there's a 2006 post from the ex-head of CGC about this on their forums. SOME safes are not safe to store slabs in as they can cause rusty staples.
The gist: "....because of the chemical compound used to make his safe fireproof or fire resistant... We have strong reason to believe that ANY fireproof or fire resistant safe might create a harmful storage environment for your comics. Yesterday, we also learned that fireproof/fire resistant safes are prone to develop moisture. Many fire resistant safes contain insulation, which in turn, contains water crystals; thus the high content of moisture."

https://www.cgccomics.com/boards/topic/61106-important-information-about-storing-comic-books-in-fire-proofresistant-safes/
and another thread: https://www.cgccomics.com/boards/topic/444413-cgc-slabs-storing-in-a-safe/

I didn't search it, but pretty sure there's a few discussions there about storing them horizontally vs vertically, and flat vs standing, so you can find those yourself. I store mine standing up, like normal comics, so I take less of a chance of having a spine 'bow' a little over time if it's on the 'down' side (even tho the inner bag should stop most of that, they're not real tight so as not to cause the comics to get waves/warps), or having gravity shift them to one side or the other and POSSIBLY mushing the page edge against the side of the inner well/bag, especially if that edge has overrun of the cover.
so now you have more readin' material to pass the pandemic time..
edited by collectibleshop on 6/28/2020