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Deep stops for recreational diving

Discussion in 'Ask Dr. Decompression' started by scubadada, Jul 25, 2010.

  1. CandiveOz

    CandiveOz Barracuda

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    I agree, and maybe this is the reason why, in light of the current studies you outlined in your article, dive computer manufacturers haven't come out with Diver Alert notifications to stop using the deep stop function on their computers. In reality, what you are doing is simply creating a multilevel dive on a no stop dive. But what I wouldn't recommend is reducing your safety stop time because you made this deeper stop.

    Maybe "deep stop" is actually the wrong term for these types of stops since they are not as deep as say a first stop from a 90 metre tech dive.They tend to be just one stop, maybe two but don't even follow the Pyle protocol so the sceptic in me thinks the added functionality was just a marketing gimmick to jump on the popularity of deep stops at the time. Due to the depth and time limits of recreational diving, they are more of an intermediate stop rather than a deep stop associated with a deep technical dive.

    Then again, maybe there is something to it. No stop diving is different to deep diving in that divers can do up to 4 dives or more a day! They are accumulating and off gassing nitrogen through a series of dives rather than one very deep dive. Perhaps a different ascent protocol is necessary for this type of diving. While the slow compartments are very important during a deep dive, perhaps the fast and intermediate compartments take precedence during these shallow multilevel no stop dives. I honestly don't know but its an interesting issue. This is where more research is needed. And this seems to be still the case since @scubadada asked this question back in 2010.
     
    scubadada likes this.
  2. boulderjohn

    boulderjohn Technical Instructor ScubaBoard Supporter

    # of Dives: 1,000 - 2,499
    Location: Boulder, CO
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    A little history may be helpful here.

    When you read article on the history of deep stops, they usually reference Richard Pyle's "fish nerd" article suggesting them as the beginning. In reality, though, Pyle's article references slightly earlier work by Yount and Wienke in extolling their then new VPM and RGBM theories. These so-called bubble models used much deeper first stops than the standard gas content models of the day. They still do, and some dive computers still use those algorithms. Yount is no longer alive. Wienke still advocates deep stops. When you hear of a dive computer having deep stop functionality, it is usually running Wienke's RGBM model.

    A study by Fraedrich (December 2018) looked at computers using different algorithms to see if their settings could be manipulated to produce ascent profiles consistent with the U.S. Navy NEDU study of 2008. He discovered that a computer running VPM will produce a first stop the Navy considers to be too deep in all of its possible settings. The Suunto RGBM computers he examined will produce a first stop that is too deep when the deep stop function is enabled, but if the deep stop function is turned off, it will be in the acceptable range according to the NEDU study.
     
  3. W W Meixner

    W W Meixner Rebreather Pilot

    # of Dives: 500 - 999
    Location: Ontario Canada
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    Sure...

    I do...no reason not to...I max out at 130'...conduct deep stops at 60'...as advised by my computer...with the rebreather I have lots of gas...lots of time...I'm usually down for approx 30 min per 130' dive...

    I never paid much attention to what was in vogue...and what wasn't...

    Serves me well...just me...

    W...
     
  4. dmaziuk

    dmaziuk Orca

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    You could read the DSAT report from 1994 and notice how it shows significant on-gassing in slow tissues by day 6. Maybe read some Wienke where he advocates 36 hours for the "repetitive diving" interval, too.

    You could also consider how fast is "fast": a 2.5-minute tissue compartment found in e.g. my computer will on-gas twice as fast as the 5-minute one found in other computers. And of course hit the NDL twice as fast -- but then it'd off-gas twice as fast too, so that would all cancel itself out. In a strictly symmetrical model, that is.
     
  5. CandiveOz

    CandiveOz Barracuda

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    I'm still waiting from the library to send me the complete Fraedrich study. In addition to the GF recommendation in the study, I'm interested in what version of RGBM was tested. Sunnto now offers 4 versions of the model and the Fused and Fused 2 generate quite different deco profiles at deeper depths compared to Tech and original RGBM. All versions initiate deep dives at 20 meters but when the depth exceeds 33 meters, depending on the time at depth, the deep stops tend to drop off from the Fused versions leaving a pretty standard deco profile. You can test this yourself using the DM5 software offered by Suunto. Of course this is the approximate depth they "fused" the Tech algorithm to the full RGBM. In essence, there is one algorithm for depths up to 30 meters and another for deeper technical dives. From my preliminary testing,(I need to run more scenarios) it looks like the deep stops are applied to the recreational depths to slow ascent, but aren't applied to the deeper dives.
     
  6. tursiops

    tursiops Marine Scientist and Master Instructor ScubaBoard Supporter

    # of Dives: 2,500 - 4,999
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    No, it depends on the M-values. The 5-min and the 2.5-min compartments do not have the same M-values, so when you reach the limit is not just related to the half-times.
     
  7. dmaziuk

    dmaziuk Orca

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    There's 3 kinds of people: those who understand math, and those who don't.
     
  8. tursiops

    tursiops Marine Scientist and Master Instructor ScubaBoard Supporter

    # of Dives: 2,500 - 4,999
    Location: U.S. East Coast
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    Hardly original. Try saying something original and cogent.
     

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