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Deep Stops Increases DCS

Discussion in 'Technical Diving' started by Divetech99, Dec 8, 2014.

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  1. Akimbo

    Akimbo Just a diver Staff Member ScubaBoard Supporter

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    We had days of sitting around and talking as topside support during saturation decompression (early 1970s). There was always a diving medical officer onboard and several divers and officers that had been stationed at EDU. I got the impression that the knowledge, or at least strong suspicion, that different tissues ingassed and outgassed at different rates goes back to Haldane's original work.

    The real issue wasn't what tissues were faster or slower, only the nucleation of bubbles that would block blood flow and damage tissues. One of the reasons that pure oxygen during decompression was so popular with the hyperbaric research types was eliminating the tedious manual calculations required to account for faster tissues reabsorbing gas during stops and overloading bubble nucleation at the very next stop.

    EDU had access to expensive computer time as batch processes by that time but there weren't that many people that could program them. We had a Wang mini-computer onboard but it was mainly a glorified black box calculator running more or less de-bugged programs. As an electronics tech, I was one of the few guys onboard that had been (barely) introduced to binary and octal programming theory.

    Computing all the moving parts in decompression has become trivial in the last 25 years. It is hard to appreciate what a barrier it was to hyperbaric research in the post WWII years, let alone in the first half of the 1900s when the pioneers started their work.
     
  2. Kevrumbo

    Kevrumbo Banned

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    ......
     
  3. Akimbo

    Akimbo Just a diver Staff Member ScubaBoard Supporter

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    Kevrumbo, good example. It really makes you wonder what history would be like if Newton had a modern laptop... or even a slide rule. You don’t have to be a mathematician to appreciate the laborious work that scientists and engineers had to do in order to prove and disprove ideas not all that long ago. You also have to wonder how many world-changing ideas took decades longer to discover because a math error indicated it wouldn’t work.
     
  4. rjack321

    rjack321 Captain

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    I'm still willing to generally accept RD as a curve fitting exercise, but at least 6 or 7 years ago I figured out that it was aggressive as hell and needed fewer deep stops and more time shallow. I managed to convince my buddies that 80% of ATAs was a ridiculously deep first stop and get that moved up to 2 ATAs off the bottom. But after that they still like things like 2 min deep stops starting at 50% of the depth. I went along with those but add time shallow. For our mostly 140 to 210ft local OC diving this was most effectively implemented by doing all the shallow O2 time at 20ft. Then I could do extra time I wanted at 10ft.

    So on a 200ft dive the first stop moved up to 140ft (so up from 80% of ATAs which is 160ft wtf?). and there would be 1 min stops from 140 to 100 and then 2 min stops from 100 to 70ft. 12 mins to get up to your EAN50 deco gas, hmmmm.... I knew this was all stupid deep, but what the hell there's no rush IMO to get out of the water. Adding time at 10ft was my compensation for all that extra time on-gassing to correct AGs bogus theories. Since O2 is the best solution for all that extra slow tissue ongassing anyway. It worked fine for me although I got the reputation as "deco sensitive" which I think was misapplied.

    The fact that RD has not changed in over 10 years despite the DiveTech GF study finding that 30/85 was too aggressive and 30/70 had dramatically lower bubble rates and the NEDU study finding that time deep cannot be substituted for time shallow is quite telling to me. Its like the worst of deco-gospel. Inviolate and static despite advancing science to the contrary.

    Now that I am on a CCR I'm not sure what I'm going to do yet. I have yet to use it for an actual deco dive. I sure as hell won't be diving RD. I don't think I will be doing very many short exposures with it and if I do end up on 20-25 BT dives in the 150-200 range I can make do for profile matching. Thankfully my OC buddies won't be doing 3 hour dives with me, so when the durations get way out there and RD is really breaking down I will be using an actual scientific model not just a mishmash of science and repudiated theories.

    And Kev I don't think stops starting at 160ft coming up from a 200ft dive would be considered a deep stop by anyone but AG. I can see the merits of slowing and even stopping at the 130-120ft depths and maybe even slightly deeper. But 12 mins to go from 200ft to 70ft starting at 160ft is far slower and longer and deeper than any bubble model would predict. Those are no longer deep stops its practically multi-leveling the dive. VPM brings you up to 130 but those stops are short, only the 80 and 90ft stops get lengthened appreciably (on 18/45). Even RDs deep stops are miss-shapen, the lower ones are too long and the shallower ones (at 80ft) are too short.
     
