Who should use a CCR?

[rx7diver]

Rich people!

You must be a lot of fun at parties!

 

[PfcAJ]

Hmm, seems like something I said might have prompted this thread.

Deep? Deep in a cave? Doing those things regularly? RB is reasonable.

 

[doctormike]

Hmm, seems like something I said might have prompted this thread.

Deep? Deep in a cave? Doing those things regularly? RB is reasonable.

I wasn't trolling. You actually got me thinking about it.

 

[PfcAJ]

I wasn't trolling. You actually got me thinking about it.

I appreciate that.

Obvi people can ultimately do whatever they want. But I'm glad at least someone is entertaining the idea I proposed.

 

[lermontov]

i never thought id bother but I have been considering it for the following reasons
a) cost and effort involved in getting to dive sites i want to maximise dive times
b) wreck diving deep penetrations with more time to explore
c) no bubbles - reducing silt stirring
d) shorter deco times

 

[kelemvor]

i never thought id bother but I have been considering it for the following reasons
a) cost and effort involved in getting to dive sites i want to maximise dive times
b) wreck diving deep penetrations with more time to explore
c) no bubbles - reducing silt stirring
d) shorter deco times

RB laymen here.

How does a RB reduce deco times?

I thought the benefits were just the other three you listed. More time being the primary thing I'd been interested in previously. Along with the ability to reuse helium (I think?) so you can dive trimix/heliox on a reasonable budget and without the guilt of wasting so much of the stuff.

 

[tbone1004]

i never thought id bother but I have been considering it for the following reasons
a) cost and effort involved in getting to dive sites i want to maximise dive times
b) wreck diving deep penetrations with more time to explore
c) no bubbles - reducing silt stirring
d) shorter deco times

D is only accurate under certain conditions. Remember that on a CCR you are typically diving with a lower setpoint that you would on OC so you may actually have longer deco times.

I.e. MOD for EAN32 is 111 at a pO2 of 1.4. If you do a dive to 111 ft and stay there the whole time, the CCR is 99% going to give you a longer deco time because your pO2 will be set lower *depending on who you are and the conditions etc, between 1.0 and 1.3. This applies as long as you are using an OC pO2 that is above what the setpoint on the breather is, so anyone using best mixes in their nitrox diving isn't going to get a deco advantage.
Where you do get an advantage is where you are diving shallower than the MOD of your gas mix on OC, but still deep enough for it to matter. CCR's are usually set around 1.2 or 1.3 in order to keep the CNS clock ticking relatively slowly. That's between 90/100ft on EAN32. If you are doing a long dive at 80ft, you're probably still going to be on EAN32 because that's what is available, but your pO2 is going to be 1.1. Assuming no helium in the CCR, the CCR is going to be at a higher pO2 which means a lower pN2 which is what the deco algorithms actually care about, and your deco obligation will be shorter. Why? Your CCR will essentially be mixing EAN36 for you where your OC buddies will be on EAN32. Less N2 in your breather, less deco obligation for you.

 

[doctormike]

RB laymen here.

How does a RB reduce deco times?

To put it another way: I just did a dive with an average depth of 60 feet. Two hour bottom time and didn't get near NDL.

60 feet is 2.8 ATA. For setpoint of 1.3, that means that my CCR is providing me with EAN 46, a mix that you don't normally get from a dive shop for back gas.

So you always have close to the ideal mix.

 

[Daedalus]

The following people should use rebreathers:

(A) People who:
(1) have extensive open circuit dive experience;
(2) are detail and safety oriented;
(3) are in reasonable health;
(4) for whom a rebreather will increase the safety and/or convenience of the dives they wish to perform; and
(5) want a rebreather.
-or-
(B) People who:
(1) like to live dangerously; and
(2) want a rebreather.

 

[Capt Jim Wyatt]

*IF* you already are diving a RB - you should use it on all your dives to keep muscle memory intact.