how long

[DaFadda]

, take the primers AND the powder out of the safe. A web search will provide you with the plans to build an acceptable powder/primer storage area. Its the primers that are really explosive, which is why they are packed no more than 100 per package for reloading.

When I was a 14 year old boy, I set off a 2.5" black cat firecracker in my basement. In an effort to dull the sound of it going off, I threw it into a galvanized garbage can and put the lid on it. I learned that evening what happens when we contain an explosive charge. It was 5 times as loud, and my old man kicked my butt all the way up the stairs!!!!!

But to make it even more clear...

Storage cabinets containing only primers are recommended. These cabinets should be ruggedly constructed of lumber at least 1” nominal thickness to delay or minimize the
transmission of heat in the event of fire. SAAMI recommends
against storing primers in sealed or pressurized containers.

For the entire article:
http://www.saami.org/specifications_...01-Primers.pdf

And for an article on powder storage:
http://www.saami.org/specifications_...ess_Powder.pdf