I finally get it (or, gauges and why they make sense)

[limeyx]

Any standard you want. The point is not having one standard for everyone, it's that for someone who doesn't have thousands of dives to know what they can personally get away with, knowing where you stand in relation to some validated model is a good idea. Again, the fact that one person can get away with a given profile doesn't mean that anyone can.

Well, I dont think I can be of any more help to you.
Good luck figuring it out, and make sure you come back and report the results of your findings once you work it all out.

Safe diving.

Nick

 

[ucfdiver]

I wonder if there is data on which standard model is correlated with the lowest incidence of DCS. Is anyone aware of such a study? If not, Ill have to root around in the rubicon.

Real world dives rarely intentionally follow DCS models exactly, most implement personal preference (based off of experience, or in some case, an instructors shared conclusions). Of those who try to hit everything exact, very few can do it, with currents, odd cave profiles, or whatever. Then let's add being cold, dehydrated, lack of sleep, physical fitness, exertion during/after dive, etc and these data models just aren't consistent.

 

[ScubaFeenD]

Real world dives rarely intentionally follow DCS models exactly, most implement personal preference (based off of experience, or in some case, an instructors shared conclusions).

This is something that would make testing more difficult. I would think that they must be based on some standard model though. Im not really experienced enough to know beyond VPM and such, but you would probably no more.

Of those who try to hit everything exact, very few can do it, with currents, odd cave profiles, or whatever. Then let's add being cold, dehydrated, lack of sleep, physical fitness, exertion during/after dive, etc and these data models just aren't consistent.

This would certainly make it more difficult to determine super strong correlations, but I just wonder what you would see if you compared groups using the different standard models. More of a thought experiment i suppose.

 

[Rainer]

I wonder if there is data on which standard model is correlated with the lowest incidence of DCS.

I know of one model that has a perfect (r=1) correlation...

 

[gsk3]

* Well, actually, they're designed around something >90th percentile of physiology.

Where did you get this from? Wait you made it up because Nick's statements about SIs seem so aggressive to you...

(1) There is unmeasurable variation in individual susceptibility to DCI
(2) The deco algorithms are designed to minimize population DCI risk. I say population risk because the individual susceptibility is unmeasurable (from (1) ), and therefore cannot be built into the models.
(3) Minimizing population DCI risk while using the average susceptibility to DCI as a parameter your implicit model likely doesn't get you to the true minimum. To truly minimize risk, you'd need to design the algorithm around the absolute most susceptible person's tolerance. But we don't truly minimize risk, we balance the risk with the harm of over-compensating for that risk in the form of extra time. So you pick a number somewhere in the high 90's and go with it.

But thanks for assuming I make very specific statistical statements for no reason. It turns out that my career relies on my not doing so. Therefore I'm quite cautious about such statements.

I understand being upset that folks without proper deco training want to know deco theory--because there's a risk they will do things while thinking they know more than they do. But this is something that Fundies explicitly says should be done, and even (off the record) provides specific advice how to do. So even at our level of training, we should be seeking to understand the MDL guidelines. I compared them against tables, and have some thoughts for doing a more extensive analysis to understand them in the future. If I ever get around to it, I will post the results.

As for the statements about SIs seeming to be aggressive to me, I thought we agreed earlier in this thread that "aggressive" could only be judged relative to a particular standard. One standard might be, "What Nick has done and not had a problem with." I'm fine with that statement for Nick, but as I pointed out, his physiology may be different than what we would want to base our ideal method on. It's the classic issue of the Navy tables being studied in 18yo very fit divers, which makes it riskier for out-of-shape 60yo divers than is necessary. Another standard is to pick a table and see how they compare. Nick suggested that in days of heavy diving he had not found surface intervals to be necessary, even while doing something at or faster than the standard MDL ascent. The tables I consulted suggest that's very aggressive. It works for Nick, and on the basis of age and fitness I'm willing to say it would work for me, but that doesn't mean it would work for any random stranger reading this page. Relative to the PADI RDP and the rule of 130, Nick's protocol is aggressive.

