Modern Ratio Deco usage?

[boulderjohn]

I don't have any research that supports 20/85 (which is what that ascent rate is trying to mimick). Lots of anecdotal evidence, but that isn't what you're asking about.

What do gradient factors have to do with those ascent rates?

 

[boulderjohn]

A system that's designed to mimick 20/85 will not put out an ascent that's the same as 50/80.

I am not talking about the stops. I am talking about the ascent rates. between the stops. My question had nothing to do with the gradient factors.

 

[Kevrumbo]

This was not in my training, and i was trained by the other side anyway. So please help me to understand.

In another post in one of the threads on this topic I mentioned that I had put a dive profile to 200 feet into Multi-Deco with GFs of 50/80, and it had my first stop at 90 feet. My gas switch to 50% would have been at 70 feet. That means that with a steady 30 FPM ascent rate, I would reach that first stop in just under 4 minutes. My ascent (not counting stops) to the gas switch would be another minute. That means I would reach 70 feet after 5 minutes of ascent plus the remaining time for the stops at 90 and 80 feet.

If I were using ratio deco instead, it would take me not quite 2 minutes to reach the first stop at 150 feet. It would then take me 5 minutes of ascent plus the remaining time at 5 deco stops to reach 100 feet. It would then take me 6 minutes to reach my first gas switch at 70 feet. Is that correct?

Yes . . .For a maximum bottom time of 20 min at 60m/200', you would have 1min deep stops every 10' starting at 150' (30 seconds hold & 30 seconds to ascend 10' to the next stop); reaching 100' you would do 2min stops every 10' (1.5 min hold & 30 seconds ascend) until you reach your deco gas Eanx50 switch at 70'.

In summary, with Buhlmann at 50/80, it would take me 5 minutes of ascent time plus the remaining time at 2 deco stops to reach 70 feet. With ratio deco, it would take me 13 minutes of ascent time plus the remaining time at 8 deco stops to reach 70 feet. Is that accurate?

Yes . . .(I think you meant deep stops instead of "deco" stops prior to the gas switch at 21m/70')

 

[PfcAJ]

I am not talking about the stops. I am talking about the ascent rates. between the stops. My question had nothing to do with the gradient factors.

The ascent rates shake out to be the same as the lengt of a stop.

A 2min ascent across 10ft is also 5fpm.

Even a min deco ascent is 1min per 10ft segment. That's fundamentals level stuff and again highlights the importance of gaining understanding through the system. It's incredibly hard to "teach" this stuff through the internet. Maybe (apparently at least for me) impossible even.

 

[johnkendall]

We still use Ratio deco at a Tech 1 level, but spend more time on the classes running decoplanner schedules, and then adjusting them to make them easier to remember. At a T2 level Ratio deco isn't really mentioned anymore.

In terms of the GFs that we use, GUE standards say 20/85 for classes. We are aware of the work that the NEDU and others have been doing, and are in constant conversation with David Doulette/Simon Mitchell etc but currently do not see compelling evidence to change our standard. While the work done does seem to show that over emphasis of deeper stops is a bad idea, it doesn't give us an alternative that has been adequately tested. Finally we have many years of using those settings successfully.

Thanks
John

 

[Kevrumbo]

We still use Ratio deco at a Tech 1 level, but spend more time on the classes running decoplanner schedules, and then adjusting them to make them easier to remember. At a T2 level Ratio deco isn't really mentioned anymore.

In terms of the GFs that we use, GUE standards say 20/85 for classes. We are aware of the work that the NEDU and others have been doing, and are in constant conversation with David Doulette/Simon Mitchell etc but currently do not see compelling evidence to change our standard. While the work done does seem to show that over emphasis of deeper stops is a bad idea, it doesn't give us an alternative that has been adequately tested. Finally we have many years of using those settings successfully.

Thanks
John

Such is the state of the "Art" at the moment -only to arbitrarily adjust GF's to de-emphasize the deep stops as well as provide more shallow time to clean up the slow tissues.

Simon Mitchell was the attending Hyperbaric Physician and Rebreather Diver on a 2013 Bikini Atoll Expedition I was on (as well as my treatment Doctor for an IWR session during that same expedition), and he lectured us on the results of the NEDU Deep Stops Study -his only recommendation at the time was to start with 40/70 GF's and see how it works & feels post-dive for us as different individual divers.

Here's a dialog between Simon and me with regard to retaining bubble/dual phase models which utilize deep stops such as VPM, RGBM as well as a method like Ratio Deco which has the "deepest & longest" deep stops by comparison:

The best most prudent compromise to practically apply from the NEDU Study & discussion, is to do the Deep Stops, and extend out the O2 profile at 6meters such that you have a surfacing Gradient Factor of 60% or less (per the readout of a Petrel Computer upon surfacing from your O2 deco stop) --to ensure inert gas elimination from those Slow Tissues. This is especially warranted if you're doing multiple deco dives per day for a week or more -and I would also recommend taking a day-off/break after three consecutive days of multiple deep deco dives per day. . .

