Does gas go bad / expire / go stale in a tank?

Discussion in 'Tanks, Valves and Bands' started by Pierre Siquet, May 22, 2004.

  1. Pierre Siquet

    Pierre Siquet Angel Fish

    35
    0
    0
    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
     
  2. Drew Sailbum

    Drew Sailbum Scuba Instructor

    # of Dives:
    Location: Grand Cayman
    2,124
    53
    48
    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.
     
  3. mustfajohnson

    mustfajohnson Angel Fish

    61
    0
    0
    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?
     
  4. Pierre Siquet

    Pierre Siquet Angel Fish

    35
    0
    0
    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
     
  5. Al Mialkovsky

    Al Mialkovsky Scuba Instructor

    # of Dives: I'm a Fish!
    Location: Butte Falls Oregon
    4,684
    28
    0
    So where does the O2 go??
     
  6. Sideband

    Sideband Surface Interval Member

    # of Dives: 200 - 499
    Location: Carol Stream, IL
    1,514
    3
    0
    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
     
  7. Sideband

    Sideband Surface Interval Member

    # of Dives: 200 - 499
    Location: Carol Stream, IL
    1,514
    3
    0
    It is 'lost' when it bonds to the iron in the steel to create iron oxide, rust.
     
  8. KidK9

    KidK9 Loggerhead Turtle

    # of Dives: 100 - 199
    Location: Columbus, Ohio
    1,338
    0
    0
    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.
     
  9. archman

    archman Divemaster

    # of Dives: 200 - 499
    Location: SE Florida
    4,955
    49
    0
    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.
     
  10. miketsp

    miketsp Great White

    # of Dives: 500 - 999
    Location: São Paulo, Brazil
    3,462
    120
    63
    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? ;)
     
  11. KidK9

    KidK9 Loggerhead Turtle

    # of Dives: 100 - 199
    Location: Columbus, Ohio
    1,338
    0
    0
    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??
     
  12. miketsp

    miketsp Great White

    # of Dives: 500 - 999
    Location: São Paulo, Brazil
    3,462
    120
    63
    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
     
  13. miketsp

    miketsp Great White

    # of Dives: 500 - 999
    Location: São Paulo, Brazil
    3,462
    120
    63
    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.
     
  14. Pierre Siquet

    Pierre Siquet Angel Fish

    35
    0
    0
    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
     
  15. Web Monkey

    Web Monkey Omniheurist ScubaBoard Supporter

    # of Dives: I just don't log dives
    Location:
    6,921
    12
    0
    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


     
  16. Pierre Siquet

    Pierre Siquet Angel Fish

    35
    0
    0
  17. Henry

    Henry Barracuda

    # of Dives:
    Location: North Vancouver, British Columbia, Canada
    255
    9
    18

    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
     
  18. Pierre Siquet

    Pierre Siquet Angel Fish

    35
    0
    0
    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!
     
  19. Curt Bowen

    Curt Bowen ScubaBoard Author

    # of Dives:
    Location: Sarasota, FL
    1,110
    67
    0

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

    Pierre Siquet Angel Fish

    35
    0
    0
    Lots of talk, because the place I can refill is 8 hours drive to go.
     

Share This Page