Redistribution of decompression stops to optimise integral supersaturation

[LFMarm]

This looks like a great analysis. How do we interpret these results? Why is ISS reduction beneficial vs surfGF? Are there practical learnings that we can apply?

 

[JMarc]

Limiting GF limits the instantaneous decompression stress, minimizing the ISS minimizes the decompression stress for the whole exit process. Both aspects are probably needed.

 

[inquis]

I believe that ISS is part of the pDCS calculation for [ETA: some of] the Navy's probabilistic algorithms. Researchers have also stated that ISS has comparative value for similar profiles.

 

[JMarc]

I believe that ISS is part of the pDCS calculation for the Navy's probabilistic algorithms.

Interesting. Do you have a source where to get more information about that aspect?

 

[ofg-1]

Are there practical learnings that we can apply?

Yes. You can learn that people on SB love solving math problems and quibbling over decompression theory. As an engineer, I also enjoy math, however, this is mostly an exercise in mathematical masturbation.

Is anybody aware of any proper research on the optimal depth for the last stop?

David.

David, that depends on what you call "proper" research. If you mean basing air deco on young physically fit men, go back and look through the Comex papers from the 1970's when they were developing their own tables.

If you are looking for something that has a baseline that reflects who is actually diving today, men and women, 16-70plus, from serious athletes to couch potatoes, people that dive every week or 3 times a year, from people that can figure out these algorithms, to those that just shell out $1200 for a new Shearwater and jump in, people who are healthy to those being treated for chronic cyclops of the blowhole, then I am totally unaware of any "proper" research. I would love to see it also.

Your optimal stop depth changes depending on environmental conditions.. If you have a flat calm day with no current, or 4-5 foot rollers with a knot and a half surface current. Your stress levels at the surface are different if you can calmly swim to a dive platform, take off your fins, and climb up, OR, if the Gulfstream is dragging your ass towards Newfoundland and the dive platform is trying to bash your teeth out at the same time the captain is turning the props.

At best, these algorithms are mathematical simulations of metabolic processes that are not necessarily constant from person to person. If you can get to a confidence interval of say 90- 95%, I think you are doing real good.

Finally, I have watched these discussions, here and elsewhere, for the last 35 or so years to the point that I think we have fogged up the overall purpose of decompression. It is not to minimize the amount of deco you do, it is to avoid getting DCS. Between different GF,s, conservatism settings, deep stops, shallow stops, 80% O2, 100% O2, air breaks, ratios, doppler studies, microbubbles, the overall purpose should be the same.

I have been treated for DCS 3 times since 1973, trust me when I say it is far better to spend an extra 20 minutes decompressing than 5 hours in a 54" chamber with no bunk, no restroom other than a bucket, and a pissed off retired Master Chief raggin on you the entire time. Remember, if the Chief don't sleep, no one does.

@David Carron, Your spreadsheet is good, If you wish to improve it, go in and come up with a function that will change your units to something that actually shows up on a dive computer. Meters and tenths, minutes. Figure out how many significant digits matter. You may get very different results.

 

[inquis]

Do you have a source where to get more information about that aspect?

Nothing detailed, unfortunately. On one of the threads devolving into deep-stop bickering on CCRExplorers, Dr. David Doolette is quoted as saying:

The U. S. Navy has some very successful probabilistic models in which the risk of decompression sickness is a function of the time integral supersaturation (ISS) in all compartments.

The NEDU deep stop study (NEDU TR 2011-06) specifically mentions the NMRI98 (gas-centric) and BVM(3) (bubble-centric) algorithms, but the above quote suggests there may be others as well.

 

[David Carron]

@David Carron, Your spreadsheet is good, If you wish to improve it, go in and come up with a function that will change your units to something that actually shows up on a dive computer. Meters and tenths, minutes. Figure out how many significant digits matter. You may get very different results.

The data file really just contains the raw numbers in as lossless and neutral a format as possible; I'm sure whichever spreadsheet application you're using can be convinced to convert units and round values appropriately for your particular display cases.