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Deep stops for recreational diving

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

  1. danvolker

    danvolker Dive Shop

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    Personally, I hate the idea of the deep stops. It drastically increase the volume of air the diver will need to bring with them, and potentially increases the saturation of nitrogen in some tissues....it annoys me on 90 foot dives, and on 130 foot or deeper dives it gets ridiculous.


    With all the speculating and modeling that allowed this to become a new "concept" in theoretical Deco....how about some of the study going to figuring individual body types and VO2 Max and their effect on the shape of the ideal ascent....It would be my expectation, that high fat, low VO2 max individuals, need deeper stops, and that leaner/fitter individuals need to avoid the deeper stops to increase safety margins and reduce the convolution factor of making yourself do "deco for your deco".

    I have been diving since 72, with far more deep ( 250 to 300 ft) than most in this period. Never got a hit, never close to one. Never did deep stops in the current sense---with trimix dives, you do a deeper stop than with air, but the deep stops are very short so they don't hurt your overall deco time very much. This conversation is not about technical deco on trimix though--it is about air or nitrox deco in less than 140 feet( at least that is what I gather from this thread).

    I see this move to deeper stops as forcing the minimum gas requirements to go way up....where you would have been fine with an Hp 100, now you may need doubles or some stupidly negative 130. I've got many decades proving to me that the hp hundred approach and the shallower stop profile, is going to get me out of the water safer and sooner....the idea that none of this happened over the last 40 years, and that suddenly I need more air and that I must do much deeper stops to be safe, annoys the piss out of me.
     
    Dsix36 likes this.
  2. KD8NPB

    KD8NPB Solo Diver

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    What about a deep stop performed on an oxygen enriched gas not exceed a ppO2 of 1.4?
     
  3. danvolker

    danvolker Dive Shop

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    I'd consider a 20 foot stop on 100% O2 after a long dive at 130.....not sure what kind of dive you are talking about....but as a 2nd mix for deco, the only choice on a non-tech depth dive is 100% ( not 80-20 :) and not 50%. there is insufficient gradient to accomplish the desired effect.
     
  4. Searcaigh

    Searcaigh Chromodoris gordonii Staff Member ScubaBoard Supporter

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  5. Duke Dive Medicine

    Duke Dive Medicine Medical Moderator Staff Member

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    I hope it at least goes into your wetsuit and keeps you warm. :wink:

    But seriously, isn't diving safety advanced through research? The safety stop itself came out of scientific studies, one of which was Donna Uggucione's (formerly of DAN) master's thesis.

    Doppler Detection of Silent Venous Gas Emboli in Non-Decompression Diving Involving Safety Stops

    Did people who didn't want to do safety stops get the piss annoyed out of them? And exactly how much gas would you expect to consume hanging at 50 feet, at rest, for five minutes?

    Best regards,
    DDM
     
    uncfnp likes this.
  6. danvolker

    danvolker Dive Shop

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    DDM,
    My issue with studies like this one, is that they mix so many body types, so many different VO2 max potentials, divers with PFO's and those without, that I have almost no interest in their conclusions, compared to the actual experiences of WKPP divers over several decades, and of the large group that I dive with....this meaning the fitness levels, ascent and deco shape, durrations of dives, etc. At least this group had removed all PFO's, their were no divers with poor fitness levels, and most with athlete level VO2 max scores. Perfusion was/is much better than in the populations being referenced in studies like the one you listed......and WKPP had some extensive Doppler studies done a decade ago, that showed George Irvine and Bill Mee's ideas on how offgassing was occurring in our population of divers was consistant with the special tables they created with the help of Dr. Bill Hamilton.
    I won't get preachy about this, and I don't want to suggest that any divers should abandon the current set of theories....but I do think that tables based on the huge mix of body types, different fitness levels, different deco shapes, is very far from being an accurate model for an "individual", unless they are close to some kind of an "average" of the members of the population tested....and even then....the population with PFO's and other medical issues, introduces flaws into the entire model that will hurt predictability for healthy divers..... At least that is my take. And again, I have many more tech dives than most tech instructors will ever have, and many more 150 to 120 foot dives over 40 years than most divers--period..and I have NEVER had any type of DCS. So at least my understanding of the bubble mechanics my body experiences, works for me :)
    And of course it has worked for an awful lot of my buddies through the years....Given the current model with deep stops still has divers getting bent, I think mine shows better statistical validity, for me :)
     
  7. DiveNav

    DiveNav ScubaBoard Supporter ScubaBoard Supporter

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    A while ago I wrote a post on the subject and, mainly from a theoretical overpressure gradient point of view, deep stops DO make sense.


    [​IMG]

    Alberto (aka eDiver)
     
  8. Duke Dive Medicine

    Duke Dive Medicine Medical Moderator Staff Member

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    Dan,

    WKPP folks are a breed apart, and I mean that as a compliment. The diving they do is in an entirely different category than recreational diving. It's like comparing flying a Cessna to flying an F-18. It's hard to argue with a safety record like your own, and what you're doing clearly works for you.

    No decompression model is perfect. That's been proven time and again, and even the late Dr. Hamilton would have agreed. Also, venous bubbling is a measure of decompression stress but it's not 100% predictive of decompression sickness. That said, the research is what it is, and for the general diving population, I think that there's a decent argument for deep stops <edit six years later follows> as directed by established decompression profiles.

    Best regards,
    DDM
     
  9. danvolker

    danvolker Dive Shop

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    DDM,
    First, I would never want to be in an argument with you :) , and second, I totally agree that the discussion is for the general population anyway, so my points are really irrelevant..... I had to rant a little, because with a major change like this, it actually impacts on me when I go out on a boat with a bunch of new tech divers...all carrying way more gas than Bill or me, and all getting shocked that we dont do the same stops that they do :) ... So I have to constantly explain that we don't like the deep stops....and usually these new tech divers just shake their heads in dismay, sure that Bill and I will suffer a serious problem from this, some time soon :)
     
    Duke Dive Medicine likes this.
  10. DocVikingo

    DocVikingo Senior Member

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    Morning Dan,

    I'd be very interested to know how you are able to determine with such certainty that you've never approximated sustaining an incident of DCI.


    That would depend on what kind of deep stops are being done during recreational diving (the OP topic), wouldn't it?

    But, I don't believe that a need for exponentially more gas is the case. For example, NAUI recommends that a deep stop should be done for recreational dives deeper than 40 feet, with a one-minute stop incorporated at half of a dive&#8217;s max depth, followed by a two-minute safety stop at the 15- to 20-foot level.

    And Dr. Peter B. Bennet indicates that a "deep stop at half the depth for 2.5 minutes significantly reduces not only bubbles, but also the critical gas supersaturation in the 'fast' tissue compartments (like the spinal cord's 13.5 minutes) without increasing the 'slow' compartments usually related to limb pain."

    Seems to me that the performance of these sorts of deep stops within recreational diving limits would require only trivially more gas.

    Cheers,

    DocVikingo
     

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