Training for "Recreational Trimix"?

[rx7diver]

rjack, isn't it the *type* of bends hit one is likely to suffer that is the main concern with recreational tri-mix in this scenario?

 

[dumpsterDiver]

There are several dives in our locale in the 100 to 135 foot range that are available to us. I am interested in getting training for trimix diving at these depths to reduce nacrossis. I would also expect this training to include deco theory and basic one-stop decompression dive planning. We are diving big singles 120-130 cf and would carry a 19 cf pony for deco mix. It wouild be trimix diving with never less than 21% O2.

We don't expect to move to doubles, or do dive deeper than 135-140 max, ever. I know that gas planning will limit our dive times but would expect gas management to be part of the course.

What training route would be best and fastest for this level. It seems that most tech courses assume that trimix will be for extreme deep diving with 02 less than 21% and require many courses before trimix is even mentioned.

However, some divers we know say that trimix is a real benefit at "recreational" depths and I have seen reference to "recreational trimix" courses that introduce trimix more early on in the training sequence.

Any suggestions for a training path? IANTD, TDI, GUE, others?

Is the whole thing a bad idea, or could this improve our safety and enjoyment on these deeper dives?

Thanks,

Guy

OR,,, you could just fill the big tank with nitrox and the little tank with air and go diving. The people I hang out with dive deeper than that and nobody uses He for dives that shallow. Is it even environmentally responsible to consume something as scarce as helium for a 100 ft dive?

 

[waterpirate]

Once you go 20% you never go back. While helium does wonders for narcosis, a deco plan does wonders for your bottom time, and overall safety. A used set of steel 72's banded and manifolded goes for under 500. A used set of hp 100's banded and manifolded is around 500.

My suggestion to you if narcosis is not your primary concern, is to go the deco procedures and advanced nitrox route and see how that suits you. Either way the bottom line is that you are going to have to change some, if not all your gear.
Eric

 

[TSandM]

I don't think it's unreasonable to add some helium to your arsenal for dives in the deep recreational range. Helium is, or is thought to be, far more unforgiving of excessive ascent rates, which means the training has to include a lot of scenarios to be sure that you can problem-solve underwater, and remain calm and control your subsequent ascent. I am QUITE sure that the UTD Rec 3 class would be like that (having essentially taken it, before UTD existed and the class had a name). If your gas planning is correct and you can handle serious gear failures, there is probably no reason you HAVE to have doubles. It lowers the likelihood of an air-sharing abort of the dive. But I'd rather see somebody contemplating an occasional dive to 130 using a 25/25 mix and getting good stress management training, than see them decide to do the same dives on air.

 

[manni-yunk]

Recreational trimix seems to make sense to me. Why dive drunk? Check out PSAI and their new Triox classes.

They have 3 levels of Triox. Sounds like the first is exactly what you need.

 

[NAM001]

I did mine with IANTD and it went quite well. Knowledge wise it was , for me, like a nitrox course. My deco bottle is a al 40 though and not a 19. I would think about a larger pony espeially if you are planning on 50% deco. Bounce the size issue on your instructor when you start using the tables and know better what you gas needs could be.

There are several dives in our locale in the 100 to 135 foot range that are available to us. I am interested in getting training for trimix diving at these depths to reduce nacrossis. I would also expect this training to include deco theory and basic one-stop decompression dive planning. We are diving big singles 120-130 cf and would carry a 19 cf pony for deco mix. It wouild be trimix diving with never less than 21% O2.

We don't expect to move to doubles, or do dive deeper than 135-140 max, ever. I know that gas planning will limit our dive times but would expect gas management to be part of the course.

What training route would be best and fastest for this level. It seems that most tech courses assume that trimix will be for extreme deep diving with 02 less than 21% and require many courses before trimix is even mentioned.

However, some divers we know say that trimix is a real benefit at "recreational" depths and I have seen reference to "recreational trimix" courses that introduce trimix more early on in the training sequence.

