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The New Generation Fire Shelter
Understanding how the fire shelter protects you as well as the factors that limit its performance will help you decide how best to deploy your shelter.
Types of HeatRadiant Heat: Radiant heat travels in a straight line through space without heating the space itself. It turns into heat when it contacts a cooler surface. When you stand close to a campfire, radiant heat warms you. No air movement is required for the transfer of radiant heat. Convective Heat: Convective heat requires air movement. Think of it as a blast of hot air. When flames or hot gases move past a surface, the hot air molecules transfer their heat to that surface. The hotter the air and the faster the air movement, the greater the convective heating. |
The new generation fire shelter protects primarily by reflecting radiant heat and trapping breathable air (figure 1). The new shelter has two layers. The outer layer is aluminum foil bonded to woven silica cloth. The foil reflects radiant heat and the silica material slows the passage of heat to the inside of the shelter. An inner layer of aluminum foil laminated to fiberglass prevents heat from reradiating to the person inside the shelter. When these layers are sewn together, the air gap between them offers further insulation.
Figure 1—The new generation fire shelter reflects
radiant heat and absorbs convective heat.
The outer layer of foil reflects about 95 percent of the radiant heat that reaches it. Because only 5 percent is absorbed into the shelter materials, the temperature of the material rises slowly. Unlike radiant heat, convective heat (from flames and hot gases) is easily absorbed by the fire shelter, allowing the temperature of the material to rise rapidly. When the material reaches about 500 °F, the glue that bonds the layers begins to break down. The layers can separate, allowing the foil to be torn by turbulent winds. Without the foil, the shelter loses much of its ability to reflect radiant heat. The silica material will slow heat transfer, but offers significantly less protection without the foil.
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The right side of my shelter delaminated and the foil flipped over onto the left side. I really started to get burned at that point because the only thing that was on that side of my shelter was the glass mesh. [When] there was still a tremendous amount of radiant heat coming off the surrounding area, a wind blew the shelter half back on to the other side, back to where it belonged, and it was like somebody closing a door on the oven. The radiant heat difference that just that little piece of foil made was absolutely amazing. Entrapment survivor |
The shelter’s shape allows you to lie flat. The ground protects the underside of your body and your airway is protected as you breathe the cooler, cleaner air next to the ground. The shelter’s holddown straps and wide floor allow you to hold it down in high winds. You must be holding the fire shelter down before the flame front arrives.
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The shelters really do an amazing job of reflecting that radiant heat. When that shelter lifted up and you got that radiant heat directly, and the convective heat that was coming [in], it was just an incredible change in what you felt in there. Entrapment survivor |
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