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Thread: How deep on air?

  1. #21
    Registered Users myscubastory's Avatar
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    Stay within the limits! Its hard to imagine how quick things can turn bad
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    Quote Originally Posted by myscubastory View Post
    Stay within the limits! Its hard to imagine how quick things can turn bad
    My qualifications state '60m on air', I try to stay within those limits but occaisionally go a little deeper.
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    Wreck Diving Moderator acelockco's Avatar
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    Quote Originally Posted by Okeanos View Post
    My qualifications state '60m on air', I try to stay within those limits but occaisionally go a little deeper.
    What agency makes that statement?

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    I think most would be fairly narced at 180 feet on air.....
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    Quote Originally Posted by acelockco View Post
    What agency makes that statement?
    My TDI Extended Range did when I did it.
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    Wreck Diving Moderator acelockco's Avatar
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    Quote Originally Posted by Okeanos View Post
    My TDI Extended Range did when I did it.
    I see they do, doesn't sound like the safest or smartest thing to do in my opinion but then again I can't imagine doing that dive anyway. I imagine you would have to do a bounce dive (hit bottom and start your way back up right away) or have to carry so many cylinders it would be a workout at minimum. With mixed gasses and especially re-breather technology as advanced as it is there are safer and easier options.

    I think for most diver keeping at recreational depths gives them much more for their diving dollar. Diving reefs and shallow wrecks is within the reaches of just about every diver. The cost of diving deeper in classes and gear would surely add up to more then the cost of an extreme number of dives.

    Like I said, for most, and there are always people that want to go beyond that, which is great as it helps improve our knowledge and diving technology.

  7. #27
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    Quote Originally Posted by acelockco View Post
    I see they do, doesn't sound like the safest or smartest thing to do in my opinion but then again I can't imagine doing that dive anyway. I imagine you would have to do a bounce dive (hit bottom and start your way back up right away) or have to carry so many cylinders it would be a workout at minimum. With mixed gasses and especially re-breather technology as advanced as it is there are safer and easier options.
    60m is relatively shallow in the technical world. 30 minutes at 60m would require 2 x 12L (Ali 80) and 2 x 7L (Ali 50'ish). The bottom time difference between air and mixed gasses is negligeable or even equal as is the deco that follows. The mixed gas (Helium in the mix) reduces the narcosis (and helps reduce PPO2 to a safe level) and that's it. Air at 60m is actually a higher PPO2 than recommended but it does reduce your deco I am quite happy doing a 50m dive for 25 minutes with a single cylinder (100cuft) on my back and 2 x 3L (1 of air, 1 of oxygen) side slung.

    If you want to trust a rebreather then the weight would be similar to the 2 x 12's. If, like me, you wouldn't trust the rebreather you'd need to take as much gas as if it was open circuit to be able to bail out of the rebreather and finish the dive safely.

    Open circuit is the safest for several reason, below 40m most people would add Helium, on a rebreather anyone with any sense would add Helium deeper than 40m. World record is 320m for OC, far deeper deeper than a rebreather. The main advantage of a rebreather is saving Helium, it is an expensive gas and is going to get more expensive every year until we run out in 2015/6.
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  8. #28
    Registered Users myscubastory's Avatar
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    Max partial pressure for O2 is 1.4 and the contingency is 1.6 - this is but one of the reason why recreational diving doesnt go deeper than 40m
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    Wreck Diving Moderator acelockco's Avatar
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    Quote Originally Posted by Okeanos View Post

    Helium, it is an expensive gas and is going to get more expensive every year until we run out in 2015/6.

    No No No.....Helium Privatization Act of 1996 stipulates that the US National Helium Reserve must all be sold off by 2015. At that point Helium will be available as we have not mined it all, but the prices will go up a HUGE amount as the market will dictate prices again.

  10. #30
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    Quote Originally Posted by myscubastory View Post
    Max partial pressure for O2 is 1.4 and the contingency is 1.6 - this is but one of the reason why recreational diving doesnt go deeper than 40m
    PPO2 of 1.4 gives you 56m on air, PPO2 1.6 gives you 66m on air. You stay safe and the within limits you are qualified to and have experience of.
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