Rebreathers, CCR & SCR Risks, vs. OC Scuba

[Rick Inman]

I know very little about rebreathers, but I buddy with one guy who dives a SCR and another who dives a CCR. I know enough to be an OK buddy, I guess - the symptoms of O2tox and hypoxia, how to read the buddy computer on the SCR, how to do a bubble check, etc. I've done air share drills with both of them. One guy likes to do a few mins at 10' before descending and the other likes to breath off his at the trucks for a while. No problem.

Here's my question. Are there greater risks using a rebreather vs. OC scuba? How about SCR vs. CCR? Both of the rebreathers seem to have a zillion failure points. Does one have greater risk than the other? If so, how much? Or are rebreathers just as safe as OC scuba.

 

[DiveTub]

There are more risks diving any type of Rebreather over OC.
The three main ones

Hypoxia (Too little O2 in the Loop)
Hyperoxic (Too Much O2 in the Loop)
Hypercapnia (Too Much CO2 in the Loop)

The very real problem with the 3 above is they can happen very quickly with the very real danger of death. All three can happen on both SCR and CCR's. Most Rebreathers have ways of monitoring the Partial Pressure or amount of Oxygen in he loop, however unfortunalty there is yet no way of monitoring for CO2 in the loop.

For Rebreather diving is all about constant diligence of the Rebreather and your own physiology. Monitoring both for any signs of problems, knowing the PO2 in the loop at all times and being comfortable to call a dive at anytime.

There are many more risks associate with Rebreather diving, the Electronic CCR’s are high end bits of kit, they require LOTS of maintenance and the risks of injury or dying on them is way above your basic OW diver. The Skill set in diving them is heavy and there is plenty to learn. However in saying the rewards and benefits in diving a CCR IMHO far outweigh the risks.

I applaud you for taking the time as an OC diver to want to learn more about the kit your buddies are diving on. When I dive with OC buddies I ensure the following.

1: They know how to close the DSV
2: If they see any bubbles at all (on a CCR they tell me)
3: They know how to add Diluant to the loop manually
4: I am carrying enough bailout gas that if the CCR where to fail I can get myself out
5: I explain what the lights mean on the HUD and they know the basics of too much or too little O2 in the loop.
6: They are unde NO obligation to help either me out of a situation and NOT to put their life at risk to attempt a rescue.

Have a read of this excellent article, the chart at the bottom would be worthwhile printing out and laminating
http://www.rebreatherworld.com/gene...537-how-deal-convulsing-rebreather-diver.html

I would also suggest you log onto Rebreather World and have a good look around.
http://www.rebreatherworld.com

Cheers
Chris

 

[TSandM]

It's a good question, Rick, and thanks for asking it. I was going to do a dive today with a friend who is trying to log time on her Inspiration, and I was a little nervous about buddying with her, because I really know very little at all about rebreathers, and that little is the theory, not the practice of how they work, how to debug or what to do if something goes wrong.

 

[Rick Inman]

1: They know how to close the DSV
2: If they see any bubbles at all (on a CCR they tell me)
3: They know how to add Diluant to the loop manually
4: I am carrying enough bailout gas that if the CCR where to fail I can get myself out
5: I explain what the lights mean on the HUD and they know the basics of too much or too little O2 in the loop.
6: They are unde NO obligation to help either me out of a situation and NOT to put their life at risk to attempt a rescue.

Humm... now that you mention it, I guess I have also been briefed on 1 thru 5. Neither have mentioned #6.

 

[DiveTub]

#6 is more of a personal thing,

You mentioned the guys doing two things
"Breathing the unit before getting in the water", what he is doing is Prebreathing the loop, this gets the Sorb up to temprature so it is working at optimum temp to scrub out the CO2

"Stopping just below the surface", this is a bubble check to make sure all the systems are working on the units and to check for leaks before the descent.

Cheers
Chris

 

[AndyNZ]

I dive occasionally with a couple of people who dive Inspo's. In addition to Chris's recommendations, you also need to adjust the way you dive a little bit to be a "good buddy".

Most (all?) CCRs vent gas from the loop on ascent, so going over an obstacle loses gas from the CCR more than going around it and staying at the same level.

 

[MPR]

Sydney Diver hit it on the head. It's good to know what your buddy is diving.

However, rebreathers were meant for one purpose and if you are not involved in that purpose, then why dive it? There are many more failure points and opportunities for proplems with the CCR and SCR. Personally, I wouldn't bother with a CCR or a SCR if recreational scuba is your goal. But that is just my $.02
Now if you are going to board a ship...

 

[Rick Inman]

(EDIT: Was typing this before MPR's post appeared above, which better addresses the subject.)

Well, maybe I didn't phrase the question properly. This is all good stuff, about how to be a good rebreather buddy. But really, I'm interested in the difference in risks inherent in diving a rebreather over OC, and the difference in risks associated in diving SCR vs CCR. Seems like there are so many possible failure points in rebreather diving that the risks in diving them go way up for both the diver and his/her buddy.

 

[wedivebc]

Not a safety issue but when mixing OC and CCR diving remember CCR divers would rather swim around an obsticle than go over it. It waste gas changing depth continuously.

 

[DiveTub]

(EDIT: Was typing this before MPR's post appeared above, which better addresses the subject.)

Well, maybe I didn't phrase the question properly. This is all good stuff, about how to be a good rebreather buddy. But really, I'm interested in the difference in risks inherent in diving a rebreather over OC, and the difference in risks associated in diving SCR vs CCR. Seems like there are so many possible failure points in rebreather diving that the risks in diving them go way up for both the diver and his/her buddy.

Ok basic risks of diving CCR that are not in Recreational OC diving, just off the top of my head.

Hypoxia: Both SCR and CCR
Hyperoxia: Both SCR and CCR
Hypercapnia: Both SCR and CCR
Flooded Loop: Both SCR and CCR
Computer Failure: ECCR Only
Computer malfunction: ECCR Only
Cell Failure: Both SCR and CCR
Solenoid Failure Open: ECCR Only
Solenoid Failure Closed: ECCR Only
Jet Blockage: SCR and MCCR
Putting it together wrong: Both SCR and CCR
Incorrect Calibration: Both SCR and CCR
Wong jet to gas use: SCR
Not carrying enough Bailout: Both SCR and CCR
Incorrect packing of Scrubber: Both SCR and CCR
Scrubber Breakthrough: Both SCR and CCR
Not Analysing gas correctly: Both SCR and CCR

These are basic for rebreather, there are other issues with each SCR/CCR make so the list goes on, but above is a pretty basic outline of what each rebreather diver is monitoring.

As an OC diver, as long as the Rebreather diver is carrying enough slung gas that if you have a problem there is ample for you to get to the surface, there is no more or less danger for you than diving with an OC buddy.

Just as an aside IMHO SCR's are just a waste of time for any type of diving, they do not significantly extend Bottom time or No deco time over a tank of OC Nitrox, they still vent gas and scare the fish away and the buoyancy on them is not easy. Having owned a SCR Dolphin for a while I would prefer to dive OC than a SCR. On the other hand a good CCR is just a pleasure to dive and I find it very hard to dive OC for anything now including Recreatioanl dives.

What I dont like about OC
Really Cold Air
VERY VERY noisy
Limited Bottom Time, my usual recreational dive is a minimum 2 hours often longer
Scare all the fish away
Short No Deco times

Cheers
Chris