Simon replies:
I would agree that this is a workable compromise. Deep stops can be safely incorporated into a dive profile if you want to use them. However, there is no evidence that you gain anything by doing so, and the available evidence suggests that their use is not the most efficient use of deco time. Thus, if you have a fixed amount of decompression time, the decompression will become less safe if you over-emphasize deep stops.

Kevrumbo:
Simon, I'm simply not willing to risk bubble nucleation & formation in my Fast Tissues for the sake of not loading/supersaturating my Slow Tissues later on in the deco profile (per indication of those "heat maps" by UW Sojourner); essentially a "Robbing Peter to pay Paul" dilemma. And yes, I have plenty of time and an 11L Cylinder (AL80) full of O2 to clean-up those Slow Tissues. . .

Simon Mitchell replies:
Hello Kev,

I guess this is the sticking point. It is an article of faith for you that allowing fast tissues to supersaturate early in a profile that places less deep stops in your ascent is harmful, and there is probably nothing I can do to change your mind on that. However, I must point out that you only believe that because someone has told you it is so. It is an attractive theoretical assumption that many people believe(d) in the absence of any confirmatory data. The point is, that there is now data that challenge the idea. As UWSojourner's heat maps have illustrated the NEDU deep stops profile did reduce fast tissue supersaturation compared to the shallow stops profile, but this did not result in better outcomes. If tight control of fast tissue supersaturation early in the ascent is as important as you believe, why did the profile with the best control of fast tissue supersaturation early in the ascent produce the highest DCS rate?

Anyway bud, if you do what you say you are going to do and significantly pad your shallow oxygen decompression it may not matter too much what you do earlier. Just don't have a seizure please! . . .

Simon

Deep Stops Increases DCS

 

[Remy B.]

At what depth one shall stop using one and use the other ?, it seems that for certain depths some algorithms don't have issues but if you go deeper there are indications of DCS and other algorithms don't have issues but possibly at opposite depths, for what I have read, from web information of the friend of a friend that knows another friend which is friend from a diver that got a DCS because he used X algorithm, but who known what was really behind that dive in that particular day, by the other hand there are people that had experienced some degree of DCS and demonize that X algorithm, and then comes another expert that says he had been using it for thousands of years without problems doing the same dive profiles or even deeper.

Since all I see are things that I don't understand and see in my ignorant eyes as hypothesis and studies where it appears they where not comparing apples to apples, and online stories that have different followers and haters, all in all with some much unknown and the different human physiological responds, as we are not exactly equals, I only can hope that VPM and extending my stops from 12m-9m and 6m will minimize my unknown.( I keep the deeper stops of VPM as is ), and my Deco dives have been very insignificant/light Decos.

Even with the baby tec dives I do, I stay on my 50% or 80% until it is finish or almost finish ( small tanks ) because there is no conclusive info, I use VPM and extent my shallow stops specially the 6m one, it seems that you take the both more popular Algorithms and try to make the best out of them.

 

[Kevrumbo]

At what depth one shall stop using one and use the other ?. . . , I only can hope that VPM and extending my stops from 12m-9m and 6m will minimize my unknown.( I keep the deeper stops of VPM as is ), and my Deco dives have been very insignificant/light Decos.

Even with the baby tec dives I do, I stay on my 50% or 80% until it is finish or almost finish ( small tanks ) because there is no conclusive info, I use VPM and extent my shallow stops specially the 6m one, it seems that you take the both more popular Algorithms and try to make the best out of them.

Well, the other alternative is to minimize or discount the deep stops (like a 50 or higher GF lo) or to radically do away with deep stops altogether. The issue in this instance then becomes how robust are your Fast Tissues in handling supersaturation and will there be any neuro DCI pathogenesis as a result of using such a deco profile over time?

Obviously, you have to make some sort of compromise to relieve both Fast & Slow tissue supersaturation -and that involves using some percentage GF lo of deep stops and extending out shallow O2 stops out as needed. GF's 40/70 as initially recommended above seems to be a reasonable start & baseline.

 

[Macan]

Well, the other alternative is to minimize or discount the deep stops (like a 50 or higher GF lo) or to radically do away with deep stops altogether. The issue in this instance then becomes how robust are your Fast Tissues in handling supersaturation and will there be any neuro DCI pathogenesis as a result of using such a deco profile over time?

Obviously, you have to make some sort of compromise to relieve both Fast & Slow tissue supersaturation -and that involves using some percentage GF lo of deep stops and extending out shallow O2 stops out as needed. GF's 40/70 as initially recommended above seems to be a reasnable start & baseline.

@boulderjohn mentioned that Dr. Mitchell is now recommending a GF of 50/80. Two years ago, I think Dr. Mitchell suggested 40/70. Do you know the reason for this change? It seems to imply that faster tissues can handle a higher level of supersaturation and the last stop can be shortened to surface at a higher GFHigh of 80 vs. 70.

 

[Remy B.]

I Follow VPM +3 and add arbitrarily time on the shallower stops, but the GF 40/70 is quite different.

