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, offgassing 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 as 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. 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.