Review: TDI Normoxic Trimix with John Chatterton, November 2019

[Wookie]

They do them with sensible reg hose connections now too!

What's the benefit to moving up quicker than waiting out the stop tho?

Gets you out of the water faster?

 

[JonG1]

Why that over changing GF or gas tho

 

[rjack321]

Why that over changing GF or gas tho

we don't need no fancy 'puter stuff!

 

[JonG1]

JC seems really keen on pdcs tho from various threads, but also tts and adherence to plan.

This almost sounds contradictory in that the pdc can fill in the blanks that old skool tables and DTs couldn't.

I like to pad as required and plan reserves accordingly.

 

[KenGordon]

According to my TDI book, ICD isn’t an issue at normoxic depths, even at the end of a dive switching at deco time. This was *early* in the dive and at a much shallower depth than hypoxic depths, with much less saturated tissues. Plus, this is not terribly far off from travel gas use. And I have heard of lots of other divers doing this in Trimix classes. (Sure, normalization of deviance.)

I cannot claim to fully understand ICD and especially inner ear DCS, my main take away from the explanation I extracted was that it is quite complicated but not a serious consideration. However that is for the switch from high He to high N2, not the reverse, since He is faster than N2 it seems more worrying.

I’d love to give OC air divers a few breaths of my deep bailout to let them understand that they are properly narc’ed and it is time to do a helium course. Currently I am scared the result might be vertigo and quite a tricky chat with a bloke or three wearing a silly with sitting on a bench. I have not heard of this being done. I have only done hypoxia mix on CCR where you certainly only worry about these things for a bailout ascent, on OC I’d guess a descent only needs travel gas to maybe 20m and a trivial N2 load so the switch to high He should be ok. Switching at 40m plus might not be so clever.

 

[Jay]

The techniques used for narcosis management are things that should be taught anyways. Streamlining, managing exertion, proper buoyancy, reading flow/current, recognizing when to kick vs pull and glide, etc. I don't think anyone discounts their value.

One technique to reduce narcosis an experienced Tec Instructor told me was a slower descent from 25m and deeper. I hadn't heard of that previously.

 

[wetb4igetinthewater]

One technique to reduce narcosis an experienced Tec Instructor told me was a slower descent from 25m and deeper. I hadn't heard of that previously.

While I'm not an experienced tec instructor, I would advise against relying on that.

 

[Colliam7]

One technique to reduce narcosis an experienced Tec Instructor told me was a slower descent from 25m and deeper.

While I'm not an experienced tec instructor, I would advise against relying on that.

While I would not rely on it, either, as a certain measure, I have had a similar experience with a dive buddy / team member. He describes experiencing conspicuous 'narcosis', or at least a degree of mental cloudiness, lasting for several minutes, after rapid descents to depth (50 m). He has tested the impact of descent rate - for HIM - i.e. done the same descent rapidly and at a metered pace (60 fpm) and says it is reproducible. I haven't really noticed it but he is a capable, experienced diver and says it is real - again for him.

From my perspective, I now try to keep my descent rate close to 60 fpm, as a general precaution, 'just in case'. I have dive bombed some wrecks and not had a problem but I see no harm in limiting the descent rate whenever practical.

 

[wetb4igetinthewater]

While I would not rely on it, either, as a certain measure, I have had a similar experience with a dive buddy / team member. He describes experiencing conspicuous 'narcosis', or at least a degree of mental cloudiness, lasting for several minutes, after rapid descents to depth (50 m). He has tested the impact of descent rate - for HIM - i.e. done the same descent rapidly and at a metered pace (60 fpm) and says it is reproducible. I haven't really noticed it but he is a capable, experienced diver and says it is real - again for him.

I'd be curious to see the results of scientific studies on this. The one problem of self testing is always the placebo effect.

 

[johndiver999]

I thought it was common knowledge that rapid descents on air to significant depths increases the severity of narcosis?

I know people who ride a scooter (and are consequently not exerting themselves by swimming down hard) and they STILL need to descend much slower than they can equalize if they want to avoid too much narcosis.