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Accumulated 02 following a large number of repetitive Nitrox dives over 3 days.

Discussion in 'Advanced Scuba' started by Astran, Sep 30, 2019.

  1. jgttrey

    jgttrey ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 200 - 499
    Location: Houston
    694
    859
    Who does that? Maybe at the fill station someone might say "this one's got 100 bar of O2 in it" but if someone said here's a cylinder with a "PO2 of 100bar" I think we'd look at him like he had rocks in his head.
     
    Madacub and rjack321 like this.
  2. jgttrey

    jgttrey ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 200 - 499
    Location: Houston
    694
    859
    I think they are used interchangeably by divers who actually use those terms on regular basis.

    Yes, I get that some posters have wondered if there is a difference, but in actual practice I've never, ever heard someone use "PO2" to mean anything other than PPO2.
     
  3. BlueTrin

    BlueTrin ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 100 - 199
    Location: London
    1,710
    834
    When I try to google it, PO2 seems to be used for partial pressure of O2 but in your blood (for medical sources)
     
  4. GJC

    GJC Solo Diver

    # of Dives: 200 - 499
    Location: Southern California, USA
    657
    560
    I have a suggestion.

    Because the p's mean different things to different people and because the p's by themselves don't provide enough information on exactly what you are referring to, let's eliminate the p's.

    You can say O2 percent
    You can say O2 pressure using whatever pressure measurement you prefer.
    But you can't use p by itself anymore.

    I might even remove the p from my keyboard to prevent me from using p's in the future.
     
    BlueTrin likes this.
  5. doctormike

    doctormike Medical Moderator Staff Member

    # of Dives: 1,000 - 2,499
    Location: New York City
    6,875
    6,990
    Science doesn't work if "the p's mean different things to different people", and neither does scuba training.

    PO2 1.4 means that the partial pressure of oxygen in the gas that you are breathing is 1.4 ATA. It is the product of the percentage of O2 in the gas (FiO2) and the depth in atmosphere.

    Not sure what you mean by "pressure delivered", but PO2 is a partial pressure of O2. It's on a scale where 100% O2 at sea level is PO2 of 1.0. For the purposes of scuba physiology, we assume that we are always breathing gas at pretty close to ambient pressure, because otherwise you get pulmonary barotrauma.

    "O2 percent" is FiO2, which is the percentage of all of the gas molecules in the mix that are O2

    "O2 pressure" is a non-standard term, so I don't know what it means. "Tank pressure" - I know what that means, no matter what is in the tank

    "P" means nothing in the context of this discussion. Pt or Ptotal are used to mean total gas pressure (i.e ambient pressure).

    PO2 is used pretty widely in diving. I occasionally see PPO2 but I'm not sure what you are getting for the extra letter, since PO2 is such a standard usage. Insisting on PPO2 because it's more descriptive begs the question why we don't insist on writing out "Partial Pressure of Oxygen". We don't. We use PO2.
     
  6. BlueTrin

    BlueTrin ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 100 - 199
    Location: London
    1,710
    834
    Let’s hope someone does make his own definition of O then :)
     
  7. Madacub

    Madacub Contributor

    # of Dives: 1,000 - 2,499
    Location:
    216
    29

    Hi GJC, thanks for your response. I don't understand part of it. You say "The pulmonary symptoms just show up first". I think it depends. If you go straight to 140 feet on EAN32, CNS will show up first. Of course you know that. So I don't understand what you wrote.
     
  8. uncfnp

    uncfnp Solo Diver ScubaBoard Supporter

    # of Dives: 500 - 999
    Location: North Carolina
    6,642
    5,429
    I don’t believe the definition or abbreviation for partial pressure changes just because it is at depth.

    Virtually every medical text or scientific article I can find uses PO2 for partial pressure of oxygen. It seems that the diving community has adopted ppO2. And yes, in that context, they do seem to be used interchangably.
     
    Madacub likes this.
  9. Madacub

    Madacub Contributor

    # of Dives: 1,000 - 2,499
    Location:
    216
    29
    Hi doctormike, thanks for your response. Let me digest those bits regarding the Shearwater manual and the Shearwater blog post for a bit. (I had read the manual earlier, as well as the Shearwater blog post).

    I think going down the path of OTUs is not going to add clarity at this time.

    The Diverite article says "Note that these air breaks are intended to forestall symptoms of pulmonary oxygen toxicity; there is no risk of seizure or other CNS manifestations in these circumstances.". This seems to buttress what I am saying (?).
     
  10. Madacub

    Madacub Contributor

    # of Dives: 1,000 - 2,499
    Location:
    216
    29
    I really don't think he was trolling. It seems a long, long, long way to go for that purpose. But maybe I am too naive in the ways of the interwebs......(Or maybe there was more going on behind the scenes)
     

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