 

[TSandM]

All of the models currently in use produce DCS rates that are acceptably low -- meaning, the vast majority of dives are executed without DCS. It's VERY difficult to track the success rate of a model, once it is in general use. This is part of the reason it's so hard to say definitively that bubble models are "better" that pure dissolved gas (Buhlmann) models. Data on DCS cases aren't centralized, with the exception of the cases that DAN gets involved with.

I think it is probably reasonable to compare any strategy you are going to use to any one of the commonly utilized algorithms, but be aware that, whichever one you choose, you may find as much variation between that one and other generally used tables/computers as you find between it and whatever strategy you are using. I've told the story before of a dive done by five divers, all of whom had been diving together all day, where four people had no deco obligation (as determined by three different models) and the last person had 20 minutes of deco. So if I was the person using RD, was I adequately conservative (as it would seem, comparing it with two of the three other systems) or horribly aggressive (as compared with Peter's Suunto)?

 

[limeyx]

Nick suggested that in days of heavy diving he had not found surface intervals to be necessary, even while doing something at or faster than the standard MDL ascent. The tables I consulted suggest that's very aggressive. It works for Nick, and on the basis of age and fitness I'm willing to say it would work for me, but that doesn't mean it would work for any random stranger reading this page. Relative to the PADI RDP and the rule of 130, Nick's protocol is aggressive.

Heh, either you (or I) need to be more careful in our statements.
I said (or intended to) that *90 min* SI's are not necessary, and that realistically having an SI less than 60 on boat dives here was not usually going to happen.

That said, I have jumped in right after a dive to 100 or 120 feet, and helped free the boat anchor with virtually no SI, and no huge consideration for extending our stops because of it, not that I especially recommend doing so.

I dont use a dive computer but I highly doubt if you plotted my recreational protocols, the Multi-level RDP and/or rule of 130 would say I am in any way aggressive for open water dives.

Long cave dives(probably), and mandatory decompression dives are highly subject too.

EDIT: 1/2 the confusion was a confusing statement by me, the other 1/2 (the SI thing) I think you

I said something like "sometimes on dive #2 and #3 we do a 4-6 min ascent sometimes not"

What I *meant* was sometimes we do a 4-6 min ascent from 20 to the surface on #2 and #3.
Of course, we still do the standard "min deco" of 1 min stops from 1/2 depth.
That was a confusing statement by me.

 

[gsk3]

Heh, either you (or I) need to be more careful in our statements.
I said (or intended to) that *90 min* SI's are not necessary, and that realistically having an SI less than 60 on boat dives here was not usually going to happen.

That said, I have jumped in right after a dive to 100 or 120 feet, and helped free the boat anchor with virtually no SI, and no huge consideration for extending our stops because of it, not that I especially recommend doing so.

I dont use a dive computer but I highly doubt if you plotted my recreational protocols, the Multi-level RDP and/or rule of 130 would say I am in any way aggressive for open water dives.

Long cave dives(probably), and mandatory decompression dives are highly subject too.

EDIT: 1/2 the confusion was a confusing statement by me, the other 1/2 (the SI thing) I think you

I said something like "sometimes on dive #2 and #3 we do a 4-6 min ascent sometimes not"

What I *meant* was sometimes we do a 4-6 min ascent from 20 to the surface on #2 and #3.
Of course, we still do the standard "min deco" of 1 min stops from 1/2 depth.
That was a confusing statement by me.

Ah, that makes more sense. So it sounds like much of the time you're doing something approximating what "the rule" says to do: double the shallow stops. The other times you're relying on your knowledge of your own body's reaction. "Aggressive" moniker withdrawn ;-)

 

[rakpix]

this thread makes me very glad i NEVER actually purchased that vyper air / vytec ds i was pining for a few months ago. if i'm going to go the gue/utd route, it'd just be in gauge mode anyway so i'll keep diving my trusty timex helix for now!