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  1. #21
    Old but keen Mark Chase's Avatar
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    Dec 2012
    Kent UK
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    Quote Originally Posted by JonG View Post
    Ok so it is accepted fact that helium is great for reducing narcosis and decreasing breathing gas density, but it's molecular structure means it saturates the fast tissues quicker than n2 so more care is needed on ascent to off gas it correctly.

    In the NEDU studies and commercial arena though it is accepted that He and o2 are a better choice than trimix due to the higher prevalence of bends on trimix as compared to heliox albeit that the sample sizes are small.

    So what we don't know them it appears is what mixtures of He, N2, O2 are more or less safe than others, ergo using large proportions of He arbitrarily may or may not be safer than using smaller proportions.

    About as much clarity as ever then. Or am i missing something?
    Imho the key point your missing is balanced risk

    The risk of poor decision making due to narcosis and the risk of retained c02 due to high density gas, far outweighing the manageable risk of helium decompression which can be mitigated with conservative decompression choices.

    When we planned a 140m dive I was lucky enough to talk to some people at Comex and their attitude 15 years ago was Nitrogen had no place in a deep diving gas.

  2. #22
    Established TDF Member
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    Apr 2017
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    Have no fear I am too much of a fuckwit above water never mind under it to be twatting about with mind bending ENDs.

    In the 90s mix was hard to come by so mostly we were on air with long durations at 50 and shorter excursions to 60-70, the lack of paranoia and sense of impending doom on a mix at depth now is much more enjoyable.

    It was more of an academic interest in the change of opinion from the 90s to now. Does anyone know what caused the negative mindset back then? It was very much the norm to get off it quickly and have in mind that a helium bend was hard to treat, but that may have been due to the fact that we weren't properly decompressing the squishy grey bits properly so neuros were more common perhaps.

    I never bent on mix, just air but with a tea bag for a ticker it could have been either anyway.

    If there was a bias of safety towards either end of the scale it would all be marginal gains and balancing pros and cons.

    The current trust in high fraction trimix seems a little misplaced imho in the absence of more testing to understand the implications of a cocktail in comparison with heliox.

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