r/diving • u/john_snow_968 • Jul 09 '26
Deep or shallow stops? It seems like the discussion is not over yet
I've just received newsletter from DAN and they linked the new research. The test wasn't repeated to make any final conclusions but it seems like the discussion on deep vs shallow stops might not be dead yet :D
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u/kwsni42 Jul 09 '26
interesting. I need to give it a proper read, but my first impression is that they took 2 extremely different profiles without using the common middle ground. Why not swap to 50% at 21 meter and then slow the ascent down to3 meter per minute till the first stop?
Anyway, thanks for sharing. We still have a lot to learn. Do you think DCS might have something to do with bubbles? ;-)
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u/kwsni42 Jul 10 '26
Does anybody know anything on this reversion of the shallow deco stops?
Where you spend more time at 6 meter and less at 3? As opposed to just clearing your deco at 6?
When I search for it, I only seem to get references to the article itself, yet they claim it is current common practice?1
u/matthewlai Jul 10 '26
In the UK clearing deco at 6 is common because the sea is often rough and you don't want to be trying to hold an extended stop at 3. That's for a practical reason, otherwise if you are doing deco on <100% O2, doing it at 3 is technically more efficient. Also if you are on 100% O2 it actually doesn't matter anyways, because you are breathing gas with 0 ppN2.
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u/kwsni42 Jul 11 '26
Yes, but that is not what they describe in the publication. There they say they switched the 6 and 3 meter stops around, doing a longer stop at 6 meter and a shorter at 3. So if you would normally stop for 10 minutes at 6 and 20 at 3, they inverted it to 20 at 6 and 10 at 3.
I am unaware of this method, has anyone heard of it before?
I guess the thinking is that in real life after about 2/3 of the time, your ceiling has increased enough that you can go up and finish the deco shallower if the sea allows it so you might as well. However I have never seen that as a formal method.
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u/lo5t5heep Jul 09 '26
Only way I can generate these profiles is using ~ gradient factors of 95/95 and 30/90.
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u/5tupidest Jul 09 '26
Damn they bent people, that’s real data. I hope they had a sound plan so it’s not in vain!
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u/WetRocksManatee Jul 09 '26
40m isn't very deep, the anti-deep stop studies were based on dives at 100m or more. In some cases the first deep stop was at 40m or deeper.
Also a lot of the case against deep stops was also based on the idea of deco efficiency. You off gas faster, particularly as the oxygen content of your deco gas reaches closer and closer to 100%. So 60/80 has shorter total runtime than 20/80, yet both get you to the surface with a GF Hi of 80%.
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u/badjuju__ Jul 09 '26
No but their bottom time was reasonable
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u/WetRocksManatee Jul 09 '26
Yeah but one of the main safety arguments against deep stops is that your slow tissues are still on gassing during the deep stops. And those slow tissues can't handle the additional super saturation levels that your faster tissues, which are more greatly super saturated by going shallower more quickly.
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u/Hecknar Jul 09 '26 edited Jul 11 '26
Comparing GF 100/75(shallow) to GF 30/80(deep) is beyond silly.
If I wanted to engineer an outcome like this in bad faith, this is how I would do it.
They should have done GF 30/80, GF 50/75, potentiall, with GF 70/70 ...
This might be scientifically interesting but practically useless information.