Padi Advanced OW - Deep stops??

[scubadada]

Missing deep or deco stops will lock you out of air and nitrox modes for 24 hours. It will only function as a bottom timer during that period. The algorithm is not RGBM. It is Mares-RGBM. Missing SS's does not lock you out. The manual doesn't say if you will be penalized. It makes sense that the Oceanic won't penalize you since deep stops are an option. Deep stops are mandatory for the Puck.

Wow, I'm surprised that your computer might put you in violation gauge mode for skipping the deep stops, a steep penalty to pay for a practice that is not widely accepted in recreational diving. In the planning mode, how does you computer give you an NDL for a given depth and time, does it include the deep stops? With mandatory stops, seems like this is no longer NDL. Obviously, I'm confused about the Mares-Wienke RGBM algorithm.

 

[archer1960]

It's interesting that some dive computers insist on deep stops when the NEDU did controlled tests and found that the DCS incidence was significantly higher with deep stops than with standard deco protocols, for the same overall deco time.I have seen the report, but it would take me some time to dig it up again.

 

[scubadada]

It's interesting that some dive computers insist on deep stops when the NEDU did controlled tests and found that the DCS incidence was significantly higher with deep stops than with standard deco protocols, for the same overall deco time.I have seen the report, but it would take me some time to dig it up again.

This thread was about deep stops for recreational diving, the NEDU study has nothing to do with this.

 

[archer1960]

This thread was about deep stops for recreational diving, the NEDU study has nothing to do with this.

True to a certain extent, but is there any reason to believe that the results would be different for a recreational dive than for a planned deco dive? I.E, if you take the time you spent doing a deep stop, and instead spend it on a slow ascent, or on extending your safety stop, would you be more or less likely to suffer DCS? And yes, I understand that DCS is already extremely rare for dives that stay within recreational/NDL limits...

 

[scubadada]

True to a certain extent, but is there any reason to believe that the results would be different for a recreational dive than for a planned deco dive? I.E, if you take the time you spent doing a deep stop, and instead spend it on a slow ascent, or on extending your safety stop, would you be more or less likely to suffer DCS? And yes, I understand that DCS is already extremely rare for dives that stay within recreational/NDL limits...

The NEDU study is not generalizable to no stop diving.

 

[DevonDiver]

True to a certain extent, but is there any reason to believe that the results would be different for a recreational dive than for a planned deco dive? I.E, if you take the time you spent doing a deep stop, and instead spend it on a slow ascent, or on extending your safety stop, would you be more or less likely to suffer DCS? And yes, I understand that DCS is already extremely rare for dives that stay within recreational/NDL limits...

Yes, the results could easily be different. The issue with decompression dive aligns with slow tissue saturation. Recreational diving does not permit parameters that allow significant slow tissue saturation on a single dive, nor as controlling compartments.

Staged stops on ascent are not the same as a slow ascent from depth to surface. Ascending to a level where higher tissue-ambient gradients promote off-gassing, then spending time at that level to allow off-gassing....is not the same as moving slowly through a depth range where much of the time insufficient gradient exists to allow significant desaturation.

Deep stops are about surface tension 'sweet spot' bubble control. Shallow stops are about tissue-ambient gradient driven desaturation .Entirely different mechanisms.

Traditional safety stops are proven effective and should be the prime method used by recreational divers to reduce surfacing tissue gradients below an already 'statistically' very safe limit.

 

[KenGordon]

Multi-Deco and PastoDeco both give a stop based on GF Lo. Subsurface does not. And, I ran a dive simulation on my SeaBear H3 computer. It also does not give a stop based on the GF Lo.

As far as the open nature, I again note that this fine point is only relevant for the small window during a dive where GF Hi does not dictate a stop, but GF Lo does (or would, if used in that way).

When I have a few minutes, I want to re-read Baker's paper on GF and see if his original work actually specifies this detail regarding how the algorithm is to be implemented. I also have a friend who knows and trains with Mark Powell. I think I will get my friend to ask him about his thoughts on this as well.

