Why CCR?

[wedivebc]

Another reason I try to avoid the solenoid firing is because IMO, the Meg is hard on batteries. The solenoid seems to require a lot of juice to fire it and can wear the battery out on long dives. I think the battery design is one of the flaws in the Meg. .

You either have an old meg or there is something wrong with yours. Using the Jaksa solenoid and flying eCCR mode I get about 100hrs from my primary which is pretty typical. Or maybe you do really long dives.

 

[HowardE]

Say I'm a newly certified recreational diver (air/nitrox). I purchase a CCR and want to take instruction. No minimum number of previous dives are required for me to commence the training program. I'm not centering out IANTD here, but an example may be beneficial.

IANTD Prerequisites:

Open Water CCR (Max depth 100'): Nitrox Diver, No other requirements
Course duration: 5 hours in-water training, 4 dives

Normoxic trimix CCR (Max depth 200'): 100 dives, of which at least 30 were deeper than 90 FSW, 20 dives and 25 hours on the CCR being used. No decompression experience required.
Course duration: 5 hours in-water training, 4 dives

Trimix CCR (Max depth 333'): 200 dives, 50 hours of dive time is required on the specific Rebreather for which the diver is being trained.
Course duration: 2.5 hours in-water training, 2 dives

I'm sorry, but I don't think a diver is ready to be certified with CCR to 200' with less than 5 hours of decompression experience. Additionally, I can't see how the person can add 25 hours on a CCR and in 2.5 additional hours and 2 dives can be certified to dive to 333'! Where's the deep water experience?

If there is a "death zone" (less than 20 hours of CCR use) the answer is to add 30 hours of experience and go from 100' to over 300'? I don't get it. I would think that the training times would be increased prior to initial certification by 20 hours and remove the "death zone" entirely. Increased training times have been beneficial for other recreational activities (including flying).

TDI requires 2 hours of Pool, and 10 hours of open water for the Air Diluent CCR Diver certification; advanced nitrox is also a pre-requisite AFAIK. This is for Air Diluent only with no-deco diving and depths are limited to recreational depths.

AFAIK, the TDI requirement for Normoxic Trimix is 50 hours of time on your rebreather.

The "death zone" also refers to a period of time when the diver is comfortable on their rig, and gains a feeling of invincibility. This can also lead to complacency. TDI warns of this in their instruction manuals. Reminding students to avoid complacency... Always know your PO2, and they recommend to look at your handset frequently.

 

[Kevin Carlisle]

Kevin, just forget all that CCR crap -- you don't need it when you have this:
http://www.scubaboard.com/forums/4851557-post14.html

OMG.. That wont fit in my truck .. I am not gonna dive CCR. I want to understand them tho. There are a lot of bad opinions about them that I dont see as true. Thats why I started this thread. After reading some of it I can say my beliefs are pretty much reinforced. Ego's and complacity seem to be the biggest factors in some and probably most deaths on CCR.

I think you have to enjoy the challenge and work at that challenge before you can reap the rewards they offer. I now have a better view of why and I believe that for those up to it that the rewards are great. I still believe that it takes a very focused and devoted diver to be able to use it safely, just the nature of the machine. I also believe its for a small percentage of divers, most on here would not fit into that. I do 8-15 dives a month that most would call technical dives but i still consider myself an average diver and they are not for me.

Thanks for all the information shared so far guys. Be great to read any more that you have to offer.

 

[Matt S.]

I am an OC diver who is very interested in CCRs, in the same way that I am interested in motorcycles, jets, and hang gliders. I mean, wow, neat gadget, but that's not for me. I like lazing around at 60 ft in open water, looking at fish. I don't want to trust my life to a gadget more complicated than my OC regulator.

I have a few questions if anyone's got a minute to indulge me.

Sometimes, I dive a RB because I just don't want to carry a bunch of heavy gear. One of my RBs has two 6CF tanks and weighs half as much as an AL80. I use it a lot for relaxing beach dives.

