UTD Ratio deco discussion

[boulderjohn]

Why did they not think any programs were good?

Just saying something doesn't make it true.

The entire premise of UTDs deco teachings seem to be based on appeal to authority.

They were no good because they did not match the UTD RD results.

When I took the RD class, every time Andrew had us run a profile, another instructor in the room put the dive plan into one of several desktop programs. The RD profile never matched any on them, which was considered proof that they were all wrong. We were also shown graphs comparing desktop profiles with "proper" RD profiles so we could see how wrong they all were.

Note that the baseline assumption was that RD was correct. I first tried to take RD from Andrew via a webinar, but for some reason we only did part one--part 2 was never scheduled to my knowledge.. During that webinar, one of the participants asked how he knew RD was correct, and he said, "You have to have faith." "Faith in you?" she asked. "Yes," he answered.

 

[JohnnyC]

Put parameters in decoplanner (or whatever), see if there's a handy ratio. Make tables. Go dive.

Pretty much what I figured. I've never really seen the appeal to doing deco by cult of personality.....

 

[CAPTAIN SINBAD]

There is no "correct" in technical diving unfortunately. Even Dr. Mitchell does not have the correct answer so when he recommends the gradients factors of 50/80 these are his "non-scientific recommendations totally unsupported by science" as many on this thread pointed out earlier. When this language is used by the worlds leading scientist to suggest a profile, then Buhlmann Gradient Factors of 50/80 become as much a personality driven cult as the ratio-deco by UTD.

Instead of trying to find which personality cult is wrong and which of the two is right, I think it would serve us all better if we start to understand the areas that both decompression religions consider dangerous. In that regards, I am glad to see that UTD ratio deco 2.0 is starting to look more like a Buhlmann model than its predecessor Ratio Deco. Instead of 75% stops they are now making 66% stops (higher GF lo) and while they have started to add time to the shallower stops, it is not as much as the faithful believers of Buhlmann model would like to see. Still the difference is less today than it was before the UTD Italian study was carried out so the agreed upon grey area has gotten narrower which is great!

When we combine what perspectives as they presently stand, then we can be sure that:

a) Stops deeper than 66% depth are outside anything being recommended by anyone today.
b) GF low higher than 50% are shallower than anything being recommended by anyone today.

For a 150 ft dive this means that as long as you are making your first stop between 99feet and 50 feet then you are in the 49 feet of arguable sanity. If your first stop happens any deeper than 99 feet then you are in the zone of Scientology. Yes you can add time to your shallower stop and your Scientology may become acceptable to the Church of Buhlmann but the decision to make that deep stop was still motivated by Scientology rather than Churches with a larger and more self-convinced following. Similarly you may choose to make your first stop shallower than 50 feet and that would push you into Amish community who is denying the last few hundred years.

So while you do your 150 ft decompression dive, it is important to remember that between the deepest 51 feet of pure modern Scientology (that starts from the bottom 150 feet and ends at 99 feet) and the last 50 feet of ultra-rigid traditional Amish polygamy (that extends from the last 50 feet all the way up to the surface) lies the 49 feet of arguable and highly debated sanity.

Until more people get bent or further research is carried out, as long as some planning tool is putting you in those 49 feet of arguable and highly debated sanity you are within reasonable risk. If you think you need a Shearwater to land in those 49 feet of arguable sanity then no problems. If you think that 49 feet is such a wide area that a simple ratio-deco mental roadmap can put you in there then no problem either. At least not at this point in history.

 

[Kevrumbo]

There is no "correct" in technical diving unfortunately. Even Dr. Mitchell does not have the correct answer so when he recommends the gradients factors of 50/80 these are his "non-scientific recommendations totally unsupported by science" as many on this thread pointed out earlier. When this language is used by the worlds leading scientist to suggest a profile, then Buhlmann Gradient Factors of 50/80 become as much a personality driven cult as the ratio-deco by UTD.

Instead of trying to find which personality cult is wrong and which of the two is right, I think it would serve us all better if we start to understand the areas that both decompression religions consider dangerous. In that regards, I am glad to see that UTD ratio deco 2.0 is starting to look more like a Buhlmann model than its predecessor Ratio Deco. Instead of 75% stops they are now making 66% stops (higher GF lo) and while they have started to add time to the shallower stops, it is not as much as the faithful believers of Buhlmann model would like to see. Still the difference is less today than it was before the UTD Italian study was carried out so the agreed upon grey area has gotten narrower which is great!

When we combine what perspectives as they presently stand, then we can be sure that:

a) Stops deeper than 66% depth are outside anything being recommended by anyone today.
b) GF low higher than 50% are shallower than anything being recommended by anyone today.

