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View Full Version : Does gas go bad / expire / go stale in a tank?



Pierre Siquet
May 22nd, 2004, 05:06 AM
Hi all,

Got steel tanks filled now for over a year. Is there any health problem in breathing this air? I know it is recommended to change every 6 months, but why?

Thanks for your ideas.

Pierre

Drew Sailbum
May 22nd, 2004, 07:59 AM
In steel tanks, if there is even a small amount of water rust can form. As rust forms, the oxygen in the breathing gas is consumed. This can reduce the oxygen concentration below that necessary to sustain conciousness at low pressures.

While you can empty the cylinder and then refill it, you could just test the oxygen content with an analyzer used for nitrox. Use a freshly filled cylinder to calibrate the sensor. If the oxygen content is below atmospheric, you should have your cylinder inspected for rust damage.

mustfajohnson
May 22nd, 2004, 08:00 AM
An answer depends on the the condition of the interior of your cylinders. Certainly you need to have your cylinders visually inspected. I don't know where you are diving but in the USA your cylinder should be visually inspected if it has been sitting idle for so long. Depending on the amount of rust, I believe figure is you can lose up to 6% of the O2 content monthly. At 6% it doen't take long before the O2 level is at dangerously low levels. I would have to drag out my manual to be sure but you can probably check Bill High's website http://www.psicylinders.com and try to send him an email. Why risk your life for the price of a VIP and air fill?

Pierre Siquet
May 22nd, 2004, 08:16 AM
OK, I got the point, Thanks a lot. I did not know it would be O2 depletion, which actually is very logic. Actually, my tanks are almost brand new (just couple of dives), so i believe it is OK. If I do not post within 6 months, then there was not enough O2.

Thanks again

Pierre

Al Mialkovsky
May 22nd, 2004, 08:50 AM
So where does the O2 go??

Sideband
May 22nd, 2004, 08:55 AM
Why risk your life for the price of a VIP and air fill?

It's worse than that. It's a risk for just the cost of an air fill. He will have to have the VIP anyway to get them refilled. (assuming US diving anyway)

Joe

Sideband
May 22nd, 2004, 08:58 AM
So where does the O2 go??

It is 'lost' when it bonds to the iron in the steel to create iron oxide, rust.

KidK9
May 22nd, 2004, 04:55 PM
Hey all, bought a new AL80 last year (Luxfer), and wondering how long my 32% Nitrox is good for. It was filled and checked last September - so the air is around 8 months old.

archman
May 22nd, 2004, 05:25 PM
Now that's a question I've never heard before, and a very good one at that. I too await the posts by the compressed air technophiles.

miketsp
May 22nd, 2004, 05:34 PM
Hey all, bought a new AL80 last year (Luxfer), and wondering how long my 32% Nitrox is good for. It was filled and checked last September - so the air is around 8 months old.

Air/Nitrox in a cylinder is valid indefinitely. If you think about it after each dive you only top up the cylinder so you are always breathing some old air.
In practice you may or not have to empty it at each annual inspection - varies from country to country. Most countries require internal visual each year so tap has to be removed.

But of course you will recheck the O2 PP prior to the dive won't you? ;)

KidK9
May 22nd, 2004, 06:20 PM
Of course I'll check the O2. So how long does anybody think that should be good for? I plan on going to the shop tomorrow to use their analyzer, anybody wanna guess what it'll read??

miketsp
May 22nd, 2004, 07:18 PM
Being a high grade aluminium alloy cylinder I would expect it to read the same as it did 8 months ago.
The only place for the oxygen to go would be if it could combine with something in the inner surface of the cylinder or in the actual air mixture - oxidation. The inner surface of the cylinder should already have oxidised to its maximum extent before you had it filled and there should be no significant impurities in the nitrox mix.
But you still test with your O2 analyser to make sure.

If it was a steel cylinder with any humidity in the mix then other factors would come into play.
See thread
http://www.scubaboard.com/t57807.html

miketsp
May 22nd, 2004, 07:36 PM
I gave the answer above because I remember looking into this after my Nitrox course some time ago but then I became curious about O2 PP above 40% so I researched several sites of cylinder manufacturers and medical gas suppliers.
The general opinion from the manufacturers is that compressed medical gas products, including pure O2, do not degrade over time. The only check necessary apart from periodic cylinder structural testing is remaining pressure.

