NEDU Study

[Dr Simon Mitchell]

It is an artificial limit, that always favors the shallow profiles.

No it doesn't. The ultimate shallow profile is simply to come straight to the surface. We all understand that this will kill you. Coming too shallow too quickly is clearly bad. And you are going to have to get your head around the reciprocal concept that staying too deep for too long is also bad. Somewhere in between is a sweet spot, and that is what we all seek.

Real models are not constrained this way.

Yes, of course they are. A VPM user will have a duration of decompression prescribed. The question is: Are the stops prescribed by VPM the most efficient way of using that duration.

Simon M

 

[Schwob]

No its not a fallacy Ross. Equivalent run times is a simple requirement, recognised by all experts in decompression, that must be adhered to if you want to answer the relevant question. That question is:

"If I have x amount of time to spend decompressing, what is the most effective way of distributing my decompression time among the various stop depths. If the run times are different, you cannot answer that question?"

Translated to a more specific situation, if a diver is a VPM user, the algorithm will prescribe a specific duration of decompression and a pattern of stops to complete. The question the diver might ask is: "is that pattern of stops suggested by VPM the most effective way of using the total period of decompression that VPM has prescribed?"

UW Sojourner is presenting us with evidence that there are more effective ways of using the total decompression time prescribed by VPM, by distributing the stops differently. The evidence is based on analysis of supersaturation patterns and total integral supersaturation. Contrary to your claims, these are not invalid or untested measures. Summed integral supersaturation is commonly used as a parameter in decompression algorithms (including your own) and the supersaturation patterns produced by a shallower distribution of stops than prescribed by bubble models (like VPM) were shown to be more successful in the NEDU study.



You don't have outcomes for these dives so the mere fact that they have been done is totally irrelevant.

Simon M

You are an ingredibly patient man Dr. Simon Mitchell!

 

[Remy B.]

You are an ingredibly patient man Dr. Simon Mitchell!

And show a very professional behavior as well, something that Mr. Ross shows here to lack of, with the way he answer with derogatory comments.

 

[Remy B.]

Coming too shallow too quickly is clearly bad. And you are going to have to get your head around the reciprocal concept that staying too deep for too long is also bad. Somewhere in between is a sweet spot, and that is what we all seek.

Simon M

Mr. Ross, it seems that you are missing the point that the US Navy divers branch wanted to use VPM as a new way for their divers to do decompression dives, ( you understand that THEY ACTUALLY WANTED TO USE A "VPM" MODEL because it seemed the logical thing, keeping the bubbles small and in controlled expansion ) but like in any serious and organized Company or Organization, you have to justify that change and demonstrate with research and tests, and proof that this change is of mayor benefit, the result of the Study is that it didn't benefit nor justified to change what they were doing.

The way I understand it, ( and please anyone correct me if I understood incorrectly ) is that in any way Dr. David D. and Simon M. and the other scientists were NOT against the VPM model, they were actually seeking to proof that it works, but to their surprise the research and tests turned out to not be more beneficial of what the US Navy was already trying/using.

The Study result only showed that the Deep Deco Stop were affecting negatively the slow tissues. and had a greater number of DCS type 2, where as the other model had DCS's type 1 but as well in a lesser quantity of the Type 2 of the VPM.

Dr. David and Simon have in any way said that they have found the magic bullet, they just witness what didn't work and unexpectedly were contrary to their initial believe or reasoning.

THE CONCLUSION IS THAT THE MAGIC BULLET HAS NOT YET BEEN FOUND, both models produce DSC in one way or the other, in more or lesser ways.

The only way to validate your arguments is to build or rent your own Deco Chamber, get your volunteers that believe in VPM to do the tests and that those tests are scrutinized, monitored and Audited by a 3rd party like Bereau Veritas or other big certifying bodies, in show that VPM works 100% and is that magic bullet that everyone is wishing for, until that is not done, every body will make their own decision and judgement of what model to use exclusively or depending the dive profile.

I'm personally happy with your product "Multi-Deco" in my lack of technical diving experience I find it a nice tool for planning and comparing dive profiles, you will honestly gain more customers if you show a more composed way of arguing and using less derogatory comments, that actually are hurting you more than you think.

