Understanding deco theory

jsevland · 17th September 2007, 10:42

Hi all

I have been making a mess of the Buhlmann algorithm over the week-end.
Initally, I only want a rough implementation, to make my Evo-sim "look better".

http://www.rebreatherworld.com/surfa...tml#post130806

Looks like I'm able to add dive segments and update the compartments, when I take snapshots - comparing it to some of the examples on the net.

But no-deco-time is still spitting out garbage ;-)
... not on my sharpest last night - after a severe party on saturday ;-)

Anyway, the little math I did grasp, has long gone - and if any of you have an old Java implementation of Buhlmann - sitting collecting dust - I sure could use some help.

My goal is not to make a dive planner (or even model deco-dives), I just want a simple Evo-sim to play with - until I get to play with the real thing.

Yours
jsevland

Woz · 17th September 2007, 11:00

Mark Powell, a tech instructor here in the UK is writing a book "Decompression Theory and Physiology". I don't know how close he is to publishing it but it gives an excellent insight into the current position regarding deco theory and will save you all the trouble of wading through unintelligible academic papers. You can contact Mark through his website, Dive-Tech: TDI, PSAI, BSAC and ITDA Nitrox, trimix and technical diver training courses with instructor Mark Powell

Hope that helps.

Simon Mitchell · 19th September 2007, 22:02

Quote: (Originally Posted by ScubaDadMiami)

For example, in RGBM for the Layperson (Sources, Fourth Quarter 2004), Weinke lists a six year trial consisting of 32,000 open circuit mixed gas dives down to as deep as 350 fsw without incident; over 300,000 dives using decometers without incident (though this would be no-stop and multilevel dives), and others.

Hmmmm, I'll preface this by saying that I am pro RGBM and other bubble models, and Bruce is a respected colleague whom I am working closely with at present to organise a decompression and deep stops workshop at the UHMS Meeting next year. Having said that, I have serious reservations about the appropriateness of referring to the above data as having come from a "trial". This would imply institution of a formal data collection system to accurately record the number and nature of dives and their outcome. I am virtually certain this has not been done, and I'm equally certain that Bruce would have published the data in a proper scientific journal if he had. I suspect that these numbers are estimates which may or may not be correct.

The most suspect part of the quote is the zero incidence of problems. I'm just not sure how anyone would know this unless the divers were properly followed. 300,000 dives without incident is highly unlikely, even allowing for the fact that many of the dives are no stop dives and well within the limits prescribed by the RGBM. And therein lies another weakness of the claims: a table is not being tested as such unless the dives performed are to its limits. Saying that you are "diving RGBM" 0r any other algorithm (because you own it or its on your computer) but then performing an uneventful dive well inside the prescribed limits demonstrates absolutely nothing in relation to the validity of the algorithm.

Regarding Andy's report of USN testing, as stated previously, I would be interested in seeing the data. But depending on the type of dives performed 3000 dives without incident would not necessarily be unusual. The incidence of DCI in recreational diving (all comers using all tables / computers) is only 1:10,000 (but that includes many dives that are not to the limit of the table or computer used).

This thread is a good advertisement for the decompression and deep stops workshop (organised by Bruce, Peter Bennett and myself) to be held at the UHMS meeting in Salt Lake City in mid 2008. Similarly for the DAN Technical Diving Workshop being held at Durham NC in late January 2008. Anyone who finds the stuff discussed on these forums interesting would be mad to miss either of these events!

Warm regards,

Simon M

***ScubaDadMiami*** · 20th September 2007, 00:36

For those of us that can't make it, I hope that the proceedings will be available.

Gene_Hobbs · 20th September 2007, 01:18

Quote: (Originally Posted by Simon Mitchell)

This thread is a good advertisement for the decompression and deep stops workshop (organised by Bruce, Peter Bennett and myself) to be held at the UHMS meeting in Salt Lake City in mid 2008. Similarly for the DAN Technical Diving Workshop being held at Durham NC in late January 2008. Anyone who finds the stuff discussed on these forums interesting would be mad to miss either of these events!

As a reminder, the early registration deadline for the DAN Technical Conference is the last day of the month. After that, the price goes up by $US100.00.

