Know Your Fire Shelter

Understanding how the fire shelter protects you and the factors that limit its performance will help you decide how best to deploy your shelter (see Figure 1 and 2).

Figure 1 Labeled parts of the complete fire shelter.

Figure 2 Effects of radiant vs. convective heat on a fire shelter.

How the Fire Shelter Works

Figure 3 Cut away to show the inner and outer shell of the fire shelter.

The fire shelter protects primarily by reflecting radiant heat and trapping breathable air. The shelter is composed of two layers (see Figure 3). 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 and protects the occupant from exposure to any gases released from the outer layer as it is heated up. When these layers are sewn together, the air gap between them offers further insulation.

The outer layer of foil reflects about 95 percent of the radiant heat that reaches it. Because only 5 percent of radiant heat 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 adhesive 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. Therefore, it is important to select the best available site for deployment, one that will minimize the exposure to convective heat and flame contact as much as possible.

Fire Shelter Sizing

The fire shelter is available in two sizes, regular, and large (see Figure 4 and 5).

Figure 4 Large and regular fire shelters in carry cases.

Figure 5 Side by side comparison of the large and regular fire shelters.

The two sizes of fire shelter are easily distinguishable by the yellow pull strap (regular shelter) or the orange pull strap (large shelter) with LARGE stenciled on it, both are sewn to the polyvinyl chloride (PCV) bag. The large shelter fits easily into the hard plastic liner and case used for the regular shelter, however, there is a difference of 0.6 pounds between the regular and large shelters.

The large shelter was developed for firefighters 6’1” and taller or whose girth is greater than 53 inches (see Figure 6 and 7). The large shelter will provide better protection for larger firefighters by increasing the amount of insulative air inside the shelter and reducing body contact with shelter material.

Figure 6 Deployed regular (left) and large (right) fire shelters.

Figure 7 Overhead view of deployed regular (left) and large (right) fire shelters.

To determine if a regular shelter is the right size for you, get inside a regular practice shelter (see Figure 8). When you are inside a shelter you should be able to:

• Lie face down in the shelter with your helmet and boots on without pushing against the ends of the shelter.
• Lie in the shelter with your arms through the hold down straps.
• Fold your elbows next to your chest and protect the sides of your face with your hands with only minimal contact with the sides of the shelter.

Figure 8 Appropriately sized shelter.

If you do not meet any of the above bullets, you should strongly consider carrying a large fire shelter.

Can the Large Be Too Big?

In trials using fans to generate wind, individuals under 5’7” had difficulty deploying and holding down the large shelter. Individuals under 5’7” whose girth is larger than 53 inches should practice with a large fire shelter in strong wind to determine which shelter is right for them. Firefighters under 5’7” can use a large shelter in an emergency if a regular is unavailable. Smaller firefighters should:

• Hold the large fire shelter down by placing their feet far into one end of the shelter to prevent the foot end from catching in the wind and exposing their body to hot gases.
• Place their arms through the hold down straps up to the elbows.

• Gather the floor material with their hands to help control the shelter and to hold the edge down to the ground as best as possible.

Ensuring you have the appropriate shelter is in your best interest. If you are near the height or girth dimensions for a large shelter, take the time to determine which shelter is best for you. Your safety could be at stake!