Tech class and narcosis?

[boulderjohn]

PADI used to have students do a task on the surface and then do it at depth during the deep dive of the AOW class. Many instructors had them do math problems. They ended that without an explanation that I saw, but I think I know why. In my experience, the students usually did better at depth than they did on the surface. I suspect that was probably because the practice on the surface got them back into practice for something they had not done much in a while.

 

[Michael Guerrero]

I just did mine on air and didn't have difficulty responding to the prompts from my instructor. It also made me feel comfortable diving at those depths on air, makes for super convenient diving since you can get air anywhere, but not helium, and was a lot nicer on my wallet.

 

[KevinNM]

PADI used to have students do a task on the surface and then do it at depth during the deep dive of the AOW class. Many instructors had them do math problems. They ended that without an explanation that I saw, but I think I know why. In my experience, the students usually did better at depth than they did on the surface. I suspect that was probably because the practice on the surface got them back into practice for something they had not done much in a while.

He had me do it at 130, and then at 20. And it wasn't a math problem, it was touch the numbers from 1-100 (scattered over this 10x10 matrix) in sequence. The other one (iirc) involved dissembling bolts and washers and then reassembling them correctly.

 

[Kevrumbo]

So I'm interested in taking a tech class at some point in the future. Looking at TDI AN/DP and GUE Tech 1. My only reservation with TDI is diving that deep and getting narked. What mix do people normally use for AN/DP? 24 or 25%? Air? The max depth is 150' and even if you are using 25%, doesn't that almost guarantee that you will get narked? Being narked makes you stupid and I would prefer to not be stupid, especially so when doing a dive that incurs more risk than what I normally have done so far. Is there any way to do TDI classes from the beginning using some helium?

The worst possible scenario for any Tech Diving Student (or any diver in general) is to be in physical exertion breathing Air at deep depth AND not being able to eliminate metabolic CO2 fast enough, developing the vicious cycle of CO2 poisoning as well as falling under the extreme effects of Nitrogen Narcosis. . .

The reason why you want to use a helium bottom mix is primarily for reducing the gas density and resultant Work-of-Breathing that you would otherwise have breathing Air or a Nitrox bottom mix -along with the anti-narcotic benefits of having less Nitrogen in a Trimix bottom gas.

In other words, If you expect to be working hard at depth, with physical exertion and heavy exhaustive breathing (i.e. finning into a strong current), then you would want to be using a less dense gas to help offset Work-of Breathing CO2 retention and build-up leading into Hypercapnia, which is IMHO, more insidiously dangerous and malignant than just Nitrogen Narcosis by itself.

(The only way to consciously recover from Hypercapnia at depth is to cease & desist the physical activity: rest & relax with full inspiratory/expiratory breathing to get rid of the excess CO2, and then abort the dive as necessary).

 

[DevonDiver]

If you want to demonstrate narcosis on recreational deep dive (when doing the timed problem solving exercise), simply make the student's undergo some exertion preceding the test. They'll also learn an important lesson about CO2 retention and rapid narcosis onset.

PADI do have 'bolt-on' normoxic trimix extension for the Tec45 and Tec50 courses. Minimum 21% O2 and maximum 20% He.

 

[AJ]

Exactly, did not notice anything until task loaded. Then it hit me what narcosis is all about.

 

[kensuf]

To the OP: With TDI, IANTD, and NAUI you can use helium mixes (up to 20%) in your initial decompression training. TDI and NAUI call it "Helitrox" and IANTD calls it "ART" (Advanced Recreational Trimix).

There are places around here in cave country that allow me to take students to 130' without too much difficulty (Hudson Grotto), but they're anything but pretty. My AN/DP students get to enjoy a couple of dives there because I have a hard time issuing a card that says they're good to go to 140-150' without having been at a similar depths under supervision.

 

[rivers]

To the OP: With TDI, IANTD, and NAUI you can use helium mixes (up to 20%) in your initial decompression training. TDI and NAUI call it "Helitrox" and IANTD calls it "ART" (Advanced Recreational Trimix).

There are places around here in cave country that allow me to take students to 130' without too much difficulty (Hudson Grotto), but they're anything but pretty. My AN/DP students get to enjoy a couple of dives there because I have a hard time issuing a card that says they're good to go to 140-150' without having been at a similar depths under supervision.

There is no helium limit in ART. The back of my card states "Qualified to dive EANx max PO2 1.5 combined with helium max END 24m"

 

[kensuf]

Correct, IANTD limits just the maximum END (80') and a maximum depth of 160'.

TDI limits Helitrox to 20% helium and 150', NAUI helitrox is 26% oxygen/17% helium and a depth of 150'. The reasoning why TDI and NAUI have their limits on the upper helium % is so that standard nitrox/air tables can be used.

 

[decompression]

Out here I use a wall dive that gives depths to 300'.........we used to use air to about 150-170 but it was pretty obvious watching the students (to different extents) work through Narcosis and the challenges they had. Now its helium below 100' and the difference is notable.