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Manual calculation for accelerated deco

Discussion in 'Technical Diving' started by hanymamdouh, Dec 4, 2017.

  1. boulderjohn

    boulderjohn Technical Instructor ScubaBoard Supporter

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    This post is just stunning. I have nothing more to say.
     
    victorzamora and PfcAJ like this.
  2. Dan_P

    Dan_P DIR Practitioner

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    Petty insults, bravo

    You're saying you don't have scientific proof for your statements, and yet are bashing me for not presenting scientific proof.

    I'm not saying you're wrong or that I don't grasp what you're saying, or that you're idiots.

    I'm arguing principally that the on-gassing of slow tissues would seem less problematic to me than bubble propagation, given the relative pressure diffential is increased compared to normal levels.

    That's a far cry from sny remarks, personal insults and slander, but I guess you feel those are what discussions are good for - that's your problem, not mine :)
     
  3. lowviz

    lowviz Solo Diver ScubaBoard Supporter

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    It isn't about you.

    Other divers read this stuff. Let's take it from the top. Everything is based on ATA's or ATM's, right?

    Sea level is accepted as 1 atmosphere of pressure, correct?

    Water is the same density at any elevation that it can be dived (dove).

    You add a standard sea level atmosphere for each 33 ft of salt water or 34 feet of fresh water at sea level, right?

    When you are at elevation, 1 ATM is no longer 760 mm Hg. There is nothing magical about that number. It is nothing more than what we were given on the planet Earth at sea level. Add more gas to our atmosphere and it would be a bigger number at sea level. Go to elevation and it becomes less. Keep going and it becomes zero.

    Assuming that you are at elevation and equilibrated, you can't use values from some other atmospheric pressure.

    You really need to grasp this before you make UTD look stupid.
     
  4. KenGordon

    KenGordon Rebreather Pilot

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    Consider how you get the 1.6 tissue saturation. It is not by spending a very long time at 6m, in which case you would be correct, a long time at 6m at 2000m altitude would result in a saturation of 1.4 (0.6 due to depth and 0.8 due to atmospheric pressure). In fact you get a 1.6 tissue saturation by going deeper, picking up a much higher saturation and then coming up slowly to control the tissue saturation compared to ambient. You cannot go up, to a lower ambient, until your tissues are not excessively saturated compared to that ambient. To arrive at the surface with equivalent safety you need to reduce your tissues to lower than the 1.6 of a sea level ascent, this makes the shallow stops longer.

    We can more or less ignore the 2m ‘credit’ during the dive, the penalty at surfacing is much worse.
     
    BenjaminF likes this.
  5. bluemed

    bluemed Master Instructor

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    I didn't read everything but like always people make conclusions, and start to say this is right and that is wrong.. Buhlmann profiles or whatever profiles don't give you an guarantee, neither does RD (ratio deco), neither does anything.
    We are all different, bodyweight, mass, fat% and the list goes on so the diver with his/her experience must find out what works best.
    In this sense I like ratio deco, since you can manipulate it (like GF's), if you understand RD it is very easy to make come very close to a Buhlmann profile 30/70 between 25/80 if you forget about the S curve around the O2 window and look at it more like an exponential curves an deduct a few minutes from the deeper part of the s curves and start slowing down around 50% of maximum depth you get a Buhlamnn profile.
     
  6. lowviz

    lowviz Solo Diver ScubaBoard Supporter

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    Yes, they do. And there is room for that in this discussion.

    You like RD, I'm fine with that. But RD assumes one standard atmosphere. So let's do the math and then let it go.

    The density of water is 1000kg/m^3. The acceleration of gravity that gives water its weight is 9.8 m/s^2. One standard atmosphere is 101325 Pascals.

    So 101325/(1000*9.8) = 10.3 meters.

    10.3 meters ~ 33.8 feet. (fresh water)

    Now, if you reduce the atmospheric pressure by going to elevation, the water depth (that one finds for one atmosphere) is also reduced. This is a problem for RD. BSAC has been doing this for years, it seems that it is obvious to them.

    Bubbling is concerned with RATIOS of pressures, not absolute pressures. I don't care what procedure that you dive, physics says that your stop/safety depths will change with elevation.
     
  7. kensuf

    kensuf ScubaBoard Sponsor ScubaBoard Sponsor

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    Now all we need is Ross to come in talking about the superiority of bubble models.