Pierre Siquet
May 22nd, 2004, 07:59 PM
Do not know what VIP is, but refilling is 8 hours drive from here to go and extra 8 back. But I am going to refill it as I am also going to dive at 8 hours drive.

Cheers

Web Monkey
May 23rd, 2004, 10:19 AM
VIP = Visual Inspection Program

Someone lets the air out, removes the valve and inspects the inside of the tank for rust, cracks, etc. (or in my case, some type of small mysterious green slimy smear that appeared on the bottom of my pony after a trip to Florida).

Terry



Do not know what VIP is, but refilling is 8 hours drive from here to go and extra 8 back. But I am going to refill it as I am also going to dive at 8 hours drive.

Cheers

Pierre Siquet
May 24th, 2004, 12:43 AM
Thanks

Henry
May 25th, 2004, 01:25 AM
Do not know what VIP is, but refilling is 8 hours drive from here to go and extra 8 back. But I am going to refill it as I am also going to dive at 8 hours drive.

Cheers


Seriously, move closer to dive shop and dive site. It will make your life easier and I will feel less pain when I read you posts.

Henry

Pierre Siquet
May 25th, 2004, 05:03 AM
Seriously, move closer to dive shop and dive site. It will make your life easier and I will feel less pain when I read you posts.

Henry
Yep Henry, I have the same pain than you when I read myself. I will get them inspected and rifilled. Actually, the risk of problem is very low, as Tanks are almost brand new.

Feel released!

Curt Bowen
May 25th, 2004, 07:13 AM
Hi all,

Got steel tanks filled now for over a year. Is there any health problem in breathing this air? I know it is recommended to change every 6 months, but why?

Thanks for your ideas.

Pierre


Seems like a lot of talk when its much easier just to drain and refill if your concerned.

Pierre Siquet
May 26th, 2004, 12:59 AM
Lots of talk, because the place I can refill is 8 hours drive to go.

jlayman800
May 26th, 2004, 09:42 AM
If somebody hasn't broken in and added or taken out some O2, it will still be the same precentage it was when it was filled. There is no magic. The precent O2 doesn't change.

Particularly with Nitrox, the air mixture in the tank is good for as long as you have it. The air and O2 put in your tank was particularly clean if it came from a qualified Nitrox fill station and the tank was particularly clean because it is a Nitrox tank. I believe you are safe holding it for as long as you want.


Of course I'll check the O2. So how long does anybody think that should be good for? I plan on going to the shop tomorrow to use their analyzer, anybody wanna guess what it'll read??

rescuediver009
May 26th, 2004, 10:43 AM
Although the gas does nto expire, I onceserviced a tank that was an AL19 cu ft. It was reserved as a bailout bottle only and it had a 36% mix in it for a year as the guy never used it. Well, when I opened it up there was a nice racing stripe of oxidation on the side it was stored on. Not the end of the world but I would recommend that it be cycled through soon.

KidK9
May 26th, 2004, 04:02 PM
Yeah, I had it analyzed at the shop, ot read 32.1%, as I kinda expected. It'll get used this weekend in Ginnie Springs.

pescador775
May 26th, 2004, 04:49 PM
Air or Nitrox stored in an aluminum tank can take on a funky smell. This happens over a couple years if the tank has any moisture inside. The O2 level won't vary much, IMO.


Yeah, I had it analyzed at the shop, ot read 32.1%, as I kinda expected. It'll get used this weekend in Ginnie Springs.

matt_unique
May 27th, 2004, 10:27 AM
Yeah, I had it analyzed at the shop, ot read 32.1%, as I kinda expected. It'll get used this weekend in Ginnie Springs.

With AL tanks serviced and maintained you should be fine but it's just a good idea to have it reanalyzed and take a breath for a taste test.

