Overshooting NDL and mandatory deco stops

[RayfromTX]

The NEDU man-tests decompression profiles to establish quantified risk.

First, let me just say that I believe that you know far more about all of this than I do. Period. Having said that and with great respect for you and your experience I will offer this response and clarification to my understanding of the matter.

The conclusion reached by the deep-stop study, as an example, was very limited. They basically said that deep stops were not inherently safer. They were not able nor did they attempt to prove that they were more dangerous. That would have required a longer and more lengthy study. They were not able nor did they attempt to show what gradient factors should be used to create safer profiles. They are not able to provide conclusive findings on the safest approach to decompressing from helium loading in tissues. Each of these separate issues would require multiple studies that are more complex, risky and costly than the deep stop study.

My understanding, while quite limited, is that the DCS associated with these tests could be resolved with treatment but I think the days of substantial and wide ranging human testing with this level of risk has fallen out of favor and is mostly limited to the pharmaceutical trials that pay poor people to take drugs and report their side effects.

I am not saying that we don't know stuff from testing that has been done by NEDU and others or that we are totally in the dark. I'm just saying that there are limits to our ability to state with certainty where the safe line is for an individual or what gradient factor is the correct one to use for a defined associated risk tolerance. The lines are fuzzy and gaining a more thorough understanding through scientific testing is a huge challenge.

@Dr Simon Mitchell Please correct me if I misunderstand these issues and perhaps fill in the substantial blanks in my perception of the challenges faced by the deco science world.

 

[NAM001]

From the perdix Rec manual "The Low setting is similar to PADI and NOAA no-stop time tables for air and nitrox diving."

now if wome one can make a table of the rest of the brands divers with mis matched computers can figure it out.

 

[Gareth J]

First, let me just say that I believe that you know far more about all of this than I do. Period. Having said that and with great respect for you and your experience I will offer this response and clarification to my understanding of the matter.

The conclusion reached by the deep-stop study, as an example, was very limited. They basically said that deep stops were not inherently safer. They were not able nor did they attempt to prove that they were more dangerous. That would have required a longer and more lengthy study. They were not able nor did they attempt to show what gradient factors should be used to create safer profiles. They are not able to provide conclusive findings on the safest approach to decompressing from helium loading in tissues. Each of these separate issues would require multiple studies that are more complex, risky and costly than the deep stop study.

My understanding, while quite limited, is that the DCS associated with these tests could be resolved with treatment but I think the days of substantial and wide ranging human testing with this level of risk has fallen out of favor and is mostly limited to the pharmaceutical trials that pay poor people to take drugs and report their side effects.

I am not saying that we don't know stuff from testing that has been done by NEDU and others or that we are totally in the dark. I'm just saying that there are limits to our ability to state with certainty where the safe line is for an individual or what gradient factor is the correct one to use for a defined associated risk tolerance. The lines are fuzzy and gaining a more thorough understanding through scientific testing is a huge challenge.

@Dr Simon Mitchell Please correct me if I misunderstand these issues and perhaps fill in the substantial blanks in my perception of the challenges faced by the deco science world.

I wrote a quite long post for this thread on Sunday, partly because i am certainly no expert. I didn't post it.
Part of my deleted reply was what you said in the highlighted text. I believe that the balance of opinion now, is that it is not ethical to test on humans, i.e. bend someone on purpose (or potentially bend someone).

From my limited understanding, and my memory from the 90's. A lot of the current GF settings are based on both theoretical data from physiologists, and data from those doing the dives.
The safety settings used on the VR3 by my compatriots at the time (I stayed on hard table), was based on feedback from other divers. One issue that was well known, is you might well make 100 dives successfully on a set of settings, and then bend on the next.

 

[Storker]

My understanding, while quite limited, is that the DCS associated with these tests could be resolved with treatment but I think the days of substantial and wide ranging human testing with this level of risk has fallen out of favor

Absolutely. Im pretty certain that no ethics board would approve an ante hoc study which provided enough data to give reliable quantification of the risk. However, when the new tables have been used for a while, the data you need for a comprehensive post hoc quantification are (should be) available. The only downside would be that the data would also include bounce dives which didn't require decomression, but with good record-keeping, those dives could be filtered out from the dataset. That would be a cohort study, which isn't as strong as a double blinded randomized control trial (which an ante hoc study ideally should be), but definitely be better than nothing.

