Slow tissue on gas from stops

[Patoux01]

 

[Dan_P]

Good job finding all that straw at this time of the year.

How very confident of you

 

[UWSojourner]

To those prior, I offer the following retort:
So, you know deep stops to be a sham then, do ya?
Set your decometre to GF100/100 and crack on, then.

This statement is misleading, either from a lack of understanding, or intentionally.

What you might say instead is: "If you think deep stops are a sham" (as you put it) ...

... then take the time you normally spend decompressing on your VPM-B+3 or RD profile, and figure a GF40/X, or GF 50/X, etc., profile with the same decompression time. If you do that, then you're likely to be lowering your decompression risk. Same decompression time, lower risk.

There's no sense in going to GF100/100 unless you're diving VPM+x profiles that gives you the same decompression time as a GF100/100 profile. Then instead of doing GF100/100 you might at least consider thinking to yourself, "Why the heck did I ever trust bubble model theory so much that I got this aggressive?" and consider backing off a bit.

 

[EFX]

It's been previously mentioned that there would be less DCS risk to do the same deco time without the deep stops. This begs the question: why not eliminate the deep stop altogether and run flat GF's. An 80/80 profile will give less deco time than a 50/80. You'll probably say, "Well, a not-so-deep stop will protect the faster tissues. But, fast tissues can be protected by slowing down the ascents. Now, what say you?

 

[elmo]

It's been previously mentioned that there would be less DCS risk to do the same deco time without the deep stops. This begs the question: why not eliminate the deep stop altogether and run flat GF's. An 80/80 profile will give less deco time than a 50/80. You'll probably say, "Well, a not-so-deep stop will protect the faster tissues. But, fast tissues can be protected by slowing down the ascents. Now, what say you?

A perfectly reasonable suggestion, and some divers are running with flat gradient factors. I typically plan dives and set my computer to gf60/80, which is flatter than most (but obviously not 80/80).
One practical consideration, seperate from the most efficient decompression strategy, is gas planning. Using my last dive as an example, I used 50% as deco gas and we did our first stop at the 21m gas switch. Using gf80/80, our first stop would have been at 12m or 9m. Accordingly, we could have started devo stops then and used a richer deco mix, resulting in shorter decompression time. But it would have blown out the minimum gas calculations (based on ascending from bottom depth to the first gas change) so I would have had to call the dive earlier (or carry more bottom gas). Even though the difference in deco gas required is small, the difference in bottom gas required is significant).

 

[Dan_P]

This statement is misleading, either from a lack of understanding, or intentionally.

What you might say instead is: "If you think deep stops are a sham" (as you put it) ...

... then take the time you normally spend decompressing on your VPM-B+3 or RD profile, and figure a GF40/X, or GF 50/X, etc., profile with the same decompression time. If you do that, then you're likely to be lowering your decompression risk. Same decompression time, lower risk.

There's no sense in going to GF100/100 unless you're diving VPM+x profiles that gives you the same decompression time as a GF100/100 profile. Then instead of doing GF100/100 you might at least consider thinking to yourself, "Why the heck did I ever trust bubble model theory so much that I got this aggressive?" and consider backing off a bit.

I hear what you're saying, but that's not the point I'm making.

I understand of course that if one wants to make a comparative analysis, one would need to keep the decompression times similar.
And in practical application, less time on deco is better, all else being equal.

However, my point as it relates to discussions on this matter is, if one thinks that "deep stops have been debunked", it begs two obvious questions:

1) What is a deep stop?
This illustrates well that what we're talking about here, is where the line in the sand is. No-one is saying that "there is scientific proof that deep stops don't work". Just that they've been overemphasised by some margin. There is a massive difference between the prior and latter, the prior being a gross oversimplification. And that brings me to the next question:

2) Why not use GF100/100, then?
If "deep stops have been debunked" holds true, then surely, all that remains presently on the table in terms of decompression, is tissue gas supersaturation á la Haldane. If that is the case, logical deduction demands that one should perceive m-values pure as the optimal decompression line. Hence GF100/100.
But nobody's doing that.

