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"Undeserved" DCS hits

Discussion in 'Technical Diving' started by Tortuga68, Feb 25, 2011.

  1. Tortuga68

    Tortuga68 Divemaster

    # of Dives: 1,000 - 2,499
    Location: Puerto Galera, Philippines
    4,104
    842
    Lots of new members (including me) which is great, but not much happeneing in the T2T forum... so I thought I'd post a discussion thread

    It's common to hear people talk about "undeserved" DCS hits - I know of several people who have gotten bent on rec. dives that were well within NDLs for example, with multiple divers following the same basic profile and only one getting a (type 1) hit

    For example, there's a thread currently in Diving Medicine (just got moved there) about an OW diver getting bent during/straight after her course, on what sound like fairly benign dives and flying 24+ hours later

    When one hears these stories, it typically goes something ike this (in my experience anyway) : Diver A did a dive, followed "all the rules" and got bent but no-one else on the same dive did, and Diver A has done the same dive/profile before X times and never had any problems

    My thoughts (and they are nothing more than that) are:

    1. Deco/preventing DCS is - currently anyway - an art not a science
    2. We don't know what the "rules" are
    3. The actual "rules" (unknown) cover pre- and post-dive, not just in-dive eg hydration and rest before the dive, not doing X after a dive etc

    So my point is that I don't think there are "undeserved" hits, just unknown rules that Diver A didn't follow - or that perhaps while they followed the "in-dive" rules (not exceeding MOD, PPO2 limits, ascent rates, NDLs) they didn't follow the pre- or post-dive rules (whatever they may be, but including point 3 above and no-fly, no excercise/hot showers (debatable) etc

    Do you agree, or do you think I am just trying to rationalise in the hope that I will never experience an "undeserved" hit?

    I think it's agreed that multiple dives over several days put you outside of prevalent deco theory ie tables, is that the reason for these hits?

    I've heard that PADI DMs are a high risk group due to the above and also frequent sawtooth profiles looking after students/guests, is that factor? It's been said by some on SB.com that dive professionals are statistically going to get hit eventually, is that true in your view, or can it be avoided?

    Please quote some examples of divers you know of who got an "undeserved" hit and why you think it falls into that category

    The above examples refer mainly to non-tech profiles, so feel free to expand it into the tech/deco realm - the basic premise of "undeserved" remains the same

    On a related topic, have you ever been bent, and why?
     
  2. HowardE

    HowardE Diver Staff Member

    # of Dives: 2,500 - 4,999
    Location: Boca Raton, Florida
    19,202
    1,437
    Or they were tired, hungover, out of shape, hungry, thirsty, cold, or any number of reasons that they got bent. I don't believe in "undeserved" hits.
     
  3. Cave Diver

    Cave Diver Divemaster

    17,866
    2,518
    All things being equal, if I get a hit, I think I'd almost prefer it to be "undeserved."

    To me, that means that I think I've done everything right, profile, rest, hydration, etc. but some unknown factor out of my control just didnt line up.

    A deserved hit means I screwed up somewhere and I try pretty hard not to do that.

    I know some people equate undeserved hits with any other type of sports injuries. Do it enough and eventually something is gonna happen, even in well trained, conditioned athletes. There may be some truth to that.
     
  4. DevonDiver

    DevonDiver N/A

    # of Dives: 5,000 - ∞
    Location: Subic Bay, Philippines
    15,396
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    I think the only true undeserved DCS hits come from underlying and unknown medical conditions; most importantly PFOs.

    Staying within NDLs on recreational dives is only the tip of the iceberg...and far too many recreational divers don't look beyond that. As we (tech divers) know - your actual profile, especially the ascent, is a major determing factor in bubble formation.

    We can also debate whether other physiological factors; such as dehydration, hangover, exertion, tiredness etc, cause undeserved or deserved DCS hits. Personally, I think they are deserved hits... as every diver is educated about how these factors predispose DCS.

    When I worked as an instructor in Thailand, I heard reports on a startlingly frequent basis about recreational divers, including Open Water students, who were chambered due to hits. In most cases, hangover/alchohol played a major contributing role. One particular instructor (let's call him 'Captain Sensible USA') enjoyed making his OW students do 'loop-the-loops' on their safety stops... he also encouraged drinking binges. Is it unsurprising to learn that he has bent 2 open water students in 2 years?
     
    Last edited: Feb 25, 2011
  5. Doppler

    Doppler Dive Equipment Manufacturer

    2,480
    1,981
    I'm with Howard.

    More specifically though, I agree with my friend W.R. Morgan who, when confronted with a bent diver who was moaning about his "hit" being undeserved, explained: "You dived... on scuba... you stayed down for a while... you surfaced. That is EXACTLY the type of behavior that gets people bent all the time!?"

    Needless to say, Wayland won no new friends on the boat that day.
     
  6. Tortuga68

    Tortuga68 Divemaster

    # of Dives: 1,000 - 2,499
    Location: Puerto Galera, Philippines
    4,104
    842
    This is exactly my line of thinking...


    I don't know whether something like an ACL injury happens over time or spontaneously - maybe both can occur. What I do know is that I know technical divers that have over 10000 dives and have never been bent. That's gotta means something
     
  7. TSandM

    TSandM Missed and loved by many. Rest in Peace ScubaBoard Supporter

    36,349
    13,621
    When I watched the GUE DVD, "The Mysterious Malady", I was, even after all my reading, somewhat surprised to hear the people who are at the center of what research is still being done in this area, say over and over again that no one really understands DCS. It is clear that you have to dissolve some nitrogen in the blood to get it . . . but beyond that, much is simply unknown.

    What a lot of people don't know is that the decompression tables are probabilistic models -- none of them does, or purports to reduce the DCS risk to zero. Only staying out of the water can do that. Even the "bubble models" don't do that -- and Doppler studies have shown surprisingly poor correlation between bubble grade and symptomatic status. It is clear that, although bubbles are probably involved, they are not alone enough to cause DCS. There may be a component of immune reaction, although it's been difficult to prove. There may also be a simple intracellular process in DCS -- I had a chance to talk to some NEDU guys last year who were doing some cellular research that implied this might be true.

    I read an article by Dr. David Sawatzky a couple of years ago, and the closing paragraph made a big impression on me. His statement was that the big breakthrough on DCS was Haldane's; everything we have done since then is tinkering on the margins. Until we truly understand the mechanism of the disease, it will be impossible to eradicate it . . . in those of us who dive, anyway!
     
  8. Tortuga68

    Tortuga68 Divemaster

    # of Dives: 1,000 - 2,499
    Location: Puerto Galera, Philippines
    4,104
    842
    To throw some more fuel onto the discussion fire, anyone that has read some of my threads knows that I've done some dives that could best be described as 'adventurous' (aka stupid, depending on your viewpoint)... but so far, I am yet to get bent. Am I just lucky (so far)? Or are the divers that have been bent on "rec" dives following 'all the rules' dives unlucky?
     
  9. Rhone Man

    Rhone Man Divemaster

    # of Dives: 1,000 - 2,499
    Location: British Virgin Islands
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    Just building on that, and on Howard's earlier comment - how many people in this forum have had themselves tested for a PFO?
     
  10. Rainer

    Rainer DIR Practitioner

    6,031
    592
    I have (TCD; negative).

    Many of my buddies have as well. UCLA Medical was running a PFO/stroke study several years ago and needed controls, so was covering the cost of the PFO test. My wife had herself tested (negative) before she even started diving simply because she was there at UCLA with me for my test.
     

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