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Pure O2 and free-diving.

  1. Aug 17, 2004 #1
    Ok, i love free diving, have all my life.

    But currently i'm starting te reach my max bottom time.
    I was wondering if i could use pure O2 at the surface to boost the oxigen level in my blood/lungs in order to extend my bottom time.

    The thing i'm worried about before attempting is the fact that oxygen becomes toxic at depth.
    At times i do constant weight diving (sit on a sled with eights on it and decent along a steel cable)
    Having 9 liters of pure O2 in my lungs, might give problems when i go down on a sled.

    I reach 40 meter in quite short time, (when going down with a sled) and my body won't have used much of the O2.

    Does the O2 get toxic or is my body able to use enough of it to dilude it enough with nitrogen to keep alive?
  2. jcsd
  3. Aug 17, 2004 #2


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    I do not know, so I cannot advise you. but I believe that long exposure to o2 even at normal atm. pressure is bad for the lungs.

    We are used to O2 at partial pressure of 1/5 atm, in our normal life.
    I do not like the idea of having pure oxygen in my lungs at elevated pressures. I like to scuba but only at around 20 meters.

    I think my lungs only hold about 4 or maybe 5 liters
    Did I measure wrong? Or are you some kind of "barrel chest" giant?
    You have 9 liter lung capacity!

    I am curious about the sled experience. Do you do this in Dutch waters or do you go to clear tropical water? Open Eustachian tubes to equalize ear pressure must be critical during rapid descent!
  4. Aug 17, 2004 #3


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    The urgency to breathe is not caused by a lack of oxygen, it is caused by an abundance of carbon dioxide. I thus strongly doubt that using pure oxygen will increase your dive time.

    Acute CNS oxygen toxicity (involving convulsions and loss of consciousness) usually doesn't occur until a couple of minutes into the high-PPO2 exposure, but it can occur in seconds. Pure O2 is toxic at only 20 feet of seawater, so you're going to be > 1.6 ATA PPO2 for virtually all of your dive. Not a good idea.

    I personally wouldn't attempt this.

    - Warren
  5. Aug 18, 2004 #4
    @ marcus
    Yup, i have extremely large lungs.
    Also a ribcage to match, really nice for feediving, not so great when you want to sleep on your belly, i can't i'd be leaning on my ribs all the time.
    The sled isn't really being used in holland, there are only a couple of places deep enough to use it (and their not even really deep) and suited to use it (not to much wave action).
    You can clear pretty much all the time, just use a clamp on your nose and nog goggles.
    Or just keep your nose pinched all the way down.

    I can postpone breathing mentaly, it takes training but you can learn yourself to ignore the breathing impulse.
    But i won't try pure O2.
    The risk ain't worth it.

    Thanx guys!
    Btw, Can't wait to go to the Salem Express in Safaga, Egypt this winter.
  6. Aug 18, 2004 #5


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    Even so, my point is that even when you breath normal air, you do not consume all the oxygen in a lungful before needing to exhale it to expel carbon dioxide. I believe a normal exhaled breath still contains 15-17% O2. Even if you can ward off the breathing impulse for a longer period, you're still probably exhaling 10%+ O2. Using a higher percentage of oxygen isn't going to make any difference in that respect, but it will expose you to CNS toxicity risks.

    - Warren
  7. Aug 18, 2004 #6
    Ahh ok.
    Missed that part of it.
    So your saying that when i exhale after 5+minutes there still is around 10% of oxigen in my breath?
  8. Aug 18, 2004 #7


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    Well, I'm not sure there's 10+%, but I'd venture it's more than 0%.

    - Warren
  9. Aug 18, 2004 #8
    ok, that probably quite true.
    0% or close to it would mean that you're probably onconcious already.

    Have you been doind any freediving yourself?
  10. Nov 26, 2008 #9
    As I remember it, when the partial pressure of O2 drops below that found at an equivalent altitude of 14,000 ft you start to get hypoxic. You can train your way up to higher altitude tolerance, as mountain climbers do, but I think there is a fairly hard limit of around .16 or .14 atm ppO2 in your bloodstream, where you will lose consciousness.

    When freediving, there are two limiters--1 is your tolerance for CO2. This is what you normally are running up against when you get the feeling you have to breathe. You can reduce this through training in breathing techniques, that drive down your ppCO2 in the bloodstream so you can go a lot longer before feeling the need to breathe.

    It is then relatively easy to push this past the point where you have used up all your O2, and you run into the second limit, which is blackout--i.e. where the ppO2 drops below the threshold required for consciousness. There is an especially dangerous phenomenon called shallow water blackout, which occurs because the ppO2 in your blood is also a function of ambient pressure. At high ambient pressure, say, 2 or 3 or 4 atmospheres, you essentially are multiplying the partial pressure of O2 in your blood by the ambient pressure. You trick your body into thinking you've got a tonne of O2 available when you are deep. On your way back up, the pressure drops quickly, and a pp02 that seemed like way over .14 down deep, quickly becomes much less, and you black out on the way back up, followed by some sinking and drowning if you don't have the proper safety precautions.

    So, pure O2 is not even a consideration 1) if you don't know how to get your CO2 down by proper breathing, and 2) if you don't have proper safety in place. You should be learning these things first if you are reading this and considering any kind of freediving. The "Performance Freediving Institute" is one organization where you can at least get the right kind of training to participate in this sport.

    Now, there is a serious problem with pure O2--at 20ft depth, you've got your ppO2 over 1.6 atmospheres--and crossing this limit can cause oxygen toxicity. You have so much O2 in your blood it bonds with everything, triggers cascading reactions in your nervous system, and puts you into a seizure. Your esophagus closes, and though you have plenty of O2, you can't ascend because you will embolize. Very dangerous, and we honestly don't have data regarding pure O2 breathup for depth freediving, so we don't know what happens.

    We do know that blackouts after static apnea breathholding(breathholds that don't involve depth diving) with pure O2 are more serious than blackouts on air, because your body was used to pure O2, and this creates bigger problems for the body. Its also possible to encourage lung collapse and create other problems. There are other strange effects like the off-phenomenon that are the source of other unpredictable effects in the body... This is not an area to explore without proper research, training, and supervision.

    David Blaine did a 20 minute breath hold on O2 on the Oprah show, so it does work. However, I don't recommend messing with it, unless you know exactly what you are doing.
  11. Nov 26, 2008 #10


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    You only metabolise about 5-8% Oxygen (out of the normal 21%)
    The urge to breath comes from a build up of CO2 not a lack of O2.
    You can breath O2 before a dive to flush CO2 from your body but it isn't much more effective than hyperventilation.
    Exposure to more than 1.6 ppO2 is potentially bad, 3.2ppO2 is the absolute limit in a chamber. Having a CNS hit (the funky chicken) at 40msw is less fun than in a chamber.
    Another big danger is shallow water blackout.

    Disclaimer, do not attempt this at home, this isnt offical advice, my certification in all this stuff lapsed years ago!
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