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Thread: mCCR and zero viz exit

  1. #1
    PROTEC MEXICO mattmexico is a name known to all mattmexico is a name known to all mattmexico is a name known to all mattmexico is a name known to all mattmexico is a name known to all mattmexico is a name known to all mattmexico is a name known to all mattmexico is a name known to all mattmexico is a name known to all mattmexico is a name known to all mattmexico is a name known to all mattmexico's Avatar
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    mCCR and zero viz exit

    yo

    Particular to mCCR I had an incident a couple of month ago that had a ccr cave diver student in a high stress and work load situation on a mCCR doing a zero viz exit out of a cave ... and it could have been out of a wreck too .... and had me on my toes.

    While doing a high stress, high work load, high breathing zero viz exit out of a cave a mCCR diver exeeded his active O2 injection rate of his mCCR. While I was told by the diver upon inquiry how he is going to deal with the situation ahead of time and prior to the dive I was told he is gonna count to 120 and then inject some O2.

    In the heat of battle so to speak I had to abort the drill as I realized the diver was at at a normoxic Po2 level and was about to exit the cave in the final stage, means coming up shallow and going back to the entrance - surface.

    I amin my opinion confident that the diver would have suffered a hypoxic event even when only coming from about 40 feet - 12 meters ... but again he was at .21 when at depth.

    My point here is not so much to point fingers or make a big fuzz, it just got me thinking about mCCR in zero viz situations, especially when under high stress and work load.

    Just wanted to let the forum know about this potential issue that was prevented and how to overcome it in future procedure.

    greetings
    Matt
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    Re: mCCR and zero viz exit

    Quote Originally Posted by mattmexico  View Original Post
    yo

    Particular to mCCR I had an incident a couple of month ago that had a ccr cave diver student in a high stress and work load situation on a mCCR doing a zero viz exit out of a cave ... and it could have been out of a wreck too .... and had me on my toes.

    While doing a high stress, high work load, high breathing zero viz exit out of a cave a mCCR diver exeeded his active O2 injection rate of his mCCR. While I was told by the diver upon inquiry how he is going to deal with the situation ahead of time and prior to the dive I was told he is gonna count to 120 and then inject some O2.

    In the heat of battle so to speak I had to abort the drill as I realized the diver was at at a normoxic Po2 level and was about to exit the cave in the final stage, means coming up shallow and going back to the entrance - surface.

    I amin my opinion confident that the diver would have suffered a hypoxic event even when only coming from about 40 feet - 12 meters ... but again he was at .21 when at depth.

    My point here is not so much to point fingers or make a big fuzz, it just got me thinking about mCCR in zero viz situations, especially when under high stress and work load.

    Just wanted to let the forum know about this potential issue that was prevented and how to overcome it in future procedure.

    greetings
    Matt
    I had a similar issue, but on eCCR. We were in a wreck at 60 meters with a total silt out. I could barely see the light of my hud. It stayed green.
    This made me wonder how you would solve such a situation on mCCR; no viz, increased breathing rate, ...

  3. #3
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    Re: mCCR and zero viz exit

    Quote Originally Posted by mattmexico  View Original Post
    yo

    Particular to mCCR I had an incident a couple of month ago that had a ccr cave diver student in a high stress and work load situation on a mCCR doing a zero viz exit out of a cave ... and it could have been out of a wreck too .... and had me on my toes.

    While doing a high stress, high work load, high breathing zero viz exit out of a cave a mCCR diver exeeded his active O2 injection rate of his mCCR. While I was told by the diver upon inquiry how he is going to deal with the situation ahead of time and prior to the dive I was told he is gonna count to 120 and then inject some O2.

    In the heat of battle so to speak I had to abort the drill as I realized the diver was at at a normoxic Po2 level and was about to exit the cave in the final stage, means coming up shallow and going back to the entrance - surface.

    I amin my opinion confident that the diver would have suffered a hypoxic event even when only coming from about 40 feet - 12 meters ... but again he was at .21 when at depth.

    My point here is not so much to point fingers or make a big fuzz, it just got me thinking about mCCR in zero viz situations, especially when under high stress and work load.

    Just wanted to let the forum know about this potential issue that was prevented and how to overcome it in future procedure.

    greetings
    Matt
    I'm not a cave diver, so don't know exactly what zero vis means (I know, I know). Would a HUD have helped in this circumstance, or is this the point where only an audible or vibrating warning would have helped?