--Matt

Orlando Eric
May 28th, 2004, 02:17 PM
Now there is a question everyone strides to never ask! If my wife ever comes on here and ask how long air last or EANx tell her only about two weeks! "I have got to dive this weekend honey, my air will go bad and that would be a waste of money!"
BTW condoms only last about two weeks also.. after that they go bad, so we had better use these up tonight... :eyebrow:

Texas Diver
June 12th, 2004, 07:44 AM
The general opinion from the manufacturers is that compressed medical gas products, including pure O2, do not degrade over time. The only check necessary apart from periodic cylinder structural testing is remaining pressure.That is my understanding also.

Curt Bowen
June 12th, 2004, 08:48 AM
Hey all, bought a new AL80 last year (Luxfer), and wondering how long my 32% Nitrox is good for. It was filled and checked last September - so the air is around 8 months old.


Forever. Just analyze the gas before using it.

GotAir
June 17th, 2004, 04:06 PM
In general can air go stale in a scuba tank (Reason)I just bought a guys complete scuba gear collection and it came with 2 tanks and a bunch of other goodies. it looks like the last time he had them filled was 12 yrs ago. i was going to use the air in the tanks before I have them hydroed and filled again.

rab
June 17th, 2004, 06:23 PM
I don't think I'd trust a 12 year old fill. AL or not, it just can't be worth the few dollars.

-Rob

Kim
June 17th, 2004, 06:33 PM
Al is different to Steel - but still, 12 years is too long to my mind. If the rest of the stuff you bought didn't get used for the same length of time I would suggest that EVERYTHING you bought should be checked and serviced before you use it! You don't want your name changed from GotAir to NotGotAir now do you! :eyebrow:

NINman
June 17th, 2004, 06:34 PM
I agree with what the others have said. Get it Hydro and Inspected before even using it to test with.

roturner
June 17th, 2004, 07:03 PM
In general can air go stale in a scuba tank (Reason)I just bought a guys complete scuba gear collection and it came with 2 tanks and a bunch of other goodies. it looks like the last time he had them filled was 12 yrs ago. i was going to use the air in the tanks before I have them hydroed and filled again.

Just for curiosity sake why don't you O2 test it? I'd be interested in knowing what the results are. I'd expect that it's ok but since you need to get them hydro'd anyway I'd personally just send them for hydro now and forget it.

R..

Tx_Jeff
June 18th, 2004, 01:09 AM
We had a recent problem where a couple of tanks were overlooked and did not get a fresh fill since they were last filled six months ago (Clean/Dry/Air Compressor). The divers that used them complained of nausea, dizziness and one even complained of vomiting. We checked the remaining air in both tanks, O2 = 20.9%, CO = 0 ppm. The only thing we could figure was stale air.

SDAnderson
June 18th, 2004, 07:41 AM
In general can air go stale in a scuba tank (Reason)I just bought a guys complete scuba gear collection and it came with 2 tanks and a bunch of other goodies. it looks like the last time he had them filled was 12 yrs ago. i was going to use the air in the tanks before I have them hydroed and filled again.
I wouldn't dive the tanks until they'd been hydro'd and VIP'd. I can't give you any scientific explanation for why, but would you eat a can of soup that had been on the shelf for 12 years? It should be fine, but...

Boogie711
June 18th, 2004, 08:47 AM
Air fill = $5.

Your life > $5.

Simple math.

IslandHopper
June 19th, 2004, 12:28 AM
More important is that you don't really know WHAT is in the tanks. Aluminum is much more resistant to problems than steel.... but there could still be plenty of pitting/corrosion or organisms growing (well... grew, then died) in there after 12 years if there was any amount of moisture in it.

For the 2-4 $$ an airfill probably costs, I'd just go ahead and write-off whats in the tanks now :)

Scubakevdm
June 19th, 2004, 12:48 AM
Isn't exposure to air for prolonged periods of time the reason why stuff goes stale?

will_tekkie
June 19th, 2004, 06:41 AM
i can not believe you are seriously considering to dive with air 12 years old....(it is not a good whiskey...)

besides this...how someone store a tank 12 years with a full air charge...????tanks have to be keep a lower pressure if a long store time is expected...in this case a complete check up (hidro test included) is a must in my opinion...

