Evolving Thoughts on Deep Decompression Stops

[Manatee Diver]

Yount and Wienke thought a basic premise of dissolved gas model was wrong because bubbles are always present.

They aren't wrong, we know too little about the subject to build anything except through trail and error. Of which there has been a lot of it for the tables built off the dissolved gas model.

 

[rjack321]

So replace M-values with ISS. Or use the smaller of (M-value at 50/75, ISS). A modern computer would have more than enough cycles to run this in real time. Either way, what you are saying is the basic premise of the dissolved gas model: that you're "safe enough" as long as you're under M-values, is wrong.

Yount and Wienke thought a basic premise of dissolved gas model was wrong because bubbles are always present. You think a basic premise of dissolved gas model is wrong because ISS. Notice the similarity?

You really just like to hear yourself talk. And you don't know what integral super saturation actually is and are clearly unwilling to learn the concept.

100/100 can be "safe enough" (eg perhaps 15 DCS cases in 500 dives)
AND
10/90 can also be "safer" than 100/100 (fewer, like 12, DCS cases in 500 dives)
AND
70/90 can also be even more "safe" than 10/90 (even fewer still, like 9 DCS cases in 500 dives)

All of these occur at the same time and available evidence suggests this continuum is actually closest to biological reality.

 

[Dsix36]

IMHO, and from learning the hard way, GFs and ISS both go completely out the frickin window as the depths start getting extremely deep. There is much less room for error in any of the methods and everything is exponentially leaning more and more toward trying to kill you. GF and ISS both need to be accounted for at the same time to maintain any realistic form of safety from DCS.

 

[dmaziuk]

You really just like to hear yourself talk. And you don't know what integral super saturation actually is and are clearly unwilling to learn the concept.

100/100 can be "safe enough" (eg perhaps 15 DCS cases in 500 dives)
AND
10/90 can also be "safer" than 100/100 (fewer, like 12, DCS cases in 500 dives)
AND
70/90 can also be even more "safe" than 10/90 (even fewer still, like 9 DCS cases in 500 dives)

All of these occur at the same time and available evidence suggests this continuum is actually closest to biological reality.

Great, do you have a cite for this?

Spisni study shows that 30/80 has fewer "inflammation markers" than RD. NEDU study shows that for constant decompression time "deep stops" are too deep. That's where "70/90 more safe than 10/90" comes from?

Don't get me wrong, I wrangle data for life scientists, statistics derived from medical studies are the subject of office jokes. I am heavily biased towards actual numbers, mea maximissima cupla.

 

[dmaziuk]

IMHO, and from learning the hard way, GFs and ISS both go completely out the frickin window as the depths start getting extremely deep.

I posted the plot of ZHL-16 M-values upthread, it allows overpressure around 18 bar in the fastest compartments at 60 msw. It may well be biologically true, but... I don't think I'd care to test that on myself. (I may have forgotten to carry the one somewhere there, though.)

 

[Storker]

I wrangle data for life scientists, statistics derived from medical studies are the subject of office jokes.

This is at least the second time you bring up your background, and it's starting to look uncomfortably like an argument from authority/appeal to authority fallacy.

I'd really appreciate if you could start playing the ball instead of the man.

 

[dmaziuk]

This is at least the second time you bring up your background, and it's starting to look uncomfortably like an argument from authority/appeal to authority fallacy.

I'd really appreciate if you could start playing the ball instead of the man.

I'm bringing it up to explain my perspective on the topic: it sounds to me like the argument here is "based on a couple of somewhat-related studies, some of more conservative settings are less safe than others". This contradicts one of the fundamental axioms of the decompression models under discussion. When that happens in science, one collects more evidence and revisits the axioms, or the argument.

SB flamefests instead go into "10/90 bad because Spisni shows deco schedule you can work out on one gloved hand gets you out of the water with bubble score no worse than that of 30/80 and RANTES score no worse than that of an average no-stop dive on air". It gives my inner small-minded binary hobgoblin fits.

At least we're not arguing GF Lo presets for no-stop diving here...

 

[rjack321]

Great, do you have a cite for this?

Spisni study shows that 30/80 has fewer "inflammation markers" than RD. NEDU study shows that for constant decompression time "deep stops" are too deep. That's where "70/90 more safe than 10/90" comes from?
.

RD is quite close to 10/90, depending on the bottom time it can be anywhere from -10/90 (negative 10 as in stopping below the depth any offgassing via Buhlmann occurs at all) and 15/110 in other cases. RD has never purported to be a an offgassing model at least. Every description I have ever heard describes it as an "ascent strategy" which has relatively little controlled testing except for the Spisni study. It is clearly an aggressive profile when compared to Buhlmann, not as aggressive compared to VPM+2 (which isn't exactly hyper conservative either)

GF lows in the 50/70 range most closely NEDUs work.

Putting them together and starting from a baseline conventional dissolved gas ascent like 30/85
A) RD is worse - at least subclinically
B) NEDU has demonstrated a higher GF low is better

Good luck getting anyone to compare 30/85 to 100/100, that might not even pass an ethics review board.

 

[rjack321]

A GF low of 10 is only "more conservative" for SOME compartments, in other not fully saturated compartments this deeper setting allows them to on-gas more and that additional tissue loading is what makes the profile as a whole less safe. Fast compartments can be made less conservative by increasing GF low, while that same adjustment makes slow compartments more conservative - to a point. ISS is a metric of the totality of the conservatism (or aggressiveness).

It gives my inner small-minded binary hobgoblin fits.

Its biology, it's almost never binary

 

[UWSojourner]

I'm bringing it up to explain my perspective on the topic: it sounds to me like the argument here is "based on a couple of somewhat-related studies, some of more conservative settings are less safe than others". ...

... by the same logic, if 50/75 is "safe enough", then any combination of GF Lo <= 50 and GF Hi <= 75 is also safe enough: 5/75 ... can't be "less safe" than your upper limit of 50/75.

As far as I can tell you're the only one making a definitive claim. Your claim is shown above -- that, for example, GF10/80 can't be less safe than GF60/80. Based on the information we have from available studies, that claim is unsupportable. And we can show one study where using lower in-water GFs and surfacing at the same high GF produced inferior results (Spisni).

The Spisni trials allowed the RD profile 44% more decompression time than the GF profile. Yet, based on the study's criteria of success, that extra time did not overcome the detrimental effects of it's ascent strategy (i.e. lower GFs until surfacing). The simple ISS measure would have signaled that this result was possible since the GF profile, even with substantially less deco time, had slightly lower ISS. But the point is that the extended decompression time did not offset the detrimental impact of the RD "strategy" of staying deeper during deco.

So my claim is not that the GF10/80 is definitely riskier than GF60/80. The claim is more modest -- the Spisni study would point to the possibility that 10/80 could be riskier (and probably depends on depth/time, etc.). Or another way to say that is -- there might be a region of possible dive profiles where the additional decompression time implicit in the GF10/80 profile (compared to GF60/80) would not overcome the detrimental impact of the additional gas loading of that schedule (analogous to the Spisni result).