DIR refined decompression

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Slamfire

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Langley, British Columbia, Canada
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I'm a Fish!
About ten years ago JJ posted this in TDS (emphasis is mine):

DIR proposes a degree of detail never before outlined or structured including but not limited to the following: team operations, balanced rig, standard gasses, defined configuration, refined decompression, sensible and standardized nitrogen and oxygen limits, structured helium break gasses, helium deco gasses together with carefully structured procedures for exploration protocol, bail out gasses, rebreather diving, multiple scooter use, multiple (ie more than two) stage bottle management, bottle marking, gas switches (location and methodology), gas sharing, emergency responses and much more.
So what is DIR refined decompression? Is it that you use DecoPlanner to cut some tables in VPM-B or Buhlmann GF and have ratio deco for contingencies? If so, do you just write the tables on your wetnotes and pull them out when you start your ascent? Is there any recommendation favoring either VPM over GF or vice-versa?

The reason why I am asking is because I have been doing some deco dives with a UTD trained friend. His training is basically limited to ratio deco. Before any dive we have comprehensive discussions about the profile. Typically we end up following ratio deco because VPM will usually clear me by the time we finish the ratio deco plan.

Occasionally, though, his ratio deco profile will not clear VPM-B on +2 conservatism. In paper, both profiles will have pretty much the same overall runtime, but ratio deco calls for deeper stops than VPM and these end up adding time to the shallower stops. The shape of the curve is slightly different. In those cases we end up padding the shallow stops until it clears vpm.

In our discussion, the question of GUE procedures has risen. Neither of us is entirely sure if GUE procedures would call for stops that start as deep as UTD ratio deco procedures. I tell him that I know GUE has DecoPlanner and that it uses VPM or GF. And I also think that RD for GUE is reserved only for contingencies. If they use VPM or GF that means they are probably not starting the stops as deeply as UTD ratio deco does. I told him I would ask around here.
 
Never been a fan of AG's devotion to ratio deco. On OC I used to use RD on the simpler, shallower dives (above 170'ish). But for the deeper and longer dives I felt that the deep stops were too deep, for too long and that over-all the deco time was too long. When I dove OC I would plan with DecoPlanner using GF and set at 20/90 or there abouts with time moved around to take advantage of the oxygen window (does anyone even talk about that concept anymore?).

I think the refined decompression JJ talked about was about changing the shape of the deco for things like the oxygen window concept, plus standard gasses, back gas breaks, etc.

Personally I'm rethinking my view on deep stops and have started using a GF low of 35-40.
 
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I went through the UTD training and did many, many decompression dives using their version of ratio deco. I had some serious doubts about some of it, and I had some debates with AG about those doubts. (I eventually took a ratio deco class from AG himself, although he never sent me the card for it.) As part of my research related to the debates, I also had some very interesting discussions with JJ, who answered my questions very thoroughly and was generally very helpful. There is much more of a difference between UTD's approach to Ratio Deco and GUE's than one might imagine, given they started in the same place.

One thing that JJ stressed to me is that GUE views RD as a way to create the kind of plan you would get from the decompression software they use. They should be pretty much the same. In my RD class, Andrew's approach was quite different. When we worked out sample profiles, Andrew had another UTD instructor run the same dive on different decompression programs to show how different it was--and the difference always meant RD was better. In the instructional materials we were given, computer-based profiles were contrasted with the "proper" profile provided by RD. The fact that a V-Planner profile is different would have been used as an example of the superiority of the RD program.

That was a couple of years ago, so some things may have changed.

In our conversation, JJ also told me that GUE had dropped its acceptance of the oxygen window theory behind the S-curve, but they were keeping the S-curve anyway because it had been working, whatever the reason may be. In our class, Andrew also said that they oxygen window theory was not as credible as once believed and was no longer the primary reason for the S-curve. (He and I had debated that previously.) He had two other reasons for keeping it, but I don't remember either one.
 
If it wasn't "different" it wouldn't be marketable. The first step to marketing is defining yourself. I think ratio deco is just that-- it really serves no useful purpose as a primary decompression tool.

Ratio deco is great when I'm diving-- I know if I stay an extra 2min at 100ft, I have 1min of deco extra as penalty, or at 180 2min on the bottom is 2min deco. That's great when you don't get accomplished what you had hoped to get accomplished on your dive and need some extra time, you can figure out if you have the deco gas on the fly. Before all my "working" dives I cut tables and try to find a trend (ratio) between bottom time and deco for the expected depth range for adjustments during the dive. Once I get to my first stop, I'll stick with a proven model.

This stuff isn't an exact science anyway. I once had a dive buddy get bent and have to take 2 chamber rides on a dive where we did extra deco, and I've missed 30 minutes of oxygen/50% before and drove 5 hours home with no symptoms. I predict that someone who was first introduced to the S curve theory will "feel better" after doing traditional deco if you put a study in front of them telling them they should, and I'd guess most people who feel better with the S curve can thank the placebo effect as well.
 
I haven't debated deep stops with AG, but when we discussed it with my friend and went over his classroom slides, all we could find were some mentions of David Yount and bubble models -- no data, just mentions saying that you start deeper to control bubble growth. I explained to him that Yount worked on VPM and yet it seemed that RD was not agreeing with VPM. May be it was closer in agreement with earlier iterations, but not with VPM-B. In any case we couldn't find a reason that explains the deviation. I wasn't in that class so I cannot comment of what was verbally communicated regarding the topic.
 
In our conversation, JJ also told me that GUE had dropped its acceptance of the oxygen window theory behind the S-curve, but they were keeping the S-curve anyway because it had been working, whatever the reason may be. In our class, Andrew also said that they oxygen window theory was not as credible as once believed and was no longer the primary reason for the S-curve. (He and I had debated that previously.) He had two other reasons for keeping it, but I don't remember either one.

It's been awhile since I've heard anyone talk about the oxygen window so I wasn't sure if the DIR agencies still followed that theory or not. Looks like not.

However even now when I'm on CC I still tend to spike my 70' stop to 1.6 and extend it for no other reason than "What's works, works.".
 
~10 years ago Vplanner didn't exist and buhlmann was "the way" - with some half proven GFs layered on top. So "refined" way back then meant doing stops deeper than Buhlmann 30/85 suggested. At the time, available computers were even penalizing those stops. Slowing down before you get to 40ft from a 150ft dive is much more accepted now...
 
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