For a 150 ft dive this means that as long as you are making your first stop between 99feet and 50 feet then you are in the 49 feet of arguable sanity. If your first stop happens any deeper than 99 feet then you are in the zone of Scientology. Yes you can add time to your shallower stop and your Scientology may become acceptable to the Church of Buhlmann but the decision to make that deep stop was still motivated by Scientology rather than Churches with a larger and more self-convinced following. Similarly you may choose to make your first stop shallower than 50 feet and that would push you into Amish community who is denying the last few hundred years.

So while you do your 150 ft decompression dive, it is important to remember that between the deepest 51 feet of pure modern Scientology (that starts from the bottom 150 feet and ends at 99 feet) and the last 50 feet of ultra-rigid traditional Amish polygamy (that extends from the last 50 feet all the way up to the surface) lies the 49 feet of arguable and highly debated sanity.

Until more people get bent or further research is carried out, as long as some planning tool is putting you in those 49 feet of arguable and highly debated sanity you are within reasonable risk. If you think you need a Shearwater to land in those 49 feet of arguable sanity then no problems. If you think that 49 feet is such a wide area that a simple ratio-deco mental roadmap can put you in there then no problem either. At least not at this point in history.

That's a fun take on the "Religion" belief allegory !

But again, what really matters is how tolerant you believe your Fast Tissues are in supersaturation:

More great @Dr Simon Mitchell snippets (sifting through the Deep Stops Increases DCS thread again):

...I am saying (based largely on the results of the NEDU study) that transient high / peak supersaturation in fast tissues does not seem to matter as much as we thought it might, and therefore that protecting fast tissues from supersaturation early in the ascent by using deep stops does not seem as effective as assumed by bubble models. This is especially so when it comes at the cost of increased supersaturation (both in terms of peak levels and duration) in slower tissues later in the ascent. The NEDU study is telling us that this is where the problems seem to come from.

@Kevrumbo asks:
. . .Explain from a physiological basis why allowing supersaturation of Fast Tissues in this instance is less risky to those tissues and results in a lower overall incidence of DCS in the shallow stops trials of the NEDU Study. . . ?

Hello Kev,

The bubble models and the deep stop approach were originally promoted on the basis that they were more successful at controlling bubble formation. The attempts to evaluate this notion in decompression dives in humans that I am aware of have shown that gas content models (or decompression procedures that have backed off deep stops to some extent) actually produce less bubbles when measured after surfacing. Neal Pollock presented some fascinating work they have been doing at the inner space event at a NOAA / AAUS rebreather diving forum I attended last week. Hopefully this will find its way into the literature at some point soon. In any event, the more we investigate it, the more the "control bubbles by deep stopping" concept appears to need reconsideration. What this is suggesting is that the bubbles are coming from the slower tissues that absorb more inert gas during the deep stops. It also implies that the faster tissues that deep stops attempt to protect from supersaturation are less prone to bubble formation when they become supersaturated. You are seeking a physiological explanation for this, and while I can't be definitive, I would suggest that it makes sense that a tissue washing inert gas out quickly might be less prone to bubble formation and growth than a tissue with slower inert gas kinetics where the supersaturation persists for longer (there's that time integral again).

Simon M

Deep Stops Increases DCS

 

[boulderjohn]

There is no "correct" in technical diving unfortunately. Even Dr. Mitchell does not have the correct answer so when he recommends the gradients factors of 50/80 these are his "non-scientific recommendations totally unsupported by science" as many on this thread pointed out earlier. When this language is used by the worlds leading scientist to suggest a profile, then Buhlmann Gradient Factors of 50/80 become as much a personality driven cult as the ratio-deco by UTD.

So, one of the world's foremost decompression scientists conducts experiments and reads the results of ALL the experiments performed by other top scientists, consults with all the top experts in the field in workshops, and then takes a wild guess guess on how to do his own decompression, a guess totally unsupported by the science he has been studying so carefully. His wild guess is just as good as the wild guess of someone who cites no research in support of his very different approach.

Got it.

 

[PfcAJ]

There is no "correct" in technical diving unfortunately. Even Dr. Mitchell does not have the correct answer so when he recommends the gradients factors of 50/80 these are his "non-scientific recommendations totally unsupported by science" as many on this thread pointed out earlier. When this language is used by the worlds leading scientist to suggest a profile, then Buhlmann Gradient Factors of 50/80 become as much a personality driven cult as the ratio-deco by UTD.

Instead of trying to find which personality cult is wrong and which of the two is right, I think it would serve us all better if we start to understand the areas that both decompression religions consider dangerous. In that regards, I am glad to see that UTD ratio deco 2.0 is starting to look more like a Buhlmann model than its predecessor Ratio Deco. Instead of 75% stops they are now making 66% stops (higher GF lo) and while they have started to add time to the shallower stops, it is not as much as the faithful believers of Buhlmann model would like to see. Still the difference is less today than it was before the UTD Italian study was carried out so the agreed upon grey area has gotten narrower which is great!