The UHMS "Decompression and the Deep Stop" pre-course will be offered on June 24-25, 2008.

silent running · 20th September 2007, 07:54

Quote: (Originally Posted by Simon Mitchell)

The most suspect part of the quote is the zero incidence of problems. I'm just not sure how anyone would know this unless the divers were properly followed. 300,000 dives without incident is highly unlikely, even allowing for the fact that many of the dives are no stop dives and well within the limits prescribed by the RGBM. And therein lies another weakness of the claims: a table is not being tested as such unless the dives performed are to its limits. Saying that you are "diving RGBM" 0r any other algorithm (because you own it or its on your computer) but then performing an uneventful dive well inside the prescribed limits demonstrates absolutely nothing in relation to the validity of the algorithm.

Regarding Andy's report of USN testing, as stated previously, I would be interested in seeing the data. But depending on the type of dives performed 3000 dives without incident would not necessarily be unusual. The incidence of DCI in recreational diving (all comers using all tables / computers) is only 1:10,000 (but that includes many dives that are not to the limit of the table or computer used).

This thread is a good advertisement for the decompression and deep stops workshop (organised by Bruce, Peter Bennett and myself) to be held at the UHMS meeting in Salt Lake City in mid 2008. Similarly for the DAN Technical Diving Workshop being held at Durham NC in late January 2008. Anyone who finds the stuff discussed on these forums interesting would be mad to miss either of these events!

Warm regards,

Simon M

Hi Simon, Tim O'Leary, my instuctor and the Naui Tech course director is out of town for a while. I will find out if the data he cited is available to the public when he returns. IIRC, the data cited in my tmix course materials-Los Alomos and Navy-was from dives using RGBM tables, which up until recently were not published.

Interesting to note that recreational divers have a 1:10,000 incidence, so 3000 without DCS incidence is not so unheard of.

And I never thought that an algo might not be considered validated until it's tested to it's limits, not just by divers doing many dives well within no deco limits, makes sense.

Another problem with the 300,000 number is that if what I've heard is true, very few if any of the computers which claim to use RGBM have implemented it properly. My understanding is that only the Explorer has properly implemented it for helium mixes, and none including the Explorer has properly implimented RGBM for air dil. It's supposed to be coming, but last I heard, the process was going very slowly... -Andy

Simon Mitchell · 21st September 2007, 00:36

Quote: (Originally Posted by silent running)

And I never thought that an algo might not be considered validated until it's tested to it's limits, not just by divers doing many dives well within no deco limits, makes sense.

Hi Andy,

This one is often missed, but it is logical if you think about it. If you perform a dive to 18m (60') for 30 minutes and nominally say that the table you use is the US Navy, that doesn't make it a test of the US Navy table. In fact, it's no more a test of the US Navy table than the RDP or DCIEM or VPM, or RGBM or any other algorithm for which the dive lies within the prescribed limits. The only way that dive becomes a test data point for the US Navy table is if you dived right up to the limit of 60 minutes and surfaced at the prescribed rate with no stops.

Thus, the "thousands of dives with no problems" claims made in respect of various algorithms have to be looked at with a great deal of suspicion, especially where "no decompression" diving is involved.

The situation is a little different for decompression diving. Any decompression dive is almost by definition conducted up to the limit of the controlling algorithm, but once again, only if the ascent rates, stops, gases etc are utilised exactly as prescribed.

Warm regards,

Simon M

Dave O · 21st September 2007, 01:09

Quote: (Originally Posted by Simon Mitchell)

Hi Andy,

This one is often missed, but it is logical if you think about it.

Simon,

That make perfect sense, but eluded me. Thank you for pointing out that simple, but important truth!

