CCR - SCR Mode

[wedivebc]

If you have a dry scrubber and a normoxic diluent I cannot see what would be dangerous, throughout the depth range from 180 feet to the surface, so long as the O2 bottle is shutdown.

One of my mentors and respected instructors who also manufactures rebreathers told me it was dangerous because when you are in SCR you are most likely ascending. If you ascend while performing SCR bailout (assuming no electronics) you don't actually know your PO2 and could go potentially hypoxic and you will not have a very good awareness of your deco status.
My counter argument to that is if you perform these drills with good electronics and get an idea of your PO2 under controlled conditions you will be better equipped to manage SCR in real world situations.

 

[Capt Jim Wyatt]

If air is the diluent you won’t go hypoxic so long as you do 2-3 breath cycles max, then flush.

Clearly this takes a thinking diver who understands the physics.

 

[Capt Jim Wyatt]

My counter argument to that is if you perform these drills with good electronics and get an idea of your PO2 under controlled conditions you will be better equipped to manage SCR in real world situations.

Yes, it must be taught and practiced with working electronics so you know how many breath cycles drops PO2, obviously the deeper you are the more breath cycles you can take due to higher ambient pressure/PO2.

 

[tbone1004]

One of my mentors and respected instructors who also manufactures rebreathers told me it was dangerous because when you are in SCR you are most likely ascending. If you ascend while performing SCR bailout (assuming no electronics) you don't actually know your PO2 and could go potentially hypoxic and you will not have a very good awareness of your deco status.
My counter argument to that is if you perform these drills with good electronics and get an idea of your PO2 under controlled conditions you will be better equipped to manage SCR in real world situations.

do a full dil flush before you go to SCR mode, and then it's no different than diving any other SCR in terms of loop po2....

 

[barrmust]

As part of the TDI course on a KISS unit it is a required skill.

Russ

 

[wedivebc]

do a full dil flush before you go to SCR mode, and then it's no different than diving any other SCR in terms of loop po2....

Sort of, but unlike passive SCR systems like RB80 SCR mode on a CCR also requires the diver to do an efficient ventilation as the volume of gas exchanged is not driven by the rebreather. It is definitely a skill worth learning but as a poorly learned skill can be dangerous.

 

[Capt Jim Wyatt]

as a poorly learned skill can be dangerous.

Yes it can be - just like many other skills.

 

[DA Aquamaster]

My instructors, yes.

The two SCR drills naysayer guys: No, OW reef/wreck background.

Sort of, but unlike passive SCR systems like RB80 SCR mode on a CCR also requires the diver to do an efficient ventilation as the volume of gas exchanged is not driven by the rebreather. It is definitely a skill worth learning but as a poorly learned skill can be dangerous.

Correct me if I am wrong (I've never taken a "recreational" CCR course) but goals in a 3 day recreational CCR class are primarily to learn to recognize when there is a problem and to bail out to OC, while the goals in a 5 day technical CCR class is recognize when there is a problem, diagnose the problem, and learn how to run the unit in SCR mode (and O2 mode when appropriate) so that you can stay on the loop, whenever possible (i.e. the scrubber is still working) in order to conserve as much bailout gas as possible in case you eventually do have to go off the loop during the exit.

From that perspective then it's the same difference as between OC recreational and technical diving. In an emergency the rec OC diver goes to the surface, while in technical OC diving the diver turns the dive, but resolves/deals with the problem at depth, with the resources at hand - since surfacing is not an option due to either a hard or soft overhead, or both.

It also makes sense that since the open water priority is on ascending to resolve any problems, that teaching a recreational CCR diver anything other than bailing out at the first indication of a problem would be construed as posing additional risk.

Personally, I think that's a bad idea, as all things being equal, I'd rather have more knowledge than less. But we unfortunately have serious lawyer infestation in the US and consequently a very litigious society.

 

[northernone]

Correct me if I am wrong (I've never taken a "recreational" CCR course) but goals in a 3 day recreational CCR class are primarily to learn to recognize when there is a problem and to bail out to OC, while the goals in a 5 day technical CCR class is recognize when there is a problem, diagnose the problem, and learn how to run the unit in SCR mode (and O2 mode when appropriate) so that you can stay on the loop, whenever possible (i.e. the scrubber is still working) in order to conserve as much bailout gas as possible in case you eventually do have to go off the loop during the exit.

From that perspective then it's the same difference as between OC recreational and technical diving. In an emergency the rec OC diver goes to the surface, while in technical OC diving the diver turns the dive, but resolves/deals with the problem at depth, with the resources at hand - since surfacing is not an option due to either a hard or soft overhead, or both.

It also makes sense that since the open water priority is on ascending to resolve any problems, that teaching a recreational CCR diver anything other than bailing out at the first indication of a problem would be construed as posing additional risk.

Personally, I think that's a bad idea, as all things being equal, I'd rather have more knowledge than less. But we unfortunately have serious lawyer infestation in the US and consequently a very litigious society.

I'll second with your observations as a ccr student. I've sat in on 3 recreational CCR cert classes, 3 different instructors. It's nearly all "There's a problem, guess the solution, you're now OC and going to the surface". While UW problem solving was taught, the "when in doubt, bail out" mantra was heavily emphasized as well as the need for further training.


In my actual technical CCR class is where we got into significant underwater problem solving in a real way. My instructor knew the route I am heading and was willing to put in personal time to help set the foundation in preparation for overhead environments. I'd hope instructors running CCR Cave for example would 100% be teaching SCR? Straw poll?

Regards,
Cameron

 

[DA Aquamaster]

Jon made it very clear in our technical CCR course that the whole purpose was to learn to take full advantage of the unit's abilities and operating modes and to stay on the unit what ever possible, to both preserve gas and keep your options open. SCR, operating it as an O2 rebreather (when appropriate), flooding and de-watering to get back on the loop were all taught, practiced and expected to be mastered, along with all the usual failure drills.