Although good at protecting their contents from fire and impact, fire and impact resistant safes are not very theft resistant.
Another downside of fireproof safes is that the interior often feels damp. Collectors have complained that papers stored inside these safes smell musty. This is due to the insulation used. Some fireproof safes are insulated with what is referred to as a “wet insulation.”
Commonly, this is a mixture of Portland cement, diatomaceous earth, glass fibers and vermiculite. As this mixture cures, the vermiculite and diatomaceous earth absorb and retain any of the moisture. In the event of a fire, they release it as steam. The moisture inherent in this kind of insulation creates the damp interior. As such, fire safes are not usually recommended for storing collections, since the higher relative humidity can lead to mold and corrosion.