I've used lots of compressed gases, but the cyls were not mine, but my employer's.
Call AirGas, they won't bite you!
I spoke with AirGas mgr. in Dover(Dovah), NH: They don't seem to get worked up as long as the cyl. has not been in a fire.
If it were I(capital EYE/ME), I would see if there is positive pressure in it, AND, let some gas into a deflated poly bag, and see if it extinguishes a burning match. If it is a flammable gas, I hereby deny any culpability: you act on your own.
These two acts determine if any crap has been sucked back into the cyl., and if it is indeed COtwo, or, at least not oxygen. Good luck.