Slow tissue on gas from stops

[Dan_P]

@Dr Simon Mitchell duly noted.
As for amends in terms of apt quotation, I'll simply let stand the following to support my point regarding the use of "unsafe" and "defective":

Hello Dan,

Since you are referring to me I just want to clarify this.

I did not state RD should not be characterised as `unsafe`; you did. The post in which that appeared was generally well reasoned, and I `liked` it, but you shouldn`t infer that I would `state` everything you said in the post.

To the specific point, I think we have ample evidence pointing to the fact that RD as it stood when Georgitsis confidently predicted its superiority was less efficient and therefore less safe than available alternatives. Whether that constitutes unsafe depends on how one would define unsafe, and we do not have the data (relative DCS rates) to resolve the debate no matter what that definition is, which is why I said:

"Setting unresolvable arguments about the magnitude of differences in risk aside, if divers seek the "truth in the universe" about the most efficient approach to decompression (least risk in the same decompression time), all the current evidence suggests that approaches which emphasise deep stops are not it."

If an individual diver (such as you Dan) has a reason to use RD based on its utility in specific situations I would not consider that irresponsible, and I could not put my hand on my heart and give you an evidence-based reason to call it unsafe (we have no data on DCS rates). But I would definitely be comfortable (based on existing evidence) to say that you are sacrificing decompression efficiency and therefore some degree of safety for whatever perceived utility exists for using it.

Simon M

That said that the proof that RD works is that people don't get bent using it. When I pointed out the number of people in our small group who got bent, they said they did not count, because they got bent for some other reason. What was that other reason? Don't know. How do you know it was not RD? Because people don't get bent using RD, so any case in which it happens has to be caused by something else.

Hard to beat that kind of logic.

The tail-biting snake can work both ways;
1) "It couldn't be ratio deco because nobody can take a hit if they use ratio deco", and
2) "It had to be ratio deco because everyone in that specific group was allegedly using ratio deco"

Obviously, I don't know the details of the dives, but the logic stands;
If groups A through C all use ratio deco, and group A has all hits while groups B and C have none, surely, claiming that ratio deco caused all the hits in group A, would look strange.

The thing that I take away is that there was a great disproportion of hits in that group, comparing to probably any control group in the history of water or bubbles.

 

[Dr Simon Mitchell]

@Dr Simon MitchellIn terms of apt quotation, I'll simply let stand the following to support my point regarding the use of "unsafe" and "defective":

Hello Dan,

Actually, no. It is a nuanced issue that is not properly summarized in that sentence. "Apt quotation" is best served by citing the entire post.

Thanks,

Simon M

 

[RayfromTX]

Dan
Simon has carefully composed many posts on this nuanced subject. He has worked with diligence to not make exaggerated statements that are unsupported by data. He also refuses to use scare tactics.

We have learned something about efficient deco strategies from this discussion. You appear to have a strong confirmation bias at work in your reasoning. It is ok for you to make your decisions about deco strategies based on this biased POV. It is not ok to misrepresent a carefully worded statement made by a scientist to remove the part that is contrary to your strongly held belief.

In diving and in other areas, confirmation bias may lead to dangerous conclusions. This may not be the worst of those but it isn’t trivial. Claiming that no allowance needs to be made for diving at altitude, on the other hand, seems very arrogant. The divers that got bent while using rd at altitude are victims of that arrogance and confirmation bias.

Your arguments are persistent yet unconvincing.

 

[boulderjohn]

One of the problems with comparing deco results in the real world to deco results in the lab is that there are two factors involved in a decompression ascent--1) the algorithm the divers are using and 2) the precision with which they execute it. In a laboratory test, the precision is carefully controlled. In the real world, the precision of the execution becomes a factor. this is true with Ratio Deco more than most systems.

When I was required to follow ratio deco, we were told that 1) it was a superior algorithm to begin with and 2) it is more likely to be followed with precision because a computer can screw up during the dive, whereas divers using ratio deco do not use fallible computers--they use "the computer between the ears," which never makes mistakes.

