Is it worth to do OC trimix before CCR Helitrox?

[NaughtyDogDiving]

I think the most important aspect is actively deco diving. As long as you are doing that, I see no reason to do the trimix courses on OC when you know you will be going CCR. There are some arguments for the importance of having a lot of OC deco dives before going CCR or taking a trimix class if you aren't sure you want to go ccr, but when you know you will 100% be going CCR, the OC trimix loses its relevance and practicality.

 

[kensuf]

I'm replying to a bunch of stuff in here...

If you already know you're going CCR Trimix, don't even waste your time/money on OC Trimix at this stage.

Since you have AN/DP and as long as you have the relevant experience, you can go direct to Mod 1 w/Helitrox (150ft). Then you have to have many dives/hours before you can go CCR Trimix. In my case at least 50-dives and 50-hours.

That's the path I'm going at least. And to put it in perspective: I'm in Florida, meaning, I have no problem getting helium. Just don't see a point in investing into something that's going to go the way of the dodo.

There are two primary advantages of doing an OC normoxic trimix program before jumping to CCR.

#1: Gaining comfort and experience with deeper diving, the gas consumption and volume needs involved in that, and the decompression obligations that are a result of this. It's very easy on a CCR to get into a situation that leaves you lacking the amount of OC bailout and deco gases to safely get back to the surface, having a strong OC background will make you appreciate the actual needs and prepare adequately. Simply stated: 2x40s of gas is probably not going to be enough to get you up from a 70 minute @ 180' dive, especially if you had to bail out in anger. The time building that experience on OC will teach you that a lot more than a couple of bailout drills in a controlled environment like a class.

#2: Gaining skill and mastery over managing multiple bottles. This will be useful if you ever need to bail out.

Certification course passes are based on the minimum standard thats acceptable - its entry level. A newly minted person holding a cert card is not the same as a veteran diver with 100s of trimix dives behind them yet they both are 'certified'
My take is that the cert scheme is still based on a single tank - twins- deco bottle progression. whereas in reality more and more people are going from single tank - sidemount-deco bottle progression which means the base skill of carrying tank in CCR BO style are already in place- any transition to ccr is not such a big jumping terms of tank management.
if you have a solid base of tank management -(and your already have ANDP so you are on that path) then forget about the OC trimix and get on the ccr - adding helium to your gas is not is not that big a deal until you get to hypoxic mixes, and then theres another thing to kill you.
Caveat- only you know if your comfortable on tank management -an ANDP cert is the entry point you need to be honest with yourself - a problem on a ccr can overwhelm you pretty quickly if your fluffing around with your BO tanks. Get your slung tank, hose routing, reg swapping skills SOLID -it will be your foundation for everything else

Yes, I agree with this. There are more ways to gain experience with multiple bottle management than just normoxic trimix too, cave diving with stage bottles can teach you quite a bit in depth ranges that nitrox is all you need. However, cave diving @100' does not give you the experience of the higher RMV's that being at 180' give you.

No one is going to let you do MOD 1 at depths where you would be narced. You can't even do deco, let alone trimix depths while you are figuring out the basics of rebreather diving. I'm not a CCR instructor, but I would be surprised if any agency let someone start their CCR training with helium as a diluent.

I never did OC trimix, I started CCR training with TDI AN/DP, like the OP. I did helitrox after doing a good bit of air diluent diving on my JJ.

Depends on the student, agency and instructor. Technically, anyone coming into a rebreather program with AN/DP (or Helitrox) behind them can begin their CCR training with a 150', full deco program that includes helium, this is with both TDI and IANTD. While TDI will not let someone without prior AN/DP training jump into their first CCR course that includes deco and helium, IANTD will via the ART program.

But I've personally had a few students that struggled through their CCR training even though they were AN/DP trained/certified and my experience has not been unique (I've heard similar things from a number of other CCR instructors). At the end of the day, it will depend on the student and their ability to master the skills, but I believe it's a fair statement to say that it is reasonable to expect moving to a CCR will set someone back in their progression by close to a season until they gain some experience on the unit.

Why? How deep were your MOD1 dives?

I just did a unit crossover (as a student) where we went to 135'. I've taught a number of MOD1 courses where we hit similar depths. I've also been narc'ed out of my gourd in 80' of water before under the wrong set of circumstances, so to discount the advantages of using helium in a MOD1 course may be a bit understated.

 

[doctormike]

I just did a unit crossover (as a student) where we went to 135'. I've taught a number of MOD1 courses where we hit similar depths. I've also been narc'ed out of my gourd in 80' of water before under the wrong set of circumstances, so to discount the advantages of using helium in a MOD1 course may be a bit understated.

Obviously I defer to your experience. This is just my opinion, I'm not an instructor, but a few points.

1) I don't think that someone's first class on the loop should involve deco. There just is a lot of new stuff, no matter how much OC experience you have. I don't think that people should do CCR deco until they have a few hours after training. I understand that some agencies may think otherwise.

2) Crossover is a different thing - all crossover students by definition are certified CCR divers.

3) Narced out of your gourd at 80 feet? I belive you if you say it happened, but that seems physiologically unusual. Sure it wasn't CO2?

