12 meter procedure - any good?

[boulderjohn]

I'm pretty sure there was a paper that found a midlevel stop substantially reduced bubble formation. hold on ...

OK. https://www.researchgate.net/public..._bubbles_and_fast_tissue_gas_tensions_Article

The authors found adding a 15m stop for 5min to a 6m stop greatly reduced bubbles. They followed this up and varied the length of the stops and found 2.5 minutes at 15m was enough.

I'm wondering now if these are the articles are the ones @boulderjohn was talking about in his first post.

Yes.

As I said, the study is not highly regarded for several reasons, not all of which are known to me. One is that it essentially showed that extra time on ascent reduced bubbles without showing that where that extra time was located had any effect. An extra couple minutes at safety stop depth might have done the same or been better. IIRC, the DAN America's article referencing the story had a disclaimer saying it no longer represented current thought. Here is a DAN discussion involving the world's foremost authorities on the topic of deep stops. It took place 6 years after this study, and you will see that none of these experts pay any attention to it. The section on deep stops on NDL dives is at the end.

Curiously, DAN Europe advocates deep stops on NDL dives, with no good evidence referenced. I have been told by someone with inside info that the differences between DAN Europe and DAN America on this and other issues (like flying after diving) is strongly related to the leadership of DAN Europe having a powerful dislike for the leadership of DAN Americas. That is, of course, hearsay.

 

[L13]

As @lowwall pointed out, there is evidence that midlevel and even deep stops reduce bubble formation usually as measured by ultrasound. This, in conjunction with anecdotal evidence, was the motivation for the development of the various bubble models/algorithms. The bubble algorithms appeared to do a better job of predicting bubbles observed with ultrasound than the Haldean algorithms.

Then the U.S. Navy (NEDU) tested the various algorithms, and found that the modern Haldean algorithms (without GF's set to produce deep stops) were better at reducing DCS than the bubble algorithms.

The upshot is, we don't understand DCS as well as we thought we did, but modern Haldean algorithms are the best tool we have right now to reduce DCS. As @boulderjohn said, there is still some debate in the community about these conclusions, but most experts seem to be converging on not doing deeper stops.

There are some very good articles and videos out there by Simon Mitchell and David Doolette, leading experts on the subject, highlighting what the current evidence shows, and how much we don't know.

 

[tursiops]

There are some very good articles and videos out there by Simon Mitchell and David Doolette, leading experts on the subject, highlighting what the current evidence shows, and how much we don't know.

What is sad is when somebody says, "Well, since we don't understand everything about deco models, we obviously know nothing. It is all a crap shoot."

 

[NothingClever]

Hello all,
I was asked to teach decompression strategies in our local diving club. We have a national diving manual which is quiet recent and a ppt is provided. However, as I like to know exactly what I'm talking about, I took some time to dig into the matter further.
Now, my question. I have to explain my students that there are several ways to make a dive safer, like a safety stop, diving nitrox but keeping your DC on air (when going not beyond mod), lowering Gf-high and something called the 12m-procedure. (In the past version of the manual, this list also mentioned deep stops.)

When a dive took more of you then expected (exertion...), you could or should wait at 12 meters (36 feet) for five minutes, before continuing. This allows offgassing before entering the shallows.
But in my understanding from all the talks of dr Mitchell and dr. Pollok and the book of Powell, you should better continue to your stop or safety stop, as shallow profiles are probably better, and use your gas to make your indicated stops longer.

Or I'm I wrong and is this 12 meter procedure a good idea?

Thanks!

@Rollin - what’s the skill qualification and experience level of the divers you will be training?

 

[boulderjohn]

Then the U.S. Navy (NEDU) tested the various algorithms, and found that the modern Haldean algorithms (without GF's set to produce deep stops) were better at reducing DCS than the bubble algorithms.

The upshot is, we don't understand DCS as well as we thought we did, but modern Haldean algorithms are the best tool we have right now to reduce DCS. As @boulderjohn said, there is still some debate in the community about these conclusions, but most experts seem to be converging on not doing deeper stops.

I want to emphasize that despite the common "all dives are decompression dives" mantra, there really is a difference between dives with required decompression and NDL dives, with a fuzzy range in between. The bubble theory created a deep stop craze without evidence to support it, and the research on decompression dives that followed seems to indicate that the deep stops then in vogue are too deep. It should be noted, though, that the same experts who are most clearly saying those stops are too deep are still using stops deeper than the pure Buhlmann algorithm.

