Deep Stops Increases DCS

[leadduck]

Nice idea, well balanced, and workable.... but...
Neither of the Nedu profiles, hit any lasting limit in any model ! They don't get anywhere near close.

Oh, they do hit the ceilings depending on the conservatism settings. This is like asking the question: "If the test subjects in the NEDU study would've had a dive computer with them, or had planned their dives on a desktop computer, which settings should they have used (VPM conservatism level, or ZHL GF) so that the software had told them that A1 profile is OK but A2 profile is not?"

If I run the profiles in subsurface, I get:

-----------------------------------------------------------------
Setting              A1 (good)      A2 (bad)        Class
-----------------------------------------------------------------
ZHL-16B GF 100/100   OK             OK              3
            90/ 90   OK             fail            1
            80/ 80   fail           fail            2
            70/ 70   fail           fail            2
            90/100   OK             OK              3
            80/100   OK             OK              3
            70/100   fail           OK              4
            80/ 90   fail           fail            2

VPM-B           +0   fail           OK              4
                +1   fail           OK              4
                +2   fail           OK              4
                +3   fail           OK              4
                +4   fail           OK              4
-----------------------------------------------------------------

I'm not confident about the VPM-B implementation in subsurface, that's why I asked that someone else run this test. For subsurface's implementation of VPM-B I can say that it always favors the high risk profile over the low risk profile, no matter what conservatism is set. That's disturbing.
For ZHL+GF it seems that GF_high needs to be 90% or less to detect that A2 is bad.

 

[rossh]

You have fallen into the trap, of assuming the nedu profiles failed due purely to "profile" stress. They did not. In fact due to there exaggerated length, there is almost no 'profile' stress remaining. All profiles failed due to excess thermal stress. The solution to this scenario, is less thermal stress, not more decompression. More decompression will not save these profiles.

So trying to compare a plan that failed from thermal stress, against profile stress - not the same thing.

Now that I see what you are doing, I can't agree with your method.

 

[PfcAJ]

You have fallen into the trap, of assuming the nedu profiles failed due purely to "profile" stress. They did not. In fact due to there exaggerated length, there is almost no 'profile' stress remaining. All profiles failed due to excess thermal stress. The solution to this scenario, is less thermal stress, not more decompression. More decompression will not save these profiles.

So trying to compare a plan that failed from thermal stress, against profile stress - not the same thing.

Now that I see what you are doing, I can't agree with your method.

If they failed due to thermal stress explain why the deep stops one had more dcs cases than the shallow stops one?

The only different was the stop distribution. Workload temp and time were all the same.

 

[rossh]

If they failed due to thermal stress explain why the deep stops one had more dcs cases than the shallow stops one?

The only different was the stop distribution. Workload temp and time were all the same.

Step back a bit.... should we blame the model for everything? Is the model here to fix every kind of ill? No. The cause and solution to the this test problem is thermal stress. Does it matter who fell over first? Making the profile longer is going to make matters worse - not better.

Deco models work by limiting profile stress - that is the only control they have. To solve a profile problem, we lower the profile stress (longer profile). Deco models do not and cannot fix thermal stress.


Now you can say its the scientific method - changing a variable... Ok good. But this test has absolutely NO deep stops. Therefore its become two assumptions... a/ exchanged thermal for profile stress, b/ exchanged shallow for deep stops. Bzzzt. too much. That is two variables, and the test is no longer provable connected.


As I said before, I don't give a crap about this nedu shallow stop, cold water test. Its NOT related to tech dive practices. Stop trying to pretend there is some connection - it is not there.

FACT: No deep stops in the test - only shallow stops.

Go find who ever makes really really shallow stop models, and tell them about it - its their problem - not mine.


.

 

[The Chairman]

At some point, I need to replace my Oceanic VT3 primary computer, I can't easily figure out how to do this from among the currently available dive computers.

Going to a rebreather pushed this question for me... Now I've got two Petrel 2s and am struggling with what gradient factor to use. My PDCs are still set to the factory defaults with no adverse effects and about 8 hours of cumulative deco. In fact, my decos are becoming so long in the caves that thermal protection is becoming an issue. I've got a new custom wetsuit on order from WetWear (can't wait).

But the problem I have is this: there doesn't seem to be a real authority by which I could learn what I need to know. This thread is not giving me the warm willies either way either. I've been diving since 1969 and have never been bent. Why? I pad all my deco obligations and safety stops. I don't see it as a waste of time.

 

[Jack Hammer]

As I said before, I don't give a crap about this nedu shallow stop, cold water test.

.

If you "don't give a crap about" this published research then why are you trying so hard to discredit it?

 

[PfcAJ]

Step back a bit.... should we blame the model for everything? Is the model here to fix every kind of ill? No. The cause and solution to the this test problem is thermal stress. Does it matter who fell over first? Making the profile longer is going to make matters worse - not better.

Deco models work by limiting profile stress - that is the only control they have. To solve a profile problem, we lower the profile stress (longer profile). Deco models do not and cannot fix thermal stress.


Now you can say its the scientific method - changing a variable... Ok good. But this test has absolutely NO deep stops. Therefore its become two assumptions... a/ exchanged thermal for profile stress, b/ exchanged shallow for deep stops. Bzzzt. too much. That is two variables, and the test is no longer provable connected.


As I said before, I don't give a crap about this nedu shallow stop, cold water test. Its NOT related to tech dive practices. Stop trying to pretend there is some connection - it is not there.

.

Its absolutely related to tech diving practices. Are you kidding? Do you even tech dive?

There's still only one variable tested: stop distribution. If the profile didn't matter DCS rates would be the same.

 

[AlexL]

cold water test.

i know i shouldn't wade into this train-wreck of a thread, but since we're now moving the goalposts to thermal stress, just want to point out that for the NEDU study, it was a wet pot dive with the temperature held at 86f/30c +-2f. thermal stress remained constant and consistent across the entirety of the dive for both profiles.

 

[rossh]

If you "don't give a crap about" this published research then why are you trying so hard to discredit it?

As you can see, there are many people who want to pretend the test applies to deep stops and the software products we supply. It does not. But they keep trying. I guess I have had enough of the fabrications and lies that go to justify this non-existent connections. Hence I need not be concerned with the test and its outcome.


The test was sort of OK... not well designed, but it did the job they wanted it to do. It almost got rejected by its own criteria, so they cut it off half way just to save the expense.

.

 

[rossh]

Its absolutely related to tech diving practices. Are you kidding? Do you even tech dive?

There's still only one variable tested: stop distribution. If the profile didn't matter DCS rates would be the same.

FACT: No deep stops in the test - only shallow stops.

Go find who ever makes really really shallow stop models, and tell them the about it - its their problem - not mine.