Below is a smaller portion of the test curve which was shown in the previous blog. Note how with the three inferior safes the inside temp shoots almost straight up at the beginning of the test. Then at about four minutes the curve turns back down slightly before shooting up again. This momentary reversal happens when the expanding heat seals get hot enough to expand. It does help, but it is clearly inadequate.
If there is a large gap between the door and the door frame, or the door does not close snugly, then heat and smoke will just pour in. In theory when the insulation gets hot enough to release moisture it provides a degree of cooling. And the resulting water vapor should create a positive pressure to keep really hot air from coming into the safe. But these affects are not enough to overcome poorly designed doors which do not seal.
So why did the American Security safe perform so well? First, these safes have plate steel doors that have tight tolerances so the doors fit properly. Second, these units have two types of seals. They have an expanding seal like other safes (top edge of door in photo above). But they also have a cold seal (in door frame) that keep out heat and smoke even before the expanding seal gets hot enough to work. Makes perfect sense, doesn’t it? None of the test safes were by Fort Knox, but most Fort Knox gun safes also use double seals. The inner seal (see photo below) expands, while the outer seal is a fin-type which is very air tight all the time. Graffunder gun safes use double seals, too — see earlier post.
Why don’t other safe manufacturers use double seals? Some choose to sacrifice real protection in favor of lower costs. When buying a gun safe, make sure the door fits properly and make sure it has both hot and cold seals