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I know you're supposed to have a visual check on tanks each year.
My wife and I bought six new tanks three years ago. All are filled and they haven't been used in three years. Actually, two have never been used.
I'd like to use them now and hate to waste the fills. Does air go bad? Would it be okay to use the air and then get the visual check done on the tanks when I have them filled? Am I being penny wise and pound foolish?
I have had a tank for 3-4 months and used it with no problem. Not sure how air would go bad. It couldn't get contaminated if the tanks where full that I know of anyway. I'll check back and see what others say.
Now let me address the other problem. Did you buy 6 tanks then not take them diving? If I lived closer I would offer to excersize them for you.
Especially if they are aluminum they are probably fine but 3 years is a long time. Any trace of anything could have become nasty. I'd get them inspected and filled fresh just to be safe.
Pete
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I'd like to use them now and hate to waste the fills.
Just pretend you dove them in your sleep. Or lie down on the couch with a watch and an SPG and get an absolute baseline SAC number. Or set one by the bathtub and practice breathing from a free-flowing regulator (which will use lots of air really quickly). Or get one of those quackers and go down to the local lake to feed some ducks. Or unscrew one of your regulator hoses to see how quickly it'll drain a tank (compare HP, LP, and no-reg, if you have three full tanks). Alternately, you can just dive them (but if they taste or smell funny, abort).
Honestly, though, I've "wasted" more than a tank a year. In fact, I just did a round of visuals and eddies on all my tanks, and I drained a couple full cylinders just so that I could finish *all* my tanks. I had fun with them, of course. They kept me cool the whole time I was working.
6 months is the longest I have let air sit, I imagine it might pick up some metallic taste over such a long time. Fills are usually cheap or free so its not worth risking it especially on a deep dive or something. I would at least take one tank and hook it up to a reg and breath for 2 minutes or so and see if anything tastes/smells funny or you get any other side affects.
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Scubapro MK17's (prefer DIN), Scubapro MK2+ (prefer DIN), Scubapro S600's, Scubapro brass Yoke adapters, tanks, reg tools, Solus lights, etc...
Does air go bad? This is a really good question, and sadly I do not have a good answer.
Can air go bad? I'd guess it could if it reacted with something in the tank (rust comes to mind.... we used to have to check the oxygen content of ships' holds or other "sealed" spaces on ships before entering because with time the process of rusting removes oxygen from the air in an enclosed space...).
I do not really know how likely this is with scuba tanks that have been inspected regularly, but for the price of an airfill vs the dire consequences of contaminated air I'd just get a refill...
For me if the air is over 6 months I refill the tank, but that's just me and might be too conservative...
I'm very interested to see what others with more knowledge than I have think:
Good Luck!
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If the tanks are clean and dry, the fill will last for a long time. However, if they were filled on a boat and a little moisure got in the tank then there can be a serious problem. Everyone knows that this will corrode the tank, but consider what happens in the process of corrosion. In a steel tank the oxygen will slowly be depleted as the Fe + O2 -> FeO2 reaction consumes it. In other words the O2 fraction will slowly decrease and the gas will eventually become anoxic. A similar effect will happen in Aluminum cylinders.
Needless to say, breathing an anoxic tank is very serious. It is rare that the corrosion is so bad that this will kill you, but it can and has happened. I wouldn't dive a tank with a fill that is older than 6 months. Air is cheap.
Three years? Aluminum tanks? Odds are the air is fine. If it were me I'd still drain it, have do a vis and get them re-filled. The tank are obviously due for vis anyway and perhaps a hydro...
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