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Thread: Deep stops debate (split from ascent rate thread)

  1. #1071
    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: Deep stops debate (split from ascent rate thread)

    Quote Originally Posted by Igor P  View Original Post
    Hi Simon, (even I do not support use of CR at +7) there are two parts/questions at which I would like you to comment:

    1. The A2 profile protected just tissue 4 and further. The 1 - 3 tissue is not protected.
    Igor,

    This is a crucial point that gets to the centre of many of the arguments we have been having. Kevin has provided a fantastic depiction of supersaturation vs time for tissues 1-3 on the previous page. Just so that it is clear what I am talking about without jumping posts, I reproduce the relevant diagram here:



    Based on the fact that the A2 profile (yellow) dips down below VPM-B+7 (red) fairly quickly, Kevin argues that it does, comparatively speaking, provide protection of these fast tissues for at least part of the relevant period early in the ascent. Based on kevin's graph this could be summarised as VPM-B+7 (red) being better for the first 10 minutes, but for most of the next 20 minutes A2 (yellow) is comparable or better. He points out that the integral supersaturation in these tissues over the relevant periods is virtually identical. I agree with him that this makes it very difficult to make a convincing argument that VPMB+7 protects the fast tissues but A2 does not.

    Nevertheless, I think that you and Ross are attempting to argue that the supersaturation in that first 10 minutes when A2 (yellow) is higher than VPM-B+7 (red) somehow causes initiation of bubble formation that sets the tone for the rest of the ascent and consequently makes the two profiles incomparable.

    The proof that this is an implausible notion is staring us in the face.

    Look at A1 (blue) compared to A2 (yellow) during that first 10 minutes. Despite Ross's claims to the contrary, it is patently obvious that A2 did protect the fast tissues from supersaturation compared to A1 during this very early part of the ascent that you infer is so critical. Now reflect on the result of the study which is our one hard data point in all of this. A1 (blue) had a significantly lower incidence of DCS than A2 (yellow) despite its markedly higher supersaturation during your critical period. So I put it to you, if protecting the fast tissues from supersaturation during this very early and short period is so magically effective and so likely to influence the outcome of the dives, why would A2 (which did protect the fast tissues over this period - compare A1 (blue) and A2 (yellow) in the diagram) have a significantly higher incidence of DCS?

    The answer to this rhetorical question (obviously) is that a very brief period of extra protection of the fastest tissues early in the ascent doesn't appear to help, and therefore, that the transient difference between A2 and VPM-B=+7 in this phase of the ascent is inconsequential in terms of comparing the profiles.

    I have said it before..... this is why the NEDU study is relevant to us. It legitimately challenges the philosophy that protecting the fast tissues from supersaturation early in the ascent is the defining component of efficient decompression. The most plausible explanation for the NEDU result is the differences in integral supersaturation in fast and slow tissues revealed in the beautifully depicted analyses of A1 and A2 on this thread, and as has also been demonstrated, it cannot be argued that these profiles are irrelevant to the deep stop profiles used by technical divers.

    I don't want to clutter this post up with other stuff, so will answer some of your other points elsewhere.

    Simon M
    Last edited by Simon Mitchell; 12th January 2014 at 09:07.

  2. #1072
    So Cal Tech Diver aainslie has a reputation beyond repute aainslie has a reputation beyond repute aainslie has a reputation beyond repute aainslie has a reputation beyond repute aainslie has a reputation beyond repute aainslie has a reputation beyond repute aainslie has a reputation beyond repute aainslie has a reputation beyond repute aainslie has a reputation beyond repute aainslie has a reputation beyond repute aainslie has a reputation beyond repute aainslie's Avatar
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    Re: Deep stops debate (split from ascent rate thread)

    Quote Originally Posted by rossh  View Original Post
    Erik Baker wrote that introduction. You don't know what Laplace Law in physics is? Try Google.


    You might like to look around at who else makes your deco model programs, and the qualifications they have. You will be surprised to find that many, like me, do not have much training in this area, but instead bring other skill to the task.

    .
    I'm going to just leave the first one.

    On the second, NONE of them have come on here and claimed to have more authority in the subject than people like Simon, or equal authority as some of the others that you have the hubris to claim as your peers.
    Andrew Ainslie

    Buhlmann = Bend and Mend
    VPM/RGBM = Mend and Bend
    GF 35-50/70-85 = Mend and Mend

  3. #1073
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    Re: Deep stops debate (split from ascent rate thread)

    Quote Originally Posted by UWSojourner  View Original Post
    The chart below compares the behavior of the fastest compartments (C1-C3) with those of the slower compartments dominating the picture upon surfacing (C10-C12). The chart shows at each point in the dive the variations in the fastest and slower compartments, thereby providing data on your question above.

    Chart 1 shows the behavior of C1-C3. First, notice that the integral SS of these fastest compartments is almost identical for VPM and A2. Total integral SS was about 37,000 mb-mins for A2 and about 38,500 for VPM. So I think it would be correct to say A2 was not substantially worse in the protection of C1-C3 than VPM. How can this be?

    If you look at the first chart you'll see that most of the action takes place early in the ascent. But notice how quickly the yellow line (A2) goes below the red line (VPM). That initial spike that looks so alarming in chart 1 of my prior post only has a 9 minute duration. So the relatively large SS difference averages 409 mb during that initial spike, but only lasts 9 minutes.

