DAN Y-40 Test on Deep Stops. Lower bubble count?

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Macan

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Scuba Instructor
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Anilao PH & New York USA
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See starting 34:07 of this video from DAN. Their Y-40 study shows that the deep stop divers have a significantly lower bubble count than shallow stop divers? I expected the opposite. What GF were the Deep and Shallow stop divers using? Sorry if this was already discussed in another thread.


 
According to the comment from Dr. Simon Mitchell, it appears that the "deep" profile was a GF low of 50 with a GF high of 100 and the shallow profile was a GF low of 100 and a GF high of 100.
 
According to the comment from Dr. Simon Mitchell, it appears that the "deep" profile was a GF low of 50 with a GF high of 100 and the shallow profile was a GF low of 100 and a GF high of 100.

Although the ascent times match these GFs fairly close, these where not Buehlman profiles. Most notably the 6 meter stop was quite a bit longer than the 3 meter stop. This is going to make a big difference when using 50% for deco.
 
GF low of 50 is not "deep"
GF high of 100 is nuts

I agree. I really liked the comment from Dr. Simon Mitchell on the video:

Dr. Simon Mitchell:
@DAN Southern Africa In respect of the pool dives (the first experiment described by Sandro), comparing a dive with GF (approx) 100:100 to one with GF approx 50:100 and then claiming that deep stops are better because 50:100 was better than 100:100 completely misses the point that technical divers are interested in. No one is saying that 100:100 is a good idea! The real question is "how deep should your deepest stop be"? and in the technical diving world, that translates into "should they be as deep as prescribed by bubble models, or are those stops too deep"? The studies of single "deep stops" in no-decompression diving mentioned in the presentation are completely irrelevant to this question. For decompression diving, all the published evidence to date suggests that bubble models prescribe deep stops that are too deep for optimal decompression. This is supported by Sandro's second experiment (the NDAC one) comparing 20/85 (very like a bubble model in terms of deep stops) with 50/75. Bubbling after the deeper stop dive is more sustained, and likely more problematic as he points out. Parenthetically, the dives in both studies were not really deep enough to fully unmask the potential disadvantages of over-emphasizing deep stops. In summary, I would characterize this body of work by saying that the first experiment demonstrates that extremely shallow stops (eg GF Lo 100) are not a good idea (but no one was claiming that), and the second experiment supports other work in suggesting that over-emphasizing deep stops to the extent seen in bubble models is also not a good idea. For some time now a number of us have been suggesting that for the typical depths of deep technical decompression dives (50 - 100m) a sweet spot probably sits somewhere near a GF Lo of 50.

I think there's still some good science left to be done on determining an optimal GF low for "average" tech divers yet. Not sure when we'll get more information on that at this point though.
 
I think there's still some good science left to be done on determining an optimal GF low for "average" tech divers yet. Not sure when we'll get more information on that at this point though.
Its going to be expensive and potentially not generalized across different ages, genders, or even depth or dives.

GFs are linear and DCS risk almost for sure isn't. At least right now you still have some luddites using VPM+1 (or various old forms of ratio deco) and then it runs the gament up to GFs of 80/90 or thereabouts. Personally I'm happy with 50/75 unless I'm feeling really far from help in which case I drop to 50/70
 
Its going to be expensive and potentially not generalized across different ages, genders, or even depth or dives.

GFs are linear and DCS risk almost for sure isn't. At least right now you still have some luddites using VPM+1 (or various old forms of ratio deco) and then it runs the gament up to GFs of 80/90 or thereabouts. Personally I'm happy with 50/75 unless I'm feeling really far from help in which case I drop to 50/70

Yeah, hence why I don't see a lot of new info coming out soon. I'm running 30/70 for now, as that's what we used for AN/DP, but plan on moving the GF low up to 50 progressively based on the studying I've been doing.
 
I just watched this video a few nights ago. Dr. Marroni is clearly a smart man and he presented some compelling data but I have to say the contrary trajectory puzzled me and made me wonder how much DAN stipulated a peer review before publishing (broadcasting).
 
Yeah, hence why I don't see a lot of new info coming out soon. I'm running 30/70 for now, as that's what we used for AN/DP, but plan on moving the GF low up to 50 progressively based on the studying I've been doing.
30 low is on the deeper side but unless you are doing 60+mins moving up to 50 low is all within the margin of error anyway.

3 or 5 more mins at intermediate stops is inconsequential in the grand scheme of things. 3 hrs of deco total with 25mins shifted "deeper" is categorically a different kind of dive than 25mins total of AN/DP level deco. For many tech1 or AN/DP level dives (150ft for 25mins) the first stop isnt even at the 70ft EAN50 switch yet no matter what GF low you choose.
 
I agree. I really liked the comment from Dr. Simon Mitchell on the video:

@jlcnuke - Could you please point out where did Dr. Mitchell wrote that? I’m interested to locate it so I can absorb the context and circulate it (full attribution to Dr. Mitchell) amongst folks here in Saudi Arabia who just posted the Dr Marroni video.
 
http://cavediveflorida.com/Rum_House.htm

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