NEDU Study

[rossh]

Ross please ...
Successful outcome is a prerequisite see wiki:

Efficiency is the (often measurable) ability to avoid wasting materials, energy, efforts, money, and time in doing something or in producing a desired result. In a more general sense, it is the ability to do things well, successfully, and without waste.[1][2][3][4][5] In more mathematical or scientific terms, it is a measure of the extent to which input is well used for an intended task or function (output). It often specifically comprises the capability of a specific application of effort to produce a specific outcome with a minimum amount or quantity of waste, expense, or unnecessary effort.

In our case the resource is deco time and the money to keep the surface support team at sea.
What they did at NEDU was assessing how many people would get bent distributing the available and fixed deco time in deeper or shallower stops. They kept bending people untill there was statistica significance. They stopped early because they were bending many more divers with one distribution than the other.

The deeper stops showed being less efficient.
Therefore at same deco time less safe. Safety intended as the probability of getting bent.
[my conclusion]
a deeper start of deco as prescribed by VPM requires me to increase the shallower stop time beyond what VPM would require, in order to achieve the same probability of getting bent.

Hi Fabio,

Decompression is in the field of physics. Efficiency in physics, is the measure of energy to achieve a result. In the case of decompression MODELS, the purpose is to return to surface safely in the shortest time. Therefore efficiency in decompression, is least time to achieve a safe ascent.

DCS rates is measured as risk probabilities, or actual result percentages, but not "efficiency".


If you guys want to abuse the proper science terms, then go ahead... why not.... add it to the list of abuses and distortions used to prop up this fallacy and attacks on VPM-B.


These guys are not comparing efficiency. They have two safe ascents, and trying to judge one better than the other, on some internal dimension..... with no valid method to judge it.


The nedu did not test deep stops.... repeat ... no amount of opinion will change that fact. The nedu tested two long shallow ascents against thermal stress... Please do not try to imply its related to deep stop, or tech practices, see: post #116


The actual nedu result showed us one thing.... models should follow the gas kinetic rules. All your / our models and dive computers, already follow gas kinetic rules: ZHL, VPM-B, etc. Those models already have the correct amount of deep-shallow balance built in... (note: all deco computers have the same kinds of gas kinetic formula too). Nothing is broken, nothing needs fixing.

If you don't agree, then show why ALL existing gas kinetic formula is wrong. You cannot isolate VPM-B and pretend all else is OK.


****

As I have said... these guys keep confusing themselves with the GF fiddling.... chasing their own tail. They create some exaggerated ascent on GF, and imagine it's an original perfect ascent. They forget that the GF profile is a made up one...

One could keep repeating this to process comparing two other GF profiles, and will always think one is better.... because the method always favors the shallow one. Eventually it will get to profiles like 150/20, and still think your ahead... the test is open ended and biased.

There is no proven method to cross compare different profile types.

***************

These guys are not interested in "efficiency", because they are NOT aiming to go fast. If they were, they would be using real ZHL, with no added GF, and be happy doing it..... any takers???

The current trend is to go longer for reasons of extra layers of safety.... i.e. in-efficient use of time.

.

 

[Patoux01]

The nedu did not test deep stops.... repeat ... no amount of opinion will change that fact. The nedu tested two long shallow ascents against thermal stress...

Why had one significantly more DCS than the other?


Edit:Based on your "definition", ZHL is not efficient, so they wouldn't take it, sorry

 

[rossh]

Why had one significantly more DCS than the other?


Edit:Based on your "definition", ZHL is not efficient, so they wouldn't take it, sorry

Because one followed closely the standard gas kinetic rules (A1), and one did not (A2). The ZHL-C and VPM-B follow those rules and are on the winning team (A1) .... nothing matches the failed A2 profile.


If you wanted to put models into order of efficiency, then the early military ones easily come first. i.e. Older, faster shallow and scary wins the race, providing they work with low enough risk. USN 56, then I would say ZHL, and then maybe newer USN tables and VPM-B about here, then DCIEM, and then...? Notice how GF is missing, because its not a defined model.

The problem still remains - no valid method exists to cross-compare these.

 

[Remy B.]

Because one followed closely the standard gas kinetic rules (A1), and one did not (A2). The ZHL-C and VPM-B follow those rules and are on the winning team (A1) .... nothing matches the failed A2 profile.


If you wanted to put models into order of efficiency, then the early military ones easily come first. i.e. Older, faster shallow and scary wins the race, providing they work with low enough risk. USN 56, then I would say ZHL, and then maybe newer USN tables and VPM-B about here, then DCIEM, and then...? Notice how GF is missing, because its not a defined model.

The problem still remains - no valid method exists to cross-compare these.

What dive profiles were tested then ? regarding Depth , Bottom Time and ascent Time ?

 

[rossh]

What dive profiles were tested then ? regarding Depth , Bottom Time and ascent Time ?

Guys.... trying to turn this into the same old "guilt through word association" game, is not a valid approach. That is not decompression and it is not science... it's just trickery.

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[Storker]

Isn't it an interesting sign of the times we live in that bending goats is no longer legal but bending navy divers is just fine!

I guess the ability to give qualified consent may have something to do with that...

 

[UWSojourner]

The ZHL-C and VPM-B follow those rules and are on the winning team (A1) ....

