The devices, which are not used in Canada, are thought to have saved hundreds of firefighters in the U.S. since the 1960s, according to the U.S. Fire Service.
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A fire shelter is a portable, one-person tent, made of heat-reflecting aluminum foil, heat-resistant silica cloth and lightweight fiberglass. As a last resort, a firefighter can dig into the ground, deploy the shelter, hunker down and hope that it keeps him or her safe until the fire has passed.
All 19 of the firefighters who died in Yarnell had deployed their fire shelters, and fire officials are currently investigating to try to figure out why none of them survived, and whether the deaths had anything to do with the fire shelters themselves.
"We have no idea if they failed," said George Broyles, fire project leader at the U.S. Fire Service's San Dimas Technology and Devleopment Centre in California, at a news conference Monday. "We have no idea what transpired."
The fire shelter is designed to slow the transfer of heat between outside and the inside of the tent, and to trap breathable air for the firefighter, said Tony Petrelli, an equipment specialist who deals with fire shelters and personal protective equipment at the U.S. Fire Service's Missoula Technology and Development Centre, at the news conference.
Similar shelters have been used in the U.S. since the 1960s and became mandatory there in 1977. The first generation was estimated to have saved 300 lives and the new generation, introduced in 2003, has saved 21 lives and prevented 90 burn injuries so far, the U.S. Forest Service reports.
Prior to Sunday's incident, only two firefighters had died while using the new shelter, one in 2008 and one in 2011.
Contact with flames destroys glue
However, the shelters have their limitations, Petrelli said.
They work best if they don't come in direct contact with flames, which can break down the glue that holds the materials together, making it easier for the heat to enter.
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Petrelli said firefighters are told the key to surviving inside a fire shelter is to find the best deployment site.
"It's a decision that has to be made on the ground at that time and it's not always an easy decision," Petrelli said.
He noted that it's not something that firefighters plan out in advance because the tents are only used as a last resort. Instead, firefighters are taught to focus on an escape route to a zone where they will be safe from the fire.
No fire shelters in Canada since 2005
In Canada, fire shelters are no longer used at all. Marc Mousseau, chair of the fire equipment working group for the Canadian Interagency Forest Fire Centre, said they were never widely deployed, and B.C. became the last province to stop deploying them in 2005.
Lucy Tower, manager of B.C.'s fire equipment depot, told CBCNews.ca Tuesday that the decision was made because the province's firefighters are never put in a situation where they would need to deploy a fire shelter. Much of the terrain where wildfires occur in Canada is also densely forested.
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That type of terrain is unsuitable for using the shelters, said John Flinn, equipment coordinator for the New Brunswick provincial fire warehouse.
"You have to have some place open … where you can get away from adjacent fuels," he said in a phone interview Tuesday. "There's no place in the Maritimes you can do that, really."
In general, Canadian wildfire fighters are equipped with the view that firefighters should avoid putting themselves in harm's way to begin with.
For example, there is a national standard for their heat-resistant clothing, which is far lighter than what urban firefighters wear, Mousseau said.
"The intent of the clothing is that if you do get into trouble, it will save you as you are leaving," he says.
Mousseau noted that bush and forest firefighters are in their clothing for up to 16 hours a day, several days in a row, so they can't wear anything heavy or bulky.
Less protective clothing, in many cases, may actually be safer, said Flinn, as too much protection dulls the senses.
"If you can't feel the heat on your hands," he said, "you're going to be in harm's way longer than maybe you should be."
Canadian forest-fire fighters don’t carry breathing equipment such as respirators either. Mousseau said that's partly because of the nature of what is burning. In an urban setting that may include plastics and toxic chemicals, while the fuel tends to be mainly plant matter in a grassland or forest fire.
But it's also because, like fire shelters, special breathing equipment isn't considered necessary.
"Our general consensus is that if you can't breathe, you should leave," he said.
Communication, planning are key
In fact, to stay safe, wildfire fighters rely far less on their protective equipment, and far more on communication and planning, Canadian fire officials say.
All wildfire operations are carefully planned and mapped based on where the fire is and is expected to move, and all firefighters are thoroughly briefed in advance and are in constant communication with a command centre, where the weather conditions are monitored and where everyone knows where each firefighter is and should be, New Brunswick's Flinn said.
A key part of every fire operation, he added, is an established escape route to a safety zone, an area nearby that is safe from the fire because of its natural geography, or perhaps because it has already been burnt over.
Meanwhile, Mousseau said improving communications technology, such as better satellite phones, GPS and instant messaging, has also "certainly" improved safety for wildfire fighters, by making it possible to change and communicate plans on the fly based on the latest data.
"Accurate information is more readily available."