Question CCR for recreational depths

[CT-Rich]

Enlighten me, what’s the bailout for, if not the rebreather tries to kill you with oxygen or co2

The king has no clothes.

So you dive OC with no redundancy? Same fan, different sh*t, maybe?

 

[Celt]

So you dive OC with no redundancy? Same fan, different sh*t, maybe?

OC and rebreather diving are totally different things. Promoting rebreathers to recreational divers as been the same thing as open circuit, and possible a better idea in case they get lost or entangled is the craziest thing I’ve read in a long time.

 

[Celt]

CCR is unquestionably more complex than open circuit. This leads to many different failure modes which have to be trained to monitor, mitigate and manage. One of the benefits of CCR is flexibility where issues can be managed, for example oxygen partial pressures to change CNS loadings, optimise decompression, deal with unexpected depths, etc. Similarly removing gas anxiety if "lost" or entangled. Running SCR mode, offboard, oxygen rebreather, etc.

Open Circuit too has many failure modes which need to be trained and practised. The challenge with OC is there’s much less flexibility. It’s down to pre-planning, ensuring one failure can be handled.

CCR and OC are different. Both need failure mitigation strategies. CCR offers many more mitigation options than OC.

How is it a good idea to move to a piece of equipment, that’s 10 times more likely to fail, if lost or entangled. If something doesn’t make sense it can’t be right.

 

[MichaelMc]

Every new diver using a rebreather is unrealistic and unneeded. It complicates training and the maintenance is harder.

But for an experienced diver it has benefits with some tradeoffs, if you don't like them, stick with OC.

 

[Celt]

Every new diver using a rebreather is unrealistic and unneeded. It complicates training and the maintenance is harder.

But for an experienced diver it has benefits with some tradeoffs, if you don't like them, stick with OC.

Ok that’s fair.

 

[Angelo Farina]

Man, the only thing i can say - Cressi ARO is a toy. You can't span your ARO experience to all rebreathers.
Me own DIY KISS. Dove it for 13 years up to 40 meters deep with slight deco.

This makes your eyes blind.

An ARO IS a CC rebreather. More simple and cheap than modern ones, so more suitable for being used as the introductory breathing appartus to novice divers.
After mastering it, you can step up to a mechanical SCR (which is just an ARO with a constant flow of Nitrox).
But this is already more complex: I used the Caimano IV SCR, while working with SIEL: it allows for greater depths (36 m) and, after my modifications, almost as silent as a CCR.
But it is even more complex than an ARO!
And modern CC rebreathers with electronics and electronically-controlled valves, sensors, solenoids, etc. are even more complex and delicate.
So, I would never teach again in OW courses using a rebreather as the first system, as it was the norm here in Italy until 1980.
If you talk about tech-trained divers who use their CCR also when diving within recreational depths, this of course makes sense for them: after investing a lot of time, money and effort for getting the equipment and learn and train for it, it is worthwile to maximise its usage even when strictly not needed.
But promoting it for novice divers, even in its more simple configuration, as it was done here for more than 30 years, is definitely impossible to come back.
After Padi has shown that it is perfectly safe to train an OW diver in just 4 days, no one would come back to OW courses lasting months...

 

[kensuf]

Maybe you can tell me why you’d need to bailout onto OC when using a rebreather.

Here's just a few to get you started on thinking about it.

Co2 buildup: possible causes, overworking, mushroom valve failure, scrubber break through - not really recoverable except the overworking problem scenario.

Low O2: possible causes, O2 off, loss of O2 (hose, first stage, burst disk), rapid ascent, blocked orifice on a leaky valve, failed solenoid (closed), stuck DIL mav/adv w/lean DIL - may be recoverable after a few OC sanity breaths.

High O2: possible causes, stuck solenoid (open), stuck O2 mav, rapid descent, exceeding MOD of DIL - may be recoverable after a few OC sanity breaths.

Flooded unit: possible causes, torn loop hoses, torn mouthpiece, torn counterlungs, broken hoses - unit dependent but probably not recoverable, however some units handle water a lot better than others.

 

[Wibble]

Here's just a few to get you started on thinking about it.

Co2 buildup: possible causes, overworking, mushroom valve failure, scrubber break through - not really recoverable except the overworking problem scenario.

Low O2: possible causes, O2 off, loss of O2 (hose, first stage, burst disk), rapid ascent, blocked orifice on a leaky valve, failed solenoid (closed), stuck DIL mav/adv w/lean DIL - may be recoverable after a few OC sanity breaths.

High O2: possible causes, stuck solenoid (open), stuck O2 mav, rapid descent, exceeding MOD of DIL - may be recoverable after a few OC sanity breaths.

Flooded unit: possible causes, torn loop hoses, torn mouthpiece, torn counterlungs, broken hoses - unit dependent but probably not recoverable, however some units handle water a lot better than others.

Hence they need training and practice. This means:

• Always know your PPO2
• Always be aware of CO2
• Frequently practice bailing out, even if it’s for sanity breaths.

Once you’ve been diving CCR for some time this becomes second nature.

But most of all, complacency kills!

 

[TuckerIdaho]

Hence they need training and practice. This means:

• Always know your PPO2
• Always be aware of CO2
• Frequently practice bailing out, even if it’s for sanity breaths.

Once you’ve been diving CCR for some time this becomes second nature.

But most of all, complacency kills!

You forgot practice a drill every dive.

 

[Sure Squintsalot]

What an illuminating thread. Having just gone through all 33 pages, the answer is pretty clear.​