Fire shelter training stresses the importance of deploying in an area where there will be no direct flame contact. Recent tests by the Missoula Technology & Development Center, though, have shown that avoiding flame contact is far more important than was understood before. Improvements in video recording equipment have shown that direct flame contact can cause fire shelter materials to break down; glue used in the shelter material produces gas and can fill the shelter with smoke. The gas and smoke are flammable, and if flame enters the shelter through a pinhole or under the edge, the gases can ignite and cause a flashover. The shelter material continues to burn after the flashover, and damage ranges from small holes in the aluminum outer layer to large holes in the aluminum and fiberglass cloth to total destruction of the shelter. Similar damage can occur from flames in grass and ground litter or from intense flame fronts.
The limiting factor on the shelter's durability appears to be off-gassing and ignition of the adhesive. The precise temperature or heat flux that causes this is not yet known, but recent test results indicate that the temperature is much lower than previously thought. The ignition inside the shelter causes rapid delamination and flaking of the aluminum foil, but when the heat load outside is reduced, the shelter material stops burning in a matter of seconds. If the intense external heat load continues, off-gassing and combustion also continue.
Firefighters have survived entrapments in shelters with areas of delamination and missing foil. They may have experienced fire within their shelters. We still believe that the conditions inside the shelter are safer than those outside the shelter, but flame contact does reduce the protection offered by the shelter.
Fire shelters do have limitations. In light of these new findings, it is critical that firefighters recognize the importance of deploying shelters in an area that is a large as possible and as free of fuels as possible. Suggested deployment sites include gravel or paved roads, areas cleared by dozers to mineral soil, or black areas with no residual fuel. Remember that grasses, fine fuels, ground litter, and firefighter equipment such as fusees can ignite and burn the shelter. These precautions are in addition to those listed in "Your Fire Shelter" [1995 edition] -- particularly those related to situations that could expose the shelter to flames or convective heat - such as chimneys, steep slopes, draws, etc.
First and foremost, remember that all firefighting tactics must be selected to ensure firefighter safety at all times. Escape routes and safety zones must be known by all and must be continually reevaluated. The fire shelter has limitations; it is not a guarantee of your safety. It is a last resort. If you must deploy a fire shelter, it is extremely important that you deploy in an area where flames will not contact the shelter.
For more information, visit Storm King Mountain's website.
