So you want to purchase a Decompression Computer...

[Dr. Lecter]

Would be hard, don't you think? Something less than 1% of divers are taught that method (I'm guessing).

Shouldn't be hard at all. I'm not asking for a comprehensive analysis, just an aggregation of data I'm guessing they'd collect if they could for a chamber ride (i.e., what was your profile? how many dives had you done that day and/or in the preceding days? what computer were you on? what were its settings?). Analysis would be up to the reviewer of the data. If DAN treated 1000 DCS cases last year, and 700 of them had no model data while the rest were evenly split between ratio deco (150) and other models (50 VPM, 40 GF, 60 RGBM)...eh. If there's model data for 900 of their 1000 DCS cases, maybe I care a bit more about what the breakdown is (assuming it's not a roughly equal split amongst models).

Maybe the data collection is more focused on exposure and duration for treatment than understanding what model (if any) led to the exposure...but the above anecdote indicates they have some idea of what models are in use when divers present with DCS.

 

[DCBC]

Maybe the data collection is more focused on exposure and duration for treatment than understanding what model (if any) led to the exposure...but the above anecdote indicates they have some idea of what models are in use when divers present with DCS.

I agree. It would seem that not enough is being done when the opportunity presents itself. One can wonder why?

The Wienke Reduced Gradient Bubble Model (RGBM) and the Yount Variable Permeability Model (VPM) both attempt to predict when bubbles form and then calculate decompressions to prevent bubble formation before surfacing. NAUI technical divers have used the Wienke RGBM model quite extensively with no recorded incidence of DCS.

This data and DAN research were discussed in October 2003 at the NAUI Decompression Workshop in Florida . As a result, NAUI has suggested that a deep stop might well be incorporated in recreational diving by taking a one-minute stop at half the depth and followed by a two-minute safety stop at the 15- to 20-foor level instead of the three minutes currently recommended. This is an example of what organizations can do for the betterment of Divers. Too bad the Decompression Computer manufacturers don't seem to be on-board...

What seems to work the best either isn't known or there is a reluctance to integrate a "best practice algorithm" into the computers that are being sold. As no model is perfect, the manufacturers can take a view that one algorithm is as good as another. The fact that Decompression Computers are not required to be validated (regardless of the algorithm used) adds to the problem.

 

[Dr. Lecter]

If they don't see any instant medical utility presented by knowledge of the model, as opposed to the raw exposure data, I can see it being a waste of time and effort for them. OTHO, it might be medically helpful in the broader sense that divers would have more info from which to make model decisions in the future and thus hopefully make better decisions.

Still, even if they only collected, aggregated, and released the raw data itself...one should be able to determine what model (if any) was being used on a given dive with relative accuracy.

Your point about (what I assume is a full implementation of) RGBM makes me wish it was an option on my Shearwaters and/or that I didn't hate the hose on my Cobalt so much.

 

[rhwestfall]

Yet, we constantly see complaints about computers beeing too conservative....

 

[Dr. Lecter]

And maybe 99.8% of the time, that's true. But damn, those other 0.2% sure can hurt.

 

[waterpirate]

In the end I think that in the grand experiment the concept of " dive,rinse,repeat if it does not hurt " is the best model. It has been my observation that divers who experiance no visible symptoms tend to dial it back untill it hurts too much, or go to far and take a chamber ride. The occurance of a so called un deserved hit must also be looked at.

I think far to little time is spent in the entry level courses discusing the real world of deco. What I see is a cavalier attitude, and you will die attitude, with no middle ground. The real focus should be " slow and easy with good technique " vs. any of the above.

The obvious is: good physical conditioning, know and understand your body and your limits, listen to your body.
Eric

 

[scubadada]

Agree entirely, a concise staterment would be very valuable. Any useful information from PDE would also be invaluable. Any significant differnces in the risk of DCS by decompression algorithm would be a tremendous advance. I am not optimistic.

The rate of DCS is so low in PDE that the power to detect differences in various decompression algorithms would be very low

 

[DCBC]

What I see is a cavalier attitude, and you will die attitude, with no middle ground. The real focus should be " slow and easy with good technique " vs. any of the above. The obvious is: good physical conditioning, know and understand your body and your limits, listen to your body.

Unfortunately, it seems that the majority of Divers don't seem to appreciate how easy it is to push the limits of Decompression too far. I was just discussing DCS on another thread and mentioned a Type I hit that I experienced many years ago. At the time, I was the Diving Operations Officer (Navy) at DCIEM. I was a young fit Navy Diver undertaking testing in the Chamber under the Direction of two very experienced Hyperbaric Physicians. I left for the day to later develop worsening symptoms that required recompression. Fortunately, no permanent damage was done.

If a hit can happen to a fit Navy Diver under the guidance of Hyperbaric Physicians in controlled conditions, how can unfit, overweight, civilian Divers think that they can not use conservation and dive safely? If you are fit and follow the USN Tables precisely, you will statistically experience DCS. As I mentioned, no table is totally safe for all divers under all conditions. Pushing the tables, ascending without a safety stop and coming to the surface at a rate faster than recommended is a recipe for disaster.

People have told me while recreational/technical diving that I dive like an old lady. I normally just smile, knowing that I've made a living in military and commercial diving (including saturation) to retirement by not breaking the rules and adding conservation. The saying once again rings in my head... "There are old Divers and bold Divers, but no old bold Divers."

Twenty percent of this survey doesn't add conservation. That says something about how people look at decompression today...

 

[mathauck0814]

Twenty percent of this survey doesn't add conservation. That says something about how people look at decompression today...

I wonder how many people don't understand that they really are adding conservatism by virtue of the default settings on their device. Many computers are inherently conservative as their algorithm is configured in that manner. Similarly, a Shearwater will come with the gradient factors at 30/85 which is unto itself a relative degree of conservatism. If folks are "not adding conservatism" by simply following their computers' direction, they're ignorant to it but they are probably keeping it between the lines.

Whether or not it's acceptable for folks to not understand what their computer is doing and how the various settings impact their physical well being is another category, but I suspect that the vast majority of divers are not pulling out the USN tables and diving right up to the edge of the NDL limits.

 

[waterpirate]

Divers are not useing the tables right to the limit, but I see them dialing back the settings on their computers, both desk and in water to shorten the hang. It is like a crucible of nothing happened yesterday so today I will dial it back. I find the hang very relaxing and am not in a rush to get out. So if I spend another 10 minutes at 10fsw on deco gas so what?

Again I will re emphasise that this all goes sideways for divers at the first level of training. They are not taught enough about the big experiment to make good choices about deco going forward. A freind of mine took a hit 4 years ago. Took a chamber ride and all is well. Over beer later we learned that he had been diving his puter set on 0. a very aggressive profile to say the least. He had gotten away with it for several years prior to the hit. It just reinforces the concept of it could happen to anybody on any given Sunday.
Eric