A recent visit, for the purpose of registering a vehicle and paying some taxes, to the local county courthouse involved standing at a counter across from the large safe or strong room used by that office.
The safe is of a type still seen, although it's probably a hundred or more years old. The door, ajar during office hours, is a deep dark green, and about three or four inches thick, and several round steel bars protrude from it to lock it to the jamb when it's closed, these pieces being about two inches in diameter.
This old safe is, of course, still in daily use, and is probably only one of many such still in use.
Of course, it's a safe bet that none of them have been hit by an airplane, nor dropped from hundreds of feet through a burning, falling, skyscraper.
Therefore, there is no reason to expect them to be anything other than still serviceable, as per the well-known durability of steel and the other metals used in their construction. If protected from moisture and steam, acids and bases, high temperatures and extreme shocks, they should last thousands of years, and more.
My 1969 edition of the Encyclopedia Britannica, in the article SAFES, STRONG ROOMS AND VAULTS, reports that
Many safes and their contents survived the Chicago fire of 1871, even after falling from considerable heights through fire-ravaged buildings.
It's true that many of these were damaged from the warping caused by heat, and the contents ruined; but the safes were intact enough to be recognizable.
How many large office safes would have been at the World Trade enter complex?
There is information, on line, about the underground gold, but what about the scores, or hundreds of small safes, throughout the Twin Towers and Building 7? Shouldn't most, or many of them, have survived?
Where did all those (presumably fireproof) office safes go?
If even ten percent of offices had maintained their own safe or vault, the total number would be considerable.
Also, one would think that there would have been great interest in their recovery, and more than that, an expectation that they would be recovered.
They should have been salvageable, as most of them would have not even suffered fire damage, only the fall, and that through a falling mass that was mostly made up of small pieces of material incapable of destroying even a 200-dollar home safe from Wal-Mart.