I am a former philatalist with many volumes of stamps, mint and used.
For theft purposes they are housed in a large 6' floor safe and partiallly embeded in concrete.
Great for theft but not much count for fire although it has a high fire rating.
My take is that the fire rating has little to do with heat in the safe but rather the release of moisture to keep papers from charing and being destroyed. In my case all mint issues would be destroyed and most likely the cancelled items would be damaged due to excesive moisture. Can't win the all but better than on a shelf.
Haven't researched this in many moons so maybe something new has come to the forefront.
Wishing all enough,
Dick Staeffler R-3828