    RD has some value, but the value isn't in planning full blown deco schedules for a dive. The utility of RD is:

    1. To understand the deco implications for a given dive plan very quickly, and to make adjustments to that plan -- helps with overall understanding of deco theory, quick napkin math gas planning, etc.

    2. Make adjustments in case things don't go exactly as planned.

    It was never meant to replace tables. Period.

    Originally, RD was "discovered" by people that noticed the pattern/relationship while manually cutting a lot of tables. There was no science, it was simply an observation, that's all. I recall observations that were discussed over sushi at Lucy Ho's when someone pointed out that a 285' schedule looked a lot like a fibonacci sequence, that kind of started everyone looking at it.
     
    lowviz likes this.
  8. Dan_P

    Dan_P DIR Practitioner

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    I understand what you're saying. I am not and was not arguing what you're saying about the surface pressure being less at altitude, and I'm not in doubt about what is meant when saying that the delta across relative pressure drop for a given depth change on, say, a sea level dive and a 2000m dive, expends with approximation to the surface.

    No need to patronize anyone.

    I understand what you're saying.

    My point is, as the pressure gradient increases, so too does this to a greater effect impact bubble expansion by way of Boyle's Law.
    Solely approaching this by way of adding shallow stops - while satisfying to the understanding that the relative pressure difference is greater with approximation to the surface - doesn't relate itself to an impact of gas mechanics.

    To be sure, I would reason that such an impact would be relatively greater at altitude.
    I'm not speaking about ultimate principles here (either 100% dissolved gas, or 100% gas mechanics).

    How does one assume that the relationship of emphasis between dissolved gas and bubble mechanics should be identical across sea level and altitude, and then batter anyone saying it might not be with "you have no proof!".
    That's effectively what's at play here.

    Meanwhile, needing to look at Ratio Deco as though it's an algorithm in and by itself, is in my view a manifestation of "trust me"-mentality.
    If you want to extend the shallow stops because you're at altitude, or dehydrated, or whatever, that's what you do.
    You make that call.

    Besides, while we're on about scientific proof, I'm still waiting for someone, anyone, to present evidence of their algorithm of choice being "optimal".
    Going on Buhlmann - who actually dives Buhlmann pure, without a GF?
    And what's more, which GF is the "right" one?
    Nobody pointing their finger at me here, knows.


    I'm saying I find Ratio Deco extremely handy, for a number of reasons.
    I'm saying most discussions don't touch on the majority of those reasons.
    And I'm saying that "there's no science behind it" is a non-argument.

    If one would want to demonstrate a relationship between the most sensible emphasis on deep stops and shallow stops across sea level and altitude respectively, a trial is called for.
    I for one would be more than happy to participate.
     
    Last edited: Dec 9, 2017
  9. boulderjohn

    boulderjohn Technical Instructor ScubaBoard Supporter

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    Buhlmann's entire body of work is the reference because his tables were based in part on experimentation done at altitude, but there is much more than that.

    Buhlmann worked for decades to produce his results, with much of that work done at altitude. His studies of divers at altitude confirmed that altitude is something that must be considered in dive planning. I used the word "confirmed" purposely because every study done by every scientists in more than 100 years has agreed that altitude must be considered in dive planning. In more than 100 years off research, all studies and all algorithms created from those studies agree on this point. Since the only people who disagree with this are the UTD hierarchy, the burden of proof is on UTD to tell why everyone else in the world is wrong.

    You called the difference between diving at sea level and diving at elevation "a little burp." I showed you the math that said that the difference in surfacing gradient in the dive I analyzed was 20%. Is that "a little burp"? If I am wrong, where is my error?

    I also showed that the difference in bubble growth in that sample was 21%. "Is that a little burp"? If I am wrong, where is my error?

    Or will you follow the lead of my UTD instructor when I used that same math to show the difference in volume that occurs when you change depth at altitude as opposed to changing depth at sea level? He said the equation I used made no sense. I told him that if it made no sense, he should publish a paper explaining why it made no sense, because anyone who can show that, after hundreds of years of being accepted, Boyle's Law is wrong would become instantly famous. He didn't reply to that, but a conversation years later (following a fatal accident while diving at altitude) showed me that he still did not accept that math as valid.
     
  10. PfcAJ

    PfcAJ Contributor

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