Training for "Recreational Trimix"?

[guyharrisonphoto]

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

 

[DA Aquamaster]

I'm sure agency definitions vary a great deal, but "recreational trimix" is generally interpreted as no deco stop trimix dives, while "advanced recreational trimix" would involved staged decompression stops.

Using IANTD as an example, the former certs you to no deco dives to 130', while the latter allows dives to 160' with up to 15 minutes of decompression. In comparison, normoxic trimix would allow 200' dives on trimix with a couple deco gases and no specified deco limit. In that regard I would not bother with recreational trimix and normoxic trimix makes more sense then advanced recreational trimix.

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That aside, doing decompression with a single tank, even a 130, and a 19 cu ft pony for deco gas is a really bad idea. You'll need enough back gas to meet your longer deco obligation on back gas alone in the event the 19 cu ft bottle is not available/lost/non functional. Separate from this, you'll also need enough back gas to provide adequate gas for the buddy to safely ascend in the event he loses all his back gas. Those requirements will create fairly harsh limits on the dive profiles you can do - probably paring you back to near the NDLs on anything much deeper than 100'.

Even then, I don't know many divers who do hard or soft overhead diving without a fully redundant configuration, with perhaps a few doing it with a large tank with an H-valve - and working hard to stay within the limits of the required gas reserve.

And, 19 cu ft is not a great deal of 02 to carry on a deco dive, where at a minimum you want to have 1.5 times the planned gas available. A 30 or 40 is just as easy to sling and carry but offers a lot more gas.

In that regard, you're trying to get a little bit pregnant - doing some decompression on a recreational configuration - an approach that's been bending divers for a long time. Consistent with that IANTD won't let you do deco stops with single tanks and will require doubles with an isolator manifold as a minimum for the advanced recreational trimix course.

Other agencies *might* let you do deco with a single tank and H valve, but that would still not make it smart and I'd avoid any agency that allowed it.

 

[TSandM]

GUE's recreational trimix class requires manifolded doubles.

UTD will permit the use of single or double tanks. Their Rec 3 (recreational trimix) class is a no-deco class, which means bottom times are short. I always remember Mike Ferrara's advice on such dives . . . that rather than spend the money on helium to go down and do ten minutes of dive time, it's better to step up to tech training and do the dive as a properly planned and executed staged decompression dive, which gives you a much bigger bang for your buck.

 

[fnfalman]

If money isn't an issue then go for it. Otherwise like TSandM said, it's a pretty expensive gas fill to do ten minutes of bottom time.

I am thinking about doing recreational CCR breather. Why? I just want to play with new toys.

 

[mhosts]

I am interested in getting training for trimix diving at these depths to reduce nacrossis.

I think that's the primary point the above replies are missing.

OP, to what extent are you experiencing narcosis at the 100-135 depth range? Obviously since you're considering trimix in this range the effects must be pretty significant...

 

[Doppler]

You could consider helitrox decompression from TDI (Techdiver Training with Steve Lewis-- General Info). I teach the program regularly and have delivered the full course to divers in large volume single cylinders... but below 30 metres (100 feet) you MUST have redundant backgas to conform to standards... which at least means an H or Y valve on that tank. Also, by using a 19 cubic foot decompression bottle you are restricting yourself to dives on which less than 10 feet of deco gas is required... standards again... Each diver must carry TWICE the volume of deco gas required of the dive.

I would suggest a serious rethink. Email me if you want to chat.

 

[guyharrisonphoto]

OK, so is the consensus that we will be limited to no-deco diving if we stick with single steel 120s or 130s, even if we carried a deco pony bottle (19 or 40cf). That's fine, we can live with that, just want to get input. Safety is first, always.

TS&M and Aquamaster, I appreciate what you say, but these 130' dives will be a relatively small percentage of our diving, ie for a few select spectacular spots that are worth the extra effort (and risk) even for a short bottom time. Maybe 5 dives per year out of 50. Even if the dives stay short, we want to minimize our risk and enhance our enjoyment. Right now, doubles are not in our foreseeable future. Think of it like baby steps--if we do the basic trimix training (no-deco), and later want more, we can do more training and get the doubles. What I am interested in at first, and glad to see exists, is basic trimix training that can be used with large single tanks even if that is limited to no-deco dives to 130'.

Mhosts, Like many advanced divers, we are not "consciously" hammered with narcosis even at the 130' dive on 28%, but my research, and speaking to other divers, leads me to believe that diving with trimix makes a real, noticeable difference in both the safety and the enjoyment of the dive because, uniformly, they all say how surprisingly more alert they are during the dive and how much more they remember. I just met some GUE folks who said they regularly use trimix for pretty much any dive below 100'. As for the cost of a fill, well, no one said this is a cheap passion and for the relatively small percentage of dives we would use it for, would be worth it.

Please, keep comments coming. That's what is great about these boards!

 

[Slamfire]

Guy H.,

What specifically don't you like about doubles at this point of your scuba progression?

Is it the price that your LDS is trying to to sell them to you for? Do you have 2 aluminum 80 tanks? If so, all you need to double them are these 2 items:



This is a total $235 for brand new hardware from a trustworthy online vendor.
Personally I would much rather dive twin Al 80s than a HP 130 and a 30 cu ft stage (or 19 cu ft). You'll get a better balance and you can easily configure them to the ubiquitous North Florida cave rig (aka hogarthian). You'll be building muscle memory that will be useful on big dives requiring advanced trimix. And you can just as easily use it at the normoxic/helitrox level. You'll also be much more likely to find other divers in the same configuration, making it easy to adapt to a new team while travelling.

Another big advantage of starting with double Al80s is that when you get to the point of advancing to requiring higher volumes of gas, you repurpose those Al 80s to stage duty and use the bands and manifold on a couple of HP100s or HP120s.

I don't see much room to grow on a 19 cu ft pony. It's rather big for suit inflation and rather small for O2 deco. You'd probably have to go to rebreathers to find another use for that 19 cu ft bottle.

 

[rx7diver]

I've personally never been quite comfortable with the notion of *recreational* tri-mix. Recreational air (or nitrox) diving within 130 fsw/ffw training limits, always leaves open the extreme option to "blow and go" (i.e., to make an emergency swimming ascent, perhaps at an ascent rate exceeding 60 [sic] fpm) as a last-ditch effort. My understanding of tri-mix, though, is the prescribed maximum 30 fpm ascent rate absolutely must be respected, which suggests that the "blow and go" option is not available to a *recreational* tri-mix diver. Is this correct? Can any of you tri-mix instructors comment?


Safe Diving,

rx7diver

 

[rjack321]

I've personally never been quite comfortable with the notion of *recreational* tri-mix. Recreational air (or nitrox) diving within 130 fsw/ffw training limits, always leaves the extreme option to "blow and go" (i.e., to make an emergency swimming ascent, perhaps at an ascent rate exceeding 60 [sic] fpm) as a last-ditch effort. My understanding of tri-mix, though, is the prescribed maximum 30 fpm ascent rate absolutely must be respected, which suggests that the "blow and go" option is not available to a *recreational* tri-mix diver. Is this correct? Can any of you tri-mix instructors comment?


Safe Diving,

rx7diver

Doing a "blow and go" from 130ft on any gas is likely to get you bent. Maybe a little more likely on a "recreational trimix" like 25/25 or 26/17 than it would be on air. Its more dependent on the time at depth than the helium however. In either case, getting bent is really the least of your worries if your emergency strategy for 130ft dives is to "blow and go".

However as TS&M said, doing no deco dives in the ~120ft range is kind of silly since the bottom times are so short.