In the publication I quoted in post #146, they had used data from more than 60000 real man-dives to quantify the DCS risk while using those particular tables. I'd be surprised if the USN didn't keep as good records as our commercial diving industry is required to do, so the data ought to be out there somewhere.

 

[RayfromTX]

Who would be willing to stake their reputation of guidelines for diving that were developed by data that is self reported? The unreported DCI incidents would be left out and all the dives that never came close to the limits would be included.

If you somehow had access to dive computer logs there would be no way to correlate for physical consequences accurately. In the end you may be no better off or perhaps worse than just chatting with your buddies about what they are getting away with and then you come up against the apparent issue of some divers being more immune to being bent than the general public.

Your data set in #146 doesn't appear to represent what recreational divers do. It sounds like commercial divers.

 

[rongoodman]

now if wome one can make a table of the rest of the brands divers with mis matched computers can figure it out.

Since many of the recreational computers use proprietary algorithms, good luck with that.

 

[PfcAJ]

First, let me just say that I believe that you know far more about all of this than I do. Period. Having said that and with great respect for you and your experience I will offer this response and clarification to my understanding of the matter.

The conclusion reached by the deep-stop study, as an example, was very limited. They basically said that deep stops were not inherently safer. They were not able nor did they attempt to prove that they were more dangerous. That would have required a longer and more lengthy study. They were not able nor did they attempt to show what gradient factors should be used to create safer profiles. They are not able to provide conclusive findings on the safest approach to decompressing from helium loading in tissues. Each of these separate issues would require multiple studies that are more complex, risky and costly than the deep stop study.

My understanding, while quite limited, is that the DCS associated with these tests could be resolved with treatment but I think the days of substantial and wide ranging human testing with this level of risk has fallen out of favor and is mostly limited to the pharmaceutical trials that pay poor people to take drugs and report their side effects.

I am not saying that we don't know stuff from testing that has been done by NEDU and others or that we are totally in the dark. I'm just saying that there are limits to our ability to state with certainty where the safe line is for an individual or what gradient factor is the correct one to use for a defined associated risk tolerance. The lines are fuzzy and gaining a more thorough understanding through scientific testing is a huge challenge.

@Dr Simon Mitchell Please correct me if I misunderstand these issues and perhaps fill in the substantial blanks in my perception of the challenges faced by the deco science world.

The Navy has tested a lot more decompression strategies than just that deep stops study.

But yes I overall agree that our knowledge will be limited by ethics and funding. My bigger point is that there is data from controlled man tests out there for the interested reader.

 

[Gareth J]

Your data set in #146 doesn't appear to represent what recreational divers do. It sounds like commercial divers.

Remember, dive tables where produced for the Navy's of this world and commercial company's (Casson's disease). Recreational tables are products of the commercial data, and a late addition.

Caisson's Disease as a known decompression illness predates diving DCI I think. From mining (1840's). Mining and the Construction industry where the first to address it. The Building of the Brooklyn Bridge (1873) and the Hudson Tunnel (1890).

John Scott Haldane (1908), was one of the early pioneers of decompression tables working for the Admiralty (Royal Navy). The first to develop tissue compartments I believe.

Professor Buhlmann (1960's), who we have been discussing, used Haldane's research, among others to develop his tables. Which he put in the public domain, i.e. no copyright. Which is why they are used extensively by the recreational dive computer manufacturers, or at least derivatives of the Buhlmann tables..

A lot of the research data is owned by commercial companies, like Comex. Its commercially valuable, so not in the public domain.

 

[taimen]

My bigger point is that there is data from controlled man tests out there for the interested reader.

This is why I asked the question about relative risk inrease when going from high to medium or low conservatism.

 

[Storker]

Who would be willing to stake their reputation of guidelines for diving that were developed by data that is self reported? The unreported DCI incidents would be left out and all the dives that never came close to the limits would be included.

I'm not talking about self-reporting the way it seems that you're thinking about.

For regulated diving activity, like commercial diving or military diving, it's fairly easy to impose a regime where every dive is logged, with depth, bottom time and DCI status. Our commercial diving industry is, as far as I know and can make out from the quote I gave upthread, obliged to keep proper records. That's a consequence of the wild and hazardous practices they had during the early stages of the oil boom here, leading to a number of injuries and fatalities which would be completely unacceptable today.

So, not "self-reporting", but proper logs of every dive. And again, I'd be surprised if the USN doesn't keep logs like that.