Wildland firefighters should retire their shelter if they see one of three signs: a bag that has turned dark gray, holes in the bag, and water in the bag. A shelter bag turns dark gray if the aluminum has been rubbed off the shelter onto the PVC bag. Holes in the PVC bag can allow debris into the bag, causing abrasion of the shelter’s outer layers. A white film or dust on the aluminum foil is one sign of corrosion. This occurs if water has entered the PVC bag. Water makes it difficult to shake open the fire shelter during deployment and breaks down the bonds between aluminum foil, silica, and fiberglass cloth.