When the voracious Caldor Fire raced through the forested Phillips Tract near Sierra-at-Tahoe, it destroyed dozens of cabins but spared a couple. One was wrapped in what looks like aluminum foil, prompting some to describe it as a giant baked potato or an oversized plate of leftovers.
However odd that may sound, wrapping buildings with what are known as fire blankets or aluminized structure wrap can foil the flames of a wildfire.
The blankets are designed to help protect cabins and other structures in three ways:
• By preventing firebrands, or large burning embers, from entering buildings through gutters, eaves, vents, broken windows and roofs, or lodging in corners or other angular spot.
• By keeping homes from making direct contact with flames.
• By reflecting thermal radiation from a large fire burning nearby over a sustained period, possibly protecting the house from bursting into flames from the intense heat.
Fumiaki Takahashi, an engineering professor at the Case Western Reserve University in Cleveland, has conducted experiments in laboratories and also in a prescribed burn area and concluded that two-layer blankets with an aluminum surface can block up to 92% of the convective heat and 96% of the radiation.
“It is effective for protecting structures for a short period while the wildfire front passes — five to 10 minutes — but longer protection would be needed to prevent structure-to-structure ignition,” he told The Chronicle.
The foil, usually applied with thousands of staples, isn’t off-the-shelf Reynolds Wrap, though it is sold in rolls. It’s aluminum on the outside, woven threads of polyester and fiberglass inside, and laminated with a high-temperature adhesive, according to Dan Hirning, founder of Firezat, a San Diego company that sells the foil.
“It’s not tin foil,” he said. “It’s so perfectly engineered after all these years.”
Foil-wrapped houses may seem like a new technology, Hirning said, but the idea was born in the Yellowstone National Park fires in 1988, when firefighters working to protect a remote historic building had to flee but cut up some of their protective fire shelters and tacked them to the building.
“They think that’s part of what saved them,” he said.
Perhaps because of its origin, the U.S. Forest Service often uses his fire wrap, Hirning said, usually to protect historic cabins and other buildings off the beaten track where they can’t be guarded by fire crews with hoses and water, or when firefighters can’t wait for the flames. They’ve also been used by broadcasting and telecommunications companies to protect transmitters and repeaters as well as by homeowners, mainly people who own large remote estates or large family cabins.
But the popularity of the foil among owners of smaller mountain homes and cabins in high-fire-danger zones has grown in recent years, Hirning said. Government firefighting agencies used to account for about 95% of his business, he said, but that’s gradually shifted, and homeowners now account for about 40% of sales.
But wrapping the family cabin in protective foil isn’t something that can be easily accomplished as the fire nears. Even if a homeowner has rolls of the wrap on hand, the biggest obstacle is time. Covering a typical cabin in foil takes four to five people six to seven hours and thousands of staples.
Firezat sells 200 foot rolls of 5-foot-wide foil wrap for $687, and there are other products on the market. To install the blanket, a homeowner and helpers place the roll on a shovel or broom handle and spool out the wrap, starting at the bottom of one wall of the house, stapling it into place, then moving up, overlapping the previous layer by a couple of inches. All vents and gaps need to be covered as well as the roof, depending on the type.
Once the house is covered, Hirning recommends topping the foil shield with chicken wire to help hold it in place as the fire nears and winds pick up.
Buyers are required to sign a waiver acknowledging that the product is not guaranteed to prevent a wrapped structure from being damaged or destroyed.
Jennifer Diamond, a spokeswoman for the team fighting the Caldor Fire, wasn’t sure who wrapped the Phillips Tract cabin but said she’s helped cover a historic backcountry building with foil in the past. Aside from historic buildings, firefighters might choose to wrap a remote cabin where property owners have already cut back vegetation, cut down overhanging trees, and cleared roofs and gutters of debris.
With so many cabins and houses in the forests, the intensity of the fires and the limited number of firefighters, there’s rarely the time or people to wrap more than a single structure, much less a cluster of homes in a rural neighborhood.
“We don’t have a lot of time to do all that,” she said. “It takes a lot of time and effort and firefighters to (wrap a cabin). It’s not something we can run around and do to everything.”