Deep Stops Increases DCS

[rjack321]

Try to find a practical balance or compromise of Bubble/Dual Phase Models like RGBM, VPM, Ratio Deco -minimizing Fast Tissue Supersaturation stress with deep stops- while extending out shallow time on Oxygen to effectively off-gas the resultant inert loading on the Slow Tissues as implied by the NEDU Study.

By using & applying Buhlmann GF's for instance, if I were doing two OC deco dives per day for three or four consecutive days-in-a-row on Deep Air on a month long Indo-Pacific/Micronesia tech wreck expedition, then I would program my Petrel Computer from Day 1 thru 4 something like 40/70; 40/65; 40/60 and finally 40/50 for Day 4. On Day 5 take a break from diving to further off-gas those slow tissues & reset CNS O2 clock, and then continue the same three or four day consecutive deco dive day with one day-off schedule/pattern.

In your case, switching to a CCR would be especially valuable for 2 reasons:
1) "Best mix" during the ascent tends to protect fast tissues as the fO2 is going up before you even get to a gas switch. UWSojournor had a description of this effect in an old post somewhere, perhaps he can link it here. That would allow you to increase the GFlow to something greater than 40. And those lowest stops will probably clear as you ascend anyway, just from the fO2 increase.
2) You could add a dollop of helium to your mix for pennies. The gradient for helium on the surface is as high as it can possibly be. So there is basically no "residual helium time" to account for day after day. You still might want to take a day off or only do 1 dive in a day during the course of a week+, but it could be more at you leisure instead a hard date.

You can still extend out the shallow stops and ratchet down the GFhighs as you progress of course, but that becomes one of several tools adding together to enhance your offgassing.

 

[UWSojourner]

UWSojournor had a description of this effect in an old post somewhere, perhaps he can link it here.

I'm not sure if these are what you had in mind.

Link 1

Link 2 referencing this chart.

 

[bergersau]

@UWSojourner

Could you share some thoughts on how the NEDU study results should be treated by recreational divers?

Take 30 meters for 20 minutes at 21%. The RDP considers this profile as a no deco dive and within the RDP NDL for recreational diving (with safety stop required). However, using ZHL16 with 40/70 GF, the following are the required deco obligations for the same profile:

9 meter @ 1 min
6 meter @ 3 min
3 meter @ 6 min

So, ZHL16 with 40/70 is more conservative than the RDP. Is it more prudent for recreational divers to follow the stops above as compared to following the RDP which listed this profile as a NDL dive?

It's not quite correct to say that the RDP table lists this as a 'no deco' dive.
Within 3 pressure groups of the limit of the table the Safety Stop becomes mandatory - therefore you have a mandatory 3min at 5m stop for a 30m for 20 mins profile.

That is obviously still a lot less than the stops you listed above and doesn't invalidate your question or reasoning.

 

[rossh]

I'm not sure if these are what you had in mind.
referencing .

More errors in your heat graphs for us to discover and document? Should we do that?

Your Denial is not going to solve this issue Kevin. You need to admit it, fix the mistakes, and try to repair the enormous amount of damage that has been done to decompression knowledge, because of the errors and mistakes in your heat graphs.

.

 

[rjack321]

I'm not sure if these are what you had in mind.

Link 1

Link 2 referencing this chart.

Just the principle of the CCR being particularly good at washing out the fast compartments discussed in link 2 - from 2014! lol I guess this dialogue has been going on awhile in various places.

 

[UWSojourner]

Just the principle of the CCR being particularly good at washing out the fast compartments discussed in link 2 - from 2014! lol I guess this dialogue has been going on awhile in various places.

Yes! I could refer you to a thread in 2007 . We don't always digest scientific knowledge quickly.

 

[Kevrumbo]

In your case, switching to a CCR would be especially valuable for 2 reasons:
1) "Best mix" during the ascent tends to protect fast tissues as the fO2 is going up before you even get to a gas switch. UWSojournor had a description of this effect in an old post somewhere, perhaps he can link it here. That would allow you to increase the GFlow to something greater than 40. And those lowest stops will probably clear as you ascend anyway, just from the fO2 increase.
2) You could add a dollop of helium to your mix for pennies. The gradient for helium on the surface is as high as it can possibly be. So there is basically no "residual helium time" to account for day after day. You still might want to take a day off or only do 1 dive in a day during the course of a week+, but it could be more at you leisure instead a hard date.

You can still extend out the shallow stops and ratchet down the GFhighs as you progress of course, but that becomes one of several tools adding together to enhance your offgassing.

Just the principle of the CCR being particularly good at washing out the fast compartments discussed in link 2 - from 2014! lol I guess this dialogue has been going on awhile in various places.

Yes! I could refer you to a thread in 2007 . We don't always digest scientific knowledge quickly.