GotAir
June 19th, 2004, 10:55 AM
I see everyone has an Opinion on this. Opinions are nice but they are just that !. lets do this SB i'll go home tonight and hook a reg to them and do a taste test and report back to you soon. then i'll take them to my LDS and get the results on the o2 and report that back to ya. I'l send them off to get hydroed and VI and make a note to my LDS that the air is 12 yrs old and would like to have any info he can tell me about it. I dont need these tanks to dive with right now i have plenty of other one's that are stamped and have fresh refills in them. I was just curios and still am if air can go stale.

I'll keep you posted!

Mike

Rick Inman
June 19th, 2004, 12:36 PM
I wouldn't breath off a tank I didn't know. Who knows, maybe someone filled one with aragon!! Not likely, I'm sure, but why chance it.

GotAir
June 19th, 2004, 05:02 PM
To Funny :11ztongue Taste Test results
I went into my computer/scuba room after brushing my teeth. whipped out my favorite reg hooked it up to one of the tanks ( I know the diver so i knew there was only air put in there) opened the valve and slowly took some hits of air off the reg, swished it around like good whiskey Hmmm I said. took a few more hits of air no funny taste so I quickly put my reg on a tank that had been filled a few weeks ago. hit on that for awhile and no differance as far as taste Hmmmm.

Bottom Line!

Both tanks had less than 800 psi in them so there off to the hydro place :dazzler1:


Mike

miketsp
June 19th, 2004, 06:19 PM
Isn't exposure to air for prolonged periods of time the reason why stuff goes stale?

Yep, the process is called oxidation.
Causes changes of food flavor into stale, tasteless or fishy.
May change the nutritional value of lipids into toxic ketones and aldehydes.
May kill natural colouring.

Hope there's no food in my cylinder. ;)

Scubakevdm
June 19th, 2004, 07:37 PM
Yep, the process is called oxidation.
Causes changes of food flavor into stale, tasteless or fishy.
May change the nutritional value of lipids into toxic ketones and aldehydes.
May kill natural colouring.

Hope there's no food in my cylinder. ;)

Here's what I'm saying though, how does air go stale?

miketsp
June 19th, 2004, 08:54 PM
Here's what I'm saying though, how does air go stale?

I understand that either O2 is depleted in the gas mixture due to oxidation of the cylinder itself or other impurities or the O2 has reacted with some impurity present to form a volatile compound, ie contamination present as gas or vapour.

Kim
June 19th, 2004, 09:24 PM
I think this is more of a problem in a steel tank - the oxygen and steel will together form rust - both using up the oxygen and damaging the tank. I don't think the same applies to Aluminium.

Pierre Siquet
July 11th, 2004, 09:08 AM
12 years old air must be less poluted than nowaday's :)

miketsp
July 11th, 2004, 11:20 AM
12 years old air must be less poluted than nowaday's :)

Not necessarily, quite a few industrial cities were unbreathable 12 years ago and modern cleanup programmes have improved them. ;)

wedivebc
July 11th, 2004, 12:46 PM
12 years old air must be less poluted than nowaday's :)

I think in this country 12 yo air is more polluted (less cigarette smokers). ;)

I read a thread like this a while ago on SB where someone figured you would have to oxidize several pounds of steel to remove the O2 from the air in a tank. I will try to find it.

cheers,

miketsp
July 11th, 2004, 02:09 PM
I think in this country 12 yo air is more polluted (less cigarette smokers). ;)

I read a thread like this a while ago on SB where someone figured you would have to oxidize several pounds of steel to remove the O2 from the air in a tank. I will try to find it.

cheers,
I did a similar calculation on a previous post. Just punch in the new figures:
http://www.scubaboard.com/showpost.php?p=622009&postcount=6

wedivebc
July 11th, 2004, 02:25 PM
I did a similar calculation on a previous post. Just punch in the new figures:
http://www.scubaboard.com/showpost.php?p=622009&postcount=6

Thanks Mike,
Thats the one I was thinking of. Ok it was grams not pounds but I think the point is well taken.

cheers,


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