    I know that mCCR is statistically safer than eCCR - not a debate I want to start again , but this risk and that of the surface hypoxia that has been reported here a few times is one of the factors that led me to eCCR (i.e I'm monitoring the active management of the system, rather than both managing it and monitoring myself managing it). I'm wondering whether a Diva or Inspo like buzzer would contribute to maintaining the mCCR safety record?

    Thanks for posting.

    Cheers,

  4. #4
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    Re: mCCR and zero viz exit

    Zero viz as in- eyes shut drill or real "water full of cack" diving? Nothing I can suggest for the drill...

    I've found even in some real clag I can see my HUD, if your lucky enough to be exiting horizontally and detect a CL bottoming out (when running MLV) you have another sign.

    High work load is the kicker, it will obliterate the O2 trickle and no-one can concentrate on HUD's and MLV when working hard.

    I would toy with SCR (hands free on most units IIRC?) or bailing out till you can relax.... yes yes- stay on the loop, but only within reason.... in a cave those two aren't perhaps an option because you have potentially long exit, in open water/wreck (my kind of diving) the gas logistics are generally more forgiving/less marginal and its doable.

    I suppose this is a scenario where the MCCR parachute type system comes up... but then we're back to ECCR with all its theoretical +ve & -ve's

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    Re: mCCR and zero viz exit

    When I've been in vis bad enough not to be able to read my displays then I just switch to OC. If it's just shite kicked up in the pool or a localised mudfest (i.e. anywhere I've been scootering) then I might do a few SCR cycles until I'm through it, otherwise OC. The gas is there, better using it than risking passing out, you don't have judges holding up score cards on how skillful your exit was... Admittedly I'm a lightweight who likes easy diving :) You can always get back on the loop once you can see again.

    I find in stressful situations, counting to more than 5 takes effort (normal situations aren't much better for me).

    Some UK sump divers carry a gauge reading lens, just a bit of perspex rod. Put the lens over the display with some light and you essentially have some clear vision.

    Cheers,

    Stuart

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    Re: mCCR and zero viz exit

    Quote Originally Posted by lizardland  View Original Post
    The gas is there, better using it than risking passing out, you don't have judges holding up score cards on how skillful your exit was...
    How true... and its a damn good thing there aren't sometimes!
    I can think of a fair few "Nil Point" manouvers I've pulled in the past! :D

  7. #7
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    Re: mCCR and zero viz exit

    I've done mCCR exit in simulated zero viz (mask off, eyes firmly shut). I had no way of knowing what my ppo2 was. To start with I was running optimal loop volume so as and when there wasn't quite enough gas in the inhale lung I added just a touch of O2 to bring it back to optimal. This worked because the line I was following didn't change depth.

    I was fairly confident that this working for me for a while but as time went by I became less and less sure about what I was breathing so I bailed out. If you have no way of knowing what it is you are breathing then surely you have to get off of the loop...

    Afterwards I checked and I had maintained a 1.3 pretty much bang on up until the point at which I had bailed out where it was creeping up towards a 1.4.

    If the line changed depth then I would have bailed out immediately.

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    Re: mCCR and zero viz exit

    If the vis was SO bad that I can't see my HUD or the displays, then I would just go semi closed till the water cleared up, then reestablish the loop po2

    Cam

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    Re: mCCR and zero viz exit

    The other day I was diving in zero vis. I followed two sidemount OC divers into a really small tunnel. The first diver killed the vis. The second did not do the vis any more favors. I had to follow the line in from clear vis and feel my way through the small passage. The displays on my CK could not be read, pressed to my mask. The Shearwater HUD that I have on my unit could easily be seen and read. The green LEDs were hazy, but I could see them. This was in a nasty clay silt out.

    The next night we did a galaxy dive. Clear vis, but all the dive lights turned off. A little glow stick juice floating in the water. I could read my HUD as well as my buddy's HUD. The LED's stood out in the dark.

    I really do not like the idea of diving a rebreather without a HUD to watch my PPO2. My Shearwater HUD gives me all sort of warm fuzzy feelings while diving my KISS.

    Cheers!!

    Kevin

  10. #10
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    Re: mCCR and zero viz exit

    Quote Originally Posted by lizardland  View Original Post
    The gas is there, better using it than risking passing out, you don't have judges holding up score cards on how skillful your exit was... Admittedly I'm a lightweight who likes easy diving :) You can always get back on the loop once you can see again.
    An interesting thought and one we may forget easily. When I learned to fly, my instructor told me that three most useless things to me were: fuel in the bowser on the ground, height above me and runway behind me Available and accessible gas in cylinders when you've stopped breathing is probably even less use than those!

    Cheers,

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