Ha, had a co-worker once who went on and on about his guns, the gun
shows he attended, etc. They, he went out and bought a 'fireproof' safe
to hold all these valuable.
After a few weeks, he opened the safe, and found rust on all his
valuable collector guns. It seems this brand of 'fireproof' safe had
and inner lining of some sort of soft, porous rock, like soapstone, that
was saturated with water to protect the valuables from fire. This of
course raised the interior humidity, and thus, rusted the guns very
quickly.
It was funny, since it had cost him a bundle (even used!) and he had
regaled us for weeks on all the trouble he had moving it and installing
it (he built it into a wall...
) and now it was worthless to him!
Charlie