Why do you need training for normoxic trimix?

[rjack321]

That’s interesting, do you mean specifically related to the helium or more to the overall “you’re going deeper and you will likely incur a deco obligation so any incident will need to be solved underwater”

On 21/35 the NDL at 130ft is about 3mins, depending on computer settings. So yes by the time you want normoxic trimix you are also asking to do deco. Deco = no direct access to the surface, so you're obligated to solve problems underwater.

 

[tbone1004]

I had three friends in Diepolder. They were all wearing the same 6 computers when all 6 shut down 20 minutes into the dive at over 280'

Luckily, the guide had made this dive 100 times before and was able to remember his deco profile enough to surface. Yikes!

were they on CCR so they could at least check if they had fully offgased? It's kind of cheating, but it's effective....

Care to tell the rest of that story? What caused the failure, which computer, etc?

 

[rjack321]

were they on CCR so they could at least check if they had fully offgased? It's kind of cheating, but it's effective....

Oh you know, or maybe having a good idea what your obligation is before splashing?

Or the old RD guesstimate. 20mins * setpoint of 4 minus 10 = about 110mins. With 12/65 dil, SP= 1.2, and GFs of 50/85 multideco says 117mins so getting in the rough ballpark. Bump the SP up to 1.3 on deco and that dive is ~108mins. Not perfect, but better than trust me deco.

 

[Superlyte27]

were they on CCR so they could at least check if they had fully offgased? It's kind of cheating, but it's effective....

Care to tell the rest of that story? What caused the failure, which computer, etc?

Nope, none on CCR. I cant remember which computer. If you ever run into Mark & Annette, ask them about it.

Ultimately, there was an inherent flaw in the computer. All of that computer had the same flaw.

 

[tbone1004]

@rjack321 oh you should certainly have a vague idea, but if that 20 minutes was outside of the "vague idea", i.e. a planned 60 minute dive you may not have that. At least on the breathers you can gauge it by the ppO2 and loop volume if you pay attention.

 

[RyanT]

Back to our regularly scheduled (non-300' dive) programming...as others have mentioned, once you venture into trimix territory, you should be thinking about deco obligations. It's easy to think about trimix as a purely 200' (or deeper) dive. But even on more benign dives (i.e. 130' where helium is still beneficial) you don't have a lot of time. So it starts to make it worth your while to consider deco training. Learning to manage failures at depth is really the benefit of trimix training.

 

[tbone1004]

@RyanT or in a cave, where I find it is QUITE beneficial at 90ft, especially on CCR.... my head is infinitely clearer to that point that given the choice, I will only put trimix in my CCR....

 

[CWK]

Except its totally irrelevant for any modern OC tech diving. And certainly not important for normoxic trimix depths which usually considered to extend to ~60-70m. Unless you are switching to air way beyond recommended ENDs, like at 90m or something, IBCD is a giant nothingburger. People sure like to bring it up online though.

All I can say is that when I did my normoxic trimix, it was part of the course. My instructor was a Tech Instructor Instructor who told me of someone (whom I have actually met before) who had suffered from it. You are, however, at liberty to believe that it is not relevant.

 

[jgttrey]

were they on CCR so they could at least check if they had fully offgased? It's kind of cheating, but it's effective....

@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.

 

[CWK]

I’d be interested in what @Dr Simon Mitchell has to say on Isobaric Counterdiffusion. I’ve been told that he is studying it.