As communities grow, there are only two ways to build; up or out. Often times high rise structures near the center of a large city are already built, and are cost- or ordinance-prohibitive. The option to expand communities further into the nearby forests or brushland becomes attractive due to the affordability and “escape” from big cities. According to “Why are Wildfires More Destructive Today?” by Rachel Wisch, Yue-Jun Yin, two fires occurred in the same area with very different outcomes. In 1964, the Hanley Fire destroyed 100 homes and cabins; and in 2017, the Tubbs Fire destroyed more than 5,600 structures.
Today, not only are there many more structures in wildland-urban interface (WUI) zones, but the rising material and labor costs result in an ever-increasing total insured value exposed to wildland fires. Curtailing logging operations, reducing controlled burns that had been in place for many generations, and reapportioning funds away from maintaining the aging power grid to renewable energy has resulted in the highest wildland fire risk to date. For instance, the 2018 Camp Fire in California was caused by equipment that dates back to 1921, and was exacerbated by heavy ground cover and an exceptionally dry fall.
So, what can you do?
You can prepare your emergency response team to take clear, decisive actions when notified of a nearby wildland fire. Have a written pre-incident plan to check the back-up communication channels, remove combustible yard storage, relocate valuable stock or supplies away from the site, back up computer servers, and other property loss prevention duties. Prompt action by well-trained employees at the outbreak of a fire can minimize both property damage and the interruption of business.
As mentioned in last month’s article How to Prevent & Prepare for Wildland Fires (https://risklogic.com/wildland-fire/), ideally your site is located greater than 200 ft. from a brush/grassland area and greater than 0.5 mi. from any forest or woodland area. If your site is within either of these boundaries, preparing your team is important, but preparing your building is vital to property loss prevention in these WUI zones. Use FM Global Property Loss Prevention Data Sheet 9-19, Wildland Fire to determine whether you need to prepare for radiant heat from the fire in addition to the ember attack exposure.
Applying the mindset that a majority of losses are preventable to the ember attack and radiant heat exposures, we can use articles from organizations such as the Society of Fire Protection Engineers (SFPE) and standards like Data Sheet 9-19 as codes often fall short of true property loss prevention. Articles like “Building for Fire Safety in WUI Zones” by Rick Roos are great because they share best practices to prevent structure fires in WUI zones. Rick’s article focuses on homes, but the same concepts apply to commercial properties.
Since all buildings within WUI zones should prepare for ember attack, let’s start by defining this exposure. According to Data Sheet 9-19, ember attack is “Attack by smoldering or flaming wind-borne debris that is capable of entering or accumulating around a building and that may ignite the building or other combustible material and debris.”
To protect property from ember attack, consider the following when designing or retrofitting a site:
- Use noncombustible or FM Approved wall and Class A (per ASTM E108) roof assemblies. Ensure that all gaps are sealed and that there are no combustible exposed materials.
- Limit re-entrant corners and areas for debris to accumulate
- Seal eaves with a noncombustible or ignition-resistant material
- Use FM Approved fire barriers to seal penetrations in the exterior envelope
- Cover vents and louvers with close-weaved bronze or steel wire mesh having a maximum nominal size of 1/8-in.
- Use fire rated windows with noncombustible frames that do not operate. If operable windows are needed, cover the openings as you would the openings in vents and louvers
- Use normally closed, 1-hr. fire rated exterior doors that are designed to prevent embers from passing through the gaps
- Restrict the use of light bands and skylights. Where they are used, choose wired-glass or FM Approved materials
- Use interior roof drains with noncombustible covers and drainpipes for the first 3 ft. of the pipe, and/or scuppers in lieu of gutters
- Design fuel breaks into the landscaping by eliminating all combustible vegetation and combustible features or outdoor structures within 5 ft. of buildings and equipment, and by providing an area of reduced fuel load near critical buildings and equipment
If your building is also exposed to radiant heat from the wildland fire, passive measures to prevent the building and contents from igniting are the most reliable means to prevent widespread damage. As determined by Table 2.3.2.A and Table 2.3.2.B of Data Sheet 9-19, if the estimated radiant heat exceeds 12.5 kW/m2, a combustible wall should be retrofitted with a noncombustible or stable fire resistive wall. If the estimated radiant heat exceeds 30 kW/m2, stable fire resistive wall assemblies and fire resistive openings with a minimum 1-hr. fire rating are needed to provide adequate passive protection. Alternatively, reduce the fuel load around the buildings and/or equipment to reduce the radiant heat exposure to an acceptable level.
Are you in a WUI zone?
Do you know if your building is exposed to ember attack or the radiant heat from wildland fires?
If you are exposed, are you protected?
Engineers at Risk Logic Inc. use best practices, standards, and codes to provide a complete property assessment in WUI zones. We can assess the risk and provide concise recommendations to prevent or mitigate potential damage from the increasing wildland fire risk across the globe.
Rachel Wisch, Yue-Jun Yin (2019, October 7) Why are Wildfires More Destructive Today? Verisk https://www.air-worldwide.com/Blog/posts/2019/10/Why-Are-Wildfires-More-Destructive-Today/
Rick Roos (2021) Building for Fire Safety in WUI Zones. Fire Protection Engineering, Q4 2021.
FM Global Property Loss Prevention Data Sheet 9-19, Wildland Fire