Michael Guerrero
Contributor
I was reading the latest copy of DAN's Alert Diver magazine, and David Doolette had an interview in there talking about deep stops. His response was interesting but I think I need some help interpreting it. For no-stop dives, he said evidence is inconclusive but deep stops on these profiles are probably benign.
The second kind of deep stops he described were ones "popular in the early days of technical diving," and sound to me like adding a Pyle stop to a profile and then doing more deco shallower to account for the greater time spent at an intermediate depth.
The last one sound like a VPM-B profile where the stops are distributed much deeper than a Buhlmann profile, and the shallow stops are significantly shorter as well, which in his view was not inherently safer than a traditional profile based on recent experiments (I assume the NEDU one is part of that rationale).
Anyway, this is not a deep vs. shallow stops thread. The thing that I found interesting is the suggestion that one or a few intermediate stops before getting to the algorithm-prescribed shallower stops was potentially safer than a traditional Buhlmann profile, provided you complete additional deco to account for your time at an intermediate depth. At least this is how I interpret this part of the interview.
This would seem to be a profile like one in Blatteau, et al.'s paper in the 2008 UHMS Deep Stops Workshop (pg. 195) that showed that experimental profile 4 (EAP 4) followed the exact same profile as dissolved-gas model would predict, but added a 2-min intermediate stop at 25 msw after a 60 msw dive on air for 15 min. However, Blatteau's paper indicates no beneficial effect for this profile vs. the standard dissolved-gas profile. It states "our schedules didn't find the compromise between high gas elimination and low supersaturation to minimize bubble formation." On the other hand, in the discussion of this study published in Aviat Space Environ Med 2005; 76:490 –2, they say "deep stops might have worked better if we had also increased the duration of shallow stops." That seems to support David's response in the interview, though this study doesn't have any data to support the assertion. And this study is about bubble scores, not DCS outcomes, so the link to safety is not firm.
Importantly, they followed the same deco profile for the standard table and the one that added an extra 2-min stop at 25 msw, rather than adding on some additional deco as would be expected. For me, it intuitively makes sense that an intermediate stop before you hit your shallow stops on a Buhlmann profile would be better for the fast tissues, but that you would also incur additional deco time because while you're giving the fast tissues a brief chance to washout, you're also still on-gassing the slower tissues, depending of depth and the amount of intert gas already absorbed.
As some anecdotal evidence, I was recently doing some dives on a deco profile I don't normally do, where we dived to about 180ft for 20 min. For our deco, we moved some time to deeper stops around 70ft, then thinned out the intermediate stops working our way up to the 30ft, 20ft, and 10ft stops, where we did a good amount of shallow deco inline with what I would expect from a Buhlmann profile. These profiles had us feeling pretty good after, but I can't say I felt dramatically better than had I run a (for me) normal profile. They were also short exposures. What seems clear of course in all this is that we've arrived at a place where we can effectively repeat technical dives in a safe manner using many different profiles and that further improvement likely would have marginal impact.
The second kind of deep stops he described were ones "popular in the early days of technical diving," and sound to me like adding a Pyle stop to a profile and then doing more deco shallower to account for the greater time spent at an intermediate depth.
The last one sound like a VPM-B profile where the stops are distributed much deeper than a Buhlmann profile, and the shallow stops are significantly shorter as well, which in his view was not inherently safer than a traditional profile based on recent experiments (I assume the NEDU one is part of that rationale).
Anyway, this is not a deep vs. shallow stops thread. The thing that I found interesting is the suggestion that one or a few intermediate stops before getting to the algorithm-prescribed shallower stops was potentially safer than a traditional Buhlmann profile, provided you complete additional deco to account for your time at an intermediate depth. At least this is how I interpret this part of the interview.
This would seem to be a profile like one in Blatteau, et al.'s paper in the 2008 UHMS Deep Stops Workshop (pg. 195) that showed that experimental profile 4 (EAP 4) followed the exact same profile as dissolved-gas model would predict, but added a 2-min intermediate stop at 25 msw after a 60 msw dive on air for 15 min. However, Blatteau's paper indicates no beneficial effect for this profile vs. the standard dissolved-gas profile. It states "our schedules didn't find the compromise between high gas elimination and low supersaturation to minimize bubble formation." On the other hand, in the discussion of this study published in Aviat Space Environ Med 2005; 76:490 –2, they say "deep stops might have worked better if we had also increased the duration of shallow stops." That seems to support David's response in the interview, though this study doesn't have any data to support the assertion. And this study is about bubble scores, not DCS outcomes, so the link to safety is not firm.
Importantly, they followed the same deco profile for the standard table and the one that added an extra 2-min stop at 25 msw, rather than adding on some additional deco as would be expected. For me, it intuitively makes sense that an intermediate stop before you hit your shallow stops on a Buhlmann profile would be better for the fast tissues, but that you would also incur additional deco time because while you're giving the fast tissues a brief chance to washout, you're also still on-gassing the slower tissues, depending of depth and the amount of intert gas already absorbed.
As some anecdotal evidence, I was recently doing some dives on a deco profile I don't normally do, where we dived to about 180ft for 20 min. For our deco, we moved some time to deeper stops around 70ft, then thinned out the intermediate stops working our way up to the 30ft, 20ft, and 10ft stops, where we did a good amount of shallow deco inline with what I would expect from a Buhlmann profile. These profiles had us feeling pretty good after, but I can't say I felt dramatically better than had I run a (for me) normal profile. They were also short exposures. What seems clear of course in all this is that we've arrived at a place where we can effectively repeat technical dives in a safe manner using many different profiles and that further improvement likely would have marginal impact.
