View Poll Results: Would you do two 60m+ dives on the same scrubber

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  • Yes

    110 48.89%
  • No

    100 44.44%
  • I don't dive to 60m but I wanted to vote anyway.

    15 6.67%
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Thread: Do you do two 60+m dives on the same scrubber?

  1. #81
    RBW Member Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike's Avatar
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    Re: Do you do two 60+m dives on the same scrubber?

    Quote Originally Posted by rohan  View Original Post
    of course. But the point I was making is that in a closed loop, the C02 present will never be zero. So some is retained and this also for sure causes increase in narcosis unlike on OC.

    are you reffering to the dead space in the dsv?

  2. #82
    New Member Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell has a reputation beyond repute Simon Mitchell's Avatar
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    Re: Do you do two 60+m dives on the same scrubber?

    For Pierre and all those discussing CO2 retention on open circuit:

    Andy Pitkin is right on the money. There is a mountain of published research showing that there is a tendency to tolerate higher arterial CO2 levels (in other words, retain CO2) during diving, and this can happen on open or closed circuit. The tendency is strongest when exercising and when work of breathing is high. Work of breathing may increase because the diver is respiring dense gas, but poorly designed equipment and static lung loads can also contribute. It is as though the respiratory controller (in the brain) prefers to allow arterial CO2 to rise rather than drive the work required to lower it. There is some data supporting the notion that the controller's response may also be blunted by high PO2s and high PN2s (both of which we encounter as divers). Pierre, your analogy to emphysema is apt.... it is somewhat like acquiring instant emphysema (even though your lungs are normal). When diving rebreathers there is also the added potential for CO2 to break through the scrubber and be rebreathed, but this is a different issue (with the same potential result).

    I know I have banged on about it for ages (but that is because it took ages to get written and through the peer review process) but a very detailed paper on exactly this topic that David Doolette and I wrote for the Handbook of Physiology is finally being published in its companion scientific journal "Comprehensive Physiology". This will appear in January 2011. We have seen the galley proofs so I am sure it will happen! Everything you would want to know about this topic is in there.

    In addition, for those going to Eurotek I am devoting an entire presentation to CO2, the issues we have been debating here, and CO2 monitoring in rebreathers (including the Apoc).

    Simon M

  3. #83
    So many CCR So little etc Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase has a reputation beyond repute Mark Chase's Avatar
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    Re: Do you do two 60+m dives on the same scrubber?

    I haven't to my knowledge had a C02 attack on CCR but i believe I have had one on OC.


    I believe it was Co2 as i was diving Trimix 11/65 for a planned 100m dive with an END of 25m and i was at about 80m at the time of the incident on an END of 18m.

    Symptoms were being unable to get enough gas to breath, panic and vertigo.
    Very narcosis like but how could that be on an 18m END?

    Causes were (I believe) a crap WOB shop hire regulator, workload and stress



    Another factor in the "do i do two 60m dives on the same scrubber" argument , is threat perception.


    Janos does most of his deep diving in UK conditions where a 60m dive can be dark, low viz and cold and hes doing them on wrecks where low viz is a enhancing factor for the hazards that abound. Therefor the perceived threat level is high.

    When prepairing for a UK dive in our bit of ociean, your mind is geered to a higher level of safety than when prepairing for a blue water dive. This is of cours wrong, but you cant beet human nature. It would take an incredably diciplined mind to not act in this way.

    For many UK CCR divers a 60m dive is just another dip in the sea. Conditions can be more stable. Diving out of Plymouth for example will have a much higher probablabuility of good viz than diving out of Brighton.


    So for depth confident divers diving in more predictable conditions two dives on the same scrubber might seem an acceptable risk. However for divers where 60m is deep and conditions are 50/50? Doing a second dive on a scrubber and limiting the performance of their dive equipment (for the sake of £8.00) would seem an incredibly daft idea.


    The reality of the problems surrounding diving a half used scrubber remain the same but the perceived threat is totally different. As an example of this I did a 40m dive with my wife where we went inside the Gozo ferry and swam along the car deck in 25c water and 50m viz.

    No way would she ever do a 40m UK dive. I believe the deepest UK dive she has done is 27m


    ATB

    Mark

  4. #84
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    Re: Do you do two 60+m dives on the same scrubber?

    Quote Originally Posted by Simon Mitchell  View Original Post
    In addition, for those going to Eurotek I am devoting an entire presentation to CO2, the issues we have been debating here, and CO2 monitoring in rebreathers (including the Apoc).
    Bollocks I can't make Eurotek this year This would be worth the entry fee alone.

    Simon - if the brain isn't automatically controlling CO2 levels as low as we would like, would artificially (ie conciously) breathing deep and slow every so often be sensible to lower levels?

    Janos

  5. #85
    RBW Member matthewoutram is just really nice matthewoutram is just really nice matthewoutram is just really nice matthewoutram is just really nice matthewoutram is just really nice matthewoutram is just really nice matthewoutram is just really nice matthewoutram is just really nice matthewoutram is just really nice matthewoutram is just really nice matthewoutram is just really nice matthewoutram's Avatar
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    Re: Do you do two 60+m dives on the same scrubber?

    Quote Originally Posted by Janos  View Original Post
    As it says. Would you do 2 x 60m+ dives on the same scrubber (and I'm talking proper dives - not a bounce dive which was aborted after thirty seconds).

    Unit is pretty much irrelevant unless you've got some fancy super duper one, in which case pretend you have a 'typical' rebreather.

    Janos
    No, because I follow these guidelines:

    50 mins, depth < 50m
    140 mins, depth < 20m
    180 mins, depth 0m

    (OK, I stretch the last one to 240 mins, and I occasionally stretch the first to 60 mins).

    So to use the same scrubber for a second dive would not leave anytime.

    Interesting thread.

    Matt.

  6. #86
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    Re: Do you do two 60+m dives on the same scrubber?


    well that works

  7. #87
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    Re: Do you do two 60+m dives on the same scrubber?

    Quote Originally Posted by Janos  View Original Post
    Bollocks I can't make Eurotek this year This would be worth the entry fee alone.
    Ditto.

    Simon's talk at the last Eurotek was the highlight in terms of quality, content, humour and information retention for the members of my club that visited.

    As an aside- anyone in denial about CO2 on OC/CC- just wait till it happens to you, if your lucky you'll just need a change of underwear.
    We where looking at some old dive videos the other week and I got to watch myself overdoing it on a SK at 50mtrs, bit scary! Everyone else gets to the bottom of the shot and sets off along the wreck, I just land like a pancake and lay there motionless holding the shot panting, its not somthing I'll forget in a hurry!

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