Of the 8 cases in our group, 2 of them (a buddy team) were at least partially the result of a failure to follow the procedure properly. We only know this because of one reason--one of the divers was using a computer in gauge mode as a bottom timer, and he was able to download the profile of the dive and compare what they had actually done with what the computers between their ears thought they had done.

1. They had planned to dive for a specific depth and time. As they had been taught, they kept a running average of their depth on which to base their ascent profile. The computer showed that they repeatedly dropped below their depth and recovered. Their average depth on the dive was probably 7-8 feet deeper than what they had calculated it to be.
2. They had been taught to ascend to their first deep stop at 75% of that average depth at a rate of 30 FPM. They thought they had done that. They then noted the time and began the calculation for their deco times. They probably should have noted that the time they were starting their deco stops was several minutes later than it should have been, but they did not realize that. It had taken them 3 minutes more to ascend to that stop than it should have.
3. Once they were into the deco stops, they had to follow the RD plan, keeping track of how many minutes they were at each stop. Apparently they must have miscounted for one reason or another, because they cut their deco short by several minutes.

If they had used a computer, and if the computer had screwed up, then the UTD people would have exclaimed,"See! That's why you can't use a computer-based algorithm! Computers make mistakes! That's why you have to use Ratio Deco, because the human mind does not make mistakes!" But in this case the human mind made a series of mistakes. The UTD people therefore said, "See! It wasn't Ratio Deco's fault! These guys made mistakes!"

As for the other divers who got DCS, who know? They did not use a computer in gauge mode, so we don't know what mistakes the computers between their ears may or may not have made. None of us who used ratio Deco for years can ever be really sure how close we were to following it, since we had no computers with which we could check to see what we actually did on our dives.

Sorry--you can't have it both ways. Either the fallibility of the system is part of the system or it isn't. If Ratio Deco is supposed to be superior on the theory that the mind does not make mistakes, then you cannot dismiss the cases where the mind makes mistakes. It is an integral part of the system.

It would be interesting to see a test done on that--compare what divers without computers do on a dive compared to what they think they did.

 

[PfcAJ]

One of the problems with comparing deco results in the real world to deco results in the lab is that there are two factors involved in a decompression ascent--1) the algorithm the divers are using and 2) the precision with which they execute it. In a laboratory test, the precision is carefully controlled. In the real world, the precision of the execution becomes a factor. this is true with Ratio Deco more than most systems.

When I was required to follow ratio deco, we were told that 1) it was a superior algorithm to begin with and 2) it is more likely to be followed with precision because a computer can screw up during the dive, whereas divers using ratio deco do not use fallible computers--they use "the computer between the ears," which never makes mistakes.

Of the 8 cases in our group, 2 of them (a buddy team) were at least partially the result of a failure to follow the procedure properly. We only know this because of one reason--one of the divers was using a computer in gauge mode as a bottom timer, and he was able to download the profile of the dive and compare what they had actually done with what the computers between their ears thought they had done.

1. They had planned to dive for a specific depth and time. As they had been taught, they kept a running average of their depth on which to base their ascent profile. The computer showed that they repeatedly dropped below their depth and recovered. Their average depth on the dive was probably 7-8 feet deeper than what they had calculated it to be.
2. They had been taught to ascend to their first deep stop at 75% of that average depth at a rate of 30 FPM. They thought they had done that. They then noted the time and began the calculation for their deco times. They probably should have noted that the time they were starting their deco stops was several minutes later than it should have been, but they did not realize that. It had taken them 3 minutes more to ascend to that stop than it should have.
3. Once they were into the deco stops, they had to follow the RD plan, keeping track of how many minutes they were at each stop. Apparently they must have miscounted for one reason or another, because they cut their deco short by several minutes.

