Min Deco for 30/30

[mikeny9]

The reason I was bringing up Meyer-Overton is because it makes use of gas solubilities. Helium is indeed less soluble, we can agree on that. What we are at odds with is how Helium reacts in dissolved gas theory. When descending, or more appropriately, when there is a pressure gradient setup between a higher ambient pressure under water and a lower internal pressure of the tissue, the tissue would reach full saturation sooner with Helium that it would with Nitrogen. However, by the same property, it also exits the tissue at the same rate when the opposite gradient is setup, as long as the gas is in free-phase (not dissolved). This is all based on Henry's law. However, since Helium does not dissolve as fast as Nitrogen (about 4.47 times less soluble), gas exits the tissue at a much higher rate than Nitrogen (in theory based on Graham's law.).

The canonical example is the "sugar and sand" scenario. If you pour 1 teaspoon of sugar, simulating Nitrogen, into water at a constant rate until the glass is "saturated", the sugar eventually dissolves because of the solubility of sugar. If you pour 2.65 teaspoons of sand into a glass, simulating Helium (2.65 because that's how Buhlmann would model Helium: moving 2.65 times faster into the tissue) until that glass is saturated, it would saturate much sooner no doubt. However, the sand (Helium) would be able to be removed at the same rate it came into the glass because of it's low solubility, where the sugar (Nitrogen) would have to come out of solution first.

There's also the work done by B.R. Wienke that suggests higher soluble gases causes larger bubbles, and larger bubbles are in theory related to DCS (Buhlmann). (Deep Helium • ADVANCED DIVER MAGAZINE • By B.R. Wienke and T.R. O’Leary)

Keep in mind this is all mad science of decompression theory, i.e. the wild west of the medical research world. We are way off topic from the OP. His original question was if it was "valid" to have tables that use the same NDL (I'm assuming "min-deco limits" means NDL here) for Nitrox 32% as 30/30. In my opinion, it certainly is and is very conservative to do so, based on the theories above.

 

[PfcAJ]

What you're writing about is indeed mad science, and really best ignored.

What you've written takes so many twists and turns I can't really get what you're saying. However, if gas in your tissues isn't dissolved... then it's a bubble, and bubbles are what we're trying to avoid (simplistically). Furthermore, the article by Wienke is just an article. There's no "work", and also no citations.

I encourage readers to dismiss the idea of diving 25/25 using 32% (7% more inert gas) tables the same way I would discourage diving 15/55 using 21/35 (6% more inverts) tables. There's simply more inert gas and the only real science we have (discussion linked in my previous post) suggests that nitrogen and helium behave similarly for decompression purposes.

 

[mikeny9]

I'm sorry you can't understand what I'm saying, I tried to make it as clear as I could.

The results of the studies you linked were inconclusive, and are also mad science and by the same logic can be ignored. There is a discussion on that site, sure, similar to the one we are having. People are arguing whether it's useful or not, but it doesn't change the outcome of the studies. Invalidating my point which describes the theory that Helium can exit tissues faster that Nitrogen based on it's solubility by simply saying you can't understand it because what I've written "takes so many twists and turns" isn't very productive or useful to any reader. If you're going to write-off the research then at least just say you don't believe in those theories. Something like, "I don't believe in X, Y, Z so I advise the reader to not dive a 32% table when using 30/30 or 25/25." At least that lets the reader decide on whether they believe in those theories or not. Besides, all of decompression theory is mad science, maybe we should just ascend to 15' from 100' at 30' per minute regardless of the mix, do a 3 minute sto,p and forget about any more modern theories?

Bubbles are indeed what we're trying to avoid, and in theory (there's that word again) the solubility of Helium helps with that. Wouldn't your logic regarding inert gas and the 32% table when diving 25/25 be similar for 30/30, just slightly better (70% vs 75%)? UTD and GUE both teach using a 32% table for 30/30 and 25/25 respectively, probably for all of the reasons I mentioned above that you disregard as mad science, or that you can't understand for some reason.

I'd still like to understand exactly why you think Helium should be treated the same as Nitrogen, but I suspect you won't consider the research I've mentioned. It'd be nice for you to explain your thought, rather than linking to a discussion board that references studies with inconclusive results.

 

[PfcAJ]

Gue doesn't teach 25/25.

The difference between 3030 and 32% is 2% more inert gas with 30/30. That's insignificant. 7% is not insignificant.

You haven't linked a single piece of research to support your argument. I have.

 

[mikeny9]

I'm aware GUE teaches 30/30 and not 25/25. Is that what we are turning this thread into? There are plenty of other threads that argue 30/30 vs 25/25. UTD uses 25/25 because they believe in the research I mentioned. It's fine if you don't believe that though, everyone has their opinions. Clearly GUE does not, and they use 30/30 and Buhlmann-based computers that treat Helium just like Nitrogen. I can understand why if they aren't considering the research I mentioned.

