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Do you lie about your helium content?

Discussion in 'Rebreather Diving' started by rddvet, Nov 25, 2019.

  1. Caveeagle

    Caveeagle Rebreather Pilot

    # of Dives: 500 - 999
    Location: High Springs, FL
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    I have noticed this trend as well. I am perfectly happy to keep my Shearwater as close as possible to my actual mix for that dive. I have enough variables in my life to worry about, and see no legitimate argument to make me want to second guess the folks at Shearwater.
     
    RyanT likes this.
  2. Stoo

    Stoo NAUI Instructor

    # of Dives: 5,000 - ∞
    Location: Freelton & Tobermory, Ontario, Canada
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    I really don't understand this. There are a half-dozen ways to tweak the results you get from a Shearwater. There's literally no point feeding it wrong data.
     
    TrimixToo and RyanT like this.
  3. cerich

    cerich ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 5,000 - ∞
    Location: Georgia
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    for those that are doing multiple days of multiple dives and don't feel a small % matters.. you need to review exponential theory.
     
  4. Jack Hammer

    Jack Hammer Solo Diver

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    Lying to your modern dive computer to omit deco is a hold-over from the days of yore. Ya know, back when dive computers were less dependable, non programmable, and deep air was "cool."
     
  5. jgttrey

    jgttrey ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 200 - 499
    Location: Houston
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    I think that is a case of people hearing what they want to hear. My understanding is that it is still very much debatable whether the the "helium penalty" is (1) a myth or (2) real, but masked by the conservatism inherent in our algorithms. People that leap to the conclusion that it is #1 are probably getting ahead of the science.

    Moreover, our algorithms/settings are evolving at the same time, perhaps in a way that is less conservative with respect to a possible helium penalty. With fewer and fewer people diving VPM and ZHL with low GFLo values, the trend is moving away from those deeper stops that are probably more "helium friendly" and accounting for some conservatism (for helium anyway) to begin with.

    What might be "masked" if you're diving GF 30/70 might not be masked at 65/80 -- and my guess is that it's the very same people that are willing to assume there is no helium penalty that are also most willing to take the NEDU and Spisni studies to the extreme and dive 80/80 or even invert their GFs, as I hear some are doing.

    So, if you start lying to the computer and telling it you have no helium in the mix at the same time you are evolving your algorithm/settings away from deeper stops, you might well be eliminating that extra conservatism that was masking the helium penalty. You're changing two variables at once. I don't see any percentage in playing a guessing game about that stuff, so I tell the truth to my computer and try to, incrementally, evolve my computer settings in the direction the science seems to be headed - emphasis on incrementally.
     
    Rich1280, longk14 and rjack321 like this.
  6. Tassi Devil Diver

    Tassi Devil Diver Barracuda

    # of Dives: 1,000 - 2,499
    Location: Tasmania, Australia
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    .........we are doing the right amount of deco but probably for the wrong reason- - Dr. Simon Mitchell

    This quote from Dr Simon Mitchell from the Shearwater article sums the situation up nicely for me.

    If I think I can get away with less deco I would rather tweak the GF than lie about the He content of my gas o my computer.
     
  7. kensuf

    kensuf Cave Instructor

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    I know people who do this. I'm not one of them. Anecdotal evidence seems to indicate it's OK, but a lot of people used to feel that way about VPM until the dives started getting longer and people started getting bent.

    Having said that, I am a believer that deco when on helium mixes IS better than deco on nitrox. It may be because of the helium penalty, it may be because helium is a fast gas with smaller molecules than nitrogen so it comes out quicker. It may be other things we fail to understand.
     
    Jack Hammer, cerich and Marie13 like this.
  8. ofg-1

    ofg-1 Course Director

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    I might lie about my age, my weight, where I told my wife I was last night, if I eat bacon, but I would NEVER lie about helium.
     
    RainPilot, cerich and Graeme Fraser like this.
  9. njdiverjoe

    njdiverjoe Nassau Grouper

    # of Dives: 200 - 499
    Location: NJ
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    I really think so too.

    I'm going to be the black sheep and admit that I regularly dive mixes with no nitrogen (10/90, 15/85, etc) and tell my computer I'm diving 10/50.
     
  10. rddvet

    rddvet DIR Practitioner

    # of Dives: 50 - 99
    Location: Florida
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    I agree with that. I was taught being a fast gas helium is always preferred for "safer" or more efficient deco. I take that to mean, there's nothing wrong with a little helium even in a place like peacock where I won't be getting deco most dives. What I'm finding is there are quite a few people using it to argue that it's safe to lie to your computer. The comments are basically it's safer than nitrox, so just put your oxygen percents in. You know it will be safer since there's helium.

    I've gotten two fairly undeserved mild hits in Ginnie and once on a rece dive that I got into a little deco. I'd say conservatism is better. Adjusting my GFs and really focusing on the speed of my ascent in my opinion has been the biggest fix.
     

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