Dave

17th September 2007, 10:42	#21 (permalink)
jsevland New Member Current Rebreather/s: Evolution Other Rebreather/s: Join Date: Aug 2007 Location: Norway Posts: 51	Re: Understanding deco theory Hi all I have been making a mess of the Buhlmann algorithm over the week-end. Initally, I only want a rough implementation, to make my Evo-sim "look better". http://www.rebreatherworld.com/surfa...tml#post130806 Looks like I'm able to add dive segments and update the compartments, when I take snapshots - comparing it to some of the examples on the net. But no-deco-time is still spitting out garbage ;-) ... not on my sharpest last night - after a severe party on saturday ;-) Anyway, the little math I did grasp, has long gone - and if any of you have an old Java implementation of Buhlmann - sitting collecting dust - I sure could use some help. My goal is not to make a dive planner (or even model deco-dives), I just want a simple Evo-sim to play with - until I get to play with the real thing. Yours jsevland
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17th September 2007, 11:00	#22 (permalink)
Woz Custom Title Allowed! Current Rebreather/s: Home Build Other Rebreather/s: Home Build Join Date: Jun 2005 Location: Nottingham Posts: 185	Re: Understanding deco theory Mark Powell, a tech instructor here in the UK is writing a book "Decompression Theory and Physiology". I don't know how close he is to publishing it but it gives an excellent insight into the current position regarding deco theory and will save you all the trouble of wading through unintelligible academic papers. You can contact Mark through his website, Dive-Tech: TDI, PSAI, BSAC and ITDA Nitrox, trimix and technical diver training courses with instructor Mark Powell Hope that helps. __________________ Still punting shiny diving tatt to gullible divers www.kitfondle.co.uk
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19th September 2007, 22:02	#23 (permalink)
Simon Mitchell New Member Current Rebreather/s: MK 15.X Other Rebreather/s: Join Date: May 2005 Location: New Zealand Posts: 168	Re: Understanding deco theory Quote: (Originally Posted by ScubaDadMiami) For example, in RGBM for the Layperson (Sources, Fourth Quarter 2004), Weinke lists a six year trial consisting of 32,000 open circuit mixed gas dives down to as deep as 350 fsw without incident; over 300,000 dives using decometers without incident (though this would be no-stop and multilevel dives), and others. Hmmmm, I'll preface this by saying that I am pro RGBM and other bubble models, and Bruce is a respected colleague whom I am working closely with at present to organise a decompression and deep stops workshop at the UHMS Meeting next year. Having said that, I have serious reservations about the appropriateness of referring to the above data as having come from a "trial". This would imply institution of a formal data collection system to accurately record the number and nature of dives and their outcome. I am virtually certain this has not been done, and I'm equally certain that Bruce would have published the data in a proper scientific journal if he had. I suspect that these numbers are estimates which may or may not be correct. The most suspect part of the quote is the zero incidence of problems. I'm just not sure how anyone would know this unless the divers were properly followed. 300,000 dives without incident is highly unlikely, even allowing for the fact that many of the dives are no stop dives and well within the limits prescribed by the RGBM. And therein lies another weakness of the claims: a table is not being tested as such unless the dives performed are to its limits. Saying that you are "diving RGBM" 0r any other algorithm (because you own it or its on your computer) but then performing an uneventful dive well inside the prescribed limits demonstrates absolutely nothing in relation to the validity of the algorithm. Regarding Andy's report of USN testing, as stated previously, I would be interested in seeing the data. But depending on the type of dives performed 3000 dives without incident would not necessarily be unusual. The incidence of DCI in recreational diving (all comers using all tables / computers) is only 1:10,000 (but that includes many dives that are not to the limit of the table or computer used). This thread is a good advertisement for the decompression and deep stops workshop (organised by Bruce, Peter Bennett and myself) to be held at the UHMS meeting in Salt Lake City in mid 2008. Similarly for the DAN Technical Diving Workshop being held at Durham NC in late January 2008. Anyone who finds the stuff discussed on these forums interesting would be mad to miss either of these events! Warm regards, Simon M
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20th September 2007, 00:36	#24 (permalink)
*ScubaDadMiami* Moderator Current Rebreather/s: Optima Other Rebreather/s: Join Date: Sep 2005 Location: Florida, USA Posts: 2,075	Re: Understanding deco theory For those of us that can't make it, I hope that the proceedings will be available. __________________ Howard Packer IANTD CCR Instructor Miami Beach, Florida CCRDiveTraining.com
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20th September 2007, 01:18	#25 (permalink)
Gene_Hobbs Custom Title Allowed! Current Rebreather/s: Not Bought Yet Other Rebreather/s: Not Bought Yet Join Date: Sep 2006 Location: Durham, NC, USA Posts: 118	Re: Understanding deco theory Quote: (Originally Posted by Simon Mitchell) This thread is a good advertisement for the decompression and deep stops workshop (organised by Bruce, Peter Bennett and myself) to be held at the UHMS meeting in Salt Lake City in mid 2008. Similarly for the DAN Technical Diving Workshop being held at Durham NC in late January 2008. Anyone who finds the stuff discussed on these forums interesting would be mad to miss either of these events! As a reminder, the early registration deadline for the DAN Technical Conference is the last day of the month. After that, the price goes up by $US100.00. The UHMS "Decompression and the Deep Stop" pre-course will be offered on June 24-25, 2008. __________________ http://rubicon-foundation.org/ Home of the Rubicon Research Repository. For help getting started with the Repository, please visit our FAQ page. PLEASE support our work. "Oxygen is addictive and deadly. Everyone who uses it will eventually die" --RW Hamilton, PhD 1991
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20th September 2007, 07:54	#26 (permalink)
silent running Mature mouth breather Current Rebreather/s: Prism Topaz Other Rebreather/s: Join Date: Jun 2005 Location: U.S.A. Brooklyn, New York Posts: 1,814	Re: Understanding deco theory Quote: (Originally Posted by Simon Mitchell) The most suspect part of the quote is the zero incidence of problems. I'm just not sure how anyone would know this unless the divers were properly followed. 300,000 dives without incident is highly unlikely, even allowing for the fact that many of the dives are no stop dives and well within the limits prescribed by the RGBM. And therein lies another weakness of the claims: a table is not being tested as such unless the dives performed are to its limits. Saying that you are "diving RGBM" 0r any other algorithm (because you own it or its on your computer) but then performing an uneventful dive well inside the prescribed limits demonstrates absolutely nothing in relation to the validity of the algorithm. Regarding Andy's report of USN testing, as stated previously, I would be interested in seeing the data. But depending on the type of dives performed 3000 dives without incident would not necessarily be unusual. The incidence of DCI in recreational diving (all comers using all tables / computers) is only 1:10,000 (but that includes many dives that are not to the limit of the table or computer used). This thread is a good advertisement for the decompression and deep stops workshop (organised by Bruce, Peter Bennett and myself) to be held at the UHMS meeting in Salt Lake City in mid 2008. Similarly for the DAN Technical Diving Workshop being held at Durham NC in late January 2008. Anyone who finds the stuff discussed on these forums interesting would be mad to miss either of these events! Warm regards, Simon M Hi Simon, Tim O'Leary, my instuctor and the Naui Tech course director is out of town for a while. I will find out if the data he cited is available to the public when he returns. IIRC, the data cited in my tmix course materials-Los Alomos and Navy-was from dives using RGBM tables, which up until recently were not published. Interesting to note that recreational divers have a 1:10,000 incidence, so 3000 without DCS incidence is not so unheard of. And I never thought that an algo might not be considered validated until it's tested to it's limits, not just by divers doing many dives well within no deco limits, makes sense. Another problem with the 300,000 number is that if what I've heard is true, very few if any of the computers which claim to use RGBM have implemented it properly. My understanding is that only the Explorer has properly implemented it for helium mixes, and none including the Explorer has properly implimented RGBM for air dil. It's supposed to be coming, but last I heard, the process was going very slowly... -Andy
(Offline)

