NEDU Study

[rossh]

Yes, they did get the DCS they were looking for. That was the point of the test. But they got roughly 3x the DCS using the <INVALID TEXT REMOVED> elongated shallow stop profile (A2). That is the point.

The <invalid text removed> A2 profile resulted in a higher DCS rate for the exact same dive under the exact same conditions.

Bold are my changes

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.

We tech divers do not normally have either of those condition in our diving, and certainly never to such extremes, or paired together like that.

The bottom line of the test is this: follow the standard gas kinetics - they work. That is something that existing ZHL and VPM-B do now.... nothing is broken, nothing needs fixing.


.

 

[scubadada]

Yes, they did get the DCS they were looking for. That was the point of the test. But they got roughly 3x the DCS using the deep stop profile (A2). That is the point.

The deep stop profile resulted in a higher DCS rate for the exact same dive under the exact same conditions.

What I also found very interesting was the predicted rates of DCS going into the study. For the deterministic gas content model, VVAL 18 Thalmann, the predicted DCS rate was 4.4-6.1%, they ended up getting 1.6%. For the probabilistic bubble model, BVM(3), the predicted rate of DCS was 3.7-5.9%, they ended up getting 5.0%. I believe the investigators were surprised by their findings.

 

[cerich]

We don't 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.

We don't normally have either of those condition in tech diving, and certainly never to such extremes.

The bottom line of the test is this: follow the standard gas kinetics - they work, which is something that existing ZHL and VPM-B do now....

who is this royal "we"

Seriously.

Look, I am pretty good with regs, but I'm not a engineer. I say to my engineer what I want, come up with ideas then work with said engineer to make it happen. The good thing is that there are objective testing I can and do do to test my regs. However, I would never claim to be a regulator engineer.

You are a software guy, very familiar with deco, when did you decide you were a deco scientist? I really feel you were early on the bubble models getting popular..but so stuck on it that you feel you need to defend your product, even as time has marched on and there has been some scientific studies that point to some flaws. It's not like you invented VPM so why so stuck on it?

For the "average" tech diver..I believe there is enough data points out there that the moderate exposure tech dives can generally be done using a variety of the tools out there, however to me at least it's become obvious that at the far end, on truly big dives by any metric that the bubble models are falling down. Technology is marching along, and more and more people are doing the bleeding edge dives than ever before...and just gonna suggest that while you may be still riding the bubble model train, the end station is in sight.

 

[fsardone]

We don't 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.

.

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

 

[cerich]

Ross,
the point is both groups the shallower ones and the deeper ones did the same: a lot of work deep (facilitated on gassing) and still during deco (impeded off gassing). Why the shallower got bent less than the deeper according to you?

Your experience is anecdotal and therefore remains a good story to tell whilst drinking a beer ...

Cheers

Fabio

dude, Ross seems to think that sitting on a rock at 165' is enough for him to feel safe doing a working dive using those models.

Having a somewhat passing knowledge of the DCIEM validation... I am not surprised he could get out without issues after sitting on a rock, because DCIEM tables were validated in cold and working conditions.

 

[UWSojourner]

We don't 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.

We don't normally have either of those condition in tech diving, and certainly never to such extremes, or paired together like that.

The bottom line of the test is this: follow the standard gas kinetics - they work. That is something that existing ZHL and VPM-B do now.... nothing is broken, nothing needs fixing.

That's really good to know. So listen up everyone -- if you take advice on physiology and decompression science from a hand-waving VPM-B salesman and programmer, please disregard the NEDU's highly controlled, landmark decompression study.

All others might appreciate this quote from Dr. Neal Pollock:

"The impact of deep stops is not that they target some different physical reality. It is actually quite simple; the extra time spent deep allows more inert gas uptake in the relatively undersaturated intermediate and slow tissues. This is simply a loading problem that subsequently produces a higher degree of decompression stress. If there is less uptake at depth, ascent to a relatively shallow stop has much less risk. The idea that deep stops controlled bubble growth is one of the armchair arguments that has not lived up to human testing ... As with all the protocols we developed and subsequently saw fail, it is time to respect the data over the hand-waving."

 

[rossh]

What I also found very interesting was the predicted rates of DCS going into the study. For the deterministic gas content model, VVAL 18 Thalmann, the predicted DCS rate was 4.4-6.1%, they ended up getting 1.6%. For the probabilistic bubble model, BVM(3), the predicted rate of DCS was 3.7-5.9%, they ended up getting 5.0%. I believe the investigators were surprised by their findings.

