Consumers are usually surprised to find that the majority of gun safes use dry-wall for insulation — aka sheetrock, wall board, etc. Commercial and residential fire safes are not built this way, but dry-wall construction allows gun safe makers to have lower start-up costs and faster production speeds.
Dry-wall contains moisture which gets forced out by the heat of a fire, in the form of water vapor. That happens at about 300 to 330 degrees, and it actually provides cooling, similar to water evaporating off your skin. The water vapor then creates a positive steam pressure inside the safe. This pressure will minimize heat and smoke infiltration if there is a good fit between the door and frame (something missing in many safes).
There are several types of dry-wall. As far as I can tell every gun safe manufacturer that uses dry-wall, except for Fort Knox, use “Type X”. As “type X” dry-wall loses moisture it wants to contract and will eventually break into pieces similar to a dry mud puddle. Then it can cave in like it did in the gun safe shown below. Fort Knox uses “Type C” dry-wall, which is more expensive. But Type C has a component which prevents cracking and caving in. Obviously, this is better.
Also important is how the drywall is installed. Most companies pack it in tight to the steel of the safe body, so as soon as any heat hits the steel the insulation gets hot, too. Fort Knox builds an air pocket between the steel and the insulation to slow down heat transfer. (Think of the effectiveness of the air gap in a double pane window.)
Some manufacturers talk about how many layers of dry-wall they use but then cut away big chunks of it which creates hot spots when exposed to heat. When a safe has internal hinges, look and you may see that all the insulation is cut away (right down to the steel) where the hinge straps move as the door closes. Recessed holes in the ceiling for lights mean insulation is missing there, too. If you had a fire and burning wood falls on top of your safe, wouldn’t it be best for all the insulation to be in place? Purchase a low-end safe made in China and there is a chance that the dry-wall is actually construction scraps. I have seen inside a number of doors on Chinese safes where pieces of dry-wall as small as 5-inch squares are pieced together and glued in place. And people wonder why they cost so much less?
More on insulation soon . . .