Air in tanks: how old is too old?

[tcpip95]

I filled out tanks last summer for a dive trip that didn’t happen. Forgot all about the tanks until yesterday. I’m assuming the air is too old to use on an upcoming trip so I emptied both tanks and will refill. It got me wondering though... how old is too old?

 

[grf88]

The atoms comprising the air in your tanks were created a few billion years ago so unless anything happened to them in the interim they have a long shelf life. They may have been recycled a few times but they probably have not changed unless exposed to some nuclear reaction. If the air was moist and in a steel tank there is the possibility of changes to the O2 content due to oxidation of the steel which can be verified by testing the O2 percentage. In an aluminum tank no changes can be realistically expected.

 

[tcpip95]

Thanks. I thought I read somewhere that air left in a tank too long turned toxic, so didn’t want to take a chance.

 

[grf88]

As long as no chemical reaction such as oxidation of a steel tank has occurred then the shelf life is almost indefinite but it is best to check the O2 content on steel tanks if they have been sitting a long time.

 

[Scuba Lawyer]

I ain't got enought sciency knowhow to give a correct answer. However, just this morning the ocean looked calm so I rooted around in my garage for a full tank to go diving with. All I had was a steel 71.2 that was hydroed and filled three years ago. I tested the air and it came out to 21% 02. Smelled ok. Tasted fine. Took it for a great dive today. Still alive. Got back, took the valve off for a visual and it was pristine inside. YMMV. Mark

 

[grf88]

I ain't got enought sciency knowhow to give a correct answer. However, just this morning the ocean looked calm so I rooted around in my garage for a full tank to go diving with. All I had was a steel 71.2 that was hydroed and filled three years ago. I tested the air and it came out to 21% 02. Smelled ok. Tasted fine. Took it for a great dive today. Still alive. Got back, took the valve off for a visual and it was pristine inside. YMMV. Mark

Hope you shook the tank a few time first to re-homongenize the gases.








Just kidding.

 

[Scuba Lawyer]

Hope you shook the tank a few time first to re-homongenize the gases.

Just kidding.

BUT OF COURSE! If you hold the tank in front of you and do the Macarena it mixes it just right!