I'm not surprised. Basic gas kinetic rules predicted the A2 was a flop. Plain common sense says A2 would be a flop, and that is what they got.

Do not be confused.... the A2 profile is not a real model profile - its a test design. The A2 is 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.


As I said above.... existing tech models follow the standard gas kinetic formula, as used in the successful A1 profile.

The NEDU study illustrated the general principal that continued slower tissue gas uptake offsets the benefits of reduced bubble growth at deeper stops. This general principal also applies to VPM.

For sure... It demonstrated that existing gas kinetic formula work (A1).... It showed the unconventional gas formula in the BVM(3) design failed (A2).


Did you know, that both VPM-B and ZHL follows the same standard gas kinetic formula, and that those formula are typical of the A1 successful profile gas kinetics too.

Did you know that if you plan a dive in ZHL or VPM-B, and force more deep time into it, that will automatically adds extra shallow time? Also, if you force those nedu profiles into ZHL or VPM-B plan, then both will give longer deco time for A2.

Did you know that all dive computers follow those same gas kinetic formula as well, meaning we fully trust theses formula now, to do any kind of ascent.

So...The existing gas kinetic formula, already fully account for on gassing and off gassing in any portion of the ascent, and do it correctly right now. They can handle any kind of ascent, up, down, left right - anything you like, and still correctly track on / off gassing.

***********

I think many people here seem to have forgotten something... the deepest stop of all... is the bottom stop. Otherwise known as... bottom time. It's been overlooked that we on gas at the fastest rate on the bottom, and the standard gas kinetic formula handle this correctly too...


This current concern that some seem to be making here - that a significant amount of extra on gassing occurs in deeper stops, and then somehow this extra goes unnoticed by the standard gas kinetic formula.... is a nonsense., for 2 reasons...


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.


2/ In a typical 60 min dive, the 'extra' on gassing that happens from the deep stop portion alone, compared to a shallow version plan, is about a 1/40 increase of the total. i.e. deep stops add a few extra mins over the shallow version plan, starting at half depth. That is loosely equivalent to adding about of about 2.5% to the bottom time of a shallow plan. Not a whole lot really. But, as already stated, the gas kinetic formula account for that correctly now, and the shallow run time extends automatically.


There is nothing broken here, there is nothing to fix. No one needs to manually add more time... the models and formula do that for you now, automatically.

****

The problem all along, is the people who do NOT follow a model plan... its the people who make up or modify their own ascent, and consequently do too much deep time, and not enough shallow time, that are at biggest risk here.

.

 

[cerich]

2/ In a typical 60 min dive, the 'extra' on gassing that happens from the deep stop portion alone, compared to a shallow version plan, is about a 1/40 increase of the total. i.e. deep stops add a few extra mins over the shallow version plan, starting at half depth. That is loosely equivalent to adding about of about 2.5% to the bottom time of a shallow plan. Not a whole lot really. But, as already stated, the gas kinetic formula account for that correctly now, and the shallow run time extends automatically.


There is nothing broken here, there is nothing to fix. No one needs to manually add more time... the models and formula do that for you now, automatically.

****

The problem all along, is the people who do NOT follow a model plan... its the people who make up or modify thier own ascent, and consequently do too much deep time, and not enough shallow time, that are at biggest risk here.

and when a 3 hour ccr dive?

 

[Storker]

The existing gas kinetic formula already fully address, any kind of ascent, deep shallow, elongated, multilevel....

Unlike others, I won't claim any expertise in decompression science, but I do believe I have a pretty decent grasp of chemistry and physics. Based on that, I have a hard time understanding what "gas kinetic formula" means. Last time I checked, the only thing all decompression models had in common was equilibrium phenomena like dissolved gas content. Which kinetic parameters are actually determined and used in the different deco models?

Since you - based on your own statements - are more qualified than internationally recognized decompression scientists with multiple peer-reviewed publications (such as Drs Mitchell, Doolette, Pollock and Møllerløkken to name a few), I expect that you can enlighten me.

 

[scubadada]

...There is nothing broken here, there is nothing to fix. No one needs to manually add more time... the models and formula do that for you now, automatically...

Hi @rossh

Why then, in MultiDeco, is the surfacing for VPM-B, limited to the more conservative of VPM-B or Buhlmann ZH-L16C? One has the option of choosing a GF as high as 100, or as low as 70. I have seen examples of native VPM-B resulting in surfacing with a GF in excess of 100. @UWSojourner had an example, earlier in this thread, with a VPM-B+2 profile surfacing with a GF of 107.