Regarding research, do you want me to actually link the Meyer-Overton research? Anyone can google it. The link you provided was to a discussion about two inconclusive research studies, not incredibly useful.

Again, you're still haven't explained why Helium should be treated like Nitrogen. Also, who's to say 2% is insignificant? Is that another one of your assumptions? Who's to say 7% is not insignificant? If you get a fill from a station who gives you 29% instead of 32%, do you use a 32% table? Is 3% significant? Where's the border line?

 

[LiteHedded]

I treat 21/35 like 25/25 cus it's only 4% different. I dive 32% tables down to 150'

 

[PfcAJ]

Again, you've linked no research. Zero. Goose egg.

Buhlmann does treat helium differently. That was established earlier in this thread.

2% is about the variance you'll get out of an analyzer. If I got 29% instead of 32% I'd probably balk at that. If I asked for 15/55 and got 12/55 I'd bitch for sure. Generally I'm happy when an analysis is within 1%. 3030 vs 32 is real whatever.

I've already explained and linked to why I feel helium and nitrogen can be treated equally.

Ps: I'm quite familiar with Meyer Overton. It's the correlation between lipid solubility and narcosis.

 

[mikeny9]

The study that’s talked about in the discussion you linked was for determining whether the US Navy should switch from using heliox to trimix. The results found that there was no statistical significance between the heliox (12/88) vs trimix (12/44) for the same 200’ profile. The study concluded that decompression from trimix is not more efficient than heliox and that the US Navy shouldn’t switch from heliox to trimix. You're jumping to your own conclusions if you interpret the research as "nitrogen and helium behave similarly for decompression." The conclusions fit a hypothesis where heliox is a cleaner mix as well, since the trimix is no worse than the heliox. That's not what they proved, but they certainly didn't prove that helium is just as bad as nitrogen for decompression.

If the study were to choose a more aggressive nitrogen mix and longer bottom times, and found a similar number of incidents of DCS from using the heliox versus the more aggressive Nitrogen-rich trimix, it might support your claim that helium is just as bad as nitrogen from a decompression standpoint. It does help to link to the actual study by the way, not a discussion about the study; here’s the study the people in the discussion you linked to are talking about: http://archive.rubicon-foundation.o.../123456789/10576/NEDU_TR_15-04.pdf?sequence=1.

Furthermore, the study you linked actually supports the idea that usage of Helium shouldn’t penalize the diver if greater mixtures of Helium are used in the mix since it compares heliox to trimix and found no statistically significant DCS incidents on the same profile with the two gases. One of the researchers, David Doolette, is actually giving a presentation on this next week in Mexico (See: Helium Penalty by Dr. David Doolette, also mentioned here: Helium Penalty? - TEKDiveUSA, and here in DAN’s Alert Diver NEDU Milestones, "2015: Conducted a trimix/heliox comparison that showed that there is no 'helium penalty' for decompression”: Alert Diver | Navy Experimental Diving Unit (NEDU) Milestones).

My claim that Helium moves in out of tissues faster is based on Graham’s law (Graham's law - Wikipedia), particularly because it will diffuse and effuse much faster than Nitrogen based on it’s molecular weight, so theoretically it will move in and out of the tissue faster. The "Helium penalty" comes about in Buhlmann models because it’s assigning theoretical m-values for Helium. These m-values were never empirically verified because Buhlmann died before he could do any research with Helium. In mine and several other divers' opinion, these m-values are very incorrect. To be fair, there is no research that suggests the m-values are correct or incorrect. However, because Helium is not as soluble, it does not dissolve as fast into liquid in the tissue due to the solubility properties of the gas when compared to Nitrogen. What Buhlmann forgot to account for was the rate at which Helium exits the tissue based on the same math behind Graham’s law.

All of this is really moot though because I think your original argument was how "reckless" using a 32% table is when diving 25/25. In what way, other than assuming a 7% difference in the inert gas is “significant," while having no evidence for determining what is significant and what isn't?

All of the dive tables I've seen, to include GUEs and UTDs, are based on the EAD of the mix. The EAD of 25/25 at 100’, when you consider the Helium to be just as bad as Nitrogen for decompression and use .75 FO2, is 93’. Some divers would roundup to use a more conservative 100', which the NOAA air table provides 25 min of NDL, only 5 min less than 32/00 and 30/30. Some would round down and use the 90' entry of 30 min (same as your 32% and 30/30). Keep in mind the NOAA table also assumes no deco time. For a 100’ recreational dive, both UTD and GUE follow a “min deco" ascent profile and would have the diver stop for 5 min total (50’, 40’, 30’, 20’, 10’ for 1 min). The diver is completing 5 min of deco on back gas (hence the “min” part of the “min deco” expression), which accounts for the 5 min over the NDL time when using 25/25. So I ask again, how precisely is it "reckless" to use a 32% table then when using 25/25 at 100'?