 

[AJ]

1) I don't think that someone's first class on the loop should involve deco. There just is a lot of new stuff, no matter how much OC experience you have. I don't think that people should do CCR deco until they have a few hours after training. I understand that some agencies may think otherwise.

Agree, started in february with CCR training. Done about 50 hours since on the loop then and MOD 2 (next month deep certification dives) is still a big step. There's a lot to learn without the burden of multiple stages and deco, even for experienced divers.

 

[kensuf]

Obviously I defer to your experience. This is just my opinion, I'm not an instructor, but a few points.

1) I don't think that someone's first class on the loop should involve deco. There just is a lot of new stuff, no matter how much OC experience you have. I don't think that people should do CCR deco until they have a few hours after training. I understand that some agencies may think otherwise.

2) Crossover is a different thing - all crossover students by definition are certified CCR divers.

3) Narced out of your gourd at 80 feet? I belive you if you say it happened, but that seems physiologically unusual. Sure it wasn't CO2?

1. Generally speaking, it's a mixed bag. 1 in 4 is a superstar and takes to the unit. 1 in 4 (more like 1 in 10) struggles really badly. The other two are ok.

2. Sure, but the point was it was within standards for an initial unit course.

3. Of course it was CO2, I never once said or implied it was nitrogen. I said narc'ed out of my gourd under the wrong set of circumstances, not nitrogen narcosis. The particular situation was physically and mentally exhausted from a 12 hour work shift followed by swimming like a lunatic against a hard flow while diving.

 

[jadairiii]

3) Narced out of your gourd at 80 feet? I belive you if you say it happened, but that seems physiologically unusual. Sure it wasn't CO2?

wont bore you with the details, but I did a 90' dive with 21/35 mix, it was the strangest feeling, everything was so "crisp", I remembered everything. Very odd, you dont realize just the amount of nitrogen narcosis that shallow. My buddies and I will lobster the deep reef (110 +/-) on 30/30, we catch a lot of lobsters!

 

[doctormike]

3. Of course it was CO2, I never once said or implied it was nitrogen. I said narc'ed out of my gourd under the wrong set of circumstances, not nitrogen narcosis. The particular situation was physically and mentally exhausted from a 12 hour work shift followed by swimming like a lunatic against a hard flow while diving.

OK, guess I was reading "narced" as nitrogen narcosis. I guess it's not wrong to use it in terms of hypercapnea, just less common, so that's why I must have misunderstood what you were saying.

Are you saying that the helium would have enough of an effect on gas viscosity to make the difference if you were overbreathing your scrubber at 80 feet (assuming CCR)?

 

[barth]

Obviously I defer to your experience. This is just my opinion, I'm not an instructor, but a few points.

1) I don't think that someone's first class on the loop should involve deco. There just is a lot of new stuff, no matter how much OC experience you have. I don't think that people should do CCR deco until they have a few hours after training. I understand that some agencies may think otherwise.

2) Crossover is a different thing - all crossover students by definition are certified CCR divers.

3) Narced out of your gourd at 80 feet? I belive you if you say it happened, but that seems physiologically unusual. Sure it wasn't CO2?

3 : Gue requires trimix for ccr diving deeper then 50 feet.

Gue ccr standard gasses:

Ean32 max depth 50 feet / 15 meter
21/35 max depth 100 feet / 30 meter
18/45 max depth 150 feet / 45 meter
15/55 max depth 200 feet / 60 meter

 

[Wibble]

Can only comment on my personal experience moving through OC to CCR and am not an instructor.


Had three years experience with Normoxic trimix beyond ANDP. The main benefit of the Normoxic course was learning how to handle multiple stage cylinders, OK two. When diving this effectively meant you needed to calculate your min gas to the second decompression stop. This opened up much longer bottom times even if not using trimix.

When moving to CCR, this meant that bailouts were a lot easier to plan and perform.

However, when moving to CCR, it is a slow progression to sort out the skills and build experience as one progresses deeper. Stayed around 30m/100ft for a while before slowly progressing to two bailouts for the 40m/130ft dives. Helium in the mix wasn't a big thing as that was normal for Normoxic diving, although a hell of a lot cheaper on CCR.

Moving deeper was again just a progression. Eventually to MOD2 and again there's no rush for deeper dives, just sort out your skills and slowly progress as you build up experience.

Often think that in this day and age where helium is very expensive it would be great if the stage handling and planning for Normoxic depths (60m/200ft) could be done without helium (or very little helium -- helitrox), but maybe down to 40ish metres / 130ish feet. Think of it as ANDP++

 

[sea_ledford]

Not to be dickish, but were you teaching the class or taking the class while not being able to calculate END? If you are teaching that very skill, it shouldn't be difficult for you.

21/35 at 150' gives you an END of 86'. That isn't inconsequential, not even a little bit. It is the difference between safe and possibly not.

As to getting the helium, it is definitely iffy these days, but still possible with some digging.

No, I calculated END on 20% not 35% He. We used 20% in class based on getting an END of less than 100 for our max depth, which was 130 due to low lake levels. I then calculated the END for 150 using 20%, mistakenly thinking that was the max allowed during class.

And I agree, 21/35 is not inconsequential. But that wasn't what I used to calculate it for my post.