What can I learn from PADI Tec 40 course?

[Karl_H]

Who'd have thought a technical thread could end up in a deep air or not deep air conversation?

I think the governing factor in this whole deep air argument is 99% down to two factors already mentioned, cost and availability. Is using air deeper than 30m more risky than using trimix at these depths? Yes would be the general consensus, is it risky enough to add the extra cost and availability logistics into the equation? Probably not for most circumstances, but in some overhead environments I'd be vary caucious in using a narcotic depth greater than 30m. It's simply a case of risk vs reward, the additional safety for a warm water dive with experienced diver at 40m with helium vs air is generally not even close enough to justify the additional costs, 50m starts to be more difficult to call, 60m and air really isn't safe in my mind.

The argument for using EAN 50 only and not getting clean deco is valid in my opinion, but cetainly not for Tec40 level dives. In fact EAN 50 should give much cleaner deco for the limits of these dives - its dives that load up the slow tissues which are harder to clean up without O2, getting on the deco gas earlier in Tec40 dives should be seen as more of an advantage than a disadvantage?

If cost and availibility were taken out of the equation I think most people would use light trimix gases for dives below 30m, using a rebreather I would very rarely even think of using anything but trimix - the main reason been it's very cheap when used in a rebreather and relatively easy to get as I use larger tanks with onboard bailout so it last for a lot of dives in CCR mode - hence availability isn't much of an issue.

The only risk I can see with going to Tec40 using helium is poor buoyancy and helium based mixes don't go well, although there's an easy solution here - don't go to 40m if you have poor buoyancy

Personally I think diving below 30m with a single 12l tank is a bad idea in general, it's not a particularly dangerous bad idea but using two tank, through either sidemount or back mount, is a far better idea. To ascent from 40m in a OOA situation with both divers breathing heavily at 30l/min and just a 1 minute safety stop still needs around 120 bar of gas - not much for a single tank, even from 30m it's close to 90 bar to ascend - realistically using two tanks within Tec40 limits makes this a much safer course to consider - the irony been that in order to learn this you need to have made 10 or more 'bad idea' dives

I would rarely go below 30m without a second tank, so can fully see the logic in going Tec40 over deep. I'll regularly go up to 50m on air in warm tropical waters if teaching, but in most cases I'd rather use CCR for anything below 40m and keep the narcotic depth to 25-30m using helium based mixes and driving down the max PPO2 to 1.0. I think the narcotic depth at 40m is more than manageable for most skills if they have been learned correctly, for 40-50m I have mixed feelings and do feel this has a major impact on dive skills - however the simple facts are that the cost and availability issues of helium make air a lot more suitable for the majority of us here when making these dives.

I personally thought Tec40 was a bit of a non-sense course, almost everyone doing this couse is probably already doing Tec40 level dives or above (if not, most people probably aren't ready!), but the concept of doing Tec40 in place of Deep is a very good idea and puts the course is a slightly new light for me.

 

[DevonDiver]

the governing factor in this whole deep air argument is 99% down to two factors already mentioned, cost and availability.

[h=2]Other than using trimix, instead of air, for a 30m recreational dive; here are the (other) 17 most ridiculously expensive versions of every day items....[/h]

Toilet paper: $1.3 million 3-ply 22 carat gold flake paper.

Reddit user​

Bottled water: $60, 000 per 750 ml Acqua di Cristallo Tributo a Modigliani

Reddit user​

Beer: $800 – $1,815 per bottle Antarctic Nail Ale

Reddit user​

Shirt: $250,000 gold shirt

Reddit user​

Hot dog: $2,300 230 FIFTH dog

Reddit user​

Pen: $1.47 million Aurora Diamante fountain pen

Reddit user​

Popcorn: $250/gallon Berco’s Billion Dollar Popcorn

Reddit user​

Sunglasses: $408,496 Chopard sunglasses

Reddit user​

Alcohol: $2 million Henri IV Dudognon Heritage Cognac Grande Champagne

Reddit user​

Coffee: $600/lb Kopi Luwak

Reddit user​

Socks: $3,300 Vicuna socks

Reddit user​

Cupcake: $1,060 Golden Phoenix

Reddit user​

iPod dock: $527,463 AeroDream One

Reddit user​

Board game: $9.8 million Royale Diamond chess set

Reddit user​

Stool: $1.3 million gold stool (110lbs)

Reddit user​

Toothpaste: $300 Theodent toothpaste

Reddit user​

Book: $30.8 million Codex Leicester of Leonardo da Vinci

Reddit user​

​

 

[Karl_H]

Shirt: $250,000 gold shirt

Andy - I think this one is mis-categorized?

