Deep Stops Increases DCS

[Jax]

NO BIG DEAL

's Okay, I'll take your opinion, too!

It's all data, to be tempered with experience and education . . .

 

[LiteHedded]

my opinion is that 30 minutes less on an algorithm that seems to be bending people (subjectively) is something that should be approached with caution.

also that on a 20 minute bottom time, things will mostly look the same with all of them. and you can mostly get away with anything. but once you get into real exposures the nonsense with vpm becomes very apparent

 

[PfcAJ]

I see an issue in the production of "numbers" from a computer program. Let me try a simpler analogy:

The temperature is forecast to go from 95 to 100 over a two hour period. What is the probability of a heat injury, and how severe?

You simply cannot take that at face value, because there are so many more factors.

Conditions - glaring sun, or in shade, windy, breezy, still, dry heat, moist heat?

Person - skinny, fat, hydrated, not hydrated, fit, not fit, young, middle-aged, older, wearing a hat, not wearing a hat, clothing?

Activity - digging a ditch, lifting weight, lying down, barbecue, running, walking?

Health - organs, pulmonary, heart, etc.


Therefore, my statement that a SWAG based on input is what deco is. No computer, no planner *gives* safety - just some numbers that are sometimes based on empirical data that someone else manipulated into a model . . . but the model is "good" over a given range.

I don't think you're understanding what I'm driving at. I've explained this a few times now in this very thread, and I guess I'll have to do it again.

AJ, does your emphasis on probabilistic analysis make you a fan of the US Navy Medical Research Institute's (NMRI's) Maximum Likelihood Statistical Method model, then? The NMRI's tables were considerably more conservative than the Navy tables that existed at the time, had a 2.3% incidence of DCI, and were met by considerable resistance by the Navy divers. [Deco for Divers, 2nd Ed]

It might. I haven't dived that particular model. Flat risk, especially user adjustable risk, is what I'd really like. At the moment, its not an option though, at least not for the general diving public (myself included). And to be clear, when I say "risk" I want a number with it. Not some arbitrary 'high' or 'low' thing.

Now to try and reiterate what I've been driving at for a while now:
For a dive at "x" feet for "y" minutes, a deco algorithm (VPM and Buhlmann) will produce a schedule with "z" risk.
If you keep "x" the same, but increase "y", "z" goes up. To me, thats bad. I wanna keep "z" the same, and ideally I'd like to be able to manipulate "z" by doing longer or shorter deco times.

Knowing that "z" goes up at "y" increases with BOTH algorithms, why on earth would someone choose a shorter deco time if you're trying to keep "z" constant? VPM+3 reliably gives shorter decompression times, less time on deco gases, and less time on oxygen than 40/70. All you end up with is a higher "z". And again, to me, that's bad.



This to read:
http://archive.rubicon-foundation.o...33/2009_UHMS_Risk_poster_final.pdf?sequence=1
[abstract] DECOMPRESSION RISK ANALYSIS COMPARING OXYGEN AND 50% NITROX DECOMPRESSION STOPS.
[abstract] THE EFFECT OF FINAL OXYGEN DECOMPRESSION STOP DEPTH ON DCS RISK: 20 FSW VS. 10 FSW.
[abstract] DECOMPRESSION RISK ANALYSIS COMPARING OXYGEN AND 50% NITROX DECOMPRESSION STOPS.
[abstract] DECOMPRESSION RISK EVALUATION OF COMMERCIALLY AVAILABLE DESKTOP DECOMPRESSION ALGORITHMS
[abstract]DECOMPRESSION RISK EVALUATION FOR TRIMIX DIVES DERIVED FROM COMMERCIALLY AVAILABLE DESKTOP DECOMPRESSION ALGORITHMS

 

[Jax]

It might. I haven't dived that particular model. Flat risk, especially user adjustable risk, is what I'd really like. At the moment, its not an option though, at least not for the general diving public (myself included). And to be clear, when I say "risk" I want a number with it. Not some arbitrary 'high' or 'low' thing.

Now to try and reiterate what I've been driving at for a while now:
For a dive at "x" feet for "y" minutes, a deco algorithm (VPM and Buhlmann) will produce a schedule with "z" risk.
If you keep "x" the same, but increase "y", "z" goes up. To me, thats bad. I wanna keep "z" the same, and ideally I'd like to be able to manipulate "z" be doing longer or shorter deco times.

Thank you, I've read some of those and look forward to the others.

From a pure risk analysis standpoint - I am NOT any kind of deco guru - I believe what you are asking for is not in the available realm of deco software as it is right now.

However, if one could collect all the data on dives and the actual DCI incidents, that would be a lovely project for a graduate software engineer to feed into an Artificial Intelligence engine. I do not, however, believe there will ever be a pure "Z" algorithm due to the many individual and personal factors that affect a diver.

 

[PfcAJ]

Thank you, I've read some of those and look forward to the others.

From a pure risk analysis standpoint - I am NOT any kind of deco guru - I believe what you are asking for is not in the available realm of deco software as it is right now.

However, if one could collect all the data on dives and the actual DCI incidents, that would be a lovely project for a graduate software engineer to feed into an Artificial Intelligence engine. I do not, however, believe there will ever be a pure "Z" algorithm due to the many individual and personal factors that affect a diver.

It does exist. Its just not commercially available. Calibrated against controlled dives. User adjustable risk. The whole deal.

 

[shoredivr]

It does exist. Its just not commercially available. Calibrated against controlled dives. User adjustable risk. The whole deal.

Man, hope that changes soon.

 

[PfcAJ]

Man, hope that changes soon.

Me too! They could sell DOZENS!!

 

[rjack321]

:lolabove:
C'mon - there are so many factors that go into all that! Would YOU make that decisions based on some numbers in a dive planner?

What are the diving conditions? Warm, icy, dark, current, stressful, wreck, working? So many factors beyond just the condition.

I do the O2 time. If its too cold or current swept to do the O2 time I modify the plan to do the deco necessary or shorten the bottom time, or skip the dive.

I have been bent before skimming off the shallow stops (e.g. with straight RD or VPM2). For at least the past 7 years I've been adding O2 time to ratio deco, or bumping up my VPM to +4. Which is becoming more and more the norm as many diver's GF highs keep going down. They used to be 85 and now more and more are 80 or 75 or less. All of which is increasing O2 time. Taking off 20mins of O2 time is like bumping up the GF high to 95, maybe more. No bueno.

I'm sure some of this thread's participants consider it my fault, but I don't get bent with the longer shallow time. So for me this means VPM4 to 5 or a GF high of ~75.

 

[Remy B.]

What kind of software or calculations use the Commercial diver, as they increase depth and time and they are put in a chamber and for what I heard they get out quickier than what tec diver do out of the water, this is what I heard, I'm not saying it is true what I heard.

Taking in account that the tec-diver does a perfect ascent, no fluctuation in depth while on stops ( what a chamber does of keeping pressure perfect for a period of time )

I know we are not comparing apples to apples, as a chamber has controllet heat and there is no task load, all this keeping exotic gasses out just O2 as deco gas.

Are they using something that much different of what GF and VPM in our DC. ???

 

[kensuf]

AJ & Brian, I love you guys.