    TSandM, Rainer, Slamfire and 3 others like this.
  5. Kevrumbo

    Kevrumbo Banned

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    Um no Richard . . .the correct first Deep Stop from a 200'/60m dive is 75% of this max (or average depth). So 75% of 60m is 45m/150'.

    My dive on the Oite Destroyer in Truk was 57m/190' for 50min (rounded deeper to 60m/200'); using RD1:2, my first deep stop was at 45m for 2min (1min 30sec hold and then 30sec ascent to next higher 3m stop at 42m --hold for 1min 30sec and then slide up another 3m to 39m and so on. . .); my 50% stops began at 30m for 4min (3min 30sec hold/30sec slide up) until I intercepted my Eanx50 deco stop at 21m.

    Intermediate deco stops on Eanx50 were 10min each from 21m to 9m, while on subsequent dives later in the week on Oite, I did an S-Curve which profiled at 21m for 15min; 18m for 15min; 15m for 5min; 12m for 5min; and 9m for 10min including 5min backgas break.

    Oxygen stops at 6m were 50min, plus another 30min to clean up slow tissues after previous weeks of Deep Air Diving (O2 10min breathing:then Air Break 5min). And just like yourself Richard, I elected to extend my O2 shallow profile -in my case because of the high FN2 inert loading of my Air Bottom Mix, and because of possible inadvertent on-gassing even at my intermediate Eanx50 deco stops (as implied by the NEDU Study, even though no Nitrox or O2 was used in that experimental paradigm. btw, Simon Mitchell, M.D. Ph.d was my treating Physician for my IWR session on last year's June Bikini Atoll Expedition, so I got the big "captive patient" lecture on the NEDU Study as Dr. Mitchell also started my Plasmalyte w/ Caldolor (Ibuprofen) drip IV after surfacing from the long IWR profile).

    All this doesn't invalidate Ratio Deco; it just means reapplying it to the parameters you've chosen to dive with and trial & error with the profile strategy to get back on the surface without acute type I DCS (signs & symptoms that you and I both know very well).
     
    Last edited: Dec 17, 2014
  6. PfcAJ

    PfcAJ Contributor

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    You got bent again? Just last year?

    I never would've guessed!
     
  7. Kevrumbo

    Kevrumbo Banned

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    The analogy is: If you play American Football long enough, you will eventually get a concussion. It used to be okay just so you don't get a lot of serious Grade III's . . .that may be changing now with the CTE's that many late NFL Veterans have had shown upon autopsy.

    So if you do a lot of decompression diving over a week or more over several years now -especially with Air Bottom Mix- you're going to get a type I episode, either with sub-clinical or acute symptoms. How many more hits can I take? Or how well can I tolerate CNS O2 toxicity exposure during an IWR session?

    Don't know . . .but serious questions that I don't take lightly (nor you AJ, should make light example of at my expense).
     
  8. Kevrumbo

    Kevrumbo Banned

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    From UTD's Student & Diver Procedures Manual v2.0 (abridged):

     

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    Last edited: Dec 17, 2014
  9. nadwidny

    nadwidny Instructor, Scuba

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    The reality is: If you listen to Kevrumbo you will eventually get bent.
     
  10. Kevrumbo

    Kevrumbo Banned

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    The analogy is: If you play American Football long enough, you will eventually get a concussion. It used to be okay just so you don't get a lot of serious Grade III's . . .that may be changing now with the CTE's that many late NFL Veterans have had shown upon autopsy.

    So if you do a lot of decompression diving over a week or more over several years now -especially with Air Bottom Mix- you're going to get a type I episode, either with sub-clinical or acute symptoms. How many more hits can I take? Or how well can I tolerate CNS O2 toxicity exposure during an IWR session?

    Don't know . . .but serious questions that I don't take lightly (nor you AJ, should make light example of at my expense).

    The reality for you nad's, you keep sticking your tongue on light poles this time of year up there in Edmonton, it will obviously keep on getting stuck. . .

    If I'm still alive & writing about what's been happening in my experience . . .then do as I say as lesson-learned and not as I did wrong in hindsight. . .
     
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