Is it safe to use old air in a dive tank?

Answer 1

Usually it is fine. Air has been filtered before being compressed in the cylinder, and it does not go "off". However, if it is a really really old cylinder, the cylinder itself may have deteriorated and may not be safe to use until it has been hydrostatically tested.

Answer 2

Think about it. If it can't get out, nothing can get in. I have never had a problem with "stale" air in a Scuba tank. An air fill is relatively cheap so if in doubt, dump it out and refill.You want to be as comfortable as you can on your dive, no sense in worrying about your air quality.

Answer 3

The nitrogen and oxygen we breathe on this planet is a billion years old and still is safe. So I doubt nitrogen and oxygen in a scuba tank would make any difference.