How great is the risk (in your perception)?

[CAPTAIN SINBAD]

How risky are rebreathers as compared to open circuit at technical depths (below 130)? What is the greatest risk? Unit flooding? O2 sensors going wonkers? If someone could offer insights into the risk of rebreather diving in comparison with open circuit technical diving what would be great!

Thanks.

 

[2airishuman]

I'll be interested to see the sorts of replies you get. I've read through a bunch of statistics and have concluded that RB diving at present carries safety risks that I am unwilling to accept while OC technical diving does not.

I think much of the answer turns on how confident you are that you would never be "that guy" who dives a RB with known deficiencies -- warning lights, known bad components, cylinders not full, etc.

 

[Bierstadt]

I'll be interested to see the replies as well.

 

[KenGordon]

The main issue I see with a rebreather is failing to properly monitor the machine (cell readings) or failing to monitor yourself (co2).

If you do those things you should notice a failure in time to sort it out and make a safe ascent.

The advantages of a rebreather are time and mix. You will use more helium because it is cheap. Of course the mix matters more in a rebreather, so maybe that is just a mitigation.

The scary thing about a deep OC dive is having enough gas. There are some minor risks about gas switching but I worry about working too hard and using my gas faster than planned or overstaying and not having enough gas. Again monitoring is your friend.

Where I dive there is a risk of accidentally going inside a wreck due to poor vis an a lack of ambient light. There is often fishing line or net on the wrecks. These are less serious problems when you have plenty of time.

Past 60m it starts to be difficult to carry enough gas for OC dives so OC risks increase more quickly than the CCR risks.

Personally I think the risks are acceptable both ways. I mostly dive CCR to keep my skills up, even though for a shallow dive twin 12s would have fewer ways to fail and be arguably safer.

Diving is reasonably safe. Read the incident reports and you see that largely people get hurt not following their training rather than through bad luck. The training is informed by past failures and introduces fall backs so that if something goes wrong you are not always dead. Of course very little goes wrong so people push their luck. They may start to regard their own experience as significant and begin to disregard the 'nannying' training. A CCR diver who does this has more ways to fail than an OC diver.

 

[CAPTAIN SINBAD]

So here is a quote and I would like to see how far do rebreather divers agree with it.

"Fock concluded that rebreather diving is likely five to 10 times as risky as open circuit scuba diving, accounting for about four to five deaths per 100,000 dives, compared to about 0.4 to 0.5 deaths per 100,000 dives for open circuit scuba. This makes rebreather diving more risky than sky diving at .99/100k, but far less risky than base-jumping at 43 deaths/100k."

Rebreather diving: ‘Killing Them Softly’ | DIVER magazine

 

[daduls]

Interesting statistics, numbers don't lie, but they can be guilty of skewing the facts.

I'm not a rebreather diver, I've considered it but so far it's been cost prohibitive. Local dive shop is now training on the Hollis Recreational rebreather. Should I jump in?

 

[RainPilot]

So here is a quote and I would like to see how far do rebreather divers agree with it.

"Fock concluded that rebreather diving is likely five to 10 times as risky as open circuit scuba diving, accounting for about four to five deaths per 100,000 dives, compared to about 0.4 to 0.5 deaths per 100,000 dives for open circuit scuba. This makes rebreather diving more risky than sky diving at .99/100k, but far less risky than base-jumping at 43 deaths/100k."

Rebreather diving: ‘Killing Them Softly’ | DIVER magazine

Disclaimer: I am a CCR diver so self-justification is always suspected.

I do believe that the quote is factually correct BUT may not be the whole story. Lets take an example of another activity, mountain climbing. Lets say that there are 10 times as many fatalities among climbers using oxygen bottles as there are for those climbing without. Is that a reflection of the type of climbing that people are using O2 for, or a reflection on the dangers of the equipment?

I believe that the VAST majority of CCR dives done worldwide are technical dives, done to places where OC can't necessarily go. By the very nature of these dives, you will have many more incidents than in the big data pool of all OC dives. I firmly believe that if we could compare apples with apples (ie all dives done to 300' plus, OC vs CCR, deep cave penetrations etc) that the numbers would break down much more evenly. There may even be a slight safety increase for some types of incident ie where the extra time a CCR affords may prevent a fatality. Im sure @kensuf and @PfcAJ and @Capt Jim Wyatt etc may know of such cases.

I also strongly believe that there is a huge element of personality involved. There are people who will have no problem with CCR because they are really detail oriented and disciplined in the way they approach their diving, while others will always be at a higher risk because they are the kind of people to leave an old O2 sensor in, not restart a checklist if they were interrupted etc etc.

 

[KenGordon]