How long with air last?

[fookisan]

Posted this on another thread and got no replies. Hope someone has some feedback. Then again, maybe is too odd of a question and no one know for sure about shelf life of air. Was told that someone died with saltwater in a steel stank that was left in it for a year with the air, but that is my only knowledge on this subject on the shell life of air. The divemaster / shop owner that told me this story said old air in steel tanks is hazardous, but old air in aluminum tanks is OK.

Copy of my earlier post.


Got a headache and some indigestion (acid reflux) on a dive to check out a pool using a small 13 CF aluminum pony for about 12 minutes. Air was about 10 months old. Is there a shelf life with compressed air?

Also the possibly that some pool water might be in the tank from last season due to running it dry in the pool, but interior moisture in the tank is only a guess and am getting it vis inspected in any case. Cannot say for sure the symptoms are due from bad air, but they went away about a half hour after the dive.

Any thoughts on the shell life of air or the symptoms? Air was bought from a reputable scuba shop.

Thanks

Dan

 

[cmalinowski]

I think that the steel vs alum is due to the fact that steel can rust (and does) which reduces the o2 content of the gas in the tank which in turn would be bad to dive with.

 

[JustinW]

I once heard from an unrelaible source that a diver had some moisture in their tank, and the tank sat for a long time. Rust formed on the inside to the point that the steel continued to oxidize until there was no more oxygen left in the tank. The result being that the guy passed out (as he continued to offgas CO2 while breathing) and died. Apparently this happened quite shallow. Once again I cannot confirm that this story is true but seems possible in theory.

 

[wedivebc]

There was a similar post on another board a while back and someone who had way more education than I, posted the calculation that showed the amount of runst required to use up the O2 in a tank would destroy the tank before a truly hypoxic atmosphere would exist. Remember that trimix divers regularly dive with low oxygen mixes and will breath as low as 16% near the surface. Below that % you need a travel mix of some sort.
It would take a lot of rust to use up 3.5 cuft of oxygen in a 72cuft tank.

 

[fookisan]

Still have not received any feedback on how long old compressed air is good for? I inspected the pony tank in question and it was dry and clean inside. Here is a copy of my earlier post detailing the question. Would appreciate any feedback.

"Got a headache and some indigestion (acid reflux) on a dive to check out a pool using a small 13 CF aluminum pony for about 12 minutes. Air was about 10 months old. Is there a shelf life with compressed air? Cannot say for sure the symptoms are due from bad air, but they went away about a half hour after the dive."

Thanks

Dan

 

[wedivebc]

Air should be good forever in theory. Like I mentioned above O2 depletion from oxydization is minimal so what else could affect the air? Not sure what else we can tell you.

 

[DiveGolfSki]

Still have not received any feedback on how long old compressed air is good for? I inspected the pony tank in question and it was dry and clean inside. Here is a copy of my earlier post detailing the question. Would appreciate any feedback.

"Got a headache and some indigestion (acid reflux) on a dive to check out a pool using a small 13 CF aluminum pony for about 12 minutes. Air was about 10 months old. Is there a shelf life with compressed air? Cannot say for sure the symptoms are due from bad air, but they went away about a half hour after the dive."

Thanks

Dan

You have to be careful Air does spoil. It will smell like rotten eggs after a while ....

Seriously, different agencies (PADI, NAUI, etc.) have different suggestions regarding the use of air stored in scuba tanks for more than a year but the practical answer is "if you do not use your scuba tank for a year or more, you should drain and replace the air. Oxidation inside a tank can reduce or eliminate the oxygen in air when moisture is present. Following prolonged storage, you should have a tank visually inspected before refilling it."

So, 10 month old gas should be trained and if your tank (pony or otherwise) hasn't been used in a while, you should have it inspected by a qualified LDS.

 

[MrConclusion]

It's only anecdotal evidence, but in the last 50 years most of the air around here has been getting pretty nasty. Maybe high pressure speeds up the process.

Seriously though, I deal with lots of bottled high-pressure gasses. Oxygen, Nitrogen, Argon, Acetylene, Propane, Helium, R-134, CO2, NO2, etc. None of them go bad with age. If air (oxygen and nitrogen; plus a little dash of argon, CO2, & helium) don't go bad separately, and these gasses don't normally react with each other, why would we imagine that they go bad in the tank?

This supposes that the air was extremely pure when filled (and you'd bloody well want to know what happened if it wasn't!) then I would imagine that the shelf life is much, much greater than the 1-year VIP when the tank needs to be emptied anyway. Maybe greater than the 5-year hydro interval? Maybe forever (until the container deteriorats) as stated earlier?

I'd be looking for another cause of the discomfort. Or better yet, duplicate everything with a "fresh" fill and see what happens.

Please keep in mind that I'm GUESSING here.

 

[DiveGolfSki]

.....If air (oxygen and nitrogen; plus a little dash of argon, CO2, & helium) don't go bad separately, and these gasses don't normally react with each other, why would we imagine that they go bad in the tank?

But freshness tastes good !!!

You may be right about the other causes. I wonder the air in that tank can be tested.

 

[Web Monkey]

Posted this on another thread and got no replies. Hope someone has some feedback. Then again, maybe is too odd of a question and no one know for sure about shelf life of air. Was told that someone died with saltwater in a steel stank that was left in it for a year with the air, but that is my only knowledge on this subject on the shell life of air. The divemaster / shop owner that told me this story said old air in steel tanks is hazardous, but old air in aluminum tanks is OK.
Dan

Nobody can give you a valid answer without inspecting your tanks and/or analyzing your air.

If you're concerned, have the tank drained, inspected and refilled.

Terry