Exterior Wildfire Sprinkler Systems Save Homes From Fire: Wet Homes Don’t Burn!

California National Guard Photo, https://creativecommons.org/licenses/by/2.0/
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Exterior Wildfire Sprinkler Systems Save Homes From Fire: Wet Homes Don’t Burn!

IStock Image, License Granted

Drenching downpour rain storm water is overflowing off the tile shingle roof - streaming, rushing and splashing out over the overhanging eaves trough aluminum roof gutter system on a suburban residential colonial style house near Rochester, New York State, USA during a torrential mid-summer July downpour.

Do Exterior Fire Sprinklers Save Homes?

Ham Lake Fire – 188 Structures Untouched

On May 5, 2007, an unattended campfire in Minnesota’s Superior National Forest ignited the massive Ham Lake Fire. At the time, it was the second largest wildfire in the state’s history.

A dry winter and spring, coupled with strong winds, fueled the destruction of 75,000 acres and hundreds of properties.

But 188 Cook County homes and resorts were not among the casualties. Six years earlier, these properties had been retrofitted with exterior fire sprinklers.

According to the California Chaparral Institute, all 188 structures were spared — even though more than 100 of the neighboring properties didn’t make it — because of the exterior sprinklers.

“No Homes Lost”

A year after the Ham Lake Fire, a research team from the University of Minnesota concluded that “[N]o structure with a functional sprinkler system was lost to the Ham Lake Fire. This was true regardless of fire behavior, intensity, surrounding fuels, or wind.” [Emphasis added.]

Embers Are the Culprits

Exterior sprinklers work by creating an environment that extinguishes embers — the primary cause of home ignition. The sprinklers do this in three ways:

  1. Hydrating potential fuels
  2. Increasing humidity, and
  3. Creating a cooler microclimate around the home.

Prior to the Ham Lake Fire, it was believed that exterior sprinklers had to run many hours in order to fully hydrate potential fuels. But apparently not.

The crews who battled the Ham Lake Fire reported that some sprinkler systems had run for as little as two hours before the wildfire arrived. The cooler, moister environment created by the sprinklers suppressed the embers before they were able to ignite the fuels, whether structures or vegetation.

The Home Ignition Problem

While extreme, wind-driven wildfires may be inevitable, wildfire disasters are not.

As renowned fire scientist Jack Cohen has repeatedly stated, the wildland fire problem is a home ignition problem, not a wildfire control problem. In the following video clip, Cohen explains how homes ignite during wildfires, and the preventive actions homeowners can take:

Interior fire sprinklers are required in most public buildings because they’re proven life savers. But these systems are not designed to save structures. Of course, wildland firefighters strive to save as many homes as possible, but their primary focus is on suppressing vegetation fires to keep them from spreading.

For years municipal fire departments have worked to improve building codes to include more fire-resistant materials. And they’ve recently also promoted the concept of defensible space. However, last year’s deadly California wildfires indicate these measures may not be enough.

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What’s Wetter than Plain Water?

Did you know that the Class A firefighting foam used in the Frontline Wildfire Defense System actually makes water “wetter”?

Here’s how:

The foam attracts carbon and soaks into solid, combustible materials by breaking down the surface tension of the water. It helps the water penetrate the burning material to quickly suppress the fire and prevent rekindling.

National Park Service Image, Public Domain

In fact, the National Institute of Standards and Technology has estimated that water treated with Class A foam can wet a Class A fuel up to 20 times more rapidly than untreated water.

FEMA agrees that “Class A foam products, and other long-term fire retardants … provide greater thermal protection than water alone.” Which is why most municipal fire departments rarely use anything else.

Critical Capabilities for a Wildfire Defense System

In addition to the Ham Lake results, there are plenty of success stories where am exterior sprinkler system has protected a house from burning. You can read about two such examples of eave sprays and roof sprinkler systems that saved homes in the 2003 Cedar Fire in San Diego and the 2018 Camp Fire in Paradise. And Frontline’s customer in Wyoming saved her home in the 2018 Roosevelt Fire.

That said, when evaluating wildfire defense systems, there are a few critical capabilities. First, remote, satellite-enabled activation is key, so you can operate your system after you’ve evacuated or while travelling. Second, backup water and electricity sources are a must. And third, using an effective Class A firefighting foam, as described above, will amplify the protective wetting qualities of water.

For more on this, see our post “Three Key Questions and Capabilities for Effective Wildfire Defense Systems.”


Featured Image: IStock, License Granted

California Chaparral Institute

Univ. of Minnesota, Dept of Forest Resources


National Fire Protection Association