But that is all about decompression dives. We do not have the same kind of recent research on NDL dives. The jury seems to be very much out on those. There is no good evidence that deep stops help, but unlike decompression dives, there is no good evidence they are harmful. Maybe they help. Maybe they don't.

As for me, having given this considerable thought, here is what I do.

• On decompression dives, I talk it through with teammates so we are on the same settings, which are usually around the 60/75 range. I am flexible on that. That is nowhere near as deep as the old deep stop advocates, but it is deeper than pure Buhlman.
• On NDL dives, I am frequently doing a multi-level dive, so it can be argued that I am doing deep stops by default. If I am doing a relatively square profile, I do not do a deep stop. I set my GF high to 85. GF low doesn't matter, but I keep it at about 60 in case I end up going into deco. I ascend to safety stop depth and then decide what to do based on the SurfGF factor. I generally try to get it to drop below 70. I have at times ascended to find a Surf GF at 50 or below, in which case I only do a safety stop if teammates don't have that feature and have their eyes glued to their computers to count down the last seconds of the 3-minute stop.

 

[boulderjohn]

There has been some interesting research on deep stops and bubble formation since my article, but it did not rise to the level of quality required for publication. It was led by Mark Powell, who has in the past been a firm advocate of deep stops but who more recently joined those who said some may be too deep.

First, a word about bubble counts. Venous gas emboli (VGE) have an association with DCS, but there is no indication that they are at all causative. People with high bubble counts do not necessarily get DCS. Unfortunately, other than actually getting DCS (which no modern study is going to use), it is nearly our only measure of decompression stress.

Powell compared divers doing relatively deeper first stops with those doing relatively shallower first stops and checked bubbling. He found the bubbling was similar. Then he did something I have never seen before in research--he tested them again over periods of time. The two groups were significantly different. The shallower stop group had bubble scores drop quickly, as expected. The deeper stop group had bubble scores that stayed consistently high for a surprisingly long period of time. I do not have the data with me, but IIRC, in some cases the bubble scores of some of the deeper stop divers actually increased for a while.

 

[scubadada]

Hi @boulderjohn

I do mostly no-stop, I dive 80/95, my surfacing GFs are <80, avg in the low 50s. I do a SS, just because

 

[L13]

As for me, having given this considerable thought, here is what I do.

• On decompression dives, I talk it through with teammates so we are on the same settings, which are usually around the 60/75 range. I am flexible on that. That is nowhere near as deep as the old deep stop advocates, but it is deeper than pure Buhlman.
• On NDL dives, I am frequently doing a multi-level dive, so it can be argued that I am doing deep stops by default. If I am doing a relatively square profile, I do not do a deep stop. I set my GF high to 85. GF low doesn't matter, but I keep it at about 60 in case I end up going into deco. I ascend to safety stop depth and then decide what to do based on the SurfGF factor. I generally try to get it to drop below 70. I have at times ascended to find a Surf GF at 50 or below, in which case I only do a safety stop if teammates don't have that feature and have their eyes glued to their computers to count down the last seconds of the 3-minute stop.

I like 60/75 as well, and also like keeping the same as my teammates and will compromise within reason.

I think GF's like that are more about conservativeness than about deep stops. Deep stops result more (for the same GF Hi conservativeness) when GF Lo << GF Hi. for example 35/75.

On NDL I keep my GF's at 60/75, I prefer SurfGF < 50%, but anything less than 75% is good enough if there is a reason not to hang out at the stop (current, buddies, whatever).

 

[Alaskan Scuba Dude]

I extrapolated on this 12-metre diminishing Ratio Deco stops earlier, and drew much sarcasm. Use Multi-deco planner with 50/80 GF to simulate a 30 meter dive where you have exceeded your NDL. You are forming bad habits by not changing your dive computer to the correct Nitrox percentage.

 

[tursiops]

I extrapolated on this 12-metre diminishing Ratio Deco stops earlier, and drew much sarcasm. Use Multi-deco planner with 50/80 GF to simulate a 30 meter dive where you have exceeded your NDL. You are forming bad habits by not changing your dive computer to the correct Nitrox percentage.

Who are you talking to?
What is a "12m diminishing Ratio Deco stop?" What thread are you referring to?