The photo shows a used Mosler vault door that we just got from a bank which is being gutted. It is a U.L. certified two-hour fire rated door. Many banks have fire rated vault doors in addition to the heavy stainless steel units on their high security vault room. When these fire doors are removed carefully they remain good and flat with no distortion. All you will need to do is repaint it. When removed incorrectly they frequently have twisted frames, thresholds which are not flat, boltworks that no longer work properly, etc. Like with a gun safe, the fit of the door and seals are really important.
One of the nice things about buying a used door like this one is that they are reasonably priced. We usually sell them for $2000 or less. Another thing is that the fire ratings are legitimate. I believe there is only one company left who makes vault doors with certified fire ratings, and they are really expensive. So why is it that you can find lots of manufacturers who sell new vault doors with “fire ratings”? It is because they just make up their ratings! Their doors have never been tested, they lie to you to make a sale.
Anyway, if you want really good fire protection on that vault room you are building look for a used vault door with a U.L. Certified fire rating from companies like Molser, Schwab, Diebold or LeFebure. Check it out well to make sure it is in good condition.