USA — Firefighters who do battle with wildfires must constantly plan and revise their escape routes and safe zones in case a change in the fire’s direction or speed forces a retreat. But if they find themselves trapped by flames, their only hope is a fire shelter.
“As far as last-ditch safety equipment, that’s pretty much the one thing that we carry,” says Wildland Firefighting Team Lead Kyle Bylin of East Pierce County, Wash.
A fire shelter is made of an outer layer of aluminum foil, backed by a silica weave, that reflects heat away from the shelter. A layer of air separates this layer of foil and silica from an inner layer of foil laminated to fiberglass. In an emergency firefighters only need to grab two plastic handles and shake the shelter open like a pop-up tent.
The crew pitches their shelters as close together as possible and talk to one another until the flame front sweeps down and makes communication impossible. “If you hear anything at all, the things you hear you don’t want to hear,” said a survivor quoted in March 2003 training manual.
Each firefighter lies in his shelter with his face pressed against the ground, taking shallow breaths. Even inside the shelter hot gases can sear his lungs if he raises his head. With fire comes wind, so each firefighter lies with his arms through the shelter’s hold-down straps, struggling to keep the shelter from flipping in winds that may exceed 50 mph. This may last for up to an hour and a half.
Although the experience is harrowing, many firefighters have emerged unscathed from shelter deployments. Others have suffered burns from minor to third-degree but survived. However, not every firefighter makes it, as the loss of 19 firefighters in Arizona earlier this summer shows.
The shelter’s outer layer of foil backed by silica reflects about 95 percent of radiant heat, and the inner layer of foil laminated to fiberglass, as well as the pocket of air between the layers, provide additional protection. But the shelter simply absorbs the convective heat of direct contact with flames.
“We’re taught to pick an area that the fire won’t burn right up to the shelter; distance from flames will reduce heating,” Bylin says. “Unfortunately, when you can’t find a good location like that or the temperature is too hot, it’s made out of foil and silica, and those will slow heat transfer but won’t prevent it.” This may have been why shelters could not save the 19 members of the Granite Mountain Hotshot crew who died fighting the Yarnell Hill, Ariz., fire on June 30. “Unfortunately, it appears the situation they were in was just so far beyond the [shelters’] capacity,” Bylin says.
That capacity, according to the Forest Service, is usually around 500 degrees Fahrenheit, a limit imposed by the weakest part of the shelterthe adhesive that binds the layers together.
The aluminum foil begins to melt at 1220 F. Between 1350 and 1610 F, the fiberglass of the inner layer becomes brittle, and by 2000 F, the silica that forms the backing of the first layer is brittle. Long before those temperatures are reached, the adhesive breaks down (around 500 F), leaving the outer layer of reflective foil at the mercy of the fire’s winds. When that layer is torn away, most of the shelter’s protection goes with it.
Yet even with some limitations, the Forest Service says that fire shelters have saved approximately 300 lives since 1977, including 21 in the past decade.
Selecting Today’s Fire Shelters
The shelters used by wildland firefighters today are actually the second generation of fire shelters, and they have been standard equipment since 2002, when the Forest Service selected a design called the New Generation Fire Shelter to replace the older version.
The selection process started in the lab, where materials from each proposed design underwent small-scale testing before the full fire-shelter designs were tested. Evaluators needed to ensure that the materials used in fire shelters were strong enough for the job, would not give off toxic fumes, and would transfer as little outside heat as possible to a person inside the shelter. Because firefighters carry fire shelters and other gear into the field, Forest Service evaluators also had to consider the weight and bulk of proposed designs. The Forest Service considered over 60 materials and combinations of materials, and they eventually tested 17 full-scale fire-shelter designs.
One of those designs came from engineer Jim Roth. He claims that because the adhesive is the first thing to break down in temperatures above 500 F, fire shelters constructed without adhesive could withstand greater temperatures, possibly including direct flames. His company, Storm King Mountain Technologies, developed a fire shelter whose layers were bound by tuftingthe sewing method used to make layered winter garmentsrather than adhesive.
Ultimately, the Forest Service selected the New Generation Fire Shelter rather than Storm King Mountain’s proposed design. Roth believes that the decision was economic. At the time, Roth told PM, his design would have cost $300 per shelter, which he says was higher than the expected price tag for the New Generation Fire Shelter. Today New Generation Fire Shelter prices range from $300 to $400 at retail.
However, the Forest Service says that although all proposed designs included cost estimates, no design was turned down purely on the basis of cost. “Storm King Mountain’s proposed fire shelter design did go through preliminary and final testing along with several other designs,” said Forest Service spokesman Mike Ferris. “The final selection was based on results of extensive testing, peer review, and performance.”
The selection of the New Generation Fire Shelter made it mandatory equipment for all federal, state, and local wildland firefighters, and all agencies that fight wildfire made the transition to the new shelter by 2010. Standardization is important, partly to ensure that in the event of an emergency, all firefighters are working with the same, familiar equipment.
10-Year Track Record
During their first decade of use 116 firefighters deployed the New Generation Fire Shelters, anduntil the Yarnell Hill Fireall but two of those firefighters survived the experience. One fatality occurred during the July 2008 Panther Fire in northern California. About to be overtaken by the rapidly advancing flames, a division supervisor deployed his shelter correctly, but, in the stark language of the incident report, “the intense heat of the fire and its residence time exceeded the capability of the fire shelter.”
During the August 2011 Coal Canyon Fire in South Dakota, the leader of a fire-engine crew deployed his fire shelter in the cab of his fire engine just before flames fully engulfed the vehicle for several minutes. A later report suggested that sheltering inside a vehicle may have placed him too high off the ground, where he was vulnerable to inhaling superheated gases from the fire, although it cannot be known for certain.
The Yarnell Hill Fire claimed the lives of 19 wildland firefighters from the Prescott Fire Department. However, more firefighters have survived, thanks to their shelters. Since 2002 New Generation Fire Shelters are credited with saving 21 lives and preventing 90 probable injuries.
An Ongoing Effort
Since its adoption in 2002 the New Generation Fire Shelter has seen a few relatively minor design changes, but the Forest Service is not looking to fully replace the current design. Ferris told PM, “there is work being done both independently and in conjunction with the U.S. Forest Service to improve fire shelters.” Just after Yarnell Hill, another Forest Service spokesman told the press that much of that work focused on improvements to the adhesive that binds the layers of the shelters.
For wildland firefighters such as Bylin, “the whole goal of everybody who’s issued one is to go through a whole career and never have to pull it out of its package.”