If they had used a computer, and if the computer had screwed up, then the UTD people would have exclaimed,"See! That's why you can't use a computer-based algorithm! Computers make mistakes! That's why you have to use Ratio Deco, because the human mind does not make mistakes!" But in this case the human mind made a series of mistakes. The UTD people therefore said, "See! It wasn't Ratio Deco's fault! These guys made mistakes!"

As for the other divers who got DCS, who know? They did not use a computer in gauge mode, so we don't know what mistakes the computers between their ears may or may not have made. None of us who used ratio Deco for years can ever be really sure how close we were to following it, since we had no computers with which we could check to see what we actually did on our dives.

Sorry--you can't have it both ways. Either the fallibility of the system is part of the system or it isn't. If Ratio Deco is supposed to be superior on the theory that the mind does not make mistakes, then you cannot dismiss the cases where the mind makes mistakes. It is an integral part of the system.

It would be interesting to see a test done on that--compare what divers without computers do on a dive compared to what they think they did.

Por que no los dos?

If my computer machine spits out something different than I expect based on RD and prior planning I start investigating. SOMETHING is up. Either the avg depth was different than I thought, my math was off (likely. I run out of fingers real quick), or maybe I put something into the computer box wrong.

 

[Dan_P]

Hello Dan,

Actually, no. It is a nuanced issue that is not properly summarized in that sentence. "Apt quotation" is best served by citing the entire post.

Thanks,

Simon M

Hi Simon,
Very well, I have edited the previous post to include your entire post, and highlighted the part that previously stood.

I would hope for the same dilligence in prompting corrections when, conversely, a member of the conversation goes out and says RD is "unsafe", "defective" or similar - in fairness, I'm sure we can agree those are incorrect descriptions given all knowledge available at this time.

Hence, my point remains.
When someone posts a statement to the effect of "RD is dangerous/unsafe/defective", they have no scientific support for that claim. I'd say quite the contrary, as envelopes seemingly need pushing to an extraordinary degree, to show what I'll call a practically actionable difference in results, in regards safe/unsafe.

That's the point we keep circling back to, and I don't understand why we must.

Dan
Simon has carefully composed many posts on this nuanced subject. He has worked with diligence to not make exaggerated statements that are unsupported by data. He also refuses to use scare tactics.

We have learned something about efficient deco strategies from this discussion. You appear to have a strong confirmation bias at work in your reasoning. It is ok for you to make your decisions about deco strategies based on this biased POV. It is not ok to misrepresent a carefully worded statement made by a scientist to remove the part that is contrary to your strongly held belief.

In diving and in other areas, confirmation bias may lead to dangerous conclusions. This may not be the worst of those but it isn’t trivial. Claiming that no allowance needs to be made for diving at altitude, on the other hand, seems very arrogant. The divers that got bent while using rd at altitude are victims of that arrogance and confirmation bias.

Your arguments are persistent yet unconvincing.

What are my arguments?
That given the knowledge available to us, it's wrong to say RD is defective/dangerous/unsafe?

Absolutely!

But don't write that down to a confirmation bias on my part - I invite you to join me in obtaining and reading any and all reports referenced in any discussion you can feasibly scout out across the web, and putting a finger on a single reference that shows me incorrect in the above statement, including of course Spisni and NEDU.

Granted, if one mistakes what I'm saying for "RD is optimal in terms of decompression", I'd understand the reservation - please don't.

One of the problems with comparing deco results in the real world to deco results in the lab is that there are two factors involved in a decompression ascent--1) the algorithm the divers are using and 2) the precision with which they execute it. In a laboratory test, the precision is carefully controlled. In the real world, the precision of the execution becomes a factor. this is true with Ratio Deco more than most systems.

I don't mean to split hairs about this part, but I offer as a curiosum an idea that the accuracy factor is isolated across all methods, rather with RD, diver awareness is more apparent. If the diver "calculates wrong", "dives to wrong depth" or similar, I'd write it up to an awareness issue, not purely a dive-technical skill such as bouyancy/trim.

