Air Fills - Age of Air

[Diver Dennis]

For the cost of a fill, I would change it.

 

[String]

Id say use it. No problem with that. Rust isnt an issue, hypoxic mix isnt going to be an issue. Use it for a dive then get it filled.

 

[NSDiver]

Heh - when I got my dad back into diving about a year ago, he had an old AL 72 sitting in the basement full with air from 1978. I breathed a little of the air and it seemed fine. Wouldn't have taken it down because the tank was WELL past it's time to get a hydro. Turns out it passed the hydro and my dad usually dives with it now.

I can't see a reason not to use "old" air.

-Nick

 

[ClayJar]

Actually I think some chemical engineer on this board proved your point in an old post that I don't feel like searching for, but I agree with you.

Assuming you were remembering me (my degree is chemical engineering, although I've never worked in that capacity), you were probably remembering the stale air thread. (Of course, I'd hesitate to use the word "proved" with my back-of-the-envelope calculations, but whatever.)

 

[Guba]

If I'm not mistaken, there was a case some years ago in which a diver used a steel tank that had been stored for a year or so. He didn't come up. The investigation into his death and the ensuing autopsy cited hypoxia due to corrosion of the lining of the tank as the culprit. I'm sorry that I don't remember the publication or the date, but I'm relatively certain the facts are essentially accurate.

 

[ChrisA]

Is there a certain window of time were the air in your tank degrades and can become dangerous to breath? ... Say for example you have tank that you filled up 9 months ago but did not use but want to now? Im not in the situation but I was wondering if there is a window of time for air?

Technically you would need to have the tank inspected once every year and they would have to empty the air in order to remove the valve and do the VIP. So you'd never have air in the tank for more than a year.

But in the real world you only need to have the inspection "current" when the tank is filled. So you might fill the tank then let it sit unused for years. If there is no water in the tank then the air should last forever. Hwever if there is water inside a filled tank and it is left that way for years there could be corrosion inside to the point where the tank is not safe. So while the air would be OK, I don't think I'd want to use a tank that had been setting full for a very long or unknown abount of time. I'd get it VIP'd.

So any tank with a current VIP sticker has air that is less then a year old and should be good to go.

Back to your case: The tank was filled 9 months ago. If the inspection sticker is 21 months old then it is marginal. If the tank was filled on a boat a few times I'd have it inspected but if always filled in a shop then it's liklely dry inside. Like I said "marginal". But if the VIP is current, use the tank

 

[ChrisA]

If I'm not mistaken, there was a case some years ago in which a diver used a steel tank that had been stored for a year or so. He didn't come up. The investigation into his death and the ensuing autopsy cited hypoxia due to corrosion of the lining of the tank as the culprit. I'm sorry that I don't remember the publication or the date, but I'm relatively certain the facts are essentially accurate.

Sounds like the tank had notonly air but water in it as well. To be safe one could use an O2 analyzer in the air and if it was not "Nitrox 21" figure something is wrong.

 

[BarryNL]

Sounds like the best advice is either put an O2 analyser on it or refill it just to be on the safe side. This risk is pretty small, but for the sake of $2 I don't take any risks.

 

[lamont]

You can calculate how many moles of gas would need to react in order to drop the ppO2 from 21% down to 16% and then use that to compute the moles and grams of iron oxide that would result.

I've dove tanks with >6 month old nitrox in them. Analyzed before diving, the analysis agreed with the contents label, and the dives were fine. Recently had them VIP'd (and looked myself) and they were fine...

 

[Sylvain]

Lets face it the longest air should stay in a tank is max 1 year. VISUAL INSPECTION.... In my book it is every year.