Evaluating the Effectiveness of Mitigation Activities in the Wildland Urban Interface

Project Description

There has been relatively little research on wildland urban interface (WUI) fire spread, compared to fires within structures, despite the increasing frequency and losses from WUI fires. This research funding was used to deploy to two WUI fire events and conduct two detailed WUI case studies, and a framework was developed to quantify fire and ember exposure at the WUI and to link exposure to design and material guidance for structures in the WUI.

Purpose and Scope

Development of a framework to measure ember exposure in the wildland urban interface, and to link exposure to design and materials guidance for structures.

Implementation

The Witch/Guejito case study focused on the Trails community in San Diego, California. The Trails community was almost entirely affected by the Witch and Guejito fires and had significant structural losses.The data collection, conducted in partnership with CALFIRE and San Diego Fire and Rescue, and the subsequent data analysis highlighted the need for a wildland urban interface (WUI) data collection methodology, and such a methodology was developed.

The next case study was conducted in Amarillo, Texas, in partnership with the Texas Forest Service (TFS). TFS was trained on the data collection methodology and teams were deployed to investigate the Tanglewood Complex fire. The size of the fire enabled the response teams to investigate the entire fire. While the fire was a relatively small WUI fire, looking at the entire incident provided technical information that was not available during the Witch/Guejito case study, both in the context of exposure and defensive actions.

The third case study, the Waldo fire in Colorado Springs, Colorado, also investigated the entire fire. While resources had not been trained to respond rapidly and collect field data right after the incident, significant data was available in the form of photographic and video documentation of the fire. This information together with data from the Automatic Vehicle Location (AVL) system of the Colorado Springs Fire Department (CSFD) and the CSFD radio logs was able to provide a clear picture of what occurred across the majority of the incident. As in Amarillo, the Waldo fire investigation focused on the entire fire, which in Colorado Springs destroyed 346 destroyed homes.

Key Findings

Hazard Mitigation

• Additional field data collection studies need to be conducted to provide insight into structural response in both high and low exposure environments (Witch/Guejito)
• The exposure characteristics need to be further developed to enable valid comparisons of structural response within and across incidents (Witch/Guejito)
• The relationship of exposure and structure vulnerability needs to incorporate additional science-based understanding. This will lead to improved testing standards for new construction and improved guidance for retrofit (Witch/Guejito)
• Until a professional infrastructure can be implemented, a science-based checklist needs to be developed to facilitate the implementation of hazard reduction techniques by homeowners.
• New checklists are required for different scenarios, e.g. intermix versus interface communities; existing construction versus new construction (Witch/Guejito)
• The concept of structure vulnerability needs to be further developed. When coupled with exposure, this approach will yield improved tools for predicting structure destruction (Witch/Guejito).
• Building standards and test methods need to be updated to capture representative fire and ember exposures. Adoption of these improved test methods and building codes and standards will reduce WUI losses in new construction (Exposure Scale)
• Hazard mitigation guidance needs to be developed to help reduce hazards in and around existing high risk WUI communities (Waldo)
• Wildland fuel treatment standards needs to be developed that quantify exposure reduction for different topographical and weather conditions (Waldo)
• Ignition vulnerabilities of structures from adjacent combustibles, specifically fences and decks (Amarillo), need to be quantified.

Hazard Assessment and WUI Data

• Hazard mitigation assessments of limited scope (i.e., “drive by” studies) should be be undertaken with caution, as they can generate very erroneous data (Waldo)
• Post-fire damage assessments need to focus on damaged structures and identification of first item(s) ignited in order to gain further insight into construction vulnerabilities (Amarillo, Waldo)
• Prefire hazard assessments need to focus on identifying hazards and not prioritizing them. The identification of hazards will aid both homeowners and first responders. Quantification should factor in fuels, topography and local weather. Fuels should include (vegetative) and urban/interface fuels such wood roofs, fences and combustible decks (Exposure Scale, Amarillo, Waldo)
• A standardized WUI data collection system can generate consistent national WUI data. (Amarillo)
• A national incident centric WUI fire repository needs to be implemented to capture the scale of the WUI problem and monitor nationwide trends and losses (Amarillo)
• Detailed case studies need to be undertaken in the wildland urban intermix (Amarillo).

Defensive Actions

• First responder tactics, equipment and training need to be developed for the WUI, to bridge the gap between structural and wildland firefighting. (Waldo)
• Standard Operating Procedures (SOPs) need to be developed for the rapid deployment of first responder resources to WUI fires. First responders need to be trained in the new SOPs and practice rapid fire department response to WUI fires. SOPs need to account for responding, in the event of a specific WUI scenario, to both high and low exposure areas (Waldo). SOPs need to be science based and should be developed to enhance first responder safety.
• A science-based response time threshold needs to be developed for WUI fires the same way urban fire departments have response thresholds for responding to building fires (Waldo).