What computers are you using for tech dives?

[TrimixToo]

Tom from Suunto, nobody has asserted that ICD is not real.

However, you seem to be missing the point that the gas switch you characterized as hazardous carries an actual ICD risk that falls somewhere between zero and negligible. It's not that we do no recognize the risks of ICD given poor gas planning or procedures, or that we do not plan to mitigate or eliminate those risks. Instead, I think we believe we understand it quite well, and to me, at least, it is not apparent that you do. If you want to have a real discussion about this, you must begin by understanding when ICD poses an actual risk when switching to a particular gas at a particular depth.

 

[CAPTAIN SINBAD]

I have a Hollis TX-1 but at the level at which I am presently, I tend to agree with Ken and PfcAJ that a bottom timer and tables are the way to go about things.

 

[Tom Ahola]

Thanks Ken for clarifying. Yes you are right, that is not a gas switch with real concerns. I was blindly looking at what the Technical RGBM gave out, as the original post did run that algorithm. The TecRGBM algorithm does prolong ascent due to ICD (a bug maybe - I have no clue), so my answer was correct in this sense. But it was fun to see such adult responses to my little mistake.

The Fused RGBM used in Suunto DX and Eon computers does not give an ICD hit for this switch and the decompression time is very close to the Bühlmann 50/80.

-Tom from Suunto

 

[100days-a-year]

RGBM,Edsel,Corvair,Spruce goose,Ford Pinto

All better in a museum than in practice.

Pretty sure claiming a common practice with not a single known case of the claimed danger happening is not a small mistake.

 

[rongoodman]

I dislike getting involved in religious discussions but I wanted to explain why the algorithm works as it works with those gases.

An excellent idea. Please proceed.

The TecRGBM algorithm does prolong ascent due to ICD (a bug maybe - I have no clue), so my answer was correct in this sense.

And there in a nutshell is why most tech divers don't want anything to do with proprietary algorithms.

 

[boulderjohn]

. I dislike getting involved in religious discussions but I wanted to explain why the algorithm works as it works with those gases.

Bruce Wienke has implemented measures in the RGBM algorithm that takes into account ICD.

Here's the problem with what you wrote.

You said you wanted to explain WHY "the algorithm works with those gases." You said that "the RGBM algorithm that takes into account ICD."

Asserting that it does something does not explain WHY "the algorithm works with those gases." Saying that the RGBM algorithm that takes into account ICD" does not prove that it does. It does not give any indication how or why. Since it is a proprietary algorithm, we don't know any of that, and you don't give a clue; we just have to take your word for it.

 

[PfcAJ]

Thanks Ken for clarifying. Yes you are right, that is not a gas switch with real concerns. I was blindly looking at what the Technical RGBM gave out, as the original post did run that algorithm. The TecRGBM algorithm does prolong ascent due to ICD (a bug maybe - I have no clue), so my answer was correct in this sense. But it was fun to see such adult responses to my little mistake.

The Fused RGBM used in Suunto DX and Eon computers does not give an ICD hit for this switch and the decompression time is very close to the Bühlmann 50/80.

-Tom from Suunto

You know, if you’re going to speak on behalf of a company you should probably a) have a clue and b) be sure to not make mistakes.

I’m just cringing at these posts.

 

[Kevrumbo]

Bruce Weinke is a loon.

There, I said it.

Let's look at something real quick.

PN2 of 50% nitrox at 70': 1.6
PN2 of 18/45 at 70': 1.2
PHe of 18/45 at 70': 1.4

Going from 18/45 to 50% your change in PHe is 1.4->0. Going from 18/45 to 50% your change in PN2 is 1.2->1.6. The delta isn't enough to be a concern.

People do a switch like this every day without problems.

BTW, I find it hysterical that you're quoting an article by Weinke that talks about Mark Ellyiat and his success using RGBM schedules. You may wish to read what Mr. Ellyiat has to say about Weinke and RGBM his own web-page.

RGBM Really Good Bends Model

Actually, you have less of a potential ICD "slam" using an intermediate deco Triox gas of 50/25/25 so your delta in this instance at the 3.1 ATA depth gas switch is PHe 1.4 --> 0.76 and PN2 1.2 --> 0.76 (and then clean it all up with Oxygen at 1.6 ATA depth gas switch).

But according to BRW, a switch to Nitrox 50 coming off a Trimix bottom gas like 18/45 is still ok:

 

[Tom Ahola]

Here's the problem with what you wrote.

You said you wanted to explain WHY "the algorithm works with those gases." You said that "the RGBM algorithm that takes into account ICD."

Asserting that it does something does not explain WHY "the algorithm works with those gases." Saying that the RGBM algorithm that takes into account ICD" does not prove that it does. It does not give any indication how or why. Since it is a proprietary algorithm, we don't know any of that, and you don't give a clue; we just have to take your word for it.

Hi John,
Thanks for the feedback. Maybe my English is not good enough but I tried to say "why the algorithm works as it works" ... "with those gases", meaning that the algorithm gives a long decompression - WHY? - because of the gas switch is identified as ICD by the old Technical RGBM algorithm. I believe the long decompression was an issue in the original post I tried to reply to with a clarification and reason. The DM5 planner gives a clear indication of ICD risk, and this means the algorithm takes this into account, prolonging ascent. I don't have experience myself of the Techical RGBM, which is an old algorithm, so I cannot directly say why it gives the IDC. I could ask my colleagues if this is of real interest. However, I would recommend using the Fused RGBM instead, which does not have this problem. There are many tech divers diving with Fused RGBM and it is a safe and well-functioning algorithm. It will be even be improved soon with software updates addressing feedback received on certain issues. I'm sure the TechRGBM has given the RGBM a bad reputation in the tech diver community, but that should be in past history today, not worth picking on anymore.

Unfortunately I made some wrong choices in words and did not look into details about the gas switch and as a result a lot of naive bullying and trolling starts to pick on unimportant details, blurring the actual topic. It this typical behavior in the US tec dive community that beginners or any divers, when they make mistakes, are bullied by more experienced ones, even trainers? Here in Europe divers are buddies, more experienced ones supporting the beginners.

Regarding proprietary algorithms. Could someone give me a reference to the non-proprietary source code or algorithm description of the Bühlmann GF used in any popular tech dive computer? I would like to investigate how the depth point of the low gradient factor is implemented. This seems to be different in every Bühlmann GF implementation I have tested so far, giving different decompression results.

- Tom from Suunto

 

[Vicko]

Tom your English is perfect.