I had a similar experience with some of the GI-322 back in the 80's,,,,it was in 1 lb plastic bottles from Hodgdon and I never opend them untill the symptoms began ,,,,several of the lids were "rusted" away like the example in your pic,,,and two had a large accumulation of a tar/sludge in the bottom of the can that looked like a hockey puck,,,,it was stored with other powders that did not go bad,,,Hodgdon told me of issues with the powder being stored/handled/cared for by the govt. that they thought contributed to the powder failure,,,they replaced it pound for pound (plus a little) but it could have ruined/burned down my house,,,in any case the powder you are dealing with is bad and it seems that a bad can of it (1 lb or 8 lb) can rust its way out and ruin other cans with the toxic vapors,,,one shooter I know had the vapors ruin bullets and metal tools that were stored in the same area ,,,,get it away from your house immediately and dont burn more than a cupla pounds at a time strung out on the ground (not in a big pile) or you will hurt yourself,,,,Roger