VPM-B based on EVERY measure we've looked at ALWAYS compares closely to A2 (the failing NEDU profile) --- ALWAYS. It would be very difficult to support any conclusion but that VPM-B would have performed similarly to A2 if the NEDU had used the VPM-B profile in the test.

And that was also the conclusion of the NEDU scientists. See minute 34:30-38 of this presentation.

 

[Dr Simon Mitchell]

You are not measuring efficiency...... you are comparing two successful dives..... success vs success.

You are arguing about a concept that you don't understand, and not for the first time, you are the only person who believes your version.

Here is how they define efficiency in the NEDU deep stops study report.

Both gas content (shallow stops) and bubble model (deep stops) approaches lead to practical decompression schedules; however, whether one approach is more efficient than the other is unknown. In this context, two decompression schedules for the same dive depth and bottom time differ in efficiency if one has a shorter required decompression time for the same PDCS or a lower PDCS for the same decompression time. The U.S. Navy has a continuing need for more efficient decompression procedures.

You seem to be basing your definition of efficiency on an erroneous interpretation of the first of the options (shorter decompression time for the same probability of decompression sickness (pDCS)) articulated by the NEDU authors above. It seems you believe that the most efficient profile is the shortest one that a diver can get away with without getting bent. That might represent a form of efficiency for an individual diver on a single dive, but it does not characterise efficiency for a decompression model. The comparative efficiency of one decompression model against another can only be judged on the pDCS for a large number of dives made to see if "one has a shorter required decompression time for the same PDCS or a lower PDCS for the same decompression time". The latter of the two options is the easier one to study, and this is what was done in the NEDU study.

The USN investigated the pDCS associated with a gas content model and a bubble model decompression from a dive for the same depth, bottom time, decompression time, and dive conditions, and found a higher pDCS in the bubble model. Therefore the gas content model was more efficient than the bubble model.

Your argument is success A is better than success B, based on some internal differences in dimensions. But in both cases, neither dimension caused a problem.....

You assume your interpretations of those dimensions is a measure of risk, but you have no valid formula to verify with, or to make that assumption.

The one hard outcome we have in this entire debate is that a bubble model profile which resulted in greater slow tissue supersaturation and greater total integral supersaturation caused more DCS than a gas content model profile of identical length which resulted in less slow tissue supersaturation and less total integral supersaturation. Those differences in supersaturation are overwhelmingly the most plausible reason for the differences in outcome between the two profiles. When we analyse real world tech profiles produced by bubble models we see the same disadvantageous patterns of tissue supersaturation (greater supersaturation in slow tissues, greater total integral supersaturation) which can be ameliorated in decompressions of the same length by GF modification of the Buhlmann gas content model. In the pursuit of the most efficient approach to decompression, that seems to me to be a sensible response to the one hard outcome we have in this debate.

You guys are spinning your wheels, trying to make up justifications for inflating plans, beyond any reasonable or required amounts, based on some invalid or distorted science measure, and poorly interpreted report results and contexts.....

We are discussing a sensible response to the best data we have. You are resisting change because it casts one of your products in a less favorable light.

Please stop using VPM-B as a proxy for your problem. There is 15 years of success behind us, that does not need you lot fiddling with it.

Ross, the truth whether you like it or not is that VPM is subject to the issues we have been discussing. It probably over-emphasises deep stops, and probably does not compensate adequately for this with shallow stops. One potential fix is to keep using VPM but pad the shallow stops, yet you rubbish this notion too. So you force people like me into polarising debates which make VPM the centre of the argument. You are at least partially responsible for the focus on VPM in these discussions.

As for the 15 years of "success", what you really mean is "15 years of use". You have no outcome data for VPM dives, and consequently no clear idea of its success or lack of it. You certainly have no valid comparisons of outcome against other approaches to decompression. You cannot claim "success".

Simon M

 

[Dr Simon Mitchell]

Because one followed closely the standard gas kinetic rules (A1), and one did not (A2). The ZHL-C and VPM-B follow those rules and are on the winning team (A1)

Ross,


To equate ZHL-C and VPM-B with a claim that they "follow the same rules" is utterly ludicrous. They both use the same calculations to assess tissue gas supersaturation (as does the NEDU bubble model that produced A2 for that matter), but they use completely different rules about how to treat supersaturation in different tissues in controlling the ascent. This is candescently obvious from the fact that they prescribe completely different decompression profiles.

I cannot believe you don't understand this.

Simon M

 

[RayfromTX]

Ross- I have read your innumerable posts on different discussion forums and this is what I have noticed. You are representing your product in a very unfavorable light. You are being unreasonable in your communications and illogical in your arguments. Your approach is alienating those that are on the fence and several people have told you that as a result, they would never consider buying your product. For those people that are trying to decide whether to abandon the bubble model altogether, your demeanor and disrespect of the people involved that are highly respected in the field is causing most to throw the baby out with the bath water. In this case, that may be just the right thing to do. At the very least, you may find that a more humble and less confrontational approach may be better recieved. The people that once were willing to back you or even tolerate your abrasiveness headed for the exits long ago. This is an important issue and it's discussion does not benefit from your incessant flood of "alternative facts". I have learned a lot from these threads and appreciate those willing to participate.