[PATCHES] Vary undersaturated portion of heatmap according inert gas

Tue Oct 18 02:55:48 PDT 2016

Rick,

> On 17.10.2016, at 23:52, Rick Walsh <rickmwalsh at gmail.com> wrote:
> 
> The first patch in this series (applied on top of my last) adjusts the undersaturation zone of the heatmap (cyan to blue to black) according to the inert fraction of gas being breathed, rather than according to the inert fraction of air.
> 
> The second patch just stretches out the yellow portion, because otherwise a typical deco dive with moderate conservatism appears a bit too green for my liking.
> 
> I've attached a couple of screenshots to compare the difference.
> 
> Robert, could you please comment?

Will try. I definitely like patch 2, that’s a no-brainer.

For patch 1, I see your point (the user can see if on-gasing is happening). I am not yet convinced, though. the trouble I am having is “what is the heat-map supposed to show?”. I think, it should be a measure of deco quality (I argued for this when answering if it depends on the deco model used, and no, it does not depend on VPM and not on the gradient factors chosen). So, and I think this is a philosophical question, should it depend on what the diver is breathing? Without that patch it is only about the state of the gases in the diver’s body (and not about the time derivative as in on- vs. off-gassing). It shows the potential for bubble formation (at least that is what it is supposed to show). If we do it relative to then breathing gas, then it is more about the time derivative.

I am not really against it, just need a bit more convincing.

Anyway, here is an experiment that one should do (of course not oneself but under controlled conditions): Do an air dive with an aggressive profile that has a significant chance of causing deco symptoms (or bubble count for that matter) in the first few minutes of the 6m stop. Discard all dives where the problems occur before reaching 6m. Then have two groups: One doing the stop with air, the others with oxygen.

If it is really about the difference to ambient pressure, the incidence rate in the first minutes of the 6m stop will not depend on the gas breathed. But if it is about the inert gas gradient, there should be _more_ incidents with O2 (irrespective of the fact that for the rest of the dive and the aftermath the more effective desaturation with O2 will take over).

On an unrelated note: When googling for isobaric counter diffusion I came across http://www.advanceddivermagazine.com/articles/icd/icd.html where Wienke etal describe Mark Elliot’s plan to dive to 1049 fsw. For the fun of it I entered the gases used in our planner, see the file attached.

Turns out, with VPM-B+3 I can roughly produce that profile (that was apparently calculated in RGBM) but based on Buehlmann that guy should be dead. You need GF 150/80 or similar to get in the ball park of the runtime used. And of course the heat-map is white to a large degree… And I had always thought that you can model bubble model dives with the appropriate gradient factors...

Best
Robert

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Robert C. Helling     Elite Master Course Theoretical and Mathematical Physics
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                      Ludwig Maximilians Universitaet Muenchen, Dept. Physik
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