How long is a tank of air good?

[Daryl Morse]

containing air that had been stored in a closet for 9 years...no ill effects.

For me, the $64,000 question is why? Air is cheap, why breathe air that old?

Also, the tank should have had a vis done, if by some chance there was moisture in the fill, there could have been considerable corrosion in such a long time.