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Deepest safe depth on air?

Discussion in 'Basic Scuba Discussions' started by cloudboy55, Jan 8, 2006.

  1. do it easy

    do it easy Assistant Instructor

    # of Dives: 500 - 999
    Location: Chicagoland, USA
    The NOAA O2 exposure tables are built around a time-depth assumption:

    1.3 is "safe" for 180 (???) minutes
    1.4 is "safe" for 150 minutes
    1.6 is "safe" for 45 minutes

    Check my times, since I'm making this up from my head.

    with O2 partial pressures above 1.0 ATA there is no "safe" limit; it's only a matter of time before symptoms become more likely- similar to the dive tables.

    Edit: corrected exposure times
  2. H2Andy

    H2Andy Blue Whale

    # of Dives: 200 - 499
    Location: NE Florida

    sweet!! i'll dive a 40% Nitrox mix to 130 feet

    i should be ok since i'm within recreational depth limits


  3. cummings66

    cummings66 Solo Diver

    Divers who use Nitrox know or should know the requirements for the dive and it's not hard, but it is more difficult than a non nitrox diver is aware of as far as what you keep track of. The o2 adds up just as the nitrogen does and can definitely cause toxing well before being narc'd.

    With one foot in the tech world so to speak I'm sure you know this, but I wanted to clarify it for others. A nitrox diver keeps tabs on his O2 and Nitrogen levels, most of the time the O2 level isn't a problem because you adjust things to suit the dive, but it can be an issue if you don't pay attention to it.
  4. wedivebc

    wedivebc CCR Instructor ScubaBoard Supporter

    Actually I teach though 4 different agencies and they all follow NOAA guidelines as far as oxygen exposure limitation, and all seem to be in agreement with what I said earlier. Exposures above 1.4 do provide a non-zero risk factor but the incidence of O2 tox below 1.6 are so rare that there is little information about these levels. Mathmatical modelling is nice on paper but with so few data points it has little meaning in the real world.

    I take exception to your use of the expression "crap shoot" with regard to exposures above 1.3. That is why I asked where you got your information from. Are those your words or from some report you read?
  5. wedivebc

    wedivebc CCR Instructor ScubaBoard Supporter

    Just a quick scan of your article reveals some errors
    At this depth the 50 percent oxygen would have the same physiological effect as 100 percent oxygen at the surface. Breathing a 100 percent oxygen mix at a depth of 33 feet / 10 meters (2 ata total pressure) would be equivalent to breathing the 50 percent mix at 132 feet / 40 meters (4 ata total pressure).
  6. wardric

    wardric Divemaster

    # of Dives: 200 - 499
    Location: Eastern Townships, Qc, Canada
    I made a bad translation of the article. It in fact does not state it CAN but that it DOES have effects even at 30 ft. Sorry about that.

    Narcosis is not always an effect you can sense but at depth, everyone have narcosis in a form or another. Narcosis is not always a "drunk" effect. It can be paranoia, unfounded fears or most of the time, just slower thinking process and less awareness.

    My deepest dive on air was at 171 ft. I did not feel any narcosis effect, I did not feel drunk or paranoid or any other. During this dive, at the bottom, I had a freeflow and then my mask got bumped and so flooded. We did all the correct procedures but I can tell you that even the simple thinking process to clear the mask took much more time that on surface. It was like in slow motion. Try doing simple math or other tests at 30 ft and then at 100 ft. You will see that the time to resolve it is much longer at depth.

    Most of my dives are below 80 ft in cold 40-45 F waters (I so envy you with your 72 F waters :wink:), a good proportion are below 100ft and did many below 130. I only "felt" narcosis once, at only 90ft. I could not stop laughing and a little voice in the back of my head said: you are experiencing narcosis, be aware. Ascended a bit and it went away. So I could say I experienced Narcosis only once. But I know that rapidity and efficiency are affected at depth even if you dont notice it and that is also a narcosis effect. It does not mean it always have a debilitating effect, it can strike at a different degree and in different ways. But it is always there.

    So the diver in our example had no problems not because it wasn't effecting him but because it had no debilitating effect on him and he did not have any major problems to resolve. If you consider narcosis only the effect of losing awareness and feeling like being drunk, I agree that it does not strike that way all the time (not even often) but narcosis is much more than that.
  7. tehach

    tehach Angel Fish

    It's been a while since I read it, but didn't Chatterton, Kohler, and others regularly dive to 230' on air in "Shadow Divers"?
  8. H2Andy

    H2Andy Blue Whale

    # of Dives: 200 - 499
    Location: NE Florida
    yes.... also the Rouses, on U-869

    of course, the Rouses didn't make it. thosed depths are a very real gamble
    with air.
  9. StSomewhere

    StSomewhere Loggerhead Turtle

    That is an almost direct quote from this book. The author's premise is that there are no indications you'll ever tox at 1.3 and almost certain indications you will tox at some point at 1.7. The area inbetween is the place you should be careful, taking into account additional factors like cold water, whether its a working dive, etc. Take exception all you want but do it with the author.
  10. DiverBuoy

    DiverBuoy Instructor, Scuba

    The 1.3 is just a conservative approach that's all ...

    Folks please don't dive deep on air ... if you are diving regularly deeper than 4 atm sw give thought to alternatives, there are just too many risks on air and better solutions available.

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