It's potentially a money saver, this would save a small fortune on paying for rental weights? If you can save 20 Php per day it would more than pay for itself in just over 1500 years; assuming you'd rent weights each day, but that's not even considering inflation on weight prices - it could end up in just 1350 to 1400 with that factored in

Although, the only down side I can see is the rumours that using deep gold can lead to DCS complications?

 

[Colliam7]

It's not only being able to perform single rote tasks like simple arithmetic of the above, but also applying those tasks to complex problem solving for a particular scenario while under the influence of deep air narcosis (example of performing the arithmetic/algebra on-the-fly for a Lost Buddy Search on remaining bottom gas and executing the plan under stress).

OK, I agree, using something as simple as subjective perception, or even a very limited objective cognitive task such as an arithmetic problem, may not capture the full scope of cognitive function that may be impaired at depth, on air. But, it is a start.

I readily admit that what I have done was not controlled to the extent that science would prefer. I controlled for site and depth (repeating the tasks at the same sites and the same depths), but not for day, conditions, intersubject variation, etc., etc., etc. And, I made an active effort to point out that the experience is MINE, and the results may not be applicable to any other diver.

BUT, I am still interested in seeing ANY OBJECTIVE DATA that supports the assertion that the sequence of introduction (trimix first, followed by air at depth, vs. air at depth, followed by trimix) makes any quantifiable difference. Otherwise, the assertion is just unsubstantiated opinion. That is somewhat like divers asserting that they 'feel better' and are 'more clear headed' when using nitrox (for which data actually do indicate there is no difference, by the way). And, while I respect that individuals have a right to their opinion (myself included), I DO NOT accept an assertion that opinion alone substitutes for data. The analogy is irrelevant because it is completely unsubstantiated. Empiricism favors the null hypothesis - there IS NO DIFFERENCE. I have at least made a rudimentary attempt to objectively assess the comparative effects of air vs trimix at a particular depth. Please, do not simply assert that there is / must be a difference unless you can provide equivalent objective data. If you can, that is terrific, and I would like to be made aware of it. Even if your objective results are completely different, I would then suggest that we continue our independent objective assessments, continue to compare results, and ultimately contribute to advancement of our understanding of what is real, as opposed to what is perceived.

Beyond that, I will let Andy take it from here.

 

[Kevrumbo]

OK, I agree, using something as simple as subjective perception, or even a very limited objective cognitive task such as an arithmetic problem, may not capture the full scope of cognitive function that may be impaired at depth, on air. But, it is a start.

I readily admit that what I have done was not controlled to the extent that science would prefer. I controlled for site and depth (repeating the tasks at the same sites and the same depths), but not for day, conditions, intersubject variation, etc., etc., etc. And, I made an active effort to point out that the experience is MINE, and the results may not be applicable to any other diver.

BUT, I am still interested in seeing ANY OBJECTIVE DATA that supports the assertion that the sequence of introduction (trimix first, followed by air at depth, vs. air at depth, followed by trimix) makes any quantifiable difference. Otherwise, the assertion is just unsubstantiated opinion. That is somewhat like divers asserting that they 'feel better' and are 'more clear headed' when using nitrox (for which data actually do indicate there is no difference, by the way). And, while I respect that individuals have a right to their opinion (myself included), I DO NOT accept an assertion that opinion alone substitutes for data. The analogy is irrelevant because it is completely unsubstantiated. Empiricism favors the null hypothesis - there IS NO DIFFERENCE. I have at least made a rudimentary attempt to objectively assess the comparative effects of air vs trimix at a particular depth. Please, do not simply assert that there is / must be a difference unless you can provide equivalent objective data. If you can, that is terrific, and I would like to be made aware of it. Even if your objective results are completely different, I would then suggest that we continue our independent objective assessments, continue to compare results, and ultimately contribute to advancement of our understanding of what is real, as opposed to what is perceived.

