire events represent a disproportionately large component of the overall fire losses, it will be critical to gain a greater understanding of fuel, weather, and topography that allow extreme fire events to occur. The focus during the first phase will be to identify large scale extreme fire events and characterize which factor fuel, weather, or topography, or an interaction of multiple factors played the dominant role in the event. This will provide better insight into how to assess and track the potential for extreme fire behavior. Better design and materials for building components, structures, and communities can then be developed and implemented to reduce the vulnerability of communities to large scale extreme fire events. 


[1] Cohen, Jack, The Wildland-Urban Interface Fire Problem, Forest History Today, Fall 2008, pp 20-26.

Created January 8, 2016, Updated September 21, 2016