I went to a lecture on CCRs at my scuba club. (It was about how to safely dive with a CCR diver when you are an OC diver.) Anyway, the speaker said that CCRs need to work a lot harder on gas mixing above about 60 ft, and it is best to limit your time above 60 ft for safety.

I didn't understand why that would be the case. I mean, the loop obviously needs more O2 at low ambient pressure to meet a given PO2. But that's actually risky? If that's correct, it sounds like a big problem with doing "relaxing beach dives." Do you have any idea what the speaker may have been referring to?

Also, how do eCCRs end up killing people? Fatalities come from mismanaging oxygen levels, right? Too much PO2 and you tox, too little PO2 and you are rendered "unconscious without warning and incapable of self rescue."

But with 3 oxygen sensors and a lot of smart electronics, what's the ultimate failure point? The inattentive diver, yes, but what's going to fail in the unit on his back that puts him at risk?

I have heard of very deep CCR dives, hundreds of feet. From my limited understanding of deco diving procedures, it doesn't seem like you can carry enough OC gas to get out of the deco obligation a CCR can put you in to. Practically speaking, what kind of a deep dive can you do on a CCR with adequate bailout gas?

 

[wedivebc]

But with 3 oxygen sensors and a lot of smart electronics, what's the ultimate failure point? The inattentive diver, yes, but what's going to fail in the unit on his back that puts him at risk?

The biggest failure that kills most RB divers is between his ears.

 

[HowardE]

I have a few questions if anyone's got a minute to indulge me.
I went to a lecture on CCRs at my scuba club. (It was about how to safely dive with a CCR diver when you are an OC diver.) Anyway, the speaker said that CCRs need to work a lot harder on gas mixing above about 60 ft, and it is best to limit your time above 60 ft for safety.

You use more O2 above 60 feet. Since many fly at a setpoint of 1.2 or 1.3 PPO2. So at shallower depths, the solenoid or operator is required to add more O2 at shallower depths to maintain that setpoint. So - you use your gas supply a lot faster on shallower dives than you do on deeper dives. Which is why they would "work a lot harder"
Also - on very shallow dives, the work of breathing (for you) may be harder because there's less pressure on the counterlungs, requiring more lung power to push the air through the loop.

I didn't understand why that would be the case. I mean, the loop obviously needs more O2 at low ambient pressure to meet a given PO2. But that's actually risky? If that's correct, it sounds like a big problem with doing "relaxing beach dives." Do you have any idea what the speaker may have been referring to?

Relaxing beach dives... I guess that depends on the depths. Rebreathers don't like it too much at depths less than 20 feet. Even at the low setpoint of .7 (which is the equivalent of 70% nitrox on the surface) it's a lot of gas used, and the solenoid (if eccr) is constantly firing... and again... WOB.

Also, how do eCCRs end up killing people? Fatalities come from mismanaging oxygen levels, right? Too much PO2 and you tox, too little PO2 and you are rendered "unconscious without warning and incapable of self rescue."

None of the more recent deaths are because of ox tox, or hypoxia. On the evolution, you get a high PO2 warning at 1.6, and a LOW warning at .4. Remember... .18 is considered normoxic - we breathe .21 - so the LOW warning is more than enough time to make an adjustment, and add O2 or add diluent, or bail out if none of those options work.

But with 3 oxygen sensors and a lot of smart electronics, what's the ultimate failure point? The inattentive diver, yes, but what's going to fail in the unit on his back that puts him at risk?

Rebreather divers generally carry at the very least. 1 Oxygen bottle, 1 bottle of diluent, and 1 bailout open circuit tank. Generally the bailout is slung like a deco bottle, and can be passed off to a buddy, and also usually has the ability to be plumbed into the rebreather as a backup diluent (and/or backup O2 if the diver is carrying that as well) - So this leaves not 1 bailout option like the open circuit diver who has what? A backup regulator, and maybe a pony? But it leaves the rebreather diver 3 options when/if a problem arises.