My argument hence, is that

1) a lot of conversations relating to this debate, are skewed in the direction of an oversimplified view that there is A (gas mechanics) and B (tissue supersaturation), one of them is right and the other one is wrong.

2) a lot of conversations relating to this debate take on form of Simon Says (my apologies, I know it's childish but I couldn't resist ) where actually reading the reports that comprise the evidence available takes the back seat - and the actual expert statements are often misrepresented.
I.e.
the presently available material indicates that deep stops have probably been overemphasised becomes
scientific evidence proves deep stops are certainly wrong.
"the presently available material" leaves one wanting.
"Probably" speaks for itself.
"Overemphasised" in stark contrast to "wrong".

 

[Storker]

the presently available material indicates that deep stops have probably been overemphasised becomes
scientific evidence proves deep stops are certainly wrong.

Cite for the last part of that sentence, please?

 

[RayfromTX]

The problem with this discussion seems to be that the scientific method is by it's nature open-minded. Decompression strategies on the other hand require confidence in the basis of our understanding. Those that want a black and white answer to what is safe and correct are frustrated by the scientists' unwillingness to make a definition of what that is based on incomplete data. The data will always be incomplete.

Those that demand an answer from the scientist will point to the evolution in our understanding as evidence that science is inadequate or untrustworthy but in fact that evolution is the nature of the scientific method. Those same people make assertions that the scientist is making false claims when they are instead simply reporting the rather limited data that they have and making their next stab at explaining what the data may mean.

Science and engineering got us to the moon but not without failure and adjustments along the way.

The lay person sounds very different in their approach to this discussion than the scientists. I can hear the scientists talking and know who they are without seeing their title because their posts seem founded by the scientific method.

Those that say that deep stops have been debunked are making a lay person's statement. They want closure that a scientist is unable to provide. Those that say deep stops have not been debunked are doing the same thing.

Those that show and report data that suggests a probable over-emphasis on deep stops are thinking like scientists. If you read the scientist's statement and hear the lay person's statement and then argue with the lay person's statement then you must realize that you aren't arguing with the scientist's statement but with your perversion of it.

 

[Dan_P]

Cite for the last part of that sentence, please?

I've been pretty much called anything from a religious nut job to a convolusive weasel in conversations about the matter, which I've occasionally thought to be a bit on the strong side - but on a general level, to illustrate the sort of ultimative perceptions growing in or from these discussions, I have chosen to pick an example from a different board;

"...Criticly the recent studies have already debunked deep stop theory and called into question the validity of VPMB type profiles..."
Decompression Profile Project - UTD Ratio Deco vs Bulhmann [Archive] - The Dive Forum

My point wasn't to quote specific statements, rather to show that there is a divide across what's shown (and said) by members of the scientific milieu and how it seems to be perceived in discussions sometimes.

Again, if one believes there is nothing to deep stop theory, all that remains is m-values.
That's why when I meet divers who say things on the line of deep stop theory being bogus, I might well point out that they're probably not using GF100/100 because they don't truly believe gas mechanics theory is bogus at all.

In the end, and with what's available now, to me personally, "the ultimative answer" is more of a curiosum to spur on my reading than a practical application.

 

[Storker]

on a general level, to illustrate the sort of ultimative perceptions growing in or from these discussions, I have chosen to pick an example from a different board;

"...Criticly the recent studies have already debunked deep stop theory and called into question the validity of VPMB type profiles..."
Decompression Profile Project - UTD Ratio Deco vs Bulhmann [Archive] - The Dive Forum

Ah. My bad. Since you were bringing up that point here on SB, in this thread, I stupidly assumed that you were talking about discussions in here, which in my mind would be appropriate. Bringing in - and misquoting by embellishment - a more than three year post, on another forum, which BTW is well known for quite saltier language than what we see here on Scubaboard, looks pretty much like a strawman argument to me.