Rec Trimix

[Diesel298]

*sigh*, helium is not the central bit to the rectriox class. most of it was dealing with failures, keeping the team together, buoyancy and trim, ascent drills, mask off drills, mask off ascents, etc. its not a 'c-collector' class. if it were just about breathing helium it'd be composed of gas filling, analyzing and a little instruction not to ascend too fast....

and if you'd like to go on a dive at 100 fsw where helium makes a difference, I can arrange -- particularly after the spring plankton blooms hit here and the viz goes...

well any tech class should go thru all the skills and drills...
its just the way it should be..
as to He making a difference.. fine
but the difference it makes VS. the cost of a fill vs the cost of a Nitrox fill
a newley minted PADI aow diver can make a 100 foot dive on air...
but the super duper tech diver needs mix for a 100' dive
(just playing devils advocate here so dont get too excited)

 

[TheRedHead]

I like the tailoring aspect of TDI. The difference seems to me that with TDI, you can stop with Adv. Nitrox/Deco Proc and do baby deco dives. You don't have to take Trimix. And TDI assumes that if you do take Trimix, that you will be doing technical dives - not recreational dives on Trimix. Is this correct?

 

[TheRedHead]

You missed my point.

You missed mine too. There is an argument to be made that diving Helium on a lot of dives at 100 feet is not necessary for a safe dive. My instructor was not making an argument for deep air. 100 feet is a recreational dive. Why not Nitrox? That was my original point which seems to have gotten lost.

 

[Diesel298]

I like the tailoring aspect of TDI. The difference seems to me that with TDI, you can stop with Adv. Nitrox/Deco Proc and do baby deco dives. You don't have to take Trimix. And TDI assumes that if you do take Trimix, that you will be doing technical dives - not recreational dives on Trimix. Is this correct?

i think your not too far off.
adv, ean and deco
when you get your card on the back of the deco procedures car it says qualified to conduct deco dives planed staged deco..... blah blah
to 150 FSW (only 20 FSW more than tha you had) the adv. ean card just allows you to get the fills.
these classes are basically the OW Equivalent to Tec diving
you go with it where you want from there

 

[lamont]

wow
hit a nerve there huh.
so explain what diving you do that requires He?
your profile is a little bare.
all i see is a pic with the look at me im GUE pose

45-55F, <=20 ft viz, dark, 100 fsw, 6k ft round trip on a scooter. i've done basically the same thing without the scooter (only with around 1500' of linear distance) and the narcosis is not pleasant. add the scooter and the ability for the scooter to amplify how fast something can go wrong (particularly entanglements with monofilament and separation) and i think 30/30 is warranted. add in running your own line and exploring dive sites that you have no information on, and i think 30/30 is required.

 

[dherbman]

100 feet is a recreational dive. Why not Nitrox?

It only provides two advantages over tri that I can see: cost and availability.

 

[DA Aquamaster]

The usual thread you expect on this topic with the normal mix of dogma, dis-information, personal/agency agendas, tech wannabees, conspiracy theories, etc.

Personally, I would never place myself in a situation of having any deco obligation without being equipped with redundant doubles and a 1/3 reserve as an absolute minimum and preferrably also an accellerated deco gas. A single and a pony for deco? - not in this lifetime with or without helium.

To avoid the semantics that have popped up regarding the stops/slow ascents required with rec trimix as opposed to just calling them "deco stops". I'll define "deco" as meaning any dive where I could not do an ESA from what ever depth I am at directly to the surface. If a direct ascent is not possible, - it's an overhead dive and I will equip accordingly.

I do dive deep air to 150 ft and do it in dark, cold, freshwater environments. I accept the arguments that narcosis can impair both your problem solving skills and memory ability, but I also have to say that the degree of impairment is manageable in many circumstances and does not have to contra-indicate the dive. These dive regularly include exploratory mapping dives where we do in fact remember what we saw to an acceptable degree.

It's also an individual thing based on experience, mental capacity, training and pre-planning of the dive. I'll draw an analogy to flying an instrument landing approach on a partial panel to minimums in heavy turbulence and gusty crosswinds. Some people have the ability to do it with adequate precision while others just don't and never will. So in short, your mileage will vary.

In my opinion He has some serious limitations. It draws more heat from you through respiration which is a big issue on open circuit scuba in cold water. It also requires a separate inflation gas (air, or argon if you are overly technically inclined and like to add expense for no real gain) to reduce heat loss in your dry suit. In my experience this make He much less desireable in cold water.

Helium is a much "faster" gas in terms of ongassing so you acquire a deco obligation faster at depth (particularly shallow depths) compared to air or nitrox and as inidcated above it is more demanding in terms of ascent rates as it also off gasses faster.

It is also very expensive compared to air or Nitrox. If you have unlimited funds and it does not reduce the number of dives you do, it's perhaps not a problem. However I have met trimix divers who tend to dive trimix in any situation where they can justify it with the result that they dive a lot less due to funding limitations than they would if they spent the same available funds diving air.

And realistically, there is a trade off some where between the greater mental clarity conferred by trimix versus the value of perhaps 3-4 times the recent and lifetime experience diving air. I'd rather do several dives a week on air than maybe 1 or 2 every other week or so on trimix.

Overall, I really have a hard time seeing how the pros of trimix could outweigh the cons at depths shallower than 100-130 ft. I think in the real world it probably serves as an introductory course to develop a potential market of divers who may decide later to go on to normoxic or hypoxic trimix courses that then serve a real purpose allowing deep dives at depths below 150 ft.

 

[TheRedHead]

It only provides two advantages over tri that I can see: cost and availability.

You forgot it is possible to do that dive on Nitrox with no deco.

 

[Diesel298]

45-55F, <=20 ft viz, dark, 100 fsw, 6k ft round trip on a scooter. i've done basically the same thing without the scooter (only with around 1500' of linear distance) and the narcosis is not pleasant. add the scooter and the ability for the scooter to amplify how fast something can go wrong (particularly entanglements with monofilament and separation) and i think 30/30 is warranted. add in running your own line and exploring dive sites that you have no information on, and i think 30/30 is required.

i dive in new england so no sympathy here man
its cold, and dark.. and on the wrecks theres nets and entanglements....
being narced at 100 fsw means ya need to dive more...
but hay for the guy who dives a dozen deep dives a year and wants to stroke it out and feel good about themselves..
have at it
its your day

 

[dherbman]

You forgot it is possible to do that dive on Nitrox with no deco.

Lamont handled that earlier.

And I disagree with your instructor that 30/30 incurs any more deco than 32% does. I think that's just leftover fear of helium. It ongasses faster, so when you're actually hitting your "NDLs" at 100 fsw you'll technically have a decompression obligation (can't CESA), but it also offgasses faster so once you do your stops you're fine -- which I do anyways for 32%, so my profiles on either gas are identical and I treat the stops / ascent rate on both kinds of dives as mandatory anyway...