RGBM formulas.

[Liquid]

Hi doc!

I wandered if you could please give me the formulas used to calculate in the RGBM model. A friend of mine has built a program that works with 8 theoretical tissues, on reall time, and can give some nice layouts. I want him to try the same with RGBM and than compare the results.

P.S-
Can you please give me what you belive is the ideal variety of tissues to use in such models, with their data, and which reall tissues they are suposed to represent?

 

[omar]

This is Bruces reply to a request for the Fortran code that he has:

--------------------------------------------------
Subject:Re: RGBM
Date:Mon, 20 Mar 2000 11:06:45 -0700 (MST)
From:Wienke Bruce <brw@lanl.gov>
To:xxxxxxxxxxxxxxxxxx

Sorry, Omar -- do not pass any RGBM code out. You understand I hope.

Price is $3800.

Bruce
---------------------------------------------------

omar

 

[Dr Deco]

Dear Liquid:

I do not actually know what is in the formulation of the RGBM.

Dr Deco

 

[Liquid]

do You have any kind of information about the way it treats tissues, ascent rates etc?

I'll build some algorithms and check them VS my dive-computer (it's RGBM), my haldan program and several tables, and post the results.

 

[rcohn]

The RGBM source code is not readily available, but some information is available on the Internat.

You can read articles by Bruce Wienke on the RGBM here:
http://www.abysmal.com/pages/articles.html. Wienke's book on decompression theory, Basic Decompression Theory and Application (out of print) has additional information and graphs

While there is little information on the RGBM there is extensive information on the earlier VPM algorithm. Eric Baker's articles and Fortran source code can be found here:
ftp://ftp.decompression.org/pub/Baker/

Eric Maiken's Open Source Code VPM Bubble Model Programs and papers can be found at:
http://www.decompression.org/maiken/VPM/Bubble_Model_Program_Info.htm

Along with the information and source codes for the VPM algorithm there is a page discussing aspects of the RGBM with graphs.
http://www.decompression.org/maiken/VPM/Technical_RGBM.htm

The Suunto web page and manuals for the computers (Vyper, Stinger, Cobra, and Mosquito have limited information about the Suunto version of the RGBM algorithm. The SRGBM is a limited subset of the full RGBM. From the Mosquito manual:

It is a significant advance on the classical Haldane models, which do not predict free gas (microbubbles). It incorporates consistency with real physical laws for gas kinetics. The advantage of Suunto RGBM is additional safety through its ability to adapt to a wide variety of situations. Suunto RGBM address a number of diving circumstances outside the range of just dissolved gas models.

• Monitoring continuous multiday diving
• Computing closely spaced repetitive diving
• Reacting to a dive deeper than the previous dive
• Adapting for rapid ascents which produce high micro-bubble (silent-bubble) build-up.

SUUNTO RGBM ADAPTIVE DECOMPRESSION

The Suunto RGBM algorithm adapts its predictions of both the effects of micro-bubble build-up and adverse dive profiles in the current dive series. It will also change these calculations according to the personal adjustment you select.

The pattern and speed of decompressions at the surface is adjusted according to micro-bubble influence.

Also on repetitive dives adjustment may be applied to the maximum allowable nitrogen overpressure in each theoretical tissue group.

Depending on circumstances Suunto RGBM will adapt the decompression obligations by doing any or all of the following:

• Reducing no-decompression stop dive times
• Adding Mandatory Safety Stops
• Increasing decompression stop times
• Advising an extended surface interval (Diver Attention Symbol).

DIVER ATTENTION SYMBOL - ADVICE TO EXTEND SURFACE INTERVAL

Some patterns of diving cumulatively add a higher risk if DCI, e.g. dives with short surface intervals, repetitive dives deeper than earlier ones, multiple ascents, substantial multiday diving. When this is detected in addition to adapting the decompression algorithm Suunto RGBM will in some circumstances also advise with the Diver Attention Symbol (review chapter 3.2.3.2.) that the diver extend the surface interval.

It is clear from the manual that this computer adds several new conservative features to increase safety. How much your safety is increased is not clear. Some restrictions may be excessive, for example, the recent conclusions of the Workshop on Reverse Diving Profiles was that reverse profiles (limited to a 40 ft difference) do not pose an additional risk to divers, so this restriction may be unduly conservative. More advanced versions of the RGBM (such as the Abyss implementation) include features such as deep stops for faster safer decompression. There is no indication that deep stops are included in the SRGBM version.


Ralph

 

[Liquid]

rochn-
I thank you from the bottom of my heart. I knew already several of the links you suplied, but I am going to check the rest when I finish wrting this. Looks promising.

I am working with a friend on several algorithms. We found out it's not so different from what abbysmal usses in it's computers (they put some of the formulas in the computer page). Our problem is, that we don't have at our disposal all the studdies about silent-buubles, effects of water vapours etc. etc.. We want to check some other algorithms and compare results. So far, when compared to a diving computer we come quite close (It can never be the same when using different models).

About reverse profiles: My belife is that when using a diving computer that calculates in reall time reduces the danger cignificantly. when RGBM is used, the I belive it's eliminated.

P.S-
I own a vyper, It's a GREAT computer with some really good lay outs that are hard to find in other computers. I dived with people that use other computers and we compared data. The vyper usualy demanded slower ascent rate, but with the safety stops it was different who had the longer. Unfortunatly, it dosent use the deep stops, becouse it is a recreational computer, so I never check that.

 

[Dr Deco]

Hi Liquid:

Glad to see you have had some success. As others mentioned, much of the RGBM material is proprietary.


Dr Deco

 

[Liquid]

Hi doc!

Well, I had a bit more success.
My friend and I are still working on the algorithm, and so far we had some good results, that are more or less the same as put in some examplry dives on the web. We got a bit stuck when trying to associate some other variables to the formula (one of the things in RGBM is that it uses a lot of variables such as height and water temprature)

When we have final results I will post it.

One more thing- can you give me some data on water vapors in air, and the way it affects DCS?
Are the changes in the amount of humidity the same as the pressure changes?

Thx,

 

[Dr Deco]

The water vapor spoken of is the partial pressure of water in the tissue gas bubbles. This is 47 torr and is fixed by the temperature of the body. It does not vary with pressure.

Dr Deco

 

[Liquid]

THANK YOU THANK YOU THANK YOU!!!

For some mysteriouse reason I havent noticed this fact as of yet.

THANK YOU!

P.S-
Oh, yeah.. hmm.
What is "torr"?