High PO2... do a dil flush. Knock it down. Validate the readings from my O2 sensors (by predicting what the PO2 should be with my diluent being flushed through the loop). Are they reading correctly? Why did I have a PO2 spike? Is my solenoid stuck open? I have time to figure out the problem, and make adjustments.

Low PO2. I can do a dil flush or add O2, and in either case, I'd have a breathable gas, with a good PO2.

In any case... I can bail out to open circuit if necessary.

Rebreathers present many options that OC just can't have. Any component can fail, but you have OPTIONS to deal with a failure. Except a full flood, or hypercapnia. In those cases, abort, bail out.

I have heard of very deep CCR dives, hundreds of feet. From my limited understanding of deco diving procedures, it doesn't seem like you can carry enough OC gas to get out of the deco obligation a CCR can put you in to. Practically speaking, what kind of a deep dive can you do on a CCR with adequate bailout gas?

On most expedition type ultra deep dives... Divers often have deep support, and shallow support. Meaning. Like a dive a friend of mine did to 530 feet recently. They had support at 250, 200 and shallower. The support team had additional gas available if needed for bailing out. This gas was included in the dive plan. They had enough gas to bailout to at least past the first support diver; If something went wrong.



A good friend of mine says this about rebreathers:

Treat your rebreather like your girlfriend.... who you caught cheating on you. You love your girlfriend, but no matter how much you try, you just can't trust her 100%

 

[Thalassamania]

The biggest failure that kills most RB divers is between his ears.

That's not really fair, you're that the ultimate cause of their demise is usually a brain fart, but if something real, often with the gear, had not gone south first, they'da been fine. At least that's the way I judge it from the perspective of a part-time MK-15 pilot who has little experience with other CCRs.

 

[wedivebc]

No I am saying the brain fart occurs when they choose to use sensors that are 2 years out of date, dive with used scrubber that they had poured into a bucket then refilled the can later, used 10/50 dil on a 90ft dive, forgot to install an o-ring, forgot to get properly trained for the dive they are conducting. I could go on but I am sure you get the point.

That's not really fair, you're that the ultimate cause of their demise is usually a brain fart, but if something real, often with the gear, had not gone south first, they'da been fine. At least that's the way I judge it from the perspective of a part-time MK-15 pilot who has little experience with other CCRs.

 

[Thalassamania]

I suppose that you're right, all my CCR work (except my little Cobra) has been team based, team maintenance systems, team canister loading, need-it-or-not maintenance schedules, much more akin to military diving than to "more relaxed" recreational diving.

 

[Jeff Toorish]

I suppose you could use the premise of your question and ask "why scuba," just as easily.

For me, CCR is a tool useful for many applications, although not all. Most of the reasons to dive CCR have been stated.

I would add, as a photographer, I simply get better pictures on CCR as opposed to OC. The fish come up to me and no bubbles to scare them off.

I also believe there are a couple of other reasons that may be more esoteric, but are meaningful nonetheless. When I started diving my KISS, I believe I became a better diver, not just in terms of CCR, but in general. I also believe that CCR training incorporates more depth in many aspects of dive philosophy that is also very beneficial.

In all honesty, I have to say I think the basis of your question is actually false. I have said it before, but I think it bears repeating. Most of the fatalities and incidents we have had on CCR were not directly related to rebreather diving. They would likely have happened regardless of the gear, if the diving conditions and situation were otherwise identical.

When an OC diver dies, no one ever says, "what regs was he using, what kind of tanks?" But the first question for a rebreather fatality is "what unit was he using?" This seems to me to be a predisposition to believe there is an underlying equipment cause in CCR accidents. However, I have never seen data to support that.

Clearly, rebreathers require greater attention from the diver. By the same token, CCR divers receive greater training and are often (although not universally) more experienced because most divers tend to work up to diving CCR.

I think the benefits of diving CCR are clear. It is up to each diver to balance them with the greater requirements.

Jeff