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Flying after 20ft dive

Discussion in 'Ask Dr. Decompression' started by anchochile, Sep 20, 2018.

  1. hroark2112

    hroark2112 Tech Instructor

    # of Dives: 0 - 24
    Location: Raleigh, NC
    Do the math. Get a tank of 40% and stay above 20' and your PN2 is still lower than what you're breathing right now as you read this.

    With that information, make your own educated decision.
    flymolo, alvinsuper and Schwob like this.
  2. broncobowsher

    broncobowsher Solo Diver

    Strong O2, shallow dive, you will be on-gassing when you get out of the water.

    As others mentioned, happens all the time. Personally most everyone will do it. But nobody is going to recommend it.
    It's like doing a solo dive.
  3. Jack Hammer

    Jack Hammer Solo Diver

    I'm just gonna throw it out there for thought regarding breathing high O2 mixes to avoid Nitrogen ongassing, even though unlikely...

    Oxygen bends... you are still ongassing at depth

    ps, I'd still fly, you shouldn't
    BenjaminF likes this.
  4. Dirty-Dog

    Dirty-Dog Frequently Censored ScubaBoard Supporter

    # of Dives: 500 - 999
    Location: Pueblo West, CO, USA
    The MOD for 100% O2 is 20 feet. If you're going by the 1.4 PpO2 limit. If you go by 1.6... At the site in question, it's pretty much impossible to get below that. And keep in mind that the MOD is for a sustained (but not precisely defined) time deeper than that depth. It's not like you're going to instantly die if you do wiggle down into a depression and hit 21' for a couple minutes. You would have to reach 21.5 feet before instant death occurs. And of course, if you get as low as 22 feet, your entire family, including pets, will undergo spontaneous combustion.
    The point is that with a high octane breathing gas, the OP will still be off gassing on a 20 foot dive.
    BenjaminF and Saboteur like this.
  5. uncfnp

    uncfnp Solo Diver

    # of Dives: 500 - 999
    Location: North Carolina
    What is the maximum dive time for single exposure at 1.6? You do realize that dives at BHB can easily last 90 minutes and 120 is not unusual.

    As I said, pickup a tank of 36. Or even 38. No special equipment or training needed beyond nitrox.
  6. Jack Hammer

    Jack Hammer Solo Diver

    Check your math... :wink:

    PO2 for pure O2 at 20'/6m is 1.6. That is the max recommended for deco with minimal movement. 1.4 on O2 is 13'/4m, which is the max recommended for safe diving with movement. OPs 2 hour dive on O2 would probably be a pretty bad idea:)
    couv and chillyinCanada like this.
  7. Geobound

    Geobound Nassau Grouper

    # of Dives: 0 - 24
    Location: Ontario
    My Suunto D4i Novo tells me 12 hours every time I hit 16' for more than 30 minutes.

    I didn't realize it would be that long, but I would either skip the dive or wait the 12 hours.

    Good luck.
  8. dmaziuk

    dmaziuk Regular of the Pub

    Haldane observed that caisson workers coming up from 10 metres to the surface don't get bent no matter how long they spent there. So he set his M-values at 2/1. That's on air, without factoring in partial pressures etc. One could work out the pressure difference between 20' and cabin pressure of, say, 8000' (assuming the plane does not crash and burn killing everyone on board), and see if it's over 2/1 or not.

    The problem is coming up in the air does not work the same way as coming up in the water: air is compressible while water isn't, pressure changes linearly in the water and non-linearly in the air. So diving models don't work for coming up in the air and nobody can say if the above estimate would be worth anything.
  9. couv

    couv Instructor, Scuba

    # of Dives: 1,000 - 2,499
    Location: 13th floor of the Ivory Tower
    I miss the days when flying after diving was avoided until the diver was in pressure group D !
    rhwestfall and northernone like this.
  10. couv

    couv Instructor, Scuba

    # of Dives: 1,000 - 2,499
    Location: 13th floor of the Ivory Tower
    I know you're just kidding, but:
    .79 ata N2 at sea level on air
    .96 ata N2 at 20 feet below sea level with 60% N2
    BenjaminF and northernone like this.

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