Beyond that, I will let Andy take it from here.

That's fine . . .Go ahead retain your null hypothesis & skepticism, and wait until you finally find some definitive stochastic process & paradigm to convince you otherwise. I'd rather work with practical applied & reasonable interpretations from first principles & a few experimental studies, but mostly from my own & other's experiences with the phenomena at hand.

Here are a few important studies which influence my current "beliefs", and which every Tech Diver should be familiar with:

On adaptation to Deep Air and Nitrogen Narcosis:
"Moreover, our results suggest that experienced divers can discriminate between the behavioral and subjective components of narcosis. . .It has been proposed that the intensity of narcotic symptoms could be used by divers to gauge the extent of performance loss (10). The present results indicate that this advice is inappropriate for adapted divers because the two components of narcosis [behavioral and subjective] uncouple in a direction that could lead to an overestimation of performance capabilities --a potentially dangerous situation. On the other hand, the question arises as to whether adaptation confers any benefits on the diver, since performance efficiency is not directly improved and could be overestimated. In this regard, it could be argued that a reduction in symptom intensity reduces the possibility that attention will be focused on subjective sensations rather than the task at hand." [i.e. Subjective, sensations awareness vs. Situational, task-at-hand awareness??]
From:
p.9, Hamilton K, Laliberté MF, Fowler B. Dissociation of the behavioral and
subjective components of nitrogen narcosis and diver adaptation. Undersea Hyperb
Med. 1995 Mar;22(1):41-9. PubMed PMID: 7742709.
________

The Meyer-Overton hypothesis states that narcosis happens when the gas penetrates the lipids of the brain's nerve cells. Here it apparently interferes with the transmission of signals from one nerve cell to another. Exposure to nitrogen-oxygen mixture at high pressure induces narcosis, which can be considered as a first step toward general anesthesia. . . and narcotic potencies of inert gases are attributed to their lipid solubility." (see PADI Encyclopedia of Recreational Diving Ch.5/p22)

Of interesting empirical note, from Wienke BUBBLE MODELS AND DECOMPRESSION COMPUTATIONS:
A REVIEW p.34:

Quote:
To track gas transfer across bubble boundaries, we need mass transport coefficients . . . Table 4 lists [mass transport coefficients] for the same lipid-aqueous surfaces, using Eisenberg [28], Frenkel [33], and Bennett and Elliot [10]

Table 4. RGBM Mass Transfer Coefficients. . .

Gas (μm2/sec fsw)
Ne 10.1 × 10−6
He 18.4 × 10−6
Ar 40.7 × 10−6
O2 41.3 × 10−6
N2 56.9 × 10−6
H2 72.5 × 10−6
)
Notice that helium has a low mass transport coefficient, some 3 times smaller than nitrogen. (That is, Helium can be qualitatively evaluated to be less narcotic than Nitrogen).

______
Helium offgassing rate

From Bruce Wienke, Technical Diving in Depth, Reduced Gradient Bubble Model (RGBM) In Depth:

Quote:
Helium NDLs are actually shorter than nitrogen for shallow exposures . . . Reasons for this stem from kinetic versus solubility properties of helium and nitrogen, and go away as exposures extend beyond 150 fsw, and times extend beyond 40 min or so.