Any suggestions for a training path? IANTD, TDI, GUE, others?

Is the whole thing a bad idea, or could this improve our safety and enjoyment on these deeper dives?

Thanks,

Guy

 

[rjack321]

rjack, isn't it the *type* of bends hit one is likely to suffer that is the main concern with recreational tri-mix in this scenario?

No the main concern with your 130ft CESA is embolizing. Gas mix is irrelevant since any bubble entering your arterial system is going to have dire consequences. And air, nitrox or trimix will all carry the same risk of embolism. DAN statistics actually bear this out, most fatalities are OOA followed by an embolism. Worrying about a type 1 vs 2 DCS hit after a 5-10 min dive at 130ft is worrying about the wrong threat.

 

[rx7diver]

No the main concern with your 130ft CESA is embolizing. Gas mix is irrelevant since any bubble entering your arterial system is going to have dire consequences. And air, nitrox or trimix will all carry the same risk of embolism. DAN statistics actually bear this out, most fatalities are OOA followed by an embolism. Worrying about a type 1 vs 2 DCS hit after a 5-10 min dive at 130ft is worrying about the wrong threat.

rjack,

The helium-breathing diver here might be forced to attempt an ESA from any recreational depth (say, from 60 fsw, for example, during the ascent phase at the end of a deep dive).

My thinking is as follows:

1. What is emphasized in air/nitrox rec diving is, at any time during a dive an immediate, direct ascent to the surface is possible, and ...

2. ... an ESA is always an option (albeit an option of last resort, perhaps).

3. A 60 fpm ascent rate (as historically taught) is tolerated, often, for air (or nitrox) rec diving.

4. Helium is absorbed into and released from blood and other tissues significantly faster than nitrogen.

5. Ascent rates for divers breathing helium-based gas absolutely should not exceed 30 fpm.

6. An ESA introduces an increased likelihood of DCI (be this DCS or AGE).

My (intuition-based) conclusions:

a. Since helium releases faster from blood and other tissues faster than does nitrogen, DCS is more likely when attempting an ESA while breathing tri-mix than while breathing air/nitrox--moreover, this DCS is more likely to be Type II DCS than Type I DCS when breathing tri-mix than while breathing air/nitrox--if the ESA is attempted using a 30 [sic] fpm ascent rate. If the ESA is attempted, instead, using a 60 fpm ascent rate, the likelihood of suffering DCS is much, much greater when breathing tri-mix than when breathing air/nitrox.

b. Since helium releases faster from blood and other tissues than does nitrogen, AGE is more likely when attempting as ESA while breathing tri-mix than while breathing air/nitrox--if the ESA is attempted using a 30[sic] fpm ascent rate. If the ESA is attempted, instead, using a 60 fpm ascent rate, the likelihood of suffering AGE is much, much greater when breathing tri-mix than when breathing air/nitrox.

c. The upshot (my long-held suspicion) is, *recreational* tri-mix diving is inconsistent with being able to effect an immediate, expeditious, direct ascent to the surface from recreational diving depths. That is, *recreational* tri-mix diving is inconsistent with recreational diving.


Does any of this make sense?

rx7diver

 

[waterpirate]

Here in the mid atlantic, your statement #1 and #2 are trained out of divers once you get off the shoals. The argument is that the bail out strategy you describe may be surviveable, but it is not adviseable, and WTF?? You may want to spend some additional time on the shoals getting up to speed.
Eric

 

[TSandM]

rx7diver, the key to this type of recreational trimix training is that such dives walk the grey line between recreational and technical diving, and partake significantly of the characteristics of the latter. That's why someone who has a "deep" specialty can't just put a helium mix in their tanks and go diving, even though the actually DIVE is executed precisely the same way. Gas planning, gas reserves, and problem-solving underwater are all parts of the training in these classes. The emphasis becomes problem prevention and problem-solving, not "blow and go". These are quasi-technical classes.