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A Case Study of a Community Affected by the Witch and Guejito Fires: Report #2 – Evaluating the Effects of Hazard Mitigation Actions on Structure Ignitions



Alexander Maranghides, Derek McNamara, William Mell, Jason Trook, Blaza Toman


The National Institute of Standards and Technology (NIST) has a suite of research projects addressing risk reduction in Wildland Urban Interface (WUI) communities. The NIST WUI Team was invited by CAL FIRE to collect post incident data from the California October 2007 fires. Early on, the NIST WUI Team initiated a case study within the Witch Fire perimeter. The case study is focused on the Trails development at Rancho Bernardo, north of the city of San Diego. There were 270 homes in the Trails community, with 242 within the fire perimeter. Of these, 74 homes were completely destroyed and 16 were partly damaged. Field measurements included structure particulars, specifically roof type, proximity of combustibles to the structure, and damage to wildland and residential vegetation. Documentation included over 11,000 digital images. The data collected and the data analysis are divided into two papers. The first paper, NIST TN 1635 addressed the event timeline reconstruction and general fire behavior observations. This second paper investigates the effect of structure attributes, landscaping characteristics, topographical features and potential wildland fire exposure on structure survivability. This is the first case study that evaluates hazard mitigation technology effectiveness while accounting for fire and ember exposure and at the same time factoring in defensive actions. The majority of the hazard mitigation treatments evaluated at the Trails Community appeared to be applicable even if they were not all individually effective. The level of fire and ember exposure was identified as having played a significant role in the survivability and destruction of structures with a pattern of increased destruction of residential structures with increased exposure. Additionally, exposure was found to play a significant role in structure survivability with respect to the effectiveness of defensive actions.
Technical Note (NIST TN) - 1796
Report Number


Wildland Urban Interface, WUI, fire behavior, community, Witch fire, Guejito fire, Firewise, Firewise effectiveness


Maranghides, A. , McNamara, D. , Mell, W. , Trook, J. and Toman, B. (2013), A Case Study of a Community Affected by the Witch and Guejito Fires: Report #2 – Evaluating the Effects of Hazard Mitigation Actions on Structure Ignitions, Technical Note (NIST TN), National Institute of Standards and Technology, Gaithersburg, MD, [online], (Accessed April 22, 2024)
Created June 5, 2013, Updated November 10, 2018