Open source decompression tables?

nigelh

This is good. This means divers are being careful and showing good technique.
My concern with talking to chamber operators is that they only see bent divers not the thousands who do similar dives and have no problems. Also in the UK I am slightly concerned that the funding mechanisms for chambers means that bent divers are good. If you recompress somebody they need to go in the books as a DCI. Now I'm not complaining as we have a wonderful system here, we don't need to look for somebody's insurance cards before calling the coastguard, but a friend who was asymptomatic was recompressed because of his profile. Was he bent?

I always remember the comment from a police diver who had recovered bodies of divers who believed that failure to drop weights was the primary error because all the divers he recovered still had weights. It was a self fulfilling argument because any diver who dumped their weights would be recovered, alive or dead, at the surface and he would never be involved. It is so easy for you view point to skew the facts.

Sadly the aphorism "Bends don't read tables" is always true. DCI is something we can guard against but while we continue to dive we will be at risk.

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nigelh

rossh

A very short summary of VPM history....The VPM model and revisions are clear and straight forward.

The original is VPM (now called A): this is the original model by Yount, Hoffman, adapted for use by Maiken, Baker and others. This is what the Nautilus program uses too. VPM original has some design errors in the way it is coded, and the VPM-B revision corrects these problems.

VPM-B is the current model in widespread use today.

VPM-B/E is my extended version that gives deep divers an overlapped bubble / Buhlmann style plan that they often want to use. The VR3 attempts to emulate this version.

More detailed information on my site below (history and model references)

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Mdemon

Apologies, and thanks for the correction.

A question if I may? If Comex released all their data, how useful do you think it would be - I'm particularly thinking of the deeper stuff?

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"small minds talk about people, Average Minds Talk About Events, GREAT MINDS TALK ABOUT IDEAS!"

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lizardland

Depends. Sat diving decompression is done completely differently from open-water, independant, fairly unsupported tech diving. The ascent protocols are very slow, medical assistance is onsite and available immediately (well, limited in the time it takes to blow a med down to chamber pressure), deco is done in relative comfort (if the inside of a sat spread could be called comfort), more significantly dry (there is a big difference in deco & o2 physiology between wet & dry), decos and dives use very low ppO2s and deco also tends to be done on heliox all the way. Also sat divers on deco never face a bail out situation where less than optimal gases must be used.

Deep bounce diving in commercial terms is very uneconomical compared to ROV or sat operations so most operators shy away from it. How useful any bounce diving data collected is questionable.

Comex heliox tables were available, they wrote the French equivalent of the HSE's approved deco schedules rather than having a government table forced on them.

As Ross more politely puts it, VPM-A was shite. I was bent twice diving VPM-A profiles.

One of Bruce Wienke's big gripes on the deco list with regard to VPM was that it was tested on gel samples rather than manned diving.

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ryand

Newton's 3 laws of motion were made up too. They turned out to be a wholly inadequate way to describe how the world really works when you get to extremes of mass and velocity. The theory of gravity that NASA uses to put satellites in orbit around distant planets is known to be at best an approximation, and at worst to be totally incompatible with other tested theories of how the universe works. Those planets are right where NASA thinks they'll be, and those satellites happily orbit right on schedule. The "errors" produced by the MADE UP theories have been reduced to the point where for most real world applications they have no noticable effect.

The issue isn't "is the theory MADE UP"; the issue is "is the theory a close enough match to what really happens in the real world that it can be used safely, repeteadly, and under the wide range of conditions tech/rec divers are likely to experience"; and a good follow on would be "and how to know when the theory DOESN'T provide these factors".

Rebreather divers are on the cutting edge of the theories. They're staying down longer, breathing fluctuating gas mixes, and pushing PP02 levels. Everyone reading this message who uses a rebreather is conducting an unstructured and uncontrolled decompression experiment on themselves every time they dive.

The really unfortunate thing is that all the data is lost; or at least compartmentalized into indidual dive logs. Since the vast majority of eCCR systems use dive computers to regulate the gas mixes, and almost all those computers have a download function, it would be easy, and in everyone's best interest to create a repository of dive profile information, along with diver evaluations as to OxTox / DCS experiences. EVERY DIVE should be logged; not just the bad ones.

Then we'd actually have some statistically valid data points to work from, as opposed to a whole lot of opinion, anecdotes, and untested theory. It surely would make the idea of diving CCR a lot more palatable than it is now.

Instead, what I see on this board, and other communities of divers, is that every time there's an accident, someone says "let's not discuss it because of the pain caused to the family", or some similar obfuscation. And that's just the accidents we hear about where someone dies. Who knows how many non-lethal OxTox hits or DCS hits are happening? There's also (certainly in my mind) the implication that CCR manufacturers don't want detailed accident information distributed because of the concern that it will generate bad publicity and kill sales. (And I think there's a parallel issue of divers being embaressed if they get bent or OxTox because they're worried people will think they're unsafe divers, or stupid - so there's a lot of non-disclosure on an individual level too.)

In the end, if improvements to the deco/OxTox systems happen, even if they remain MADE UP, movement closer to an ideal that can keep a diver's chances of DCS hits, OxTox hits, etc. lower than they are now, and a better understanding of how risk factors affect individual diver profiles so that divers can make informed decisions about their diving, would be a GOOD THING for everyone. Throwing up hands and disclaiming any ability to work the problem helps nobody and is ultimately costing lives.

Ryan

abowie

Ryan the theory isn't made up. Rather it is the result of scientific investigation, but still far from a complete understanding.

The algorithms we all use are an attempt to make a bridge across the gap between what theory suggests should be happening and what the empirical evidence shows. You can describe this in a lot of ways but "made up" is as accurate as any other.

Some of the algorithms in use are proprietary and some are freely available. My point in my original post is that we currently do not have either an accurate understanding of tissue inert gas physiology or an effective way of measuring it. Until we do fiddling numbers in an algorithm isn't going to remove the intangibles (call them luck if you will) that result in people sometimes getting DCI and sometimes not.

It is the nature of humans to want to control their environment. For those of us who involve ourselves in potentially risky pursuits like deep mixed gas decompression diving it is only natural to want to minimise those risks to ourselves. Believing that by altering our deco algorithm to better suit ourself makes us feel more in control, but it is unlikely to actually have a meaningful positive effect on our outcome.

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Andrew Bowie

Rebreather-friendly Buddy

Mdemon

That's very much where I was coming from.

What we are doing is different. If data from different, but well-documented, diving could be made available then so much the better, e.g. Comex.

However, I think you make a better point about our data going to waste. Maybe the "Open Source" element would be better aimed at collecting dive data from rebreather divers, rather like DAN does? That data, made available to all the software manufacturers would at least offer some feedback where there is currently, compared with the actual dives done each year, comparatively little.

I think this discussion is very appropriate, given that today we see Cedric's account of two "firsts" (should that be three?), pushing machine and deco routines to the limits.

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www.southwestmafia.com

"small minds talk about people, Average Minds Talk About Events, GREAT MINDS TALK ABOUT IDEAS!"

The WRONG Attitude will get you killed.

"Once the agenda-monkeys and perfect-worlders have moved on, perhaps we can do some diving?"