Deep Stops Increases DCS

[rossh]

I may be missing the point, but aren't Ross's chart and the heat maps similar?

The big differences between VPM-B+3 and GF60/75 in the heat maps are the tissue loadings post surfacing. In Ross's chart, the supersaturation of the most heavily loaded compartment seems to be 55 KPA on surfacing. For GF 65/75, the maximum supersaturation appears to be just over 40 KPA. This seems consistent with the different colour on the heat map for the two algorithms.

Heat graphs are NOT similar - they have no dimensions - and compare irrelevant things. Only proper scientific charts that show real values are important. The decompression limits in models is created based on real numbers, not pretty colors.

.

 

[rossh]

As a scientist, it always raises a red flag when someone rabidly attacks a particular argument as "junk science." Ross suggests that there is no credible evidence for redistributing stops to shallower depths. The reality is that there is very little data for any decompression model. Yes, divers have been using a variety of models successfully for years, including deep stops. None of these outcomes are done under controlled conditions, however. Comparing non-DCS decompression events across divers who dived at different times, places, and conditions, doesn't really tell you much. I don't think that Doolette, Mitchell, and Watts would claim that their arguments have the backing of a tremendous volume of empirical data. What they suggest instead, is that the limited data that are available at least suggest that red-distributing deep stops to shallower levels may provide some benefit.

It is also unclear exactly what it is that Doolette, Mitchell, and Watts are marketing.

A scientist will know the importance of using validated and accepted methods and data. This mb-min ISS is none of those things. It's nothing more than eye candy. Or sometimes called Junk Science. It needs to be stopped. Same goes for "heat graphs" - eye candy - no dimensions - no scientific basis - just pretty colors.


I do not suggest anything of the sort you imply. As you say, there are many different models and deco methods, and they all work, because they all have enough deco time to do the job.

The thing I can't stand, is the rubbish justifications and junk science being used to promote attacks on VPM-B.

.

 

[Freewillow]

As a scientist, it always raises a red flag when someone rabidly attacks a particular argument as "junk science." Ross suggests that there is no credible evidence for redistributing stops to shallower depths. The reality is that there is very little data for any decompression model. Yes, divers have been using a variety of models successfully for years, including deep stops. None of these outcomes are done under controlled conditions, however. Comparing non-DCS decompression events across divers who dived at different times, places, and conditions, doesn't really tell you much. I don't think that Doolette, Mitchell, and Watts would claim that their arguments have the backing of a tremendous volume of empirical data. What they suggest instead, is that the limited data that are available at least suggest that red-distributing deep stops to shallower levels may provide some benefit.

It is also unclear exactly what it is that Doolette, Mitchell, and Watts are marketing.

I cannot agree more. I hold also a PhD and find the arguments and pseudo science of Mister Ross...........at best........quite funny.

To claim that others are paid in order to demolish his VPM - from which he is making money - is just hilarious.

Thank youNetDoc for taking my 2 "report" messages for posts from Mr. Ross that were clearly "over the border". .

 

[The Chairman]

---

---

A ScubaBoard Staff Message...

Gentlemen... please. The users of ScubaBoard are quite capable of deducing what is junk/hack/pseudo science without either of you cluing us in or using those terms. It's specious at best and it takes away from the discussion at hand. Can we get back to the relative merits/demerits of each approach without banal attempts to smear each other in the process? If not, we'll just have to close the thread and that would be a shame. Be passionate, but be polite. Thanks.

---

 

[Centrals]

I cannot agree more. I hold also a PhD and find the arguments and pseudo science of Mister Ross...........at best........quite funny.

To claim that others are paid in order to demolish his VPM - from which he is making money - is just hilarious.

Thank youNetDoc for taking my 2 "report" messages for posts from Mr. Ross that were clearly "over the border". .

Couldn't agree more!
I believe none of my buddies had tossed any money away on VPM soft ware.