When I was required to follow ratio deco, we were told that 1) it was a superior algorithm to begin with and 2) it is more likely to be followed with precision because a computer can screw up during the dive, whereas divers using ratio deco do not use fallible computers--they use "the computer between the ears," which never makes mistakes.

I've said it before, but the experiences I've had (as a student) have been fundamentally different.
Actually, per standards, I am not obligated to use RD in a course. I can use a computer with whichever algorithm I may like (personally, I'd feel robbed but that's on a personal note).
I think it's important to see RD not as an algorithm, but as a practical tool, but in either case, I think it's missing the whole point to say that the strength of RD is simply that it solves a need for computers.

Of the 8 cases in our group, 2 of them (a buddy team) were at least partially the result of a failure to follow the procedure properly. We only know this because of one reason--one of the divers was using a computer in gauge mode as a bottom timer, and he was able to download the profile of the dive and compare what they had actually done with what the computers between their ears thought they had done.

1. They had planned to dive for a specific depth and time. As they had been taught, they kept a running average of their depth on which to base their ascent profile. The computer showed that they repeatedly dropped below their depth and recovered. Their average depth on the dive was probably 7-8 feet deeper than what they had calculated it to be.
2. They had been taught to ascend to their first deep stop at 75% of that average depth at a rate of 30 FPM. They thought they had done that. They then noted the time and began the calculation for their deco times. They probably should have noted that the time they were starting their deco stops was several minutes later than it should have been, but they did not realize that. It had taken them 3 minutes more to ascend to that stop than it should have.
3. Once they were into the deco stops, they had to follow the RD plan, keeping track of how many minutes they were at each stop. Apparently they must have miscounted for one reason or another, because they cut their deco short by several minutes.

If they had used a computer, and if the computer had screwed up, then the UTD people would have exclaimed,"See! That's why you can't use a computer-based algorithm! Computers make mistakes! That's why you have to use Ratio Deco, because the human mind does not make mistakes!" But in this case the human mind made a series of mistakes. The UTD people therefore said, "See! It wasn't Ratio Deco's fault! These guys made mistakes!"

As for the other divers who got DCS, who know? They did not use a computer in gauge mode, so we don't know what mistakes the computers between their ears may or may not have made. None of us who used ratio Deco for years can ever be really sure how close we were to following it, since we had no computers with which we could check to see what we actually did on our dives.

Sorry--you can't have it both ways. Either the fallibility of the system is part of the system or it isn't. If Ratio Deco is supposed to be superior on the theory that the mind does not make mistakes, then you cannot dismiss the cases where the mind makes mistakes. It is an integral part of the system.

It would be interesting to see a test done on that--compare what divers without computers do on a dive compared to what they think they did.

Does this story include an instructor having been kicked out of UTD prior to all this?
And, am I the only one seeing that these divers were clearly diving outside of their limits? If the strength of a computer is that it helps you dive beyond your capacity, I'd say you're overrelying upon it.

In computer lingo:
If a guy who used to work for Apple sells me a machine that is rated for a certain use, and I use it beyond it's rating, I can't turn around and say "Apple did it!".
For your human computer to function, you must dive it within your limits. Surely, the analogy is apt.

Por que no los dos?

If my computer machine spits out something different than I expect based on RD and prior planning I start investigating. SOMETHING is up. Either the avg depth was different than I thought, my math was off (likely. I run out of fingers real quick), or maybe I put something into the computer box wrong.

I get what you're saying, but if I'm diving a computer well beyond my comfort zone, that's going to be difficult to pull off - see scenario above. Not saying "computers bad" here on that account, mind you.

 

[Patoux01]

Semi-offtopic question here. Why do you feel the need to use "RD" from UTD (whichever version you want, I don't care), when you could use RD to emulate a more optimal decompression schedule? It's really confusing.

 

[Dan_P]

Semi-offtopic question here. Why do you feel the need to use "RD" from UTD (whichever version you want, I don't care), whereas you could use RD to emulate a more optimal decompression schedule? It's really confusing.

Hi Patoux,

I don't think it's off-topic
First, I'll say that I'd like to use the same standard gases for the same deco blueprint across all my diving - naturally, I have some requirements for those gases in terms of max. ppO2, max. density, etc., needless to say, but;
I'd also like to have that blueprint and those gases kept the same across CCR and OC, because that way my bailout from CCR is really just turning a knob and I'll be the same tech diver I was before CCRs entered the equation.
This systems interoperability means I'll consider the approx. avg. ppO2 throughout the segments of the blueprint, even so I'm on OC.
If I change the depths, the ppO2 changes. If I change the gases, I may lose having standard gases, or suffer other practical implications.

If we're looking at the whole framework, it boils down from the relations across bottom time and O2-time in Cascade - the other ratio's (1:1, 1:2, 1:3) are more like simple observations of depth-time relations derived from within Cascade, taking into account diver limitations relating to gear and protocol.

Personally, I wouldn't bother changing further the parametres in for instance the 1:1 mode at this time, for the sake of (a bit of?) increased efficency, given the science we have available, if that would make the relation unscalable/incoreherent with the next ratio and overall relations.

All that said, I do personally adjust shallow within the frameworks, as a result of recent findings.
The workings of RD isn't exactly rigid in that sense of distribution of time within certain segments, outside of very specific parametres at least.

 

[ajduplessis]

pl

Which takes me back to my earlier post about deco plans falling somewhere on the equivalent of an archery target. The higher percentage of DCS in our small group suggests to me that the deco plan we were using was somewhere on an outer circle, one which holds the plans that have a much higher possibility of people getting bent.

It reminds me of an analogy I used to use in workshops I used to conduct (on a very different topic). I created something of a parable in which someone who survived Pickett's Charge at the Battle of Gettysburg Went on to teach military strategy after the war. Pickett's Charge is considered one of the worst military decisions in the history of warfare, with that division suffering greater than 50% casualties and accomplishing nothing. An old friend drops by one day while he is teaching, and that old friend is horrified to see him teaching the students to use the strategy Pickett had been ordered to use on that charge. The survivor/instructor responds, "It worked for me."

The fact that you survived a battle does not mean the battle strategy was a good one. The fact that you survived a dive without getting DCS does not mean the strategy you used was particularly good. Every known decompression strategy will have survivors. That does not make them all equally effective.

I see you still dont understand the definition of effective...

effective
ɪˈfɛktɪv/
adjective

1. successful in producing a desired or intended result.
   "effective solutions to environmental problems"
   synonyms: successful, effectual, efficacious, productive, constructive, fruitful, functional, potent, powerful
   
   My intent and desire is not to get bent, mission accomplished!! Dive plan effective!!
   
   I would also suggest using less aggresive decopression plans to ensure your team gets out without DCS. Simon is a good source of information to get you going, this read might also help The Relativity of Wrong by Isaac Asimov
   
   Dive safe
   ajduplessis

 

[KenGordon]

pl


I see you still dont understand the definition of effective...

effective
ɪˈfɛktɪv/
adjective

1. successful in producing a desired or intended result.
   "effective solutions to environmental problems"
   synonyms: successful, effectual, efficacious, productive, constructive, fruitful, functional, potent, powerful
   
   My intent and desire is not to get bent, mission accomplished!! Dive plan effective!!
   
   I would also suggest using less aggresive decopression plans to ensure your team gets out without DCS. Simon is a good source of information to get you going, this read might also help The Relativity of Wrong by Isaac Asimov
   
   Dive safe
   ajduplessis

By that measure, not getting in the water at all would be ‘effective’. Really there is more too it than not getting bent on one occasion. Not getting tool cold, having a reasonable bottom time, not wetting yourself are all factors that matter and come into whether the entire profile is effective.