 

[rossh]

Mr. Ross, it seems that you are missing the point that the US Navy divers branch wanted to use VPM as a new way for their divers to do decompression dives, ( you understand that THEY ACTUALLY WANTED TO USE A "VPM" MODEL because it seemed the logical thing, keeping the bubbles small and in controlled expansion ) but like in any serious and organized Company or Organization, you have to justify that change and demonstrate with research and tests, and proof that this change is of mayor benefit, the result of the Study is that it didn't benefit nor justified to change what they were doing.

The way I understand it, ( and please anyone correct me if I understood incorrectly ) is that in any way Dr. David D. and Simon M. and the other scientists were NOT against the VPM model, they were actually seeking to proof that it works, but to their surprise the research and tests turned out to not be more beneficial of what the US Navy was already trying/using.

The Study result only showed that the Deep Deco Stop were affecting negatively the slow tissues. and had a greater number of DCS type 2, where as the other model had DCS's type 1 but as well in a lesser quantity of the Type 2 of the VPM.

Dr. David and Simon have in any way said that they have found the magic bullet, they just witness what didn't work and unexpectedly were contrary to their initial believe or reasoning.

THE CONCLUSION IS THAT THE MAGIC BULLET HAS NOT YET BEEN FOUND, both models produce DSC in one way or the other, in more or lesser ways.

The only way to validate your arguments is to build or rent your own Deco Chamber, get your volunteers that believe in VPM to do the tests and that those tests are scrutinized, monitored and Audited by a 3rd party like Bereau Veritas or other big certifying bodies, in show that VPM works 100% and is that magic bullet that everyone is wishing for, until that is not done, every body will make their own decision and judgement of what model to use exclusively or depending the dive profile.

I'm personally happy with your product "Multi-Deco" in my lack of technical diving experience I find it a nice tool for planning and comparing dive profiles, you will honestly gain more customers if you show a more composed way of arguing and using less derogatory comments, that actually are hurting you more than you think.

The nedu never tested VPM or GF.

The nedu doesn't test or use anything from tech world diving.... The nedu has no connection to VPM .

Instead the nedu made and tested their own thing - the BVM(3), which is a shallow stop (TBDM) design, that represents nothing in our world. Please do not get conned with "guilt by word association games".. "bubble", "deep".

There is no real or valid connection to VPM or real world tech stops from the nedu test - none. So far its all opinion, or gross exaggeration and misrepresentations.... I have shown these to be invalid. See post# 116


The real world DCS rate has been in decline for the past 15 years, including tech diving.... During that period we have all been using deeper stops, better gas choices, better procedures and training.

Obviously we all did something right. This latest effort to over inflate the shallow time with excessive shallow stop GF plans, is a lot of fussing over nothing.

Choose the ascent you like, and stick with it - they all work, because all of today's planning techniques have sufficient inbuilt margin.


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The magic bullet: There never will be one. All diving planning is a compromise. You can improve one part of the ascent, but it will usually cause an unwanted change somewhere else.

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[rossh]

This image made using proper scientific measures, and industry accepted formula. i.e the mono-exponential gas kinetic measure of stress.

These graphs join up both the surface and dive parts, at the same scale, to show a continuous graph.

The significant stress is from the dive portion. This is where the injury starts - the surface part adds fuel to the fire.

The surface portion is declining across all cells. After an hour or two on the surface, the supersaturation has decayed to harmless amounts.


ZHL has higher dive stress than VPM-B, for the first half of the dive.


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Added: The above is part of the "profile stress" component of a DCS injury. This is the only part that the deco model has any control over. If the above profile and stress is too fast, too short, too shallow, too crazy, then an injury will likely follow. But with today's models and ascents, we are not usually threatened by "profile stress", because all models normally are slow and long enough to avoid the dangerous amounts.

Take a look at this diagram by Neil Pollock from his excellent decompression stress presentation. It shows 20 possible sources of stress. Note that deco model controls just 2 items (stops, time). Most injuries today are from one of the 18 other causes.

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[UWSojourner]

This image made using proper scientific measures, and industry accepted formula. i.e the mono-exponential gas kinetic measure of stress.

View attachment 400305


These graphs join up both the surface and dive parts, at the same scale, to show a continuous graph.

The significant stress is from the dive portion. This is where the injury starts - the surface part adds fuel to the fire.

The surface portion is declining across all cells. After an hour or two on the surface, the supersaturation has decayed to harmless amounts.


ZHL has higher dive stress than VPM-B, for the first half of the dive.

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You really have problems incorporating the idea of TIME into your thinking.

The two dives you show differ in runtime by about 12 minutes (roughly 20+% of the decompression). What is that supposed to show? That you can graph two dives?

If you want to support your case at LEAST show dives that have the same runtime. If I can be safer diving profile x FOR THE SAME RUNTIME as profile y, then I'll choose x.

Your insistence on showing drastically different runtimes in your comparisons is just a diversion and you know it.

For a comparison of deco methods WITH THE SAME RUNTIME, see this link.

 

[rossh]

You really have problems incorporating the idea of TIME into your thinking.

The two dives you show differ in runtime by about 12 minutes (roughly 20+% of the decompression). What is that supposed to show? That you can graph two dives?

If you want to support your case at LEAST show dives that have the same runtime. If I can be safer diving profile x FOR THE SAME RUNTIME as profile y, then I'll choose x.

Your insistence on showing drastically different runtimes in your comparisons is just a diversion and you know it.

For a comparison of deco methods WITH THE SAME RUNTIME, ...

I showed real models with real run times..... ie. real dive plans..... their is no obligation to make them all equal run time... that's an artificial constraint, that is being abused by your side.



TIME is incorporated into the base line measure of gas kinetics... the mono-expotential 1/2 time gas kinetic measure - the universal basis of all deco research, and a universal stress measure used throughout research.. Also used within ZHL and VPM-B. The formula already measures TIME at x stress level. Time does not need to be counted twice.

There are numerous errors and mistakes with your implementation of ISS. One is to compound time onto itself. You also have no method to discern between a high or low stress, and instead add all this up in a simplistic addition.

Another error in your use of ISS, is compounding of the same data in overlapping cells - this is not allowed in parallel model designs (ZHL/VPM-B).

Stress levels and most other levels or measures within decompression calculations, are normally exponential or logarithmic. They should not be summed up with simple addition into some giant number.

Your version and application of ISS is obviously not a valid method or stress measure.. Its has not been tested validated or proven to be correct for your method.

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The current accepted measure of stress, is what I showed above... Its in the nedu test, and many others.

Now I can certainly agree that we could all use a more friendly universally stress measure. But its still the unknown and unanswered question - how to compare different profile types?

But this simplistic ISS thing is simple not valid.

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[UWSojourner]

Now I can certainly agree that we could all use a more friendly universally stress measure. But its still the unknown and unanswered question - how to compare different profile types?

But this simplistic ISS thing is simple not valid.

How about, for this dive, the fact that VPM-B+2 surfaces at a gradient factor of 107! compared to GF50/82 surfacing at 82 FOR THE SAME RUNTIME???

Maybe some divers don't fully understand the significance of integral supersaturation. But almost all understand that surfacing with a GF of 107 is not a good idea if they can surface with a GF of 82 FOR THE SAME RUNTIME. Good luck selling that.

 

[rossh]

How about, for this dive, the fact that VPM-B+2 surfaces at a gradient factor of 107! compared to GF50/82 surfacing at 82 FOR THE SAME RUNTIME???

Maybe some divers don't fully understand the significance of integral supersaturation. But almost all understand that surfacing with a GF of 107 is not a good idea if they can surface with a GF of 82 FOR THE SAME RUNTIME. Good luck selling that.

Where is it written that GF is some universal and independent measure??? No where...

ZHL-C + GF also suffers from compounding errors... its not proportionally consistent across the dive spectrum. The shallow time feeds off its own compounding, and jumps to the next cell and exaggerates further. In addition, its a linear adjustment applied to values that are exponential in design.

GF is a nice easy add-on patch, to give a longer "dial a profile". But its not a model, not consistent, and not an
independent standard.


There is only one real ZHL-C model plan. All else is made up fiddle to fit some dive preference, or to suit some argument. i.e. "my stretched out piece of GF chewing gum plan, is longer/fatter/taller than your real model plan".... so what! The comparison is not relevant.


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I'll say it again... I'd love to see a proper validated, unbiased, realistic cross-compare tool for profile performance and stress. We don't have one..

But you guy's are trying to fill in the gap, with half measures and things that fit your argument only .... sorry - no good enough.

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