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Thread: How O2 cells die

  1. #1
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    How O2 cells die

    I am still hearing people describe how to check an O2 cell by flushing to 100% at the surface before a dive, or by pressurizing their cells for a few minutes in a cell checker. There have been several fatalities in the last few years involving divers diving cells more than two years old. The recent Wes Skiles trial highlighted it again. We had a manufacturer being sued for Sticky Water™ causing the cells to read incorrectly when the diver was using 2 year old cells.

    Old cells may show 1.6 at 20 feet with an oxygen flush at the start of the dive but will fail later in the dive. This check does not show that the cells will be working an hour into the dive.

    Cells seem to act something like an old battery. If they are checked at the beginning of the dive, they have enough power to work properly, but later in the dive, they read progressively lower. If anyone is still diving cells that are more than 12-18 months old, please replace them.

    I really don't want to see yet another fatality for this simple and easily preventable reason.

    Bruce
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    Re: How O2 cells die

    Man I wish my cells lasted more than eight months!!!! If they do not cal. at 100% with 45 millivolts or more I replace them.

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    Re: How O2 cells die

    Hi Bruce,

    Thanks for posting. Your input is highly valued here.

    For all the money that people have invested in there Rebreathers, I think it's wise to buy one new cell and at it every 4 months, meaning if you have 3 total cells they've all been changed out in 1 years time.

    Best regards,
    Chett. L

  4. #4
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    Re: How O2 cells die

    Quote Originally Posted by shagyluke  View Original Post
    Man I wish my cells lasted more than eight months!!!! If they do not cal. at 100% with 45 millivolts or more I replace them.
    I think that is Bruce's point. A cell that calibrates at 1ata and 45mv might still be current limited at 1.2 ata. and 54mv.
    If your cells are over a year old just change them. Everyone has these great ideas to save money but for my money I'd rather live to draw a pension.
    Cheers,

    Dave....

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    Re: How O2 cells die

    Quote Originally Posted by wedivebc  View Original Post
    I think that is Bruce's point. A cell that calibrates at 1ata and 45mv might still be current limited at 1.2 ata. and 54mv.
    If your cells are over a year old just change them. Everyone has these great ideas to save money but for my money I'd rather live to draw a pension.

    Whats a pension?

  6. #6
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    Re: How O2 cells die

    Quote Originally Posted by shagyluke  View Original Post
    Man I wish my cells lasted more than eight months!!!! If they do not cal. at 100% with 45 millivolts or more I replace them.
    This is exactly the problem. The only test that will probably be sufficient is to put the cells in a PPO2 of at least the highest PPO2 that will be used during the dive, for at least the time of the expected dive. You would need a pressure pot to do this.

    Another useful test could be to flush at the end of a dive to confirm that you can still get to 1.6 on resting deco.

    The basic lesson though, is to change your cells before they get old. There are lots of different ways to do this on various rebreathers, but cycling cells and bailing out if they don't agree would be a great start.

    Bruce
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  7. #7
    Steve Sprague 4ster is a glorious beacon of light 4ster is a glorious beacon of light 4ster is a glorious beacon of light 4ster is a glorious beacon of light 4ster is a glorious beacon of light 4ster is a glorious beacon of light 4ster is a glorious beacon of light 4ster is a glorious beacon of light 4ster is a glorious beacon of light 4ster is a glorious beacon of light 4ster is a glorious beacon of light 4ster's Avatar
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    Re: How O2 cells die

    Stupid question:

    Assuming a test pot that holds O2 at pressure (say 1.3 ata O2) for an extended period of time, and that the pot was initially flushed with O2: Do cells consume enough O2 to affect the O2 level in the pot an appreciable amount over the period of say 3 hours?

    My old cell checker needed constant attention to do a short term test, which as Bruce points out does not check for worn out cells current limiting over time. Unintentionally I've just built a cell checker that could hold a pressure unattended and record pressure and mV for up to 6 cells for an extended period of time. If O2 levels don't fall too much over a few hours due to cell consumption, then I should be able to write an extended test program for the new pot and do a better test.

  8. #8
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    Re: How O2 cells die

    Gotta be careful since cells are specified at so many O2 pressure hours. Doubleing the PP of the O2 halves the lifetime of the cells, assuming that the PP O2 is still in an acceptable range for the cells.

    Michael

  9. #9
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    Re: How O2 cells die

    Quote Originally Posted by 4ster  View Original Post
    Stupid question:

    Assuming a test pot that holds O2 at pressure (say 1.3 ata O2) for an extended period of time, and that the pot was initially flushed with O2: Do cells consume enough O2 to affect the O2 level in the pot an appreciable amount over the period of say 3 hours?

    My old cell checker needed constant attention to do a short term test, which as Bruce points out does not check for worn out cells current limiting over time. Unintentionally I've just built a cell checker that could hold a pressure unattended and record pressure and mV for up to 6 cells for an extended period of time. If O2 levels don't fall too much over a few hours due to cell consumption, then I should be able to write an extended test program for the new pot and do a better test.
    problem is that with a cell checker you cannot simulate a real dive
    during diving oxygen sensors also exposed to a very strong temperature profile, and to 100% humidity: this does influence the behaviour of current limited sensors
    for that reason also we suggest the check at the end of the dive
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  10. #10
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    Re: How O2 cells die

    Thanks Paul, that makes sense.

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