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Maximum Operating Depth (M.O.D.) S.C.U.B.A. Diving On Air.

Discussion in 'Advanced Scuba Discussions' started by Boston Breakwater, Jul 7, 2020.

  1. Akimbo

    Akimbo Lift to Freedom Volunteer Staff Member ScubaBoard Supporter

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    Sorry, I missed this part. I think it is fair to say that we (the entire class) were all pretty blasted at 285'/87M -- which was part of the point of the training. Nobody was completely out of control, unable to manage their equipment (deep sea gear), or respond to communications. Tasks were pretty basic like tying simple knots and verbal arithmetic questions. Knots were pretty tough even on deck in these rigs.

    [​IMG]

    Obviously this was not Scuba so risk was far more manageable. Very simple work could be accomplished, but not much more. Considerable concentration was essential. The biggest problem for most of us was compromised sensory function:
    • Tunnel vision
    • Numbness-like sensations that interfered with speech and manual dexterity
    • Hearing became distorted
    • Metallic taste sensations
    There was definitely euphoria bordering on silly but we could manage the giggles after the first run in a dry chamber.

    I know that many new divers believe that diving in 306'/93M of water on air is deadly. By extension, accomplishing complex work, like salvaging a submarine, is impossible. I guess that Chief Stillson and his crew didn't get the memo.

    US Navy Experimental Diving Unit
     
    RayfromTX, Bob DBF, JMBL and 5 others like this.
  2. lowviz

    lowviz Solo Diver ScubaBoard Supporter

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    For one who starts to exhibit (post-dive) at 80', I'm impressed...
     
    RyanT likes this.
  3. Boston Breakwater

    Boston Breakwater "Outlaw." Solo Diver ScubaBoard Supporter

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    Cheers.
     
    rsingler likes this.
  4. Akimbo

    Akimbo Lift to Freedom Volunteer Staff Member ScubaBoard Supporter

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    Thanks, but don't be. Thousands of us got our First Class Diver pin. Fifty 8 hour training days for Second Class Diving School, 90 training days for First Class School, being in your 20s, and career-level motivation makes all the difference.

    Would I dive to 285' on air again but on Scuba? ARE YOU OUT OF YOUR MIND? I am confident that it is survivable with proper training and experience. However, it is horribly unproductive and pretty pointless. That's what saturation diving systems are for if you need to get work done and rebreathers with Trimix if you are diving for fun.
     
  5. halocline

    halocline Solo Diver

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    Exactly. The two agencies that talk about trimix shallower than 130 ft are technical dive agencies that don't advocate diving with air ever. And I don't know this, but I would assume they allow 32% nitrox to 110 ft, then advocate helium blends deeper. Am I wrong about that, do they now say that the MOD for 32% is 100 ft? It's not a huge difference, I realize.

    But the larger point is that these agencies are not at all the mainstream for diving in general, that would be the recreational agencies. Regardless of what any of us think about PADI, NAUI, SDI, etc....the fact is that millions of successful dives to 130ft on air have been sanctioned by these recreational agencies. So it's not out of line at all to consider the use of helium for all dives deeper than 100ft to be unusually conservative and out of the mainstream, which is what I said was my opinion in my first post. Not that it's 'wrong' or 'foolish' just that for me, it's very conservative. I am perfectly happy diving air to recreational limits (130ft) as have been thousands and thousands and thousands of other divers for decades. They're not all dropping dead.

    Technical diving, that's a different story. Those are longer and/or deeper dives or in some other way much more challenging, and in those cases it makes sense to adhere completely with whatever practices the technical training recommends.
     
  6. boulderjohn

    boulderjohn Technical Instructor ScubaBoard Supporter

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    They do not want an END deeper than 100 feet, and they consider nitrox as narcotic as air, so their limit for EANx 32 is indeed 100 feet.
     
  7. tbone1004

    tbone1004 Technical Instructor ScubaBoard Supporter

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    @halocline unless something has changed, I believe it is EAN32 or 30/30 to 100ft, then straight to 21/35. Since we believe that O2 and N2 are comparably narcotic, the use of air or EAN32 to 100ft is irrelevant for this discussion as the END would be the same.

    Where the 100ft vs 130ft comes in, and @PfcAJ will have to correct me on this, is the ppO2 limit for bottom mixes at 1.3 due to working dives. That limits EAN32 to have a MOD of 4ata's/100ft.
     
  8. boulderjohn

    boulderjohn Technical Instructor ScubaBoard Supporter

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    When I was with UTD, the gas of choice past 100 feet was 25/25.
     
  9. Vicko

    Vicko Barracuda

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    I just spent 2 months digging out foundations at 50-60m on air as a bottom gas on scuba. Was i narced, yup. Was it anything more then inconvenience... For me not really. I had no trouble orientating in 0 visibility or measuring, recalculating and marking stuff. Biggest thing I noticed is that after doing some delicate sledgehammering it would take me a few seconds more to get my breathing under control, i'm guessing that's due to gas density.
     
    Dark Wolf and mac64 like this.
  10. tbone1004

    tbone1004 Technical Instructor ScubaBoard Supporter

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    fair enough, was going off of the WKPP standard gases, but point stands that it is some sort of trimix.
     

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