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Two German divers drown at Gran Cenote Kalimba at Tulum

Discussion in 'Accidents and Incidents' started by ibj40, Nov 15, 2018.

  1. 1atm

    1atm DIR Practitioner

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    Disclaimer first: always get the right training, don’t use the below (or rest of SB) as a surrogate ...

    with that out of the way, a few comments for non-cave trained divers to put the rule of thirds into context:

    Let’s say that in a team of two, you swim into a cave using rule of thirds. At maximum penetration, ie the point you would turn around as prescribed by the thirds gas plan, you then both have 2/3 of your gas. Let’s say a catastrophic failure occurs just then and one of you loses all their gas. Then, on rule of thirds, only one of you has 2/3, the other has 0. You would just by the bare width of a hair both reach the exit with totally empty tanks ... if, and that’s a big IF, you do this dive in dreamy wonderland. That’s because at the time of failure you have exactly enough gas for the same consumption it took you to swim in without a single second deviation. Any slightest change, such as needing some time to deal with the problem, or thinking about navigation or the quite possible case that you or your buddy start pumping some adrenaline and your consumption goes up ... you’re not making it back. (In reality there are some tiny buffers such as time saved not picking up reels/jumps/... but for the sake of a simple in-out dive to illustrate the point here, it’s less than marginal). Hence it follows that even under ideal conditions, rule of thirds is very aggressive for a team of two. It does check out much better for a team of three. There are generally accepted rules in place for how to manage gas in a two person team, but thirds alone isn’t one of them.

    Now if you add to this the fact that the team in the incident had several other things going against them:
    - they were diving a siphon, so in the open water equivalent that’s like going with the current for the first half of the dive and swimming back against the current. Now the current in this cave (which in caves we call flow), is very minor, but it is there. So you can see that if you turn on thirds, and you would have that catastrophic loss at max penetration, there would be no way to make it out alive even under perfect conditions otherwise.
    - they were spending significant time filming also on the way out and thus possibly slowing their exit more than their pace on the way in. Again in this setting the rule of thirds does not work in a two people team.

    You might wonder why the example above on “catastrophic gas loss”, as this is fairly improbable and didn’t occur in the incident, but it’s the way cave trained divers ought to think about gas planning. In this incident there likely wasn’t a catastrophic loss, but their reserves still weren’t enough to cover the other things that went wrong ...

    (Without wanting to risk an off topic discussion, but to close to loop to the open water example you referenced above ... well it depends on the environment in open water. If it is mandatory that you make it back to an upline, be it because of heavy commercial boat traffic or the risk of getting lost in open seas ... then gas planning works like in a cave. It’s different if you could surface at any time and survive, although possibly with some inconvenience).
     
  2. Izze

    Izze Solo Diver

    # of Dives: 1,000 - 2,499
    Location: Sweden
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    There is video footage during most of the dive but some key points were not captured on video (like the first jump as an example). It is often hard to pinpoint exact localization from a clip and it doesn't add all that much when the clip is done between various important checkpoints. The assumption is simply that we assume that the jump was done and the time is an approximate. The timeline could have been far more detailed but it would just have made it harder to read.

    The second half to your quote refers to the math exercise someone had done a few posts earlier. He was using the wrong numbers and then speculating from that.
     
  3. SapphireMind

    SapphireMind Nassau Grouper

    # of Dives: 0 - 24
    Location: CA, USA
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    Thanks to those that answered my questions! I'm not a cave diver and will never go into overhead environments, no matter how much training I have, that's just not something I am going to do. But I still like to understand so I can have a coherent discussion with others about the differences :) So my rule of thirds is good for me, in my recreational only no deco dives that, in a catastrophic occurrence I could go to the surface in the emergency.
     
  4. kafkaland

    kafkaland Manta Ray

    # of Dives: 200 - 499
    Location: Saline, Michigan
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    For open water, no-deco dives there are better gas planning rules than thirds that were specifically devised for that. Rock bottom would be one of them. But if you always turn your dive under these conditions at two-thirds, and are back to the up line at one third, you should have under most, but not all, circumstances plenty of gas for the ascent even in an emergency when your buddy needs your help.
     
    eleniel, SapphireMind and kensuf like this.
  5. Big Eyes

    Big Eyes Angel Fish

    # of Dives: 100 - 199
    Location: Deutschland
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    @Izze: So the first jump left in Much Maze, where you have to put a personal leash, would not have been on the videos. Have I understood that correctly? According to the report, at the time of the 99th minute there is no video material where they reach Jump 1 (Taking Back Jump 1) and the collection of the leash by the casualties was recorded on it. Is that correct?

    I believe that I now understand what is meant by the 47 and 50 minutes. From the time the dive was filmed according to the report, the time difference of 47 minutes to their stages and 50 minutes to the time of death is meant. So these times have been calculated from the time of reversal of the dive given in the report. I understand that right now, right?
     
  6. Izze

    Izze Solo Diver

    # of Dives: 1,000 - 2,499
    Location: Sweden
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    There is no video showing jump 1, either on the way in or in the way out. The last video was done around minute 93 so before taking back jump 1 and before taking in those markers.

    And yes, you've understood it correctly in regards to the time. These figures were based on the time given in the report. The most important part is that I do not think it was a big mistake to choose either exit as the difference in time required to reach either the stages or the alternative exit was quite small.
     
  7. Big Eyes

    Big Eyes Angel Fish

    # of Dives: 100 - 199
    Location: Deutschland
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    Thank you for your prompt reply. Is it correct that Much Maze has very tight spots and generally very narrow passages? Are there any areas in this area where you have more room to move up, or are the narrow passages continuous?
     
  8. Izze

    Izze Solo Diver

    # of Dives: 1,000 - 2,499
    Location: Sweden
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    I have never dove through the entirety of Much's maze but the parts I've seen and from what I've seen on video and the maps I would not call it tight. It is smaller than some of the other tunnels but there is plenty of room to move around.
     
  9. SapphireMind

    SapphireMind Nassau Grouper

    # of Dives: 0 - 24
    Location: CA, USA
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    What is your preferred gas planning in that situation? I've not found a great resource for gas planning differences for straight recreation open water diving.
     
  10. Bob DBF

    Bob DBF Solo Diver

    # of Dives: I just don't log dives
    Location: NorCal
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    Try rooting through these, you can revise your search as you find something interesting. I find using google works better than the search engine in Scubaboard, ymmv.

    gas planning for recreational dives scubaboard

    rock bottom gas management


    Have fun

    Bob
     
    SapphireMind likes this.

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