Actually Rich, as the only OC diver on that now seminal Bikini Atoll Expedition back in 2013 with Simon Mitchell who turned out to be my treating Physician, post IWR for type I DCS (as well as lecturing on the results of the NEDU Deep Stops study) -->Noticed all the CCR divers including Simon were performing somewhat similar strategies as above in retrospect, including extending out O2 shallow profiles over the course of ten consecutive days of two deep deco dives per day, with some even taking a day-off mid-week. . .

 

[rjack321]

I just did 10 dives in 6 days in Lake Huron. 39F on the bottom, 59F above about 30ft. Almost 12 CCR hours
Day 1
Typo, sank in 1899, 185ffw
SS Florida, sank in 1897, 187ffw
Day 2
Norman, sank in 1895, 200ffw
Day 3
Kyle Spangler, sank in 1860, 173ffw
Cornelia Windiate, sank in 1875, 172ffw
Day 4
SS Florida again (my favorite)
Defiance, sank in 1854, 180ffw
Day 5
Norman again
Audubon, sank in 1854, 151ffw
Day 6
Kyle Spangler again

I dove 15/55 diluent, setpoint of 1.3 bumping it up to 1.5 intermittently starting at about 60ft. Typical bottom time was 25 to 35mins. Runtime 65 to 110 mins. I dove 40/80 GF but I felt horrible after Day1. This wasn't exactly surprising to me, I am a deco lightweight and 2 dives a day are a known risk factor for me. So on subsequent 2 dive days I started extending out the second dive's deco by 5 to 10min at ~16ft (10ft stops midwater on CCR suck). Felt great from then on, no subclinical symptoms, tiredness etc. CNS was never more than about 65%, OTUs well within limits as well.

 

[leadduck]

regarding heat graphs: seems like much of this discussion is about how to measure similarity of NEDU profiles to profiles that are optimal in ZHL+GF and VPM models. You need not compare supersaturation in optimal profiles in order to compare models. Let me suggest an other way to compare models for a given profile with known experimental outcome, that may be easier to understand and agree on.

We can evaluate any profile in any model: just enter a given profile as a multilevel dive and see if it hits a ceiling in the model. So, could those of you who have the software to make such plots please do me a small favor and do this:

1) Enter NEDU A1 and NEDU A2 as multilevel dives into your software
2) Run your models and see if the profiles hit a ceiling; i.e. the model rejects the profile --> "reject". Or it doesn't hit a ceiling --> "accept".

When doing this for multiple models and model parameters (VPM conservatism settings, or GF), we can classify the models and parameter value settings, because we know from the NEDU experiment that A1 has less DCS risk than A2.

Class I: accepts A1 and rejects A2. Let's label these models & settings "efficient".
Class II: rejects both A1 and A2. "conservative"
Class III: accepts both A1 and A2. "liberal"
Class IV: rejects A1 and accepts A2. "dead wrong"

For ZHL we could even make a 2D plot over GFlow and GFhigh, marking these four regions and see which gradient factor settings are in line with the NEDU findings.

 

[rossh]

regarding heat graphs: seems like much of this discussion is about how to measure similarity of NEDU profiles to profiles that are optimal in ZHL+GF and VPM models. You need not compare supersaturation in optimal profiles in order to compare models. Let me suggest an other way to compare models for a given profile with known experimental outcome, that may be easier to understand and agree on.

We can evaluate any profile in any model: just enter a given profile as a multilevel dive and see if it hits a ceiling in the model. So, could those of you who have the software to make such plots please do me a small favor and do this:

1) Enter NEDU A1 and NEDU A2 as multilevel dives into your software
2) Run your models and see if the profiles hit a ceiling; i.e. the model rejects the profile --> "reject". Or it doesn't hit a ceiling --> "accept".

When doing this for multiple models and model parameters (VPM conservatism settings, or GF), we can classify the models and parameter value settings, because we know from the NEDU experiment that A1 has less DCS risk than A2.

Class I: accepts A1 and rejects A2. Let's label these models & settings "efficient".
Class II: rejects both A1 and A2. "conservative"
Class III: accepts both A1 and A2. "liberal"
Class IV: rejects A1 and accepts A2. "dead wrong"

For ZHL we could even make a 2D plot over GFlow and GFhigh, marking these four regions and see which gradient factor settings are in line with the NEDU findings.

Neither of the Nedu profiles, hit any lasting limit in any model ! They don't get anywhere near close.

That is because both nedu profiles are stretched out over double the actual required deco time, of ANY model (including their own published USN rev 6 table). That was the deliberate design of the test: remove most "profile" stress through exaggerated shallow stop time, and replace it with "thermal" stress (make em cold: 29C water, 4 hours, no wetsuit, sitting still in a chamber). And then assume the result means something beyond what it actually tested.


Also.. GF is not a model - it's an add on time fudge to a model to make it longer. Only real ZHL is man tested and only the ZHL model specs, can be used for valid comparisons.



GF version:

VPM-B version:

Compared to actual models: