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Characterizing Firebrand Exposure from Wildland–Urban Interface (WUI) Fires: Results from the 2007 Angora Fire

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Abstract

This study examines the size distribution and other characteristics of firebrand exposure during the 2007 Angora fire, a severe wildland–urban interface fire in California. Of the 401 houses that received direct interface fire exposure 61% were destroyed and 30% did not burn at all. The ignition of buildings by wind-driven firebrand showers and the starting of “spot fires” in unburned vegetation ahead of wildfires have been observed for some time. Empirically quantifying the exposure severity or describing how many firebrands of what size and over what duration and distance cause ignition problems of concern has not yet been possible. However, a unique opportunity to gather empirical firebrand data from an actual interface fire evolved in the days immediately following the Angora fire. Digital analyses of burn patterns from materials exposed to the Angora fire were conducted to determine firebrand size distributions. It is probable that some burn patterns were larger in area than the firebrands due to progressive combustion or melting, but it was assumed that the overall size distributions of burn pattern areas were representative of actual firebrand sizes. This assumption was investigated by exposing sections of materials collected in the Angora fire to wind driven firebrands generated in the laboratory using the unique NIST Dragon’s lofting and ignition research facility (NIST Dragon’s LAIR facility). The firebrand size distributions reported were compared to firebrand size distributions from experimental firebrand generation in both recent laboratory building ignition studies conducted by NIST and from historical firebrand field studies. Such data is needed to form the basis of effective and appropriate interface fire hazard mitigation measures as well as modeling fire spread. Comparisons are made to current wildfire protection building construction regulations and test standards. The most salient result of this study is documentation of the consistently small size of firebrands and the close correlation of these results with the sizes of experimentally generated firebrands.

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Acknowledgments

We are grateful for support on the Angora fire provided by California Interagency Incident Management Team # 1 (R. Hawkins), the County of El Dorado, the USFS Lake Tahoe Basin Management Unit, Lake Valley Fire Protection District, South Lake Tahoe City Fire Department. Data collection assistance was provided by Angora Damage Assessment Team staff, especially T. Robards and J. Cohen, and the able assistance of Mr. John Shields of EL-NIST is appreciated. Thanks to S. Dickey and A. Burg for help with the manuscript. The field data collection would not have been possible without the leadership of Fire Chief Bill Holmes and State Fire Marshal Kate Dargan. This research was funded by the Science and Technology Directorate of the US Department of Homeland Security. Mr. John M. Liu, a DHS intern and undergraduate student at Duke University, analyzed the burn patterns from the trampoline collected from the Angora fire; his assistance in appreciated.

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  1. Ethan I. D. Foote

    Present address: , 747 Beaver St., Santa Rosa, CA, 95404-3755, USA

Authors and Affiliations

  1. Fire Research Division, Engineering Laboratory (EL), National Institute of Standards and Technology (NIST), 100 Bureau Drive, Gaithersburg, MD, 20899-8662, USA

    Samuel L. Manzello

  2. Office of the State Fire Marshal (OSFM), California Department of Forestry and Fire Protection, 135 Ridgway Avenue, Santa Rosa, CA, 95401-4318, USA

    Ethan I. D. Foote

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  1. Samuel L. Manzello
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  2. Ethan I. D. Foote
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Correspondence to Samuel L. Manzello.

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Ethan I. D. Foote: Retired.

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Manzello, S.L., Foote, E.I.D. Characterizing Firebrand Exposure from Wildland–Urban Interface (WUI) Fires: Results from the 2007 Angora Fire. Fire Technol 50, 105–124 (2014). https://doi.org/10.1007/s10694-012-0295-4

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  • DOI: https://doi.org/10.1007/s10694-012-0295-4

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