Some thoughts that popped after teaching a CCR Class

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Capt Jim Wyatt

Hanging at the 10 Foot Stop
Staff member
ScubaBoard Business Sponsor
Scuba Instructor
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High Springs - Cave Country
# of dives
5000 - ∞
On occasion I teach a CM Optima course here in cave country and along with anything you teach, you learn stuff while teaching and you re-learn stuff you already knew but was maybe on a back burner.

This past week I taught two guys a Choptima class. I had previously taught them OC trimix at Eagles' Nest a few years ago.

Some of the things I relearned or pushed to the front burner are:
  • Make your rebreather your primary scuba. Get the muscle memory, learn the thing SOLID and keep on diving it.
  • Know your O2 cells intimately. Be able to predict their performance before you get into the water. If they perform differently than expected question them, doubt them and make them prove to you that they are healthy.
  • Do not be cheap by using sorb to the absolute limit. When the scrubber is nearing the end of its endurance it is not capable of challenging use. An almost used up up scrubber can’t handle a challenge.
  • Do not be cheap; change your O2 cells as directed or sooner as needed. Keep spare cells available.
  • Do not start a dive with a known failure.
  • Abort a dive when a failure occurs.
  • Know how to use SCR mode. Practice it. It can turn an 40 cubic foot bottle into essentially a 200 cubic foot bottle.
I'd appreciate some of you experienced rebreather divers adding to this list.
Sounds like you had a “well **** me running” kind of day Jim. Hope all is well.
Nothing to add
It's really bad how people has "lack of curiosity" about O2 measurement
Don’t get lazy or complacent with your equipment setup checklist when you’re setting up. Also same with your pre-dive checks/START drill/whatever you want to call it. Don‘t be lazy and half a** it and do one of those 30sec deals with your buddy were you both just go “all my stuff is working, and I have all my dive kit in my pockets. Ok lets go diving“​
If your going to be “that guy” I think this is usually how you get into trouble. That’s when you jump in the water with you onboards closed, ADV flow stop closed, you dry suit inflator hose not plugged in, or suit inflation tank not opened, your battery on your primary is super low and dies mid dive, your BO Regs are bubbling, you forgot to put your backup mask in your pocket, etc. etc. etc.​
Another thing overlooked or that gets pushed is BO planning. Yes I know He is expensive and then you have to play the game of what do I do with all the high He mix BO and you basically have to have dedicated tanks for storing trimix. But don’t be cheep be realistic about your BO planning and SAC rates. Guess what if you truly need to BO at depth due to CO2 hit or you have some kind of catastrophic failure or just the sh*t hits the fan. I don’t care who you are or how experience you think you are you are not going to have a 15l/min SAC rate its going to be more like 3-4 x that and it’s amazing how fast you can drain and S80 if you’re at depth.​
Also with BO planning play around with different BO scenarios I know a lot of people overlook the “what if scenarios”. I don’t think enough time gets spent on BO planning. I think this is actually the most important thing that just does not get taught very well.​
In particular with sub 100m dives you really need to play around with different scenarios and optimize/pick the correct mixes as it starts to become really easy to give your self an IBCD hit. Great example is lets say your doing a 150m dive and your mid way through all your deco stops you get to 21m and you have some kind of catastrophic failure so you need to BO. If you were just following your computer and plan naturally you would BO to your 50%. I can pretty much guarantee you this will give you an IBCD warning. Chances are you need to BO to your intermediate trimix and you can not safely switch to the 50% until a shallower depth like 15m. This like this need to be clearly understood as part of your dive plan between you and your buddy.​
Lastly another thing that gets really really really overlooked and is not taught much is emergency procedures. You and your dive buddies should know/have it written down in your wet notes (also each others DAN numbers, DOB, and emergency contact persons number) what the plan is for different what if scenarios. Everyone in your dive team so should know know with confidence what are you going to do if:​
- Someone has an oops loss of buoyancy at 6m and shoots to the surface when they still have 30min of deco left.​
- Someone in your team starts to get pain/symptoms of DCS at 9m​
- Someone in your team starts to have symptoms of DCS shortly after surfacing (do you guys have an in water re-compression plan)​
- Someone on your team gets sick underwater and you still have 3hr of deco left.​
- Do you actually know if there is a chamber near you and does it actually work. You would be amazed when you get outside 1st world nations how many chambers do not actually have full time operators, have o2 in stock, etc. And then in 1st world nations you would be amazed at how many will not actually accept a patient until then get all the insurance BS sorted. Just because there is a chamber near you don’t assume you can use it. You need to physically talk to the chamber operator and admin to find out all the details of how to use it if you really need to.​
And then the really hard discussions need to be had also with your team. What if someone goes unconscious, toxes, or some other scenarios where they need to be brought ot the surface ASAP but you have 3+hr of deco left. The reality is no one can skip that much deco so what are you going to do, you should have a plan between your team.​
Adding to BO planning - take care of your BO regulators, always pull negatives on the surface, and wet breathe each for ~15 seconds.

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