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Gradient factors - deep stops thread in DIR forum

Discussion in 'Technical Diving Specialties' started by Dr Simon Mitchell, Nov 2, 2019.

  1. scubadada

    scubadada Diver Staff Member ScubaBoard Supporter

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    Hi @atdotde

    You have may have taken a look at this probabilistic model Modern Decompression. So far, there is only a recreational dive planner. You can enter your desired risk, probability of DCS, and generate a bottom time. You can also enter your bottom time and generate your probability of DCS.

    In the example, I chose 80 feet on 32% with a probability of DCS of 0.1 %, 1/1000. This generated a bottom time of a little over 34 minutes.

    upload_2019-11-4_9-47-54.png

    To put this into perspective, here are the 1st clean dive NDLs for DSAT, Buhlmann ZH-L16C at a GF high of 95, and PZ+ along with their respective probabilities of DCS

    upload_2019-11-4_10-3-56.png

    Edit: sorry, see the post by taimen that came up while I was typing. It references this topic in your blog. I read it before, but forgot Fraedrich follow-up – The Theoretical Diver :)
     
    Jay likes this.
  2. dmaziuk

    dmaziuk Orca

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    There's 10 kinds of people: those who get binary and those who don't.

    I'll say this one more time and buzz off: decompression is a poorly understood, not well studied, complex subject with plenty interesting things to study. Deep stops profiles are expected, by our reference model, to result in clinical DCS. There's nothing interesting about that. Don't mix them up in the same subject line with the stuff actually worth discussing, leave them to people who think the Earth is flat and Flinstones is a documentary, and move on already.
     
    cathal likes this.
  3. DavidFL

    DavidFL Wide-eyed nube in the Pub ScubaBoard Supporter

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    Dr. Mitchell,

    Is there any speculation or beginning-of-consensus in the circles within which you work and recreate about where our current algorithms are likely to be weak when dealing with the diving style of two decompression dives per day every day for two weeks?

    Truk is on my bucket list.....
     
  4. dmaziuk

    dmaziuk Orca

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    OK, I lied, what else's new. :D

    Thank you Robert for reminding me to check your blog again. Anyone who hasn't seen Freadrich follow-up post yet and is wondering about "growing consensus" of diving GF Low of 40 or even, gasp, 50, should go read it.
     
    FreeFlyFreak likes this.
  5. tmassey

    tmassey Barracuda

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    85/85. Wow. What is old is new again: my old Oceanic Veo 180 was similar to 85/85...

    What I’m more concerned about is the whipsaw. People fought bubble models like they were Satan’s spawn, but consensus moved things in that direction.

    First Pyle stops — which started as something akin to brief safety stops on the way up. Simple and logical, especially in the time of 60 ft/s ascents...

    Then people took the more-is-better approach and we ended up with 20/70: first stops at 80% of max depth! Which seems just as unbalanced as 95/95.

    Now everyone is rushing to literally go all the way back to 1995. (Though, possibly, with slower ascent rates.). Are we overshooting *again*?

    I don’t mind change per se. I don’t even mind uncertainty where it’s unavoidable. But I do mind the manic swings. They do not seem... rational.
     
  6. dmaziuk

    dmaziuk Orca

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    Those numbers/models models are based on very black and white counting of the actual bent divers. As were the original M-values for the most part (also, goats). Why wouldn't they agree.
     
  7. scubadada

    scubadada Diver Staff Member ScubaBoard Supporter

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    So, who's going to dive 34 minutes and who is going to dive 48 minutes. I know who I am.
     
  8. Dominik_E

    Dominik_E Nassau Grouper

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    Hi,

    I think this depends quite on the dive, no? Now, sitting in front of a computer and just having the numbers to go by, of course most of us will say "34 minutes, as the risk is lower when not pushing it!". But I also have to think this logic through. The risk will go to zero for a bottom time of zero. And in a real dive, the experience may well be worth taking a 1/1000 risk. And also a 1/300 risk.
     
    FreeFlyFreak likes this.
  9. scubadada

    scubadada Diver Staff Member ScubaBoard Supporter

    # of Dives: 1,000 - 2,499
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    Yes, exactly. One has to judge and choose their own risk. The probability over many dives is shown here The Significance of DCS Probability on a Single Dive Profile | Modern Decompression It is unlikely that anybody would dive each dive to the limit to generate this risk.
     
    FreeFlyFreak likes this.
  10. BlueTrin

    BlueTrin DIR Practitioner

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    would you choose 34 mins ?

    the probabilities for 48 mins seem a bit high
     

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