• Welcome to ScubaBoard

  1. Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.

    Benefits of registering include

    • Ability to post and comment on topics and discussions.
    • A Free photo gallery to share your dive photos with the world.
    • You can make this box go away

    Joining is quick and easy. Login or Register now by clicking on the button

Likelihood of getting oxygen toxicity at 1.4 PPO

Discussion in 'Marine Science and Physiology' started by ystrout, Jun 4, 2018.

  1. boulderjohn

    boulderjohn Technical Instructor ScubaBoard Supporter

    # of Dives: 1,000 - 2,499
    Location: Boulder, CO
    25,635
    17,010
    113
    I guess it comes down to your confidence in your buoyancy skills. If you are diving 32% and believe it is all too likely that you will not be able to stop yourself from going below 130 feet for an extended period of time, then you should not be using Nitrox. As for me, as someone who dives regularly without a hard bottom to stop me from plummeting below my MOD for an extended period of time, I am pretty confident I can handle it.
     
  2. Storker

    Storker Divemaster

    # of Dives: 100 - 199
    Location: close to a Hell which occasionally freezes over
    11,453
    7,808
    113
    If you change "all too likely" to "an (IMO) unacceptable risk, given my risk acceptance and my trust in my own abilities", I believe we'll agree pretty perfectly.
     
    northernone likes this.
  3. BRT

    BRT Orca

    9,584
    5,736
    113
    On the other hand, if I thought there was much chance of a current carrying me out of control below 130' nitrox would not be my big worry.
     
  4. Diving Dubai

    Diving Dubai Instructor, Scuba

    # of Dives: 500 - 999
    Location: Dubai UAE
    2,803
    2,368
    113
    While I respect @Storker self imposed risk limitation, as some you generally dives with teh hard bottom well belom my MOD, I do agree with John

    While I understand the meaning of John's post, I feel to understate down currents is the wrong thing.

    I don't have John's dive count, however I do dive in an area once a month that has them - we chose the sites and are unguided. Each year I get hit by 6- 10 down currents of varying degrees

    Most are easy to get out of and of little problem (maybe 10m max descent) others are more challenging - depending on how you react

    Not all push you down, this weekend we had one, where we were fining to ascent from 15m to 6 we stopped a 12 with the current not allowing to ascend higher but not pushing you down. in this case we needed to inflate through it and then dump. This was an extreme site, not one someone would go to on a guided vacation. During our 3min SS we were pushed 1.5Km (1 mile) off the site into open ocean, no drama because one of the two pick up boats was positioned accordingly.
     
  5. Storker

    Storker Divemaster

    # of Dives: 100 - 199
    Location: close to a Hell which occasionally freezes over
    11,453
    7,808
    113
    It's not unlikely that I'd change my mind if I had the same experience that you have. However, I don't have that experience and thus I make my choices based on my own experience and my own risk acceptance.

    As I've said several times, others may very well choose to do otherwise from what I'd choose to do. I can only speak from my own current opinions and try pretty hard to communicate that I'm only speaking about what I'd do.
     
    RainPilot likes this.
  6. BRT

    BRT Orca

    9,584
    5,736
    113
    A 20 MPH current. That would be interesting.
     
  7. KWS

    KWS ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 500 - 999
    Location: SE TEXAS
    3,967
    843
    113
    thesae may not be the correct curves but they will do for sake of explaination. look how the curv is mostly linear up to about 1.7 then the curv becomes more exponential. that point for you may be 1.7 1.8 1.6 but as for the curve 1.4 is a long way from 1.6. the chnage between 1.7 and 2.0 is not relative the same change as between 1.0 and 1.3. You want to stay in the flat linear area that is below 1.7 +/-. When you plan your mix you plan for a ppo2 of 1.4 or less. In the event you have to go to say 1.6 or better for a very short duration. like pick up your dropped camera. you should be able to safely do that and tehn retreat shallower than the 1.4 ppo2. I am sure others have better explainations. when i forst learned it it was in the 60's it wa 10 atm to the point that teh majority of divers on air could go before having moderate to severe symptoms of ox tox most are incapacitated at 3 atmospheres of O2 and you dont make it to 4 adn come back to tell about it.. a lot has changed since the 60's. I am sure there are others that can talk more intelligently. for me teh curve going from linear to exponential at 1.7 is reason enough for me t stay on the safer side of 1.4. now the longer you are at those depths the lower of ppo2 you need to observe but with a single al80 my rule works just fine.


    Oxygen toxicity - Wikipedia
     
  8. Diving Dubai

    Diving Dubai Instructor, Scuba

    # of Dives: 500 - 999
    Location: Dubai UAE
    2,803
    2,368
    113
    Obviously you misunderstand the technique.

    Let go of rock then fly dsmb - as it would be foolish to let it go while you're hooked on. Ascend to SS level, carry out extended stop, slow ascent to surface. Maybe 10 mins can't tell you exactly I was busy

    I'll try to get the originals of the video clips posted to a closed FB group.

    If you you think I'm lying, I'm happy to host you and throw you in to our currents on a trip and see how you fair
     
  9. Diving Dubai

    Diving Dubai Instructor, Scuba

    # of Dives: 500 - 999
    Location: Dubai UAE
    2,803
    2,368
    113
    I'm not questioning your position nor your personal judgements. I like people who have boundaries, and I respect them

    Mine is small wrecks, despite having taken Adv wreck I'm not comfortable in small passages nor closed rooms. I have the training, knowledge and ability to do so, I just don't feel "right" thus I don't

    Others are different.

    Where I dive. if I were to adopt your risk aversion, then I couldn't dive without a set of cylinders and bailouts with gasses for 100m. Because generally that's where the sand is. So one needs to make a decision.

    I have been pulled down below the MOD of my pony with 21%, and I had more pressing problems than Ox Tox - which thankfully didn't happen that time.

    But all that said, I'm a proponent of diving cautiously and conservatively. While the likelyhood of havign a tox beyond 1.4 is very small it is a small possiblilty - just like a DCS is within NDL and ascent rate and a heart attack despite feeling healthy. We must all access the risks and take actions according to our outlook
     
  10. Storker

    Storker Divemaster

    # of Dives: 100 - 199
    Location: close to a Hell which occasionally freezes over
    11,453
    7,808
    113
    Given that the depth for >1.6 bar pPO2 on air is 7.6 barA, or 66m, nitrox or air would probably be a moot question for me. No matter the gas, I'd probably be so narked out of my skull that I'd die anyway.
     
    Diving Dubai likes this.

Share This Page