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  1. #1
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    CO2 symptoms deep on air

    (another one, sorry...)

    One from years ago,

    Was having a boring weeks diving due to bad weather, ended up diving a lot of shit "reefs" that quickly petered down to mud slopes, I'd had a few dives which were quite cool, on my own in the dark watching the squat lobsters having their little micro-dramas facing each other off. Anyway the dives got deeper through the week. At this time 45m wrecks felt normal, comfortable, I was happy and familiar with my kit etc. (although notably this was the year I was absolutely, definitely going to finish the rebreather project, so I'd flogged my Odins and was using conventional apekss). I'd never tried helium at this point.
    A rare, fine morning of no-hangover, a decent 260bar in my 12's, a fresh battery in the VR3 and "sod it."

    Started normally heading down the slope, every 5 kicks or so having a quick look at the depth, checked my gas around 45m and was still loads, didn't feel narked or anything much. Trying to stay a little off the bottom, though the vis wasn't great and I was enjoying watching the crustacean micro soap-operas unfolding on the way. Not really aware of much except for what was in the narrow beam of my torch. (so no awareness of any vision narrowing)

    "59.9" Ok Chris, that'll do. Still felt fine and "with it". I about turned back up the slope and followed back up alongside the silt trail from the downward leg. A few kicks into this I felt a little breathless, only slight but I paused and checked the depth again, wondering how far up I'd got "56.0". Brain said "bugger, still a long way to go. You'll feel fine once you're shallower". A few more kicks,* a few more breaths. Breathing hard now, regulator doesn't feel to be delivering enough wind "shit, am I running out of gas? No you dick you saw the spg moving, isolator must be open and you had loads". Fuck. "Got to get shallower". Kick. Breath. Kick. Heartbeat crazy loud in my ears. "Oh this is hard. Just rip all that shit off your face and take a big deep breath, that'll help."

    "Just rip all that shit off your face and take a big deep breath."

    That would not have helped at all. But the urge to do just that was powerful. In and among that a voice saying "you're a wreck diver and you're going to die on a boring bastard scenic. Ha ha.", but mercifully another thought, stronger, that came through wall-to-wall "If you do that, it will be nearly immediately fatal. Do not do that." I stopped. I did not do that. I shoved the purge button and took 5-6 massive deep breaths trying to pause at top and bottom (this was hard). It was pretty much all I could do to concentrate on breathing. It didn't take long to come back from it, I had a serious thought about shoving a big blow into the wing and sorting things out much shallower, but I had no confidence that I'd be able to stop and a polaris ascent isn't my cup of tea. Another 5 -6 breaths and I've sort of managed to clear the flood and got the brain firing on 2-3 cylinders at least. Manage to grab a gear and get my brain to actually process the numbers on the computer right under my nose, still at 50m. Somewhere at this point the fog lifted, symptoms disappeared as quickly as they'd arrived and I was fine. I swam back up the slope keeping concentration on my breathing ready to assist with the purge button if needed (it wasn't). I then did an extra 10 minutes or so at 6m once the VR3 had cleared.

    *I suspect at this time I was still neg from the descent and was expending a lot of energy kicking myself back up shallower rather than floating up neutral.



    Lessons? Err don't be a dickhead?

    Biggest lesson to pass on

    I didn't feel even slightly narked until it all went for a shit within 30 seconds

    -Anyone who says they don't get narked just hasn't scared themselves yet, or is a fucking liar
    -I don't really think nitrogen narcosis is that serious, I'm convinced it's wayyy more to do with gas density and CO2 narcosis.
    Last edited by WFO; 08-01-2019 at 12:06 PM.

  2. #2
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    I think I have read about the work of breathing becoming an issue once the gas density increases to a certain point - Simon Mitchell did a good talk about it which was primarily dealing with CCR but the principles are still valid - link.

  3. #3
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    Quote Originally Posted by Neilwood View Post
    I think I have read about the work of breathing becoming an issue once the gas density increases to a certain point - Simon Mitchell did a good talk about it which was primarily dealing with CCR but the principles are still valid - link.
    There is no "point" really just a sliding scale. This dive would have been about 8.5g/l, I think 5-6 is recommended as a sensible maximum.


    "In fact, MVV decreases approximately as a square root function of gas density"
    (Maximum Voluntary Ventilation)
    citation from Simon Mitchel paper on Dave Shaw fatality (fitting considering the date)
    Last edited by WFO; 08-01-2019 at 02:05 PM.

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    Quote Originally Posted by WFO View Post
    There is no "point" really just a sliding scale. This dive would have been about 8.5g/l, I think 5-6 is recommended as a sensible maximum.


    "In fact, MVV decreases approximately as a square root function of gas density"
    (Maximum Voluntary Ventilation)
    citation from Simon Mitchel paper on Dave Shaw fatality (fitting considering the date)
    I think that actually came out at one point in the video presentation - up to 5-6g/l still has a fairly low incident rate but after that the incident rate goes up dramatically. As he noted, the difference between the tidal volume and the maximum respiration goes to virtually nil at those sorts of depths which means all your lung effort is expended simply breathing and there is no capacity for additional load caused by working hard. From what he shows in the presentation, it seems likely that you came pretty close to the unrecoverable edge of this and realised just in time that you needed to change your actions.

    Thank you for posting your experience. It takes a lot to accept that you had a close one and hopefully other divers can learn from it.

  5. #5
    Established TDF Member MikeF's Avatar
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    good post

    From my deep air days the turn on a wall or steep slope was always the point my head flipped. Falling down a wall or finning down a slope is very easy. It's the point you stop and start to go head up and have to push yourself back up that hurts. The lesson for me was don't fin at depth, move very very slowly and if I got breathless all I needed was one finger to press the up button.

    Helium was a game changer when it came to deep dives, took all the challenge and fun out of thinking you were about to die.

  6. #6
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    Quote Originally Posted by MikeF View Post
    and fun out of thinking you were about to die.
    Part of me misses that sort of thing. Haven't had any ridiculously overpowered, ill-handling gsxrs for a few years either.

    Life's boring these days.

  7. #7
    Old but keen Mark Chase's Avatar
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    My one and only C02 hit was on a 80m OC trimix dive with a END of 25m

    Similar symptoms to those you describe all started (IMHO) by a totally unbalanced rig trying to flip me over (In Egypt using unfamiliar kit) and struggling with buoyancy / trim

    I dont remember much but I remember pre hit I was breathing a LOT in short sharp breaths and trying to hold it together as I felt my reg was underperforming. Post dive mega headache was another link to pos C02 being the issue

    Getting shallow helped a lot which made me at first suspect narcosis but id analysed the gas pre dive and that shouldn't have been an issue. This was 2000 ish and I hadn't learned about retained C02 or C02 narcosis. Looking back having discovered this link, I began to believe that was the most likely cause

  8. #8
    TDF Member germie's Avatar
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    Everybody get narked, but not everybody at the same depth, and all depending on temperature, shape of the day, etc. And it can be from nitrogen, but also from CO2. Air is thicker at 60m than at 40m.
    But even if everybody can get narked, I don't like that others decide what my air limits are. The only one who can do that is me myself. But taking helium at 30.2m is a waiste of that expensive gas.
    I had headaches after deep air dives, that is co2 also. I speak about dives over 50m depth then. But it is not allways and also depends if it is a shore dive or a boatdive (even not motion sickness, but still moves of the waves).


 

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