Wind-driven glowing embers pose a greater threat to homes than fire itself
After the 2003 Southern California wildfires, Stephen Quarles took a tour of burned-out neighborhoods.
“Home after home had noncombustible siding, roofing, dual-glazed windows,” recalled Quarles, a UC Cooperative Extension advisor. “You would have thought they had a good chance of surviving -- but they didn’t.”
It was another piece of evidence that the greatest threat to houses during wildfires isn’t a blast of flame, but a shower of fiery embers.
Embers can be as small as a pinhead or as large as a flying sheet of plywood. Winds can toss them a mile or more ahead of a wildfire. After the main flame front moves on, burning debris continues to spit them out.
“The main body of the fire will stay at a house a few minutes, no more than 10,” Quarles says. “The ember shower can last for 30 minutes or more before the fire and two hours or more after the fire has passed.”
The glowing fragments blow through house vents and pile up in attics like tiny smoldering snowdrifts. They nestle under the eaves, on decks and in roof corners.
In a lab set up in a cavernous garage on the grounds of the University of California’s Richmond station, Quarles spends his time testing fire-resistant building materials. Lately he has been experimenting with vents and embers, using a metal test box outfitted with a window so he can peer inside.
He gives a demonstration. First he pours a carefully measured scoop of wood pellets onto a grate on top of the box. Below that, he places a vent. It has a quarter-inch mesh screen, typical of the type installed in attics and eave boards in millions of houses all over California.
Beneath the vent, Quarles spreads a few pages of the Davis Enterprise newspaper.
Then he lights the wood pellets with a gas flame. After a minute, orange-red embers start falling through the vent screen like water through a sieve.
The newspaper catches fire and turns to ashes.
The vent, Quarles notes, “didn’t provide any kind of protection.”
New vent designs, developed by private companies and soon to be on the market, have done a much better job of stopping embers in his experiments. But they also reduced air flow -- a problem Quarles says could be countered by installing more vents.
One of the new designs, patterned after a snow-stopping Scandinavian vent, has metal baffles. Another has a honeycomb grill coated with a special paint that expands with heat, sealing the vent holes.
The lowly house vent could be the key to saving multimillion-dollar homes.
In the commandments of fire prevention, ember protection has joined the concept of defensible space -- clearing a home’s perimeter of flammable vegetation.
“You must have both,” says state Fire Marshal Kate Dargan. “For existing construction, if we could change the roofing and the vents and defensible space, those homes will have a likelihood of survival in the 90%-plus range.”
Under state regulations that took full effect in January, new buildings in high-fire-danger zones will have to incorporate fire-resistant building materials and designs in eaves, decks, vents and other features.
“This represents one of the largest shifts in our wildfire preparedness culture in a long time,” Dargan says. The effort was launched after the devastating 1991 Oakland Hills blaze, in which nearly 3,000 structures were destroyed and 25 people killed.
“The last several decades, our losses are escalating,” Dargan says. “We have a couple of decades of scientific evidence . . . that is showing us we can fix it with this combination of defensible space and building standards.
“We should not rely on just firefighters to address this problem.”
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