Help me understand rebreather progression please ...

[CAPTAIN SINBAD]

So I am trying to understand how rebreather training is structured. If you are an Open Circuit Trimix diver then is there any agency that enables you to do a parallel transition to rebreathers? Or do you have to take a rebreather introductory course (similar to Open Water) and the re-take all the tech levels up to Trimix and Advanced Trimix etc?

Also in Open circuit technical diving education, most of the time you will not see experience requirements from one course to another. If you are Decompression certified, you can take Trimix after 10 dives or after 200. Are there any experience hours on the unit that you have to complete at each level before you progress to the next?

Lastly, is rebreather training agency specific or is it unit specific? If you chose to go with Optima or Meg or Revo etc, would it matter which agency? Or in other words, would the agency choice restrict the models you could be training on?

Many thanks everyone.

Sinbad.

 

[sea_ledford]

There is some learning curve for switching to CCR, so a straight crossover from trimix OC to trimix CCR isn't recommend, or allowed AFAIK. Progressing too rapidly back to OC levels has been cited as a factor in several incidents and fatalities.

Looking at TDI standards, the initial training is unit specific, additional training is not. Going from one level to another does have water time requirements - 30 Hours and 6 months going from Air dil to helitrox, 50 hours to mixed gas, 100 hours for advanced mixed gas. Those times are cumulative, not since the previous class. There are other requirements for each level, but those are the time pre-reqs.

Agency-wise, it depends on if the agency certifies on the particular unit you are diving. TDI seems to have most units covered, IANTD probably does as well. NAUI has about 3 actually available options and a bunch that are current or surplus military or no longer in production. I think at this point most manufacturers require that they sign off on the instructors, not just the training agency. So I can't become an SF2 instructor just by going through TDI, I would have to involve Scuba Force as well.

-Chris

 

[KevinNM]

GUE does a single course. Post Tech 2, so you have hopefully figured out this diving thing. But I’m not sure what the suggested path provided inside the course is.

 

[tomfcrist]

IANTD will allow the instructor to certify a new rebreather diver to normoxic during the mod 1 course...assuming they are OC trimix. All the course requirements for CCR and Normoxic CCR have to be met AFAIK.

In my opinion, CCR divers that are diving deeper than say 60’ can easily benefit from putting helium in the DIL if for no other reason than affecting gas density and reducing WOB. FWIW, normoxic on CCR isn’t the same as OC...14/50 is a normoxic mix on CCR I’d you consider the same depth limit as OC normoxic....assuming the desire to leave the DIL PPO2 at 1.0 or less.

 

[kensuf]

No matter what, you're going to have to put time on the loop to get to full trimix even if you're an OC trimix diver with a lot of experience. There are some incredibly good reasons for this.

Here's the basic path with TDI and IANTD.

Step 1: Air Dil Deco (or Helitrox / Advanced Recreational Trimix)
TDI: Brand new rebreather diver with Advanced Nitrox/Deco Procedures experience/certs - course path is "Air Dil Deco" (or Helitrox Dil Deco). Limitations: 150' max depth. If you do not have OC AN/DP you must start at basic CCR and earn 30 hours (limitations of 100').
IANTD: Brand new rebreather diver w/zero previous deco experience - can include advanced EANx / ART (advanced recreational trimix) at the same time as CCR diver. Limitations: 140' (air dil) or 170' (ART), light deco (~10-15 minutes)

Step 2: Normoxic Trimix

TDI: Pre-reqs: certified air dil with deco, 50 CCR dives + 50 hours on the loop. Certification is unit specific.
IANTD: Pre-reqs: 100 logged dive (25 on CCR) + 50 hours on the loop. Certification is not unit specific. Note, if you're an OC normoxic diver you can do the normoxic CCR training at the same time as basic CCR training, but you will not earn a normoxic CCR card until you've met the dives/hours on the loop.

Step 3: Full Trimix

TDI: Pre-reqs: 100 dives/100 hours on a CCR, 50 hours on the unit you're getting trained on. At least half the dives must be deeper than 100'. Certification is unit specific.
IANTD: Pre-reqs: 100 dives/100 hours on the specific unit you're doing training on. 25 dives must be between 140-200'. Certification is not unit specific.

 

[kensuf]

IANTD will allow the instructor to certify a new rebreather diver to normoxic during the mod 1 course...assuming they are OC trimix. All the course requirements for CCR and Normoxic CCR have to be met AFAIK.

This is kind of misleading. An instructor can combine the Mod 1 and Mod 2 courses if a person is already OC full trimix certified, but a normoxic CCR card can not be issued until the student has put the 50 hours on the unit.

 

[PfcAJ]

GUE does a single course. Post Tech 2, so you have hopefully figured out this diving thing. But I’m not sure what the suggested path provided inside the course is.

