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Thread: Evidence based guidelines on gas density planning

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    RBW Member Mike Ferguson will become famous soon enough Mike Ferguson will become famous soon enough Mike Ferguson will become famous soon enough Mike Ferguson will become famous soon enough Mike Ferguson's Avatar
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    Re: Evidence based guidelines on gas density planning

    Quote Originally Posted by Mark Chase  View Original Post

    In respect of the origional topic is there a safe END that would ensure gas density is not an issue? IE if I plan 25m max END for every dive can I feel confident I dont need to do gas density calculations?
    Mark

    I looked at a few common gases.

    air hits the lower limit at 30m
    18/45 hits the lower limit at 55m with an END of 20m
    15/55 hits the lower limit at 65m with an END of 18m
    10/52 hits the lower limit at 63m with an END of 25m
    10/70 hits the lower limit at 90m with an END of 15m

  2. #32
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    Re: Evidence based guidelines on gas density planning

    Quote Originally Posted by Mike Ferguson  View Original Post
    Mark

    I looked at a few common gases.

    air hits the lower limit at 30m
    18/45 hits the lower limit at 55m with an END of 20m
    15/55 hits the lower limit at 65m with an END of 18m
    10/52 hits the lower limit at 63m with an END of 25m
    10/70 hits the lower limit at 90m with an END of 15m
    Hi Mark
    Interesting figures, when I apply these settings into IDECO as an example 10/70 @90M gives me an END of 23M with a SP of 1.3.
    Any idea where the difference arises?

    Cathal

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    Re: Evidence based guidelines on gas density planning

    Are you assuming O2 as narcotic as well, or just the N2? If you are just counting N2 as narcotic then the 15m END is correct.

    JNeves

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    Re: Evidence based guidelines on gas density planning

    Thanks for pointing that out. I did have O2 down as being narcotic.

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    Re: Evidence based guidelines on gas density planning

    Quote Originally Posted by s115  View Original Post
    Simon, I was for sure thinking this too. However, shouldn't you base the calculation on worst case scenario? ie, suspected problem with loop, I need to flush at any given depth with my selected dil, bam, suddenly im slamming myself with a much denser gas as I picked it based on the fraction of gas/pp02 calcs???
    How would dil be denser than what's in the loop before the flush? What am I missing here?

  6. #36
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    Re: Evidence based guidelines on gas density planning

    Quote Originally Posted by Mike Ferguson  View Original Post
    Mark

    I looked at a few common gases.

    air hits the lower limit at 30m
    18/45 hits the lower limit at 55m with an END of 20m
    15/55 hits the lower limit at 65m with an END of 18m
    10/52 hits the lower limit at 63m with an END of 25m
    10/70 hits the lower limit at 90m with an END of 15m

    Excelent many thanks

  7. #37
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    Re: Evidence based guidelines on gas density planning

    Pardon my ignorance, can anyone explain the theory behind having O2 entered in your dive planner as being narcotic or not.

    Much appreciated.

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    Re: Evidence based guidelines on gas density planning

    Quote Originally Posted by cb1  View Original Post
    Pardon my ignorance, can anyone explain the theory behind having O2 entered in your dive planner as being narcotic or not.

    Much appreciated.
    Many people assume that narcosis is due exclusively to Nitrogen. EAD calculations have sometimes been based on nitrogen narcosis.I believe that the NOAA diving manual actually states that Oxygen and Nitrogen should be treated as equally narcotic. There is some evidence to suggest that O2 is MORE narcotic than Nitrogen (including greater lipid solubility), but since some of the O2 is actually metabolized, perhaps it is brought back down to the level of Nitrogen.

    At the end of the day, what it means is that for EAD calculations to be more conservative...and potentially more accurate, many of us check off that "Oxygen narcotic" box in dive planning software and then utilize the corresponding EAD based on O2 being treated like Nitrogen in terms of its narcotic impact to the breathing mix. I have not clue if O2 is as, more, or less narcotic than nitrogen....but I check the box in multi deco just to get a safer narcotic depth comparison.
    Last edited by manni-yunk; 8th September 2016 at 00:18. Reason: spelling

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    Re: Evidence based guidelines on gas density planning

    Hello all, can anybody tell us what oxygen narcosis feels like? What are the symptoms? Is it similar to nitrogen narcosis? If so, I don't think I've ever felt it, not while breathing PO2's of 1.4 and above. When would it presumably kick in? -Andy

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    Re: Evidence based guidelines on gas density planning

    silent running
    Re: Evidence based guidelines on gas density planning

    Hello all, can anybody tell us what oxygen narcosis feels like? What are the symptoms? Is it similar to nitrogen narcosis? If so, I don't think I've ever felt it, not while breathing PO2's of 1.4 and above. When would it presumably kick in? -Andy
    +1


    JNeves

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