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One dead, one missing (since found), 300 foot dive - Lake Michigan

Discussion in 'Accidents and Incidents' started by DandyDon, Jun 28, 2019.

  1. chillyinCanada

    chillyinCanada Solo Diver Staff Member

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    Did I read that potentially they had "descended too fast"?! o_O
     
  2. soldsoul4foos

    soldsoul4foos ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 100 - 199
    Location: Portland, ME
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  3. soldsoul4foos

    soldsoul4foos ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 100 - 199
    Location: Portland, ME
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    Jayfarmlaw likes this.
  4. RainPilot

    RainPilot completey delusional scientology snowflake Staff Member

    # of Dives: I just don't log dives
    Location: UAE
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    Descending too fast can be an issue on CCR, your PPO2 can rise faster than you burn off oxygen.
     
  5. chillyinCanada

    chillyinCanada Solo Diver Staff Member

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    Thanks for the explanation.
     
    RainPilot likes this.
  6. uwxplorer

    uwxplorer Rebreather Pilot

    # of Dives: 500 - 999
    Location: Los Angeles
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    As usual, the devil is in the details...
    Descending compresses the lungs, which the divers need to compensate for (in order not to suffer from lung collapse - i.e. suffocate) by addition of diluent (generally done by the automatic diluent valve or ADV). That will drop the fO2, especially for low fO2 diluent as used by these divers (maybe 10% O2?), and thus, the pO2 (at constant depth/pressure).
    In parallel, of course, the divers go down so the pressure increases, and for a given fO2, the pO2 will increase. But read above... The final state depends on a lot of things, including diver lung volume versus counterlung volume, etc.
    Then there is O2 consumption and addition.
    O2 metabolism is about constant without over exertion, so that contributes a little to the drop, but not enormously. Overexert, and the picture might change (as argued in a previous exchange).
    O2 addition is zero in an electronic unit (as the rEvo should have been configured for a dive at those depth), until the divers reach final depth and set their unit to high setpoint (typically pO2 = 1-1.4, depending on diver preference). On a manual/hybrid unit, where O2 flows continuously at a constant rate (about sufficient to sustain metabolism at rest), this addition will contribute a bit to the fO2/pO2 equation, but, once the max depth for constant mass flow is reached, this is essentially shut off. And then trouble starts to happen.
     
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  7. Kay Dee

    Kay Dee Barracuda

    # of Dives: I'm a Fish!
    Location: Here, there, and everywhere
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    Any data available as to how long the wife had been down for before being found on the surface, i.e. total elapsed dive time?

    As to fast descents 'causing problems' as it were on CCR, I have (unintentionaly) pushed my po2 up well above 1.6 while descending on a scooter before I noticed / corrected it (on a Mk 15.5). And on dives less than the 100m being discussed here.
     
  8. Marie13

    Marie13 Great Lakes Mermaid ScubaBoard Supporter

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    Location: Great Lakes
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    The above quoted ME’s report has it.. The Winns descended at 1228 and the captain noticed her on the surface at 1323 when he head a splash. So 55 min.
     
    chillyinCanada likes this.
  9. Marie13

    Marie13 Great Lakes Mermaid ScubaBoard Supporter

    # of Dives: 200 - 499
    Location: Great Lakes
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    I was on Double Action’s Hammond, IN (Chicago) boat yesterday. Recreational charter, two wrecks 40-50ft. There was a guy with a RB. Not sure of model. Looked to be a lot of electronics. Anyway, I was in the cabin when he was filling out waiver and showing certs to crew. He was being asked to show RB certs. Not sure if this is new or not.
     
    Johnoly likes this.
  10. Dan

    Dan Great White

    # of Dives: 500 - 999
    Location: Texas
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    55 min = going to 300’ and back, but how fast is the descent rate?

    Took 12 min for Ahmed Gabr, World record holder with OC, to reach 332.5m. That’s 27.7m/min or 90.9 ft/min, but it took him nearly 15 hours to get back to the surface.

    CCR would need a gas blending time and feedback time from gas analyzer to O2 solenoid if I venture to guess. What would be an acceptable descent rate on CCR?
     

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