 

[Shotmaster]

I guess he can blame NEDU for publishing their findings. LOL

 

[rossh]

Integral Supersaturation (ISS) is NOT a recognized or valid method to judge decompression with. It cannot be used in this way as a whole scale raw measure of stress. It's open ended, and has no validation, or calibration to any properly recognized or scientific measure of decompression stress. It's meaningless noise.



"The key is that when assessing similarities in deco methods, keep the runtime constant."

This is a wrong - Nowhere in decompression theory does it say or prove that profiles are somehow made equal based on end run time. It's a fallacy, and just an excuse to make stuff up and compare unconnected plans.


Different deco models have different ascent criteria, make different outputs, and have different runtimes. Any one who interferes with that, is defining something different.



*************



Heat maps do not have any dimensions, or relevance to actual decompression criteria limits. They do not show actual decompression pressures. They do not show when a limit has been exceed. Instead they compare two unrelated plans, in ways that does not matter to the decompression outcome.


***************



Here are some real decompression criteria shown in graphs. These are the actual dimensions used in the very models in use today. These graphing tools are available to everyone to use in MultiDeco.

You can clearly see the differences. VPM-B prefers to keep the saturation pressure low across the whole ascent. The ZHL-C has a large initial supersaturation. This is why people have abandoned the man tested ZHL, and added fudge time to it with GF add ons.


Note how all plans finish at about the same place. The more conservative plans are a little lower. The surface decay times are pretty much the same. This really highlights a few things; Despite the subtle shallow / deep stop differences, it all equals out in the end. All this fuss about deep stop on gassing, adds up to almost nothing.


And more importantly - let the model do its job - what ever it is. The model knows when to ascend. This practice of trying to force all dives samples to the same time to compare them with, is an interference and invalid (heat graphs, +7, etc).


These supersaturation and tissue gradient graphs I show here, and the math behind it, is the recognized scientific decompression measurements, and used extensively in many model designs.

Further, this is what David Doolette says (TR11-06 introduction), which the above diagram shows.

 

[UWSojourner]

And more importantly - let the model do its job - what ever it is. The model knows when to ascend.

The NEDU study tested 2 models developed by very smart people. The deep stop bubble model produced the profile named "A2" and the shallow stop model produced the profile named "A1". Both models "knew when to ascend".

And yet when tested the deep stop profile "A2" had about a 5% DCS rate. The shallow stop profile "A1" had about a 1.6% DCS rate. A mathematical algorithm will always "know when to ascend". What the algorithm doesn't know is whether its recommendations are optimal. It only knows its own algorithm.

The NEDU study tested 2 algorithms and found by diver tested trials that the shallow model "knew best". Why? Why did the shallow model succeed while the bubble model experienced about 3x the DCS rate? See the chart below.

The pattern of decompression for A2 and A1 is shown by the heat map. Each horizontal row is one tissue compartment. The fast compartments are on the top, the slowest on the bottom. At each point of the decompression you can see whether the compartment's supersaturation is "hot" (i.e. higher than the other profile) or relatively cool (i.e. lower than the other profile). It's easy to see that A2 kept the fast tissues substantially under the supersaturation of A1. It accomplished this by "deep stops".

It's also easy to see that the "cost" of staying deeper was that A2 had higher supersaturation once the divers surfaced. And that higher supersaturation was experienced for a relatively long time.

The net cost of A2's "deep stops" is the bottom chart. This is also the best explanation of why A2 had a 5% DCS rate while A1 had a 1.6% DCS rate. The integral supersaturation (i.e. decompression-time) was about 46% higher once the diver surfaced from the dive. That higher supersaturation exposure caused by keeping the diver deeper for a longer period is the best explanation of the higher DCS rate. Since all other factors were equal (including the total runtime), the overall higher decompression stress experienced by the divers in A2 is thought to have caused the higher DCS risk.

Now look at the charts below for a typical technical diver profile (CCR 240ft 20min 10/50 1.2). Do you see the similarities?