 

[PfcAJ]

Helium penalty refers to increasing the decompression time relative to having no helium in the breathing gas.

I would expect (I'm not sitting at a laptop) 3030 to have shorter NDL times than 32% due to this "penalty". In reality it should probably be the same and result in the same risk of DCS. Helium doesn't make it worse, but it also doesn't make it better which is what you're contending. Doolette's work supports this.

Your own analysis shows a 5min difference in NDL. How on earth can you turn around and say that 5min=0min difference?

Would you do 5mins over the air NDL and expect the same DCS risk? 5mins over a 32% NDL?

Where did you get these ideas from exactly? Who taught you this?? Go sit down with a decompression algorithm (hell, use VPM if you want since buhlmann doesn't seem to be your cup of tea) and see for yourself. Do it with 32%, 25%, 3030, and 25/25.

Addition of helium does not decrease your required decompression nor does it lengthen your no decompression limits.

Do you know where that min deco ascent came from?

 

[mikeny9]

The logic you are using from the conclusion of the research paper is faulty, which makes it tiring to argue with you productively. Consider the following statement:

The number of cars in Parking Lot 2 (i.e. trimix) is less than or equal to (I.e. trimix being no worse than) the number of cars in Parking Lot 1 (i.e. heliox).

In order for the first statement to be true, one of the following must be true: Parking Lot 1 has more cars than Parking Lot 2 (i.e. heliox is better than trimix); or Parking Lot 1 has an equal amount of cars as Parking Lot 2 (i.e. heliox is no better than trimix). You are concluding the number of cars in Parking Lot 1 is equal to the number of cars in Parking Lot 2 (i.e. heliox is no better than trimix), with no proof that suggests the other condition is false: that Parking Lot 1 has more cars than Parking Lot 2 (i.e. that heliox is better than trimix).

There is absolutely nothing in the research that concludes, or even suggests, that heliox is just as good or bad as trimix for decompression. Did you actually read it? It says the opposite: trimix is no worse than heliox for decompression. It doesn't prove that trimix is equal in decompression, nor does it prove that heliox is equal for decompression, nor does it prove that heliox is better at decompression. Using the opposite statements: trimix might be just as good as heliox for decompression, heliox might be just as good as trimix for decompression, and heliox might be better than trimix for decompression. The research proves none of this. All they did was prove the null hypothesis (trimix is no worse than heliox). If you're going to refer to research papers as the basis of your argument you should really understand this logic and what the null hypothesis means.

The helium penalty does indeed refer to decompression stop times (what the OP was asking a question about), and this study proves there should be no helium penalty in terms of decompression time when following the profile they did with the mixes they used. In practice, the study ought to refute helium penalties in any model. It will be interesting to see how this research is presented next week.

Adding helium to the mix for any model will not shorten your NDL times either, because the models are still using EAD and only look at FO2, which treats Helium just as bad as Nitrogen for NDL times. Theoretically, again in my opinion, one could add NDL time when using helium since the solubility of the gas is much different from nitrogen. No agency does this however, it's merely a theory I brought up to illustrate why using a 32% table for 30/30 should be considered safe for the OP.

I did not say I turned 5 min of going over NDL into 0. What I did is what UTD would consider to be a proper amount of deco time for that profile. Keep in mind UTD doesn't accept exact Buhlmann or VPM models precisely like a deco planner or computer would, they use both a bubble growth model and a Buhlmann model to create what they believe is a proper and safe ascent strategy. Whether someone wants to believe the Buhlmann model with incorrect m-values for Helium is correct or incorrect by using a computer or planner, or similarly for VPM (in my opinion VPM has way more problems than Buhlmann with regard to super saturation time), the argument really falls into the "my model is better than your model" black magic of decompression theory. You can choose what you want to believe, and so can I, and so can the reader. Clearly you are using a Buhlmann based planner. It doesn't mean that it's correct or incorrect, or that VPM is correct or incorrect, since those words are black and white and reality there is probably some grey area of how correct or incorrect they are.

We also don't know for sure if Helium ought to decrease your decompression time. My theory is that it should, but no agency that I know of actually does this. What's worse is a Buhlmann model penalizing the diver on deco time when adding Helium to the mix, and that's what the study you are referring to for the most part refutes practically.

Lastly, I do indeed know where the min deco ascent profile came from, do you? Do you know who created it? Hint: they don't work for GUE anymore. How is this relevant to this discussion?