NEDU Study

[victorzamora]

I don't think we need to be overly concerned with the nedu test. No real deeps were tested - only exaggerated shallow stops. The test was one of thermal stress against shallow stops

[The test profiles were] an elongated shallow stop design. It does not follow the natural gas kinetic rules. It does not follow normal supersaturation patterns. It does not follow a natural curve like that of other models. The A2 represents nothing from our tech world.

...

1/ The existing gas kinetic formula already fully address, any kind of ascent, deep shallow, elongated, multilevel....anything, the existing gas kinetic formula correctly track what is going on. Deep and shallow stops are correctly accounted for.

Ross: Doesn't increasing workload on the bottom increase gas uptake? Doesn't resting on deco reduce offgassing? You said you wouldn't follow VPM on a bike at the bottom and resting on ascent....so what profile WOULD you follow?

If I had the bicycle-workload on the bottom, you can bet I'd want to rest on deco....and you can bet I'd follow something like NEDU's A1 profile up. That increased workload on bottom is something that can't be accounted for in the "normal" recreational models but is accounted for in the "elongated" deco ascents of the A1 and A2 models. You keep calling them "too long" and implying they're excessive, yet DCS rates were higher than what I'd call acceptable. Honestly? I'd stretch out my O2 stops as long as I could stand. it.

 

[Diver0001]

Ross: Doesn't increasing workload on the bottom increase gas uptake? Doesn't resting on deco reduce offgassing? You said you wouldn't follow VPM on a bike at the bottom and resting on ascent....so what profile WOULD you follow?

Victor, why do you think Ross is in a position to advise about that? His opinions about deco theory are clearly deviant in the sense that not a single decompression scientist on this planet would agree with his views (as a computer programmer) and his thinking appears to be rooted in a 15 year old paradigm that we have thoroughly transcended in terms of knowledge and understanding.

That said, your point about "padding" stops based upon "risk factors" like working hard on the bottom and resting during deco is a common practice. It is ALL done, to date, based upon "best guess" and "intuition".

If there is one thing I do agree with Ross about, it's that these kinds of factors (working hard on the bottom, post dive exercise, warm/cold profiles) are significant risk factors that will affect ALL models because not a single one of them accounts for any of that. As divers we need to "guesstimate" our way through this minefield. That he said that he wouldn't trust VPM on such a dive, I believe, is wise. I wouldn't trust ANY algorithm when you need to work hard on the bottom and the rest and get cold during deco.

The NEDU study did this deliberately, not because they thought that these were good diving practices. Obviously they did it to *push* the boundaries of the model to see where the differences were. The conclusion is that given the options, you are better off NOT doing deep stops.

I think, and I want to be fair to Ross here because I've been sitting on his neck about this, that Ross is right about one thing. For MOST real-world technical dives, particularly benign ones that don't require large amounts of deco, the model probably doesn't affect your deco result as much as the environment. This is the big picture I think I'm getting from all the information I've seen.

So where does that leave us? With (roughly) 2 imperfect models, one of which is marginally better than the other, but both of which are in need of serious attention with regards to accounting for environmental factors.

R..

 

[rossh]

It should be noted that the NEDU study is one of the most widely accepted and definitive comparative studies ever done between the workings of bubble models as compared to the workings of Buhlmann. Aside from Bruce Wienke who sees his life's work going to hell because of this study, not a single decompression scientist on the planet didn't welcome the results of that study. I would say that's a good sign of solid research.

What explanation can you offer for the fact that all of these scientists agree that this was outstanding and important work?

Can you cite one peer review criticizing this study?

What explanation do you have for the fact that you are alone in your opinion that there something wrong with that study?

R..

This is indeed what you wrote. Can you explain why not a single decompression scientist in the world is saying the same thing?

As I said above, the NEDU study is one of the most widely accepted and definitive comparative studies ever done between the workings of bubble models as compared to the workings of Buhlmann.

Can you explain why you are alone in your belief that this is not the case?

I am interpreting your choice to refuse to answer these questions (they have been asked several times) as a tacit admission that you have no grounds upon which to argue your stance. Is this the case?

R..

Hi,

Please allow me to correct you on this. The nedu has never tested Buhlmann, or VPM-B, or any tech bubble model. They only test USN and nedu ideas for their own internal use. We tech people have to pick over the available info, and try to interpret what can be fitted into our world.

Scientists almost never agree with each other publicly. They absolutely never issue public endorsements for outsiders, like me. That would be the wrong thing to do.

So your question and point is moot. The lack of endorsement is expected.

One also might expect that some scientists are not too pleased to have an outsider like me, find fault with the public stated positions some have made... As I indicated before this is a battle between stated positions, vs facts not previously realized or shown.

*****

I did not say the study was bad - I say the implied connection to tech is simply not there, and the context of the nedu study has been poorly interpreted for tech use. No one has provided real science to make this connection. I have shown and discussed why many times above in this thread.
.

 

[rossh]

Ross: Doesn't increasing workload on the bottom increase gas uptake? Doesn't resting on deco reduce offgassing? You said you wouldn't follow VPM on a bike at the bottom and resting on ascent....so what profile WOULD you follow?

If I had the bicycle-workload on the bottom, you can bet I'd want to rest on deco....and you can bet I'd follow something like NEDU's A1 profile up. That increased workload on bottom is something that can't be accounted for in the "normal" recreational models but is accounted for in the "elongated" deco ascents of the A1 and A2 models. You keep calling them "too long" and implying they're excessive, yet DCS rates were higher than what I'd call acceptable. Honestly? I'd stretch out my O2 stops as long as I could stand. it.