Ratio deco stops you at 66% because ???? and a GF stops you at a similar depth because of an algorithm based on physics. Those two things, even if they produce similar results, are NOT the same, and that's the real problem with UTD's ratio deco. The decisions to stop and how long to stop are based on absolutely nothing other than the words of some snake oil salesman.

 

[Kevrumbo]

So, one of the world's foremost decompression scientists conducts experiments and reads the results of ALL the experiments performed by other top scientists, consults with all the top experts in the field in workshops, and then takes a wild guess guess on how to do his own decompression, a guess totally unsupported by the science he has been studying so carefully. His wild guess is just as good as the wild guess of someone who cites no research in support of his very different approach.

Got it.

No John . . . @Dr Simon Mitchell still chooses not to profess an authoritative "recommendation"; only an informed "personal preference" on how to de-emphasize deepstops by starting with 40/70 or 50/80 GF's. As he is frequently the attending Hyperbaric Physician on many civilian "sport" technical dive charters and expeditions -as well as CCR diving on these trips himself, Dr Mitchell has to remain conservative in his approach viz-a-viz the results of the NEDU Study.

Ratio deco stops you at 66% because ???? and a GF stops you at a similar depth because of an algorithm based on physics. Those two things, even if they produce similar results, are NOT the same, and that's the real problem with UTD's ratio deco. The decisions to stop and how long to stop are based on absolutely nothing other than the words of some snake oil salesman.

UTD RD 2.0 now deepstops you at 66% instead of 75% because of the implied greater tolerance of the Fast Tissues to supersaturation and increased delta ambient pressure gradient, while seeking to lessen the decompression stress load and later surfacing supersaturation of the Slow Tissues (an implicit recognition of the NEDU Study, as well as the direct results of UTD's own experimental paradigm).

 

[RayfromTX]

So, one of the world's foremost decompression scientists conducts experiments and reads the results of ALL the experiments performed by other top scientists, consults with all the top experts in the field in workshops, and then takes a wild guess guess on how to do his own decompression, a guess totally unsupported by the science he has been studying so carefully. His wild guess is just as good as the wild guess of someone who cites no research in support of his very different approach.

Got it.

It sounds so silly when you put it that way except that Dr. Mitchell simply doesn't express much conviction in where he has currently landed with regards to how he personally dives. He readily admits it is only his best guess and it doesn't sound like liability driven cya rhetoric when he expresses it.

It is unfortunate that there doesn't seem to be any strong motivation by any agency or entity to conduct scientific testing on decompression science in the areas most relevant to civilian, non-commercial scuba diving. I understand that it is limited not only by resources but also by liability and the risk to test subjects. On top of all that, the risk factors for DCS are so numerous, that controlling for them would be near impossible.

We can do testing and zero in on the safe line for a control group and be completely wrong when other factors are included such as age,obesity, genetics, use of drugs, alcohol, tobacco,..... the list goes on and on.

I simply can't see a solution short of educating ourselves so we can make our own informed wild ass guess within an accepted range. Therefore my signature line will remain...

 

[huwporter]

So, one of the world's foremost decompression scientists conducts experiments and reads the results of ALL the experiments performed by other top scientists, consults with all the top experts in the field in workshops, and then takes a wild guess guess on how to do his own decompression, a guess totally unsupported by the science he has been studying so carefully. His wild guess is just as good as the wild guess of someone who cites no research in support of his very different approach.

"The strain of anti-intellectualism has been a constant thread winding its way through our political and cultural life, nurtured by the false notion that democracy means that “my ignorance is just as good as your knowledge"".

"A Cult of Ignorance" - Isaac Azimov.

 

[PfcAJ]

No John . . . @Dr Simon Mitchell still chooses not to profess an authoritative "recommendation"; only an informed "personal preference" on how to de-emphasize deepstops by starting with 40/70 or 50/80 GF's. As he is frequently the attending Hyperbaric Physician on many civilian "sport" technical dive charters and expeditions -as well as CCR diving on these trips himself, Dr Mitchell has to remain conservative in his approach viz-a-viz the results of the NEDU Study.

UTD RD 2.0 now deepstops you at 66% instead of 75% because of the implied greater tolerance of the Fast Tissues to supersaturation, while seeking to lessen the decompression stress and surfacing supersaturation of the Slow Tissues (an implicit recognition of the NEDU Study, as well as the direct results of UTD's own experimental paradigm).

Yes yes, but how did they derive 66% as the Magic Value?