    From that point on there are very short periods with small SS differences where A2 exceeds VPM in C1-C3. For example, there is a 15 minute period around 120 minutes run time where A2 SS is greater than VPM SS in C1-C3. But the average difference during that period is about 53 mb (1.7fsw).

    The bottom line is that the "+- variations" between A2 and VPM show very little actual fast compartment exposure difference . Certainly it makes it difficult to claim VPM "protects the fast tissues" while A2 does not.

    Finally, Chart 2 below is pretty easy to interpret. This is the cost of the deeper stops. A2 and VPM incur a substantially higher integral SS than A1 as shown in the inset chart.

    So even when you look at the +- variations in supersaturations, A2 and VPM appear very similar. Certainly when you consider both the magnitude of supersaturations, but also the exposure time to those pressures, A2 and VPM appear almost identical in the fastest compartments.
    Thanks for comment, can you make analysys for cells 4 to 8 please.

  4. #1074

    Re: Deep stops debate (split from ascent rate thread)

    Quote Originally Posted by Igor P  View Original Post
    Thanks for comment, can you make analysys for cells 4 to 8 please.
    See chart below.
    Attached Images

  5. #1075
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    Re: Deep stops debate (split from ascent rate thread)

    So what happened? Did you all agree to disagree or have you worn your fingers and keyboards out?

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    Re: Deep stops debate (split from ascent rate thread)

    Well, I think that the analysis of the outcomes of the test is making things very clear.

    It's easier to look at the analysis and decide.

    Sent from my GT-I9300 using Tapatalk

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    Re: Deep stops debate (split from ascent rate thread)

    Shhhhh!

    Let sleeping dogs lie, they certainly deserve a rest after all that tail chasing...

  8. #1078
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    Re: Deep stops debate (split from ascent rate thread)

    Quote Originally Posted by RedSeaDiver  View Original Post
    So what happened? Did you all agree to disagree or have you worn your fingers and keyboards out?
    Everybody's over at the other place talking about the Apoc.

  9. #1079
    So Cal Tech Diver aainslie has a reputation beyond repute aainslie has a reputation beyond repute aainslie has a reputation beyond repute aainslie has a reputation beyond repute aainslie has a reputation beyond repute aainslie has a reputation beyond repute aainslie has a reputation beyond repute aainslie has a reputation beyond repute aainslie has a reputation beyond repute aainslie has a reputation beyond repute aainslie has a reputation beyond repute aainslie's Avatar
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    Re: Deep stops debate (split from ascent rate thread)

    I have certainly learned an incredible amount from this thread. David, Simon, Kevin, Andy and others - thank you all for keeping a level head and sticking with us, ensuring that we were exposed to the latest thinking on these issues.

    I worry that, with all the yelling going on (which I'll readily admit to being partially to blame for ), some really important stuff got missed.

    Some of the most interesting parts of this thread are Kevin's (UWSojourner's) maps. These really are cutting edge, and point to what is, IMHO, the biggest anomaly in the way that we have treated DCS risk mitigation for all these years. We leave the water in a terrible state!!!

    Kevin, I still think it would be instructional to put in some of the other maps you and I discussed offline, perhaps in a new thread. VPM B +0 is terrifying! +2 isn't much better. Rebreathers don't work any better with VPM. There is little doubt in my mind at this stage that it's time to swing the pendulum back and move deep stops shallower, and shallow stops longer. A really pehnomenal proejct, if you had the willingness to expend the effort, would be a tool that we could all use to determine what that map looks like for any given profile.

    I'm still experimenting with settings on my own dives, and I'm seeing some real benefits from moving my deep GF up, and my shallow GF down. I'm hoping that this starts showing up in more instructors' discussions, and that VPM STOPS being the de facto approach of many divers. The science doesn't support it. It's a pity, as the idea made intuitive sense, but it just doesn't deliver.
    Last edited by aainslie; 21st January 2014 at 20:40.
    Andrew Ainslie

    Buhlmann = Bend and Mend
    VPM/RGBM = Mend and Bend
    GF 35-50/70-85 = Mend and Mend

  10. #1080

    Re: Deep stops debate (split from ascent rate thread)

    I've posted a Rebreather dive on the same basis as some of the charts in this thread here.


    Quote Originally Posted by aainslie  View Original Post
    I have certainly learned an incredible amount from this thread. David, Simon, Kevin, Andy and others - thank you all for keeping a level head and sticking with us, ensuring that we were exposed to the latest thinking on these issues.

    I worry that, with all the yelling going on (which I'll readily admit to being partially to blame for ), some really important stuff got missed.

    Some of the most interesting parts of this thread are Kevin's (UWSojourner's) maps. These really are cutting edge, and point to what is, IMHO, the biggest anomaly in the way that we have treated DCS risk mitigation for all these years. We leave the water in a terrible state!!!

    Kevin, I still think it would be instructional to put in some of the other maps you and I discussed offline, perhaps in a new thread. VPM B +0 is terrifying! +2 isn't much better. Rebreathers don't work any better with VPM. There is little doubt in my mind at this stage that it's time to swing the pendulum back and move deep stops shallower, and shallow stops longer. A really pehnomenal proejct, if you had the willingness to expend the effort, would be a tool that we could all use to determine what that map looks like for any given profile.

    I'm still experimenting with settings on my own dives, and I'm seeing some real benefits from moving my deep GF up, and my shallow GF down. I'm hoping that this starts showing up in more instructors' discussions, and that VPM STOPS being the de facto approach of many divers. The science doesn't support it. It's a pity, as the idea made intuitive sense, but it just doesn't deliver.

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