Recreational Trimix Diver course with Techs Mex Divers, Part I

[Reg Braithwaite]

So what mix(s) are you certified to use and are your buddies in Ontario going to be diving similarly?

You know, until the card arrives in the mail I have no idea what IANTD says I'm certified to use. Judging by the marketing materials, I'm now trained to use hyperoxic mixes that provide an EN₂D of between 40' and 80' on dives to 130'. I assume this places an upper bound on the amount of He I can use.

To give the most extreme case, if I dive to a PO₂ of 1.2, I would be diving 25% O₂. If I now want an EN₂D of 40', I need 40% He. I think that would be the riches He mix I am trained to use. And I don't think my O₂ certification is affected, I presume my limit is still 40%.

Many of the folks I know in Ontario are DIR-ty divers, so they dive EAN32 or 21/35 in doubles. Although GUE has a 30/30 standard gas, I don't know anybody who dives it (yet).

...Better yet: the dive becomes a No Stop dive (assuming the diver is competent enough to make the switch while maintaining a controlled ascent ).

I can't speak to what people are doing diving the USS Algol, however both dives on my course were minimal deco dives: I planned and executed stops at 30', 20', and 10' after performing multi-level dives that ended at 40'.

So in this one case were a stage was employed, it was still a case of switching while staying within the MDL I had planned assuming no gas switch.

I have no particular qualms about IANTD's Rec Trimix program. It seems great for people who aren't comforatable with narcosis evident in the depth ranges for which the training is designed. Hell, the book is called Tek Lite or something, right?

I haven't read that book yet

 

[rjack321]

Anyone with a GUE card, diving 21/35, is almost assuredly not doing an MDL/NDL/no stop whatever you want to call it dive. The "MDL" for that at 120ft is only 10 mins, not really worth the bother.

With Canadian He prices being what they are, I can understand the general lack of 30/30 usage. You'll probably find limited use of 25/25, its not that "widespread" of a choice.

 

[Blackwood]

You know, until the card arrives in the mail I have no idea what IANTD says I'm certified to use. Judging by the marketing materials, I'm now trained to use hyperoxic mixes that provide an EN₂D of between 40' and 80' on dives to 130'. I assume this places an upper bound on the amount of He I can use.

I bet it will put a lower bound on Oxygen, but not an upper bound on Helium. Time will tell, though.

 

[Kevrumbo]

For 5 or 10mins of BT at 120ft ICD is basically irrelevant. Where's this magic 70ft level come from?
<snip>

From Bruce R. Wienke

:. . .Please do check us out in a number of (published) sources as suggesting a conservative-to-liberal hierarchy for switching on OC that goes like this:

1 -- from Lambertson early stuff, no inert gas switching (usually the
scene in military, commercial, research, training diving);

2 -- no switches off helium mixes to nitrogen mixes below 100 fsw
(scattered tests after Lamberstson);

3 -- possible switch to EAN50 at 70 fsw (or shallower) off helium mix
(source of further testing and practice among seasoned testers
and tech types).

Rebreather World - View Single Post - RBW Interview with Bruce Wienke

 

[Reg Braithwaite]

Anyone with a GUE card, diving 21/35, is almost assuredly not doing an MDL/NDL/no stop whatever you want to call it dive. The "MDL" for that at 120ft is only 10 mins, not really worth the bother.

You may be right. Considering that I don't have a GUE card, I'm really not the right person to ask and I shouldn't have conjectured. A multi-level dive of the Forest City from its stern rail at 130 feet to its bow at 70-odd feet, spending just a few minutes at the stern before rising up to enjoy the boilers at 108' was lots of fun for me last year.

It's not for me to say whether that is worth the bother for the scooter and stage bottle crowd. If I had a GUE card with Tech 1, maybe I would know which of the standard gasses is appropriate for such a dive, or perhaps what I just described isn't a DIR dive at all.

What I do know is that I will be doing this dive in August!

 

[rjack321]

From Bruce R. WienkeRebreather World - View Single Post - RBW Interview with Bruce Wienke

Check out Caverns Measureless to Man. Considering Shek was coming off moderate He %ages (like 50-60%, he used really high ENDs back in the day) and onto air at 300+ft and never reported ICD, its reasonable to say that ICD is not a particularly relevant process for sport divers. Lately Weinke (and by extension NAUI-tech) seems to be more and more afraid of ICD - moreso than DCS. Its certainly a mysterious and obtuse phenomenon that is (by his own data) very rarely manifested.

 

[Blackwood]

Lately Weinke (and by extension NAUI-tech) seems to be more and more afraid of ICD - moreso than DCS. Its certainly a mysterious and obtuse phenomenon that is (by his own data) very rarely manifested.

Yah. That ICD comment was pretty much out of left field for a discussion about rec trimix.

I'd worry more about IBS (especially if diving dry)

 

[Kevrumbo]

Yah. That ICD comment was pretty much out of left field for a discussion about rec trimix.<snip>

No . . .it happens to be very relevant, from Wienke's RGBM deco perspective, and of course with regard to NAUI-tec's tables and teaching paradigm.

<snip> Lately Weinke (and by extension NAUI-tech) seems to be more and more afraid of ICD - moreso than DCS. Its certainly a mysterious and obtuse phenomenon that is (by his own data) very rarely manifested.

But of course it is rarely manifested (by his own data) . . .the interpretation being that it's justified if you follow the RGBM Tables:

. . .On the NAUI RGBM published tables, note these are for (very) conservative purposes -- minimal gas switches, only pure oxygen in the shallow zone, and no helium-nitrogen switches. These follow #1 above [#1 -- from Lambertson early stuff, no inert gas switching. . .];
plus are nice for training neophytes in the mixed gas, deco arena. For what we do here at C&C at LANL, check out the earlier posts on this thread. We have never experienced problems within these rules and tables. . .,

Good summary here as well:
http://www.scubaboard.com/forums/440736-post1.html

 

[Blackwood]

Everything I've read about it suggests it's not a major concern for short dives in these depth ranges. Besides, you picked up on the setup and completely ignored the punchline!

Seriously, though. what is your personal limit for %dec/%inc? I know you sometimes dive GUE gases in the T1 range. Is 18/45 to 50% too steep for you? Or do you not mind since it's at 70 feet?

 

[Kevrumbo]

Keep it simple --no Nitrox deco below 21m/70'.

Eanx50 after 18/45 bottom mix is fine if I don't go over an hour bottom time.

Approaching depths where I'm using 1:3 or 1:4 RD, then I start using GUE/5thd-x helium deco mixes.
[Hijack over]