Most gun safe manufacturers use Palusol brand intumescent fire seals, commonly called the “expanding heat seal”. Palusol is a copyrighted trademark of Odice, LLC. There are several variations of the product with slightly different characteristics, and several thicknesses are available. I believe most gun safe and vault door manufacturers use the “PM” product.
According to Odice’s sales materials, Palusol PM is hydrated sodium silicate material coated on both sides with epoxy resin, the core is reinforced with glass fiber. It is encapsulated in a rigid thermoplastic profile. Self-adhesive tape on the back allows quick installation. The appearance of this seal is a shiny clean straight line on the edge of the door or on the frame of the gun safe. At least one manufacturer uses a variation that comes in rolls rather than rigid strips; it saves time in production, but looks cheap. Pictured is the edge of an American Security BF safe door showing the rigid version Palusol seal right behind the 1/2″ plate steel door front. Tape over the corner keeps the strips from coming loose. In addition, taping over the cut ends of the Palusol prevents air and moisture infiltration which can cause deterioration of the product.
When exposed to fire Palusol’s thermoplastic covering melts. That allows the sodium silicate material to expand, filling in gaps between the door and frame of the safe. It becomes a rigid non-combustible foam with a high level of thermal insulation. According to Odice this expansion is equal to, or greater than, five times the material’s original thickness (not eight times thicker as claimed by a number of gun safe manufacturers). This makes for a barrier to the passage of fire, hot gasses, smoke, etc. Palusol has been tested by independent labs. Under normal conditions it has been shown to be effective for at least 25 years.
The next post will talk about the limitations of Palusol seals in most gun safes.