NEDU Study

[rossh]

Thank you for your reply,
is really good that we all agree here. It must have been lost in the background noise ...

Cheers

Thanks, but I don't understand the need to highlight this. Have you lot been thinking something else?

My thoughts and points have always followed the basic existing formula and model structures and basic deco sciences.... If that was your sticking point, then I'm afraid you have miss-understood somehow.

The problem all along is the nedu test has been described in ways that are invalid, or conclusions made that are out of context or wrong... still is.

.

 

[UWSojourner]

IMHO, for the tech diver doing "bimble tech dives" of less than 90-120 mins and depths less than 200 or so, they will generally have good outcomes on your stuff, start pushing it out (esp in run times) and from what I can see, the bubble models start to fall apart and for me (and many of my friends, many of who also used VPM/RGBM in the past where it belongs in my view) the higher risk in bubble models isn't worth it.

Your observation would align well with how VPM-B operates.

As you go deeper and stay longer VPM-B does not scale. In the face of mounting gas loads VPM-B is content to recommend that you surface exposed to the same supersaturations even though the exposure time is dramatically increasing. This can only do one thing -- increase DCS risk. It's up to the diver to find some way to adjust.

For context see this link and this link.

 

[KenGordon]

Your observation would align well with how VPM-B operates.

As you go deeper and stay longer VPM-B does not scale. In the face of mounting gas loads VPM-B is content to recommend that you surface exposed to the same supersaturations even though the exposure time is dramatically increasing. This can only do one thing -- increase DCS risk. It's up to the diver to find some way to adjust.

For context see this link and this link.

Is that really very different to Buhlmann? You get to surface if all the tissues are below the limit, whether only one is significant, as in a short dive, or lots are only just short of their limits from longer and more complicated profiles.

I take the point that VPM ought to better consider the surfacing supersaturation of the slower tissues because they take longer to desaturated, but if risk is a function of the integral supersaturation over all the tissues then only considering the leading one is surely a gap?

Is it the case that the half times increasing with the saturation limit decrease eliminates this problem for Buhlmann? Or do divers manually choose lower GF values for bigger dives?

 

[huwporter]

Let me put this to you again..

There is no such thing as +7. You can't buy it, you can't make it. No one has it. No one has ever dived it - it simply does not exist. Someone has cooked this up at home, for their own use. Its made up nonsense...

Now you Mr. HuwPorter, are demanding I answer to some imaginary plans...? Really.... is this how things are now? Some one makes up gossip and junk, and then everyone else has to answer to it?

Where is your sense of right and wrong? I'm not obliged to explain other peoples made up nonsense plans.

Hi Ross,

So you confirm that if you start with a VPM plan and round up the bottom time for added conservatism, at some point the plan becomes junk?

Please can you clarify at what point that happens, and why?

 

[UWSojourner]

Is that really very different to Buhlmann? You get to surface if all the tissues are below the limit, whether only one is significant, as in a short dive, or lots are only just short of their limits from longer and more complicated profiles.

It is quite different from Buhlmann. The post you're responding to was concerned about whether VPM-B "scales consistently and in the right proportions". That's techno-speak for "does VPM-B adjust appropriately for different dives?"

The referenced posts show that VPM-B does not adjust AT ALL for a particular dive in the face of mounting exposure times after the effects of the CVA wear off. Buhlmann's allowed supersaturations, on the other hand, decrease as the diver's exposures increase reflecting the lower M-Values for longer half-time compartments.

I take the point that VPM ought to better consider the surfacing supersaturation of the slower tissues because they take longer to desaturated, but if risk is a function of the integral supersaturation over all the tissues then only considering the leading one is surely a gap?

Integral supersaturation is a reasonable index of decompression stress when comparing profiles that vary only by their distribution of stop time. So it's a interesting metric to review when comparing dives of the same depth, bottom time, runtime, etc. It's also used in the development of decompression models as has been noted many times.

My post, however, was trying to describe the why of VPM-B's problems. The post shows that in the face of mounting gas loads, VPM-B keeps the recommended supersaturation limits essentially constant. This can only do one thing -- increase DCS risk.

Is it the case that the half times increasing with the saturation limit decrease eliminates this problem for Buhlmann?

I think I would just say that Buhlmann (i.e GF) is playing the right game. In other words, as the severity of the exposure increases, Buhlmann is reducing supersaturation limits. The fact that VPM-B does not means it clearly is not scaling correctly. However, to my knowledge no decompression method currently available has eliminated the problems associated with decompression diving.