Not always. Fireproof safes are rated for paper, tape or drives, as well as a time limit. A safe rated for drives will guaranteed a maximum of 55 degrees (C) inside it for the rated time, enough for drives to survive without problem when powered down.
Fair enough. Much of my experience is pretty dated, to the beginning of the time that data storage was a major concern (and much of the data of the time would do just fine in a paper-rated safe).
You do raise the point that fire ratings are for specific time limits: X minutes at Y temperature.
Another key point (my long-ago sources informed me) is that one of the most important things to do after the fire is to NOT OPEN THE SAFE (this applied to paper storage, inquire with your vendor / manufacturer for data).
The same properties which make a safe proof against fire damage mean that it retains heat once applied to it for a considerable period. Apparently it's not uncommon for people to employ a fireproof safe, secure their papers and documents within it, have the safe and documents survive the fire ... and then spontaneously combust when fresh oxygen is introduced on opening to the still-blazing-hot interior.
See: http://www.theregister.co.uk/2013/12/02/setting_the_iosafe_2...