Helium ingasses and outgasses 2.7 times faster than nitrogen, but nitrogen is 1.5 to 3.3 times more soluble in body aqueous and lipid tissue than helium. For short exposures (bounce and shallow), the faster diffusion rate of helium is more important in gas buildup than solubility, and shorter NDLs than nitrogen result. For long bottom times (deco and extended range), the lesser solubility of helium is a dominant factor in gas buildup, and helium outperforms nitrogen for staging. Thus, deep implies helium bottom and stage gas. Said another way, transient diving favors nitrogen while steady state diving favors helium as a breathing gas.
RGBM_Eanx32_Helitrox_NDL.pdf
_________________
Simon Mitchell M.D. Ph.D, on a Bikini Atoll charter 29Jun to 11July'13, gave an interesting lecture on re-examining the efficacy of deepstops based on a very contentious NEDU study (Study Conclusion: Controlling bubble formation in fast compartments with deep stops is unwarranted for air decompression dives).

These few examples above are a lot more objective than whatever scatology Andy has been spewing forth. . .

 

[victorzamora]

Kev, those studies show (as far as I can tell) the benefit of Helium in your breathing gas, as well as show a poor application for Helium. What they do not show is whether diving trimix before diving "Deep Air" or diving "Deep Air" before TriMix is better. ALWAYS diving trimix vs ALWAYS diving "Deep Air" doesn't seem to be what Andy or Colliam are proposing.

 

[Kevrumbo]

Kev, those studies show (as far as I can tell) the benefit of Helium in your breathing gas, as well as show a poor application for Helium. What they do not show is whether diving trimix before diving "Deep Air" or diving "Deep Air" before TriMix is better. ALWAYS diving trimix vs ALWAYS diving "Deep Air" doesn't seem to be what Andy or Colliam are proposing.

Correct Vic. Acquire & learn the largest knowledge base academically, practically and anecdotally. It's up to you how to arbitrarily apply it to your own diving toolset.

I come from early Trimix training, and have now learned through a lot of trial & error what my limitations on Deep Air (and 20/20 "economy" Trimix) are --those two breathing gases are the most common deep 39m to 60m bottom mixes I use on my tropical tech wreck trips along with Eanx50 and pure O2 for deco. Essentially the opposite progression of the PADI Tech training regimen --and some may quip a "regression" from the DIR orthodoxy.

I'm still waiting for you to tell us about Truk...

Attached below is my latest Truk Lagoon Helium/Oxygen Gas Bill over 12 days of diving (and I only used Air, 20/20 tmx with Eanx30, 32, 50 & 100% Oxygen). . .

 

[Michael Guerrero]

maybe I should stop drinking while I am posting

Highly inadvisable.

 

[Simon-]

Who would have thought that yesterday I must have been really pushing the boundaries, according to some on this thread.

2 dives in the 40 - 50m range, on air, in steel doubles, aluminium stages, wearing a wetsuit, double bladder wing, in one day………..how on earth am I still here to type about it?

With He not that freely available in this region, I wouldn't consider it for anything less than 50m. I have two sets of twins with 16/40 in them but they are not going to be used on a dive that I can safely do on air.

 

[Kevrumbo]

Who would have thought that yesterday I must have been really pushing the boundaries, according to some on this thread.

2 dives in the 40 - 50m range, on air, in steel doubles, aluminium stages, wearing a wetsuit, double bladder wing, in one day………..how on earth am I still here to type about it?

With He not that freely available in this region, I wouldn't consider it for anything less than 50m. I have two sets of twins with 16/40 in them but they are not going to be used on a dive that I can safely do on air.

What if you're on a tech liveaboard for a week or more to the wrecks of Bikini Atoll or Truk Lagoon?

This deep air profile of two dives per day --repetitively over several consecutive days-- is where you start to have residual N2 slow tissue loading problems, and having an additional deco stop at 6m on 100% oxygen will help to further off-gas these slow tissues more efficiently than Eanx50 alone (or worst case for a type one DCS pain-only symptom, you can go on 100% O2 for In-Water-Recompression treatment). PADI Tec 40 Certification only allows the use of a single deco gas up to Eanx50.

And even with both Eanx50 and 100% O2 deco on Deep Air or even Standard GUE Trimix bottom gases, it's good practice to take at least a day-off after two or three consecutive tech dive days to give your tissues a break from the inert gas loading, and relief from Ox-tox CNS exposure as well.