At least for rb80 the progression is tailored for the diver. Each person on my course got a different recommendation.

 

[hroark2112]

There's a bunch of good reasons for not going straight from OC trimix to CCR trimix.

First, you've got enough going on while you're learning to dive CCR already, adding in multiple bailouts and gas switching is just not a good idea. You don't know what your bailout requirements are going to be yet or what kind of stress you'll already be going through in the beginning.

I've heard more than one person say the safest hours on your rebreather are your first 25 hours. You're probably still doing written checklists, you are very likely diving very conservatively and are paying very close attention to everything. Then comes hours 26-50. Complacency starts to set in a bit, maybe you don't follow a checklist as religiously, maybe you've noticed that your PO2 doesn't fluctuate so much so you don't pay close enough attention to your computer. This, as I have heard, can be some of the most dangerous hours for a new CCR diver. Once you get 100 hours or so, you've decided you're sticking with CCR diving, you've probably fought through a few issues, maybe even a close call or two. You've see things go pear shaped and you're not so complacent...you've figured out what you did wrong to make things go pear shaped and you've learned from your mistakes.

When you're comfortable on the unit and have your buoyancy dialed in, bailing out is second nature, you've got a routine for your pre-dive and unit assembly down pat, and now you're ready for the next step. Adding additional bottles, gas switching, bail-out gas planning, and deco planning won't be as hazardous when you aren't still learning how to maintain your buoyancy and figuring out what the heck a "minimum loop volume" feels like.

After 300+ hours on the loop, I find I learn new things all the time. If I ever think I know it all, it's probably time to go back to OC.

 

[joshk]

After 300+ hours on the loop, I find I learn new things all the time.

Out of curiosity what kinds of things are you still finding to learn?

 

[Gareth J]

As others have said, and from my experience.

You cannot go from OC trimix straight to CCR trimix. It is strongly recommended by all training agencies that you take time to adjust to CCR diving, prior to progressing to CCR trimix.

I started with OC full (no limit) Trimix.
I did the MOD1 course. In my case, this resulted in an Air DIL, 40m limit. I don't remember there being any limitations on the decompression penalty you could run.
I did a lot of diving on the unit on shallow dives. Initially any dive over 30m I did on OC. I was even on a boat where I swapped from OC on the morning (deep) dives, to CCR for the afternoon shallow dives.

The credit I got for my OC Trimix ticket, was when I took the next ticket. I basically did a combined MOD2, and MOD3. Basic trimix theory doesn't change for OC or CCR. However, there are different dive practice's between OC and Trimix. The combined course was probably one of the most intense courses I have done, at least from the point of view of diving, in water skills and exercises. The theory was reasonably straight forward (I had a reasonable amount of trimix knowledge from my OC courses and experience), there where a few changes to planning to match the requirements and limitations of CCR practice.

From a personal point of view - I would strongly advise anyone transitioning from deep OC to CCR to spend at least a season if not longer on shallow diving gaining experience on the unit. Importantly, you are attempting to break a number of habits you have developed for OC diving. The more experience and aptitude you have in your OC diving, the harder in many ways to break those habits.

As an illustration. The introduction of the AP Inspiration (now known as the classic), resulted in an affordable CCR suddenly becoming available to UK divers. It was also manufactured by a reputable company with many years of supplying and building a reputation within the UK for good solid dive kit with good lifetime support (In particular the 'buddy' range of bcd's).
It wasn't a cheap unit to buy, but it was reasonable, especially if you where doing deep diving or trimix diving. The end result was a number of very well known and experienced divers and dive teams invested in the new technology. Despite the very strong statements to spend a season learning the unit and avoid deep dives, people quickly returned to the type of diving they had been doing. The end result was a huge spike in fatalities and diving incidence. The people getting hurt where not the inexperienced over extending themselves, but the very experienced divers. HOWEVER, they where inexperienced CCR divers. It took a while for people to finally accept that CCR is different to OC and you do need time to adjust and LEARN.
The inspiration gained the nick name YBOD (Yellow Box Of Death), during this period.

We (in the UK) have finally learnt the lesson. The experienced divers do take the time to adjust now. Also, people transition to CCR earlier in their diving, because of the healthy secondhand and therefore affordable market. This means they gain experience between each qualification, as they would if they stayed on OC.

In summary, if you chose to change from OC to CCR, welcome. Welcome to a world without bubbles, of a feeling of infinite gas and time. But PLEASE, take your time to learn the strange world of CCR diving. REMEMBER on OC a fault or issue is normally immediate. On CCR it slow and can creep up on you if you are not paying attention to the unit and the PO2. The upside is you normally have time to analyse and resolve the issue .

Gareth