Why do you need training for normoxic trimix?

[njdiverjoe]

@tbone1004, can you educate me on this? Either something is lost in translation or there is a hole in my education. Would be appreciative of a bit more explanation.

He's talking about that when on ccr you are off-gassing into the loop. By monitoring the stability of your loop during a stop you can estimate when you are clear.

 

[tbone1004]

@tbone1004, can you educate me on this? Either something is lost in translation or there is a hole in my education. Would be appreciative of a bit more explanation.

what @njdiverjoe said. You will see the ppO2 drop start to slow down in conjunction with the loop volume actually going back to min-loop when you stop offgasing.

 

[jgttrey]

Thanks. That's what I thought you were saying but it is honestly amazing to me, as someone relatively new to CCR.

I understand the theory, but the idea that the volume of offgassed nitrogen/helium is sufficiently large that (a) it has an influence on loop volume and rate of ppO2 change that is discernible through the "noise" in the data of adding O2, etc. and (b) that impact can be guesstimated enough to at least get some idea when "most" of the offgassing is complete and you can ascend - that all just really surprises me. Not disputing the voice of experience, but just surprised. Not something I learned about in normoxic but perhaps in my full mix class coming up.

Assuming the SHTF and you really were needing to use ppO2/loop volume to guesstimate when you've finished most off your offgassing at a given depth, is there a particular procedure you follow? Very curious about this.

 

[kensuf]

ICD - not a concern for normoxic trimix. Narcosis slam from a gas switch to nitrox at 130' CAN be though, I've personally experienced it so hard once that I had to grab a wall (and this is coming from a guy that used to switch back to air at 190' from a deep dive).

In answer to the OP's question of why is there a need for normoxic trimix traiing..

The answer is multi-factored, but the most important reason is to give a baby stepping stone instead of a giant leap. As others have said, the math is basically the same as you learned in deco, but what is different are the physical in-water skills. For instance, in Normoxic Trimix you're now working with multiple deco bottles and the gas is going quicker at 200' than it does at 130-150'. This means learning how to manage the extra gear and learning how to solve problems quicker/more efficiently because of the diminished problem solving time of being at 7ATA versus 5ATA.

Also, there's a historical reason. Prior to 1997, there was only one single trimix course. Full blown, 100m. Your choices were you either dove air, or you took full trimix, or you were a bandit and tried to figure it out on your own. There was no helium training for people that didn't want to get a card punched to go to 330', and the requirements in training were two dives deeper than 250' which upset some people that had zero interest in going that deep, but wanted to use helium at 180'. I remember very distinctly when TDI first split trimix into two courses there was a huge uproar -- "you can't do that!" Look how far we've come since then..

 

[kensuf]

BTW, you can learn to dive helium mixes shallower than 150' without taking a normoxic class.

TDI and NAUI call the course Helitrox, IANTD calls it ART. I'm not sure about GUE if it's Triox or Tech 1 now (seems they recently updated Tech 1 to be shallower than 150').

 

[tbone1004]

@kensuf I looked at the GUE standards yesterday. Still called triox and has Rec1 or Fundies Rec Pass as a pre-req. It is included in Rec 2 apparently. Tech 1 is a different animal

 

[helodriver87]

BTW, you can learn to dive helium mixes shallower than 150' without taking a normoxic class.

TDI and NAUI call the course Helitrox, IANTD calls it ART. I'm not sure about GUE if it's Triox or Tech 1 now (seems they recently updated Tech 1 to be shallower than 150').

T1 is still 170'. Just took it with Kirill a couple weeks ago. GUE teaches triox as a standalone primer if you just want access to 30/30. You can get it tacked on to a C1 class pretty easily, which is what I did. Otherwise, you get access to it at T1.

 

[RyanT]

@tbone1004, I can see that. Personally I don't use trimix at 90', but then I'm an OC diver. If I were on CCR, I wouldn't hesitate to be adding some helium at that depth.

 

[tbone1004]

@RyanT oh even at 90ft on OC in some of the high flow caves I've gotten CO2 hits, small ones, but not fun. I won't use it on OC because of how expensive it is, but on the CCR it truly is a no brainer

 

[leadduck]

That's not to say that a Normoxic class doesn't need to be taught. I think it does. But I'm not certain that ART, Normoxic AND Hypoxic all need to be taught. It's very redundant. The planning and math don't change. Sure, there's some issues like IP Pressure that is more of a problem at 400' than 200'.

Isn't the progression also about handling more stages? ART: 1 stage, normoxic: 2 stages and avoid switching error, hypoxic: leash, ...