VPM-B+3 also keeps the diver deeper for a longer period. You can see that the fast compartments are very dark while GF60/75 fast compartments are hot. That just results from the GF profile ascending to a much shallower first stop.

But VPM-B+3 also has a higher supersaturation exposure once the diver surfaces. This result is inevitable since the overall run time is the same, but the diver spent more time at deeper depths during decompression.

The net cost of VPM's deep stops is the bottom chart. The integral supersaturation (i.e. decompression-time) is about 30% higher once the diver surfaces from the dive. The overall higher decompression stress experienced by the VPM diver is about 18% higher.

The correspondences between the two decompression patterns are pretty clear. Its this pattern of decompression (deep stop models keeping you deeper longer and putting you on the boat with a higher sustained supersaturation exposure) that is leading divers to adopt a shallower stop approach such as GF. As I've said before, the GF model in almost any configuration will be better based on these patterns of decompression. Decide for yourselves. The argument is pretty compelling to me.

 

[rossh]

Here are some Nedu test facts.


There are no "tech" style deep stops in the nedu test.

The nedu "bubble model" is a shallow stop variety - no relation to VPM-B.

The nedu test measured a shallow stop profile, vs a really shallow stop profile.

The "deepest" stop in the nedu test was 70 ft (21m), which to most tech divers, is not deep at all.

The nedu stop profile is 2.5 times longer than any other normal profile for this dive, and its last stop is 90 minutes at 3m - clearly its an over exaggerated shallow profile.

The nedu test sequence was stopped half way, because it was about to fall through the bottom rejection limit and automatically invalidate its own results.

A faked up VPM-B +7 profile does not make for a valid comparison.

**********************

I don't care about the nedu test result. No deep stops - no relation to tech deep stops, no real relation to tech diving, no relation to VPM-B, a decompression test that is ridiculously elongated to be unrealistic. The test design was made to deliberately reduce supersaturation across the profile (thereby removing profile stress), and substituted in an excess thermal stress. The divers suffered from thermal stress. So stop blaming it on non-existent deep stops.



**************


Kevin, your whole Nedu argument hinges on a pretty picture - a made up heat graph, compared to a stretched out and faked up VPM profile - that does not exist.

Heat graphs are not scientific or valid in any useful way. They compare two unrelated objects, but say nothing about actual decompression limits. You are doing it again above - two unrelated objects, that look different, one of which is wholly unrealistic and not used anywhere.


Your Integral Supersaturation (ISS) mb-min graphs are not used anywhere either, except by you. One cannot validate these all on your own. They are "too simplistic" to be useful and do not show anything realistic - sorry - that's how it really is.


Further, the formula that are used in your preferred ZHL model with GF, to control on/off gas tracking, works exactly the same in VPM-B. Its a nonsense to suggest that gas tracking is OK when used in GF but not OK when used in VPM-B?

Your manual manipulation of graphs, takes the ascent decisions away from the model, thereby leaving a false impression of a models characteristics - compare real models, not stretched / GF fiddled things.


*******

AND.... most importantly. The recognized and accepted decompression stress measures - supersaturation - show no connection or similarity between nedu test and tech diving profiles..

You can see quickly, the nedu test has almost no supersaturation in either profile. Clearly the supersaturation is so low it should not have been an issue. So now one needs to explain how a small (harmless) last stop supersaturation pressure, was able to do the extra damage all on its own. ??


Have a look at this... by Neal Pollock - DAN USA.

End of story.


****************************


Now...... there is certainly a very real possibility to over-doing deep stops. No dispute about that.Clearly too much is a bad thing, but that is a problem exclusively for the RD crowd, who also have been known to make stuff up on occasions


But real models, with real gas tracking like VPM-B, like ZHL, do not have this problem - they have industry accepted gas tracking formula to make stop decisions for them.

.

 

[UWSojourner]

I'll let diver's decide for themselves. For those interested the presentation here is a good elaboration of the issues.