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125 feet air dive DCS risk?

Discussion in 'Ask Dr. Decompression' started by Into the Water, Feb 8, 2017.

  1. RyanT

    RyanT Solo Diver

    # of Dives: 500 - 999
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    I also noticed the rapid ascent from the final stop. Definitely not something you want to do. Brendon, if you look at the overall profile, it looks like the computer is rounding in smaller increments than 10'. If the last vertical segment was an artifact of rounding, then the whole profile would look stair-stepped over the same depth increments and it doesn't. OP, do you think the rapid ascent from your last stop is real or a rounding artifact?
     
  2. RainPilot

    RainPilot CCR Instructor Staff Member

    # of Dives: I just don't log dives
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    I wonder if it's not jumping suddenly to the surface mode at the end of the dive. If it's not an artefact then there is cause for concern.

    This is in dry suit otherwise I would suspect wetsuit compression and under weighting to be a factor. For an almost instantaneous ascent from exactly the same depth, I'm scratching my head as to what it could be.

    I have noticed the same thing on some of my Perdix logs and I come up so slow in the last 5m it's downright annoying.
     
  3. RyanT

    RyanT Solo Diver

    # of Dives: 500 - 999
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    Yes, good point!
     
  4. Into the Water

    Into the Water DIR Practitioner

    # of Dives: 100 - 199
    Location: Sweden, Värmland
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    But now we have possibility for making it even more safe? why to refuse it?

    Would like to see that statistics, please no offence, but really would like to know more about that, how ratio deco have more risk in DCS vs air diving.
    Totally agree that dive to 40m on air can be execute in very safe manner.
    The reality is that not everyone have your experience and sadly not many share their DCS experience, I'm diving just few years and already experienced twice (not enough for statistics but still) how AOWD diver takes 1-2 days deep diving course or divemaster and start diving over 120 feet in cold water on air with idea *Diving on air to 130 feet has been done safely for decades* promotes others and all together get bends, or go to Egypt and try deeper bounce dive for personal record . How would you deal with that? just ignore that? or just limiting them and increase their safety marginals until they start thinking and take more advanced course.

    As I wrote in the first post I'm not diving on air below 100 feet :) I can write email to that diver and ask him, it could take a while, sins she is not diving anymore.
    Have been reading few manuals (suunto dive computers) and it's written that already on depth 1.2m/4ft computer will switch over to surface mode.
     
    Last edited: Feb 12, 2017
  5. Diver0001

    Diver0001 Instructor, Scuba

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    This is what I call a logic muffin. You're throwing in several ideas and trying to make it sound as if it's one kind of argument.

    You're mentioning the relative safety of decompression algorithms. You are mentioning the aspect of experience, you are mentioning the aspect of procedures and you are mentioning the aspect of rule making (or following) and you are mentioning training aspects and you are mentioning "bad habits" that arise from paradigm thinking.

    These are all interesting but put into a logic muffin they're not going to help you make a coherent argument.

    Of the things you mentioned, I think three of them are relevant to the religious discussion surrounding DIR (effectiveness of deco algorithms, rule making and paradigm thinking) and three of them are relevant to actual diving (training, experience and procedures).

    *IF* (and that's a big "if") a diver has sufficient experience, relevant training and they follow best practices then deep diving can be done safely. As a DIR diver you aren't going to think so because my opinion doesn't fit your paradigm but if you really look carefully into accident statistics then you will see that most accidents are not precipitated by depth. In fact, the single biggest trigger for accidents (at least fatal accidents) by far is running out of air, something that should literally never happen.

    The more interesting discussion is how to train divers better so they don't run out of air. Unfortunately some divers are not trained well and I think it's obvious to both of us that these divers shouldn't be diving deep until they have accumulated sufficient experience and remedial training. So yes, for some divers, diving deep is not a good idea but that isn't going to get fixed by "going DIR".

    R..
     
    dberry and MaxBottomtime like this.
  6. Kevrumbo

    Kevrumbo Banned

    # of Dives: 1,000 - 2,499
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    Lesson learned: to recap what @Duke Dive Medicine said, if you're going to subject and handicap your tissues to the highest potential nitrogen stress and highest lung's work-of-breathing gas density by multi-level repetitive Air dives, starting at 36 meters max in 5 deg C cold water, then it's best to accelerate the inert N2 slow tissue supersaturation washout by using Nitrox50 or 100% O2 to extend a shallow deco stop -whether your dive computer or desktop computer algorithm (or Ratio Deco method) calculates you're within multi-level NDL's or not. In other words, it's very inefficient and may not prevent "idiopathic" or "unexplained" DCS even within apparent NDL's by using Air backgas for a "safety decompression stop" along with exposure to further hypothermic cold water stress.

    If you must dive Air at those depths in those environmental conditions, then get training in Advanced Nitrox/Decompression Procedures, and also consider utilizing battery powered heated undergarments, or even a wetsuit heater for long shallow deco stops to ward off the chill even in tropical waters. . .
     
    Last edited: Feb 12, 2017
    Into the Water likes this.
  7. Into the Water

    Into the Water DIR Practitioner

    # of Dives: 100 - 199
    Location: Sweden, Värmland
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    Don't see what is wrong with my *paradigm* thinking. My believe and approach to diving are based on new standards and knowledge and doesn't rely on old habits, ideas and ignorance for everything new.

    Our dialog went to completly wrong direction.
    Firstly and once again I'm not talking about different decompression algorithm, deco diving, OOA situation and other. Stop mixing everything, please show me the statistics on which is based your believe that deep air diving in cold environment is or can be safer than diving to slightly shallower depth with specific gas mix within MDL or NDL?
    How can it compromise safety by slightly introducing fresh divers to new way of diving? It's safer, faster and easier to familiarise them with MDL from DIR philosophy, introducing safe gas mixes and increasing their safety marginals by slightly limiting the diving depth instead of leting them to learn themself on their mistakes till they become mature enough for advanced diving courses.
    Again it's my opinion based on my *paradigm* thinking :wink: please respect that.

    Secondly I don't have statistics and I'm not having any experience in deep deco diving But I have two situation when fresh AOWD with PADI deep diving course and novice divemaster receiving DCS by diving deep in cold water on air, If by your logic or believe is nothing wrong with that, then I would like to wish you all the best, I respect your opinion and would like to finish our conversation.
     
    Last edited: Feb 12, 2017
  8. RainPilot

    RainPilot CCR Instructor Staff Member

    # of Dives: I just don't log dives
    Location: UAE
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    Ok, I'll bite. You keep talking about air dives, but as far as DCS, if you dive within your planned limits and ascend at the correct rates etc then the algorithm should compensate. Obviously your BT will be shorter but if you are riding NDL then you are riding NDL regardless of O2 percentage.

    The words DEEP and AIR in this context has almost exclusively been about narcosis. Unless you are advocating that these junior divers do a helitrox course (which I have no problem with) then the discussion of this persons DCS susceptibility has very little to do with the gas they are breathing and far more about individual physiology and diving techniques.

    As for technique aside from the skip from 3m to the surface, I can't see anything to be concerned about. The Dukemeister has already pointed out that a PFO is not indicated in your account (I would get a check anyway if I suffered DCS, many people have found out randomly that they have one) so all that's left is...

    Buddy seems to be allergic to bubbles. Add a lot of conservancy on future dives i.e. dive half NDL then maybe 2/3 etc.

    Sometimes stuff just happens.

    FWIW I dive nitrox at every conceivable opportunity, but in this case I don't think the mix is a major factor.
     
    Diver0001 likes this.
  9. Diver0001

    Diver0001 Instructor, Scuba

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    Your paradigm is based upon what were best practices that were emerging in a very narrow discipline 20 years ago. A lot of things have progressed, particularly in deco theory and computer technology in the last 20 years but the DIR paradigm has not kept up.

    ... and that is what is wrong with paradigm thinking in general. It's like an anchor that holds back innovation. Just to be clear, I don't want to pick on DIR in particular and over the years I have integrated a substantial number of ideas from DIR into my own diving. There was a time when I was very happy with DIR because it was the only clear statement of best practices we had in diving. However, I felt it was important to address that because your bringing that paradigm on the table in the discussion without stating it explicitly.

    If this were 1998 I probably wouldn't even have questioned what you were saying. However, the thread is about deco theory and the DIR paradigm has traditionally held on to ratio deco and RGBM, partly for reasons of habit but also partly for commercial reasons. These (deep ascent) protocols are out of favor in the technical arena and have been for some time. The beginning of the end was in 2005 and recent research has pretty much nailed that coffin shut.

    That's why I felt it was important to address the paradigm thinking directly. What you were suggesting in your posts is that if people just "went DIR" that bad stuff, including bends from seemingly safe profiles wouldn't happen. That simply isn't true.

    In the end, I don't want to convince you that you're wrong or to discourage you from pursuing DIR because you could do much worse, but what I was reading in your posts was a blind acceptance of what you have been told and I think awareness of decompression theory -- particularly the technical world, but also recreational divers as a function of access to massive amounts of information on the internet -- has progressed a lot in the last 20 years. There is still more to be done but it cannot be achieved by suggesting that everyone should just "go DIR". As related to understanding of deco theory, that would be a step backwards, in my opinion.

    All diving is decompression diving, as I believe you were trying to point out in the OP. On that we will agree since that idea is part of your paradigm. All things created equal, there are really two BIG variables that control the amount of dissolved gas in your body; depth and time. There are also a number of other variables such as water temperature, age, fitness, working hard on the bottom and post-dive physical activity that have been implicated as risk factors for divers, as is the ascent protocol.

    So the question you appear to be asking is will the amount of dissolved gas be the same if you dive to a different depth and with a different gas mix. The answer to that is no, obviously, but that is not proof that either of the dives is "safer" than the other. That's the point you seem to not understand. You can't compare apples and oranges and conclude that since an orange is a healthy fruit that apples somehow are not. The issues in diving are a lot more nuanced than that.

    What I would advise you to do now would be to read a number of books and articles to flesh out the gaps in your deco theory. I think you would benefit from reading Mike Powel's "Deco for divers" as well as two TDI texts, the extended range and Trimix books, which lay out a very sober and procedures oriented view of deco theory. Finally, I think you would benefit from reading the full NEDU study of the differences in deco stresses between bubble models and Buhlmann. That last study is important and you may need to read it more than once (as I've noticed a lot of people have) before you understand that they did not, in fact, make big mistakes in their process and that their conclusions really are relevant.

    Well.... this is a bit of tangent to the rest of the thread and it may surprise you but I actually agree with this. I wouldn't discourage anyone from learning about DIR or getting involved in their local DIR group. I spent a lot of time learning what I could about DIR when it first became "a thing" and I have benefited tremendously as a result. As a baseline for learning about some best practices it's fine. It's coherent, it's holistic and the focus on standardizing gear and perfecting certain skills is valuable to every diver. What's not to like about that? That said, however, by qualifying it as "safer" "faster" "easier" I think you show a complete misunderstanding of how other agencies approach training.

    Oh, don't take your ball and go home just yet. I'm still hoping I can help you see things in a broader context. :wink: This is the most fun I've had on Scubaboard in months.

    R..
     
    RainPilot likes this.
  10. Kevrumbo

    Kevrumbo Banned

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    The discussion very much has to do with the bottom gas that the victim was breathing along with hypothermic stress, especially now that there is a history of unexplained DCS despite the seemingly NDL multi-level repetitive profiles starting at around 36m depth: Obviously, given the victim's physiology & deco stress susceptibility, the "algorithm could not compensate" for the high FN2 load of 79% nitrogen and the 4 deg C water temp

    For better conservative deco strategy and practice even within NDL, the switch to 100% Oxygen at 6m depth with a slow controlled 1 meter/min ascent maximizes the partial pressure gradient for off-gassing supersaturated blood & tissues or pathogenic DCS causing gas bubbles, and also prevents new uptake of inerts -which is why it doesn't make smart deco strategy sense in general to use Air backgas for a "10min safety stop at 5m" in this instance. More effective resolution of surfacing slow tissue supersaturation and potential bubble formation can be accelerated by breathing 100% O2, or even Nitrox50, instead of 21% O2 and 79% Nitrogen (Air), given the additional stress of hypothermic cold water exposure conditions.
     

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