Evolving Thoughts on Deep Decompression Stops

[rjack321]

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).

If nothing else its fairly clear that lower GFs, especially the GF low, is not necessary more conservative.

 

[boulderjohn]

If nothing else its fairly clear that lower GFs, especially the GF low, is not necessary more conservative.

I have written about this before. The word "conservative" is misleading to the point of being useless in this context. When people use the term "conservative" in diving, the clear connotation is "safer." Staying deeper longer is usually called being "conservative," but whether it is safer is a serious question.

 

[Dsix36]

The other thing that needs to be accounted for is that the safest setting for one depth of dive might not be the safest for another depth of dive. The low GF number needs to be managed carefully.

Run a dive plan to 400' with 60/90 and look at the ISS. Then run a dive plan to 600' with 60/90 and look at the ISS. The difference is what makes a good day or kills you..

 

[RyanT]

Run a dive plan to 400' with 60/90 and look at the ISS. Then run a dive plan to 600' with 60/90 and look at the ISS. The difference is what makes a good day or kills you..

Don't disagree at all with you Don, but maybe suggest profiles that those of us in the rest of the 99% actually do.

 

[dmaziuk]

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).

Yes, less could be more. And now by Integrating over theoretical Super loadings in hypothetical compartments we can finally prove it. I think I'll stick to unexploded goats: they know about as much as anyone else, but at least their math is self-consistent.

 

[Dsix36]

Don't disagree at all with you Don, but maybe suggest profiles that those of us in the rest of the 99% actually do.

I understand that most Scubaboard members do not make that kind of dive. The reason I used those numbers is because it shows the drastic difference. There are similar differences in shallower dives too but just not as pronounced or as deadly.

No single setting is good for all dives, all days, or all divers. It is extremely dynamic depending on many variables.

 

[RyanT]

No single setting is good for all dives, all days, or all divers. It is extremely dynamic depending on many variables.

Agreed!

 

[markmud]

Evolving Thought on Deep Decompression Stops

Hi John,

I enjoyed reading your article. I am slowly going through your reference list. Of course, I started at the bottom with Bruce's input. Very interesting.

No matter what community of thought that I am studying, whether on a professional level or an avocational level, I always come to the same conclusion: Human beings don't know much about the world we live.

The old keeps coming back to us; the new has (in most cases) been tried already. To this rank-amateur in decompression theory, performing deep stops seems counter intuitive if your slow/moderate compartments (tissues) are still on-gassing.

Simplex veri sigillum, Lex Parsimoniae, or Ockham's razor are still phrases to live by.

The simplest strategy executed with conforming tactics is probably the best path.

I recall a few phrases that I gleaned from reading books about scuba diving that were published years ago. A few of these thoughts seem to always be top-of-mind as the various Scubaboard discussions unfold:

• "All dives are decompression dives" (John Crea);
• "If you got bent, it means you did not do enough deco." (John Chatterton), and;
• Here is one that I read this year for the first time in a DC user manual: "You really are risking your life with this activity." (Perdix AI Nitrox Manual).

Your article piqued my curiosity.

I admire tech divers for their risk-taking character. I am too conservative--and some would claim that I am somewhat gutless.

I accept both judgements.

dive on,
markm

 

[dmaziuk]

I have written about this before. The word "conservative" is misleading to the point of being useless in this context. When people use the term "conservative" in diving, the clear connotation is "safer." Staying deeper longer is usually called being "conservative," but whether it is safer is a serious question.

The model in question does not define "safer". It only tracks the binary "above M-value line"/"below M-value line". I hear USN has a couple of probabilistic models that may work for much better for discussing "more safer" vs "less conservativer". Why not run those over Spisni profiles and see if their estimates agree with the study's conclusions? Instead of arguing 10/90 may be less safe than 30/80? Sure it may be: e.g. during that extra time in the water one may catch pneumonia.

(Edit) I.e. once you have a usable way to quantify risk, then you can run it over 10/90 profiles, 50/75 profiles, deep profiles, shallow profiles, whatever profiles, and see which ones are more risky, and for what values of "more".