I have been reading the subsurface code, as well as some 2013 mailing list posts about their GF implementation. i am not wildly confident that it is correct, although to be sure I will need to grab the sources and refactor the lines I question to something readable.

if ((surface / buehlmann_inertgas_b[ci] + buehlmann_inertgas_a[ci] - surface) * gf_high + surface <
(gf_low_pressure_this_dive / buehlmann_inertgas_b[ci] + buehlmann_inertgas_a[ci] - gf_low_pressure_this_dive) * gf_low + gf_low_pressure_this_dive)
tolerated = (-buehlmann_inertgas_a[ci] * buehlmann_inertgas_b[ci] * (gf_high * gf_low_pressure_this_dive - gf_low * surface) -
(1.0 - buehlmann_inertgas_b[ci]) * (gf_high - gf_low) * gf_low_pressure_this_dive * surface +
buehlmann_inertgas_b[ci] * (gf_low_pressure_this_dive - surface) * tissue_inertgas_saturation[ci]) /
(-buehlmann_inertgas_a[ci] * buehlmann_inertgas_b[ci] * (gf_high - gf_low) +
(1.0 - buehlmann_inertgas_b[ci]) * (gf_low * gf_low_pressure_this_dive - gf_high * surface) +
buehlmann_inertgas_b[ci] * (gf_low_pressure_this_dive - surface));
else
tolerated = ret_tolerance_limit_ambient_pressure;

They seem to try to track the lowest (deepest I guess) ceiling during the dive and use that in the calculation above, perhaps that is instead of the first stop depth as the GF low anchor.

 

[admikar]

Missing deep or deco stops will lock you out of air and nitrox modes for 24 hours. It will only function as a bottom timer during that period. The algorithm is not RGBM. It is Mares-RGBM. Missing SS's does not lock you out. The manual doesn't say if you will be penalized. It makes sense that the Oceanic won't penalize you since deep stops are an option. Deep stops are mandatory for the Puck.

Wow, I'm surprised that your computer might put you in violation gauge mode for skipping the deep stops, a steep penalty to pay for a practice that is not widely accepted in recreational diving. In the planning mode, how does you computer give you an NDL for a given depth and time, does it include the deep stops? With mandatory stops, seems like this is no longer NDL. Obviously, I'm confused about the Mares-Wienke RGBM algorithm.

No, deep stops are NOT mandatory in Mares-RGBM. Deco stops are. (Page 10 of Puck pro manual and pages 13-14 of Matrix manual).

 

[scubadada]

How do you determine if a stop is required? The recent discussion was about how the GF lo affects those no stop dives. That is pertinent to anyone doing no stop dives with a GF computer.

Multi-Deco and PastoDeco both give a stop based on GF Lo. Subsurface does not. And, I ran a dive simulation on my SeaBear H3 computer. It also does not give a stop based on the GF Lo.

As far as the open nature, I again note that this fine point is only relevant for the small window during a dive where GF Hi does not dictate a stop, but GF Lo does (or would, if used in that way).

When I have a few minutes, I want to re-read Baker's paper on GF and see if his original work actually specifies this detail regarding how the algorithm is to be implemented. I also have a friend who knows and trains with Mark Powell. I think I will get my friend to ask him about his thoughts on this as well.

So, this has turned out to be a more interesting and educational thread than I would have imagined. It appears that some implementations of Buhlmann ZHL-16C always take GF lo into account when calculating the ascent profile, regardless of the GF hi setting. Others do not kick in the GF lo unless you are not able to make a no stop ascent to the surface based on the selected GF hi. I apologize to @KenGordon for previous harsh statements based on my ignorance.

@stuartv points out, MultiDeco and PastoDeco are in the former category while Subsurface and the Seabear H3 are in the latter. My Dive Rite Nitek Q is also in the latter category and NDL is dictated entirely by the GF hi without a contribution by GF lo.

I spent time yesterday with my Nitek Q and MultiDeco to more fully understand this topic. Using the Nitek Q, I determined the air, 32%, and 36% NDLs at 100 feet and a GF hi of 100. These turned out to be 15, 25, and 31 minutes and were exactly the same for the entire range I could check, 5/100 through 95/100. I then ran these NDL times on MultiDeco to look at the generated ascent profile. Down to a GF lo of 70, there was no or 15 seconds of stop time at 10 feet. Starting at a GF lo of 65, stop time started to accumulate. It did not exceed a total of 3 minutes until a GF lo of 20-30 and was 5 minutes at a GF lo of 5.

The GF lo had a relatively small, but definite, effect on the ascent for the limited number of profiles I checked. The most significant effect was in a range of GF lo below what most divers would use for recreational diving. It is interesting the Buhlmann ZHL-16C is not implemented exactly the same in all planning software and dive computers. I wonder if this should be the case?

 

[EFX]

No, deep stops are NOT mandatory in Mares-RGBM. Deco stops are. (Page 10 of Puck pro manual and pages 13-14 of Matrix manual).

I was referring to the Mares Puck, an older model than the Mares Puck Pro. The Pro may work differently than the Puck. The manual for the Puck states that omitted stops will result in a lock out. I interpret stops to mean all stops: deco and deep. For divers willing to take the responsibility the lockout can be removed prior to the 24 hours by clearing the tissue compartment gas loads.