21st September 2007, 00:36	#27 (permalink)
Simon Mitchell New Member Current Rebreather/s: MK 15.X Other Rebreather/s: Join Date: May 2005 Location: New Zealand Posts: 168	Re: Understanding deco theory Quote: (Originally Posted by silent running) And I never thought that an algo might not be considered validated until it's tested to it's limits, not just by divers doing many dives well within no deco limits, makes sense. Hi Andy, This one is often missed, but it is logical if you think about it. If you perform a dive to 18m (60') for 30 minutes and nominally say that the table you use is the US Navy, that doesn't make it a test of the US Navy table. In fact, it's no more a test of the US Navy table than the RDP or DCIEM or VPM, or RGBM or any other algorithm for which the dive lies within the prescribed limits. The only way that dive becomes a test data point for the US Navy table is if you dived right up to the limit of 60 minutes and surfaced at the prescribed rate with no stops. Thus, the "thousands of dives with no problems" claims made in respect of various algorithms have to be looked at with a great deal of suspicion, especially where "no decompression" diving is involved. The situation is a little different for decompression diving. Any decompression dive is almost by definition conducted up to the limit of the controlling algorithm, but once again, only if the ascent rates, stops, gases etc are utilised exactly as prescribed. Warm regards, Simon M
(Offline)

21st September 2007, 01:09	#28 (permalink)
Dave O Wreck Diver Current Rebreather/s: Sport Kiss Classic Kiss Other Rebreather/s: Sport Kiss Join Date: Aug 2007 Location: NJ Posts: 122	Re: Understanding deco theory Quote: (Originally Posted by Simon Mitchell) Hi Andy, This one is often missed, but it is logical if you think about it. Simon, That make perfect sense, but eluded me. Thank you for pointing out that simple, but important truth! Dave __________________ Only people who bat for the wrong team wash their undersuits......... I wanna smell piss when I go diving, not ferkin' fabric softener! <decodiver> Schizophrenics never dive solo. My Blog
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