How long does air keep?

[CalgaryDF]

That's the story with steel cylinders?

I believe he's talking about the fact that steel tanks cam rust inside lowering the oxygen content (and getting rust inside). Aluminum tanks are much less likely to oxidize because aluminum oxide forms an airtight layer over the pure metal protecting it.

 

[idocsteve]

Air goes bad?

Does that mean one morning we're all gonna wake up and take our first breath of the day and collectively say "Oh S%$T!"?

 

[Doc Harry]

That's the story with steel cylinders?

Yup, oxidation (rust) in a steel cylinder can consume the oxygen and reduce the O2 percent in the mix.

In one study at the University of Rhode Island, where cylinders were steel cylinders were stored full of air and cooked at 100 degrees for 90 days with 500ml of salt water, rust reduced oxygen to 15.0% and increased carbon monoxide to 10 ppm. Control cylinders did not demonstrate such changes in that study. (Cichy, Francis, Hilbert Schenk, and John J. McAniff. Corrosion of Steel and Aluminum Scuba Tanks, University of Rhode Island Technical Report 62, 1978.)

In 1974 there was one documented case of a death that was caused by breathing a corrosion-induced hypoxic mixture. (Schench, Hilbert V., and McAniff, John J. United States Underwater Fatality Statistics-1974. NOAA Report URI-SSR-75-10)

In this case, the diver used his steel cylinder on a dive. There was 300 psi remaining when he put it away.

Three months later, he took the same steel tank (with only 300 psi) to a depth of 12 feet to search for an outboard motor. Five minutes into the dive his bubbles were noted to cease and his body was later recovered.

Analysis of this accident revealed severe corrosion of the tank with large amounts of rust. There was 200 psig remaining but the oxygen content of the gas was measured to be only 2% to 3%.

The steel tank in this accident had neither a current hydro nor a current visual inspection.

It is unlikely that any of these scenarios would be encountered today, but it is food for thought.

 

[miketsp]

The general opinion from manufacturers of medical gases is that shelf life is indefinite and certainly longer than cylinder inspection cycles. So with the exception of the rust O2 absorption possibility mentioned in steel cylinders, don't worry about it. The air will be as good as the day they were filled. If you have stored steel cylinders for a long time just check then with an O2 analyser before use.

 

[hydrochild]

I had the same question. Answer = air is cheap -why take the risk (even if it is very small)?

 

[JBRES1]

In the off season I use the air in my cylinders to power air tools, test actuators in my shop, fill tires, use the air to dry my cylinders after I do the annual cleaning. I just about drain down my banks by early March , then re-fill them while the air cold and has low humidity in it (saves the filters).

Jim Breslin

 

[MarCn]

In the off season I use the air in my cylinders to power air tools, test actuators in my shop, fill tires, use the air to dry my cylinders after I do the annual cleaning. I just about drain down my banks by early March , then re-fill them while the air cold and has low humidity in it (saves the filters).

Jim Breslin

Thanks Jim now I know what to do.