I store all of my powders in one small room of the house. There are 30-40 one-pound canisters. Naturally, I keep the lids tightly sealed, and the temperature is never in excess of 75 degrees. However, occasionally I'll open a canister to check the amount remaining.
In spite of these storage conditions, I'm wondering if fumes might be a health hazard. A few of canisters are the older cardboard and metal containers, which probably do not seal as well as the modern plastic ones.
I'd be curious to know if workers in powder factories experience any symptoms from breathing the vapors. I know from experience that handling blasting dynamite on a regular basis can bring on wicked headaches.
Look forward to your response.