Because of my ignorance in this I choose +3 because it is half good or half bad , what I only understand ( and maybe wrong as well ) is that as shallower you go the bubbles grow bigger

Decompression model: VPM - B/E

DIVE PLAN
Surface interval = 2 day 0 hr 0 min.
Elevation = 0m
Conservatism = + 3

Dec to 60m (3) Trimix 18/40 18m/min descent.
Level 60m 26:40 (30) Trimix 18/40 1.25 ppO2, 27m ead, 32m end
Asc to 42m (32) Trimix 18/40 -8m/min ascent.

Stop at 42m 0:45 (33) Trimix 18/40 0.93 ppO2, 18m ead, 21m end
Stop at 36m 3:00 (36) Trimix 18/40 0.82 ppO2, 14m ead, 18m end
Stop at 30m 2:00 (38) Trimix 18/40 0.72 ppO2, 11m ead, 14m end
Stop at 27m 3:00 (41) Trimix 18/40 0.66 ppO2, 10m ead, 12m end
Stop at 24m 3:00 (44) Trimix 18/40 0.61 ppO2, 8m ead, 10m end
Stop at 21m 3:00 (47) Nitrox 50 1.54 ppO2, 10m ead
Stop at 18m 3:00 (50) Nitrox 50 1.39 ppO2, 8m ead
Stop at 15m 4:00 (54) Nitrox 50 1.24 ppO2, 6m ead
Stop at 12m 5:00 ( I will make it 7:00 ) (59) Nitrox 50 1.10 ppO2, 4m ead
Stop at 9m 8:00 ( I will make it 11:00 ) (67) Nitrox 80 1.51 ppO2, 0m ead
Stop at 6m 33:00 ( I will make it 40:00 )(100) Nitrox 80 1.28 ppO2, 0m ead
Surface (101) Nitrox 80 -6m/min ascent.

Off gassing starts at 45.8m

OTU's this dive: 133
CNS Total: 51.3%



============================================================================


Decompression model: ZHL16-B + GF

DIVE PLAN
Surface interval = 2 day 0 hr 0 min.
Elevation = 0m
Conservatism = GF 40/70

Dec to 60m (3) Trimix 18/40 18m/min descent.
Level 60m 26:40 (30) Trimix 18/40 1.25 ppO2, 27m ead, 32m end
Asc to 36m (33) Trimix 18/40 -8m/min ascent.

Stop at 36m 1:00 (34) Trimix 18/40 0.82 ppO2, 14m ead, 18m end
Stop at 30m 2:00 (36) Trimix 18/40 0.72 ppO2, 11m ead, 14m end
Stop at 27m 1:00 (37) Trimix 18/40 0.66 ppO2, 10m ead, 12m end
Stop at 24m 3:00 (40) Trimix 18/40 0.61 ppO2, 8m ead, 10m end
Stop at 21m 2:00 (42) Nitrox 50 1.54 ppO2, 10m ead
Stop at 18m 3:00 (45) Nitrox 50 1.39 ppO2, 8m ead
Stop at 15m 4:00 (49) Nitrox 50 1.24 ppO2, 6m ead
Stop at 12m 6:00 (55) Nitrox 50 1.10 ppO2, 4m ead
Stop at 9m 7:00 (62) Nitrox 80 1.51 ppO2, 0m ead
Stop at 6m 38:00 (100) Nitrox 80 1.28 ppO2, 0m ead
Surface (101) Nitrox 80 -6m/min ascent.

OTU's this dive: 135
CNS Total: 51.6%

============================================================================

Decompression model: VPM - B/E

DIVE PLAN
Surface interval = 2 day 0 hr 0 min.
Elevation = 0m
Conservatism = + 5

Dec to 60m (3) Trimix 18/40 18m/min descent.
Level 60m 26:40 (30) Trimix 18/40 1.25 ppO2, 27m ead, 32m end
Asc to 42m (32) Trimix 18/40 -8m/min ascent.

Stop at 42m 0:45 (33) Trimix 18/40 0.93 ppO2, 18m ead, 21m end
Stop at 36m 3:00 (36) Trimix 18/40 0.82 ppO2, 14m ead, 18m end
Stop at 30m 3:00 (39) Trimix 18/40 0.72 ppO2, 11m ead, 14m end
Stop at 27m 3:00 (42) Trimix 18/40 0.66 ppO2, 10m ead, 12m end
Stop at 24m 4:00 (46) Trimix 18/40 0.61 ppO2, 8m ead, 10m end
Stop at 21m 3:00 (49) Nitrox 50 1.54 ppO2, 10m ead
Stop at 18m 3:00 (52) Nitrox 50 1.39 ppO2, 8m ead
Stop at 15m 5:00 (57) Nitrox 50 1.24 ppO2, 6m ead
Stop at 12m 6:00 (63) Nitrox 50 1.10 ppO2, 4m ead
Stop at 9m 9:00 (72) Nitrox 80 1.51 ppO2, 0m ead
Stop at 6m 42:00 (114) Nitrox 80 1.28 ppO2, 0m ead
Surface (115) Nitrox 80 -6m/min ascent.

Off gassing starts at 45.8m

OTU's this dive: 151
CNS Total: 58.2%