[Filligree]

A fire-proof safe is a safe which won't be destroyed by a fire.

That doesn't mean it won't heat up.

[netsharc]

That would violate the laws of thermodynamics...

They usually have a rating of how much fire heat they can sustain before the insides get uncomfortable for paper...

[abofh]

About 420 degrees, the question is duration, not temperature.