Rec Trimix

[radinator]

I'm probably going to take Trimix as my next class. GUE seems to advocate Trimix at depths where I would dive air nitrox. I don't recall hearing any arguments as to the disadvantages of diving Trimix at 80 or 100 feet. There are appear to be some real ones.

I believe the advantage is having a clear head. Oxygen and Nitrogen are almost equally narcotic. Helium - not so much.

I believe the disadvantage is how quickly you ongas, as previously discussed. Buoyancy control is very necessary.

Notice the "I believe" statements above...

Ray

 

[lamont]

I think all the tech agenices care about buoyancy skills but my instructor's point of view was: why incur a deco obgligation at 100 feet on Trimix when you can dive it on Nitrox cheaper and dive it within the NDLs or with minimal deco. He thought the idea of rec divers diving Trimix kind of screwy. And most people consider a 100 ft dive suitable for recreational divers.

I get narc'd at 100 fsw. Normally its not a big deal, but if I want to remember more (e.g. boat dive on a wreck i haven't been on) or if its more task loading (3000 ft trip out and back on a scooter, or scootering and laying line at 100 fsw, or whatever) or if its just an unfamiliar site, i'll take the 30/30...

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...

 

[TheRedHead]

I don't know Lamont. My instructor is a pretty smart guy. His Trimix card was issued by Billy Deans, whom I believe was the first Trimix instructor in the USA? He's also a recompression chamber technician. I can see the benefit at 130 feet where I'm narced and really notice the denser air. I routinely dive to 100 ft on Nitrox 32 and I don't noice the narc or denser breathing, but I won't argue that I'm not somewhat impaired. Even though I am certified to dive to 150 ft on air, I don't plan to. I do plan to take Trimix later with TDI, but I'm trying to understand this 100 ft. cut-off. I don't think the average rec diver could dive Trimix at 100 ft and I think the name "recreational trimix" is a bit misleading in that regard.

 

[Marlinspike]

I disagree. I don't think there is any need for trimix for dives above 100ft that can easily be done using nitrox and accelerated deco on nitrox.

Sheesh... Some people will just do anything to appear more tech without any good reason.

One of the main concepts in REAL tech diving is the "mission" approach to diving, where you address a goal with the tools needed to acomplish the mission. Do you need a 200lb lift bag to lift that 2hp outboard? NO, and using the 200lb lift bag will only add unnecessary complexity to the situation.

Same thing in this case: Do you REALLY need trimix for a dive to 90 ft?

~Marlinspike

 

[JeffG]

I don't know Lamont. My instructor is a pretty smart guy. His Trimix card was issued by Billy Deans, whom I believe was the first Trimix instructor in the USA?

Old school vs New school. People tend to believe the first thing they learn, even though it might not be right.

 

[Kevrumbo]

I disagree. I don't think there is any need for trimix for dives above 100ft that can easily be done using nitrox and accelerated deco on nitrox.

Sheesh... Some people will just do anything to appear more tech without any good reason.

One of the main concepts in REAL tech diving is the "mission" approach to diving, where you address a goal with the tools needed to acomplish the mission. Do you need a 200lb lift bag to lift that 2hp outboard? NO, and using the 200lb lift bag will only add unnecessary complexity to the situation.

Same thing in this case: Do you REALLY need trimix for a dive to 90 ft?

~Marlinspike

Cold Water, poor viz, currents to work against, or penetrating a wreck --typical conditions here off the coast of So. Calif. . . .most definitely YES!!!

 

[mart1]

Not that I'm considering this particular class, but my TDI instructor says that shallow Trimix is a bad idea because of how quickly you acrue a deco obligation.

He is right, and this is not the only disadvantage of helium.
The thing is, helium has definite advantages for deep diving (although hydrogen would be better). But some agencys have gone a little bit overboard and now tell you nitrogen is all bad and helium is all good. I suspect this is only a response to the real deep dives made on air not too long ago, and a consensus will be reached in a few years where we will use trimix for the depths where it makes real sense.

mart

 

[TSandM]

Just to reiterate that GUE teaches RecTriox to people who have passed Fundies -- therefore buoyancy control has reached a certain level before you start. This is not "helium for the average open water diver".

I've been below a hundred feet on air in the tropics. I'm sure I was impaired, but I wasn't aware of it. But I've also had a dark narc at 100 feet in poor viz, cold water, and low light here in the Sound, and I would prefer not to repeat that experience. There are things here at those depths worth seeing (right now, there's a big octopus on eggs, which is what we went down to look at when I got narced, and I never saw) and for that reason, I'll probably go ahead and take Rec Triox (if and when I pass Fundies )

 

[Marlinspike]

Cold Water, poor viz, currents to work against, or penetrating a wreck --typical conditions here off the coast of So. Calif. . . .most definitely YES!!!

How exactly does trimix help you in cold water again?

~Marlinspike

 

[TheRedHead]

Another factor apparent from this thread seems to be conditions where cold and poor viz make helium at 100 feet more sensible. I dived to 100 feet in warm water, poor viz and didn't have a dark narc. My narcs tend to be happy ones and that only scares me afterwards. The fact that I'm not scared at 140 feet is kind of scary sometimes.