What would I do? Avoid the conditions all together. Thermal stress is a powerful thing. This test here shows how strong an unpredictable it can be. TR 06-07

In deco, we normally stay longer to get safer...i.e. increased deco time lowers stress. But getting cold works the other way - staying longer makes more thermal stress. We have declining dive profile stress, but increasing thermal stress - a bathtub curve. Where do you get out? The midpoint might be too high in total stresses anyway. So your screwed, no matter what.

The nedu test design, was deliberate - equalize the plan times, make both very low in dive profile stress (2x longer), but then add in thermal stress to compensate. Did they get the balance right? Can thermal stress be controlled with the same accuracy as tissue stresses? I don't think so.

.

 

[Diver0001]

So your question and point is moot. The lack of endorsement is expected.

Is it?

There have been several NEDU scientists on scubaboard explicitly addressing your claims. They have been very clear about what they think. It is *absolutely* clear (to paraphrase) that they think you are "out there" (and I'm putting this nicely).

It is absolutely clear that either:
(a) you do not know what you are talking about
or
(b) you have an agenda to deceive people.

Which of these are we supposed to believe, Ross?

Which of these scenarios will the international body of decompression scientists -- none of which agree with you -- believe, Ross?

Personally (I can't speak for anyone else) I believe them.... "them" being the VAST majority of international experts on decompression theory.

R..

 

[victorzamora]

What would I do? Avoid the conditions all together. Thermal stress is a powerful thing. This test here shows how strong an unpredictable it can be. TR 06-07

In deco, we normally stay longer to get safer...i.e. increased deco time lowers stress. But getting cold works the other way - staying longer makes more thermal stress. We have declining dive profile stress, but increasing thermal stress - a bathtub curve. Where do you get out? The midpoint might be too high in total stresses anyway. So your screwed, no matter what.

The nedu test design, was deliberate - equalize the plan times, make both very low in dive profile stress (2x longer), but then add in thermal stress to compensate. Did they get the balance right? Can thermal stress be controlled with the same accuracy as tissue stresses? I don't think so.

I might be misunderstanding thermal stresses, then. My understanding was that colder meant slower gas on- and off-gassing....not that being colder directly lead to increased pDCS. Even if you're cold, you're still offgassing (albeit slower)...so I don't think there's a bathtub curve, as you put it.

Like, if you were in 20ft of water on EAN50 for the same times (same temperature water, same time on a bicycle, same time sitting on deco) you could surface safely. Even if you were in colder water for longer (barring hypothermia or other medical issues) that you'd be completely fine (from a decompression perspective).

Is the above true?

 

[Patoux01]

And last question about the study of course, "how does thermal stress know it should target the deeper divers?". Bad thermal stress, bad!

 

[Diver0001]

What would I do? Avoid the conditions all together.
.

Me too. This is where Ross and I can agree. In *realistic* diving conditions, you do not want to do what NEDU did.

The NEDU study is intended to PUSH the boundaries of the *model* not push the boundaries of *realistic technical diving*.

There is a BIG difference here. NEDU is not testing what technical divers can/should do. They were looking to see if a bubble model's were "better" than Buhlmann or not. The conclusion is ABSOLUTELY clear..... "NO".

That is not to say that the dives they did were in any way "realistic". Of course not. the dives were *intended* to push the boundaries! If all of the dives were intended to be well within the realm of "normal" dives then the differences in the models would not have come out....

R..

 

[scubadada]

...The VPM-GFS was an invention by Shearwater. It runs two calculations and picks the longest of the two. The GF one is a 70/70, or 80/80 kind of thing. That caused the GF part to become effective on longer dives only. For dive of 2.5 to 3 hours or longer, the dive shallow end is GF limited. For lesser dives, it was a plain VPM-B dive. This GFS was very much like the VPM-B/E idea...

Thanks for the reply @rossh

I've only been using MultiDeco for a little less than a year and have mostly used Buhlmann. The debate around the NEDU study has led me to look at VPM-B also. I assume you have included VPM-B +GFS so that divers using Shearwater computers can plan their dives on MultiDeco. Why do you think Shearwater invented this Haldanian add on to VPM-B that allows choosing a surfacing GF of 70-100? Do you think they believe that the surfacing GFs of native VPM-B are too aggressive? In my initial question, I referenced an example where the surfacing GF of a VPM-B +2 profile was 107.

Using the NEDU dive as an example, at +2, VPM-B, VPM-B/E, and VPM-B +GFS/100, all give the exact same decompression profile. Starting at +GFS/95, additional time at shallow stops is added, leading me to believe that native VPM-B has a surfacing GF in excess of 95, but below 100. At +GFS/80, there are 22 minutes of additional decompression, 20 minutes of it at 10 feet. I bring up this last point because the NEDU dive has essentially the same run times using VPM-B +2 and Buhlmann ZH-l16C 50/80.

Your answers to my questions will help me understand this complex and interesting topic.

Good diving, Craig

 

[fsardone]

Ross,
both profile lasted the same and therefore same thermal stress in shallower and deeper profiles.
According to you, why the different (and more favourable to shallower stop time distribution) outcome?

Thanks

And last question about the study of course, "how does thermal stress know it should target the deeper divers?". Bad thermal stress, bad!

Apparently such easy questions cannot be answered.
These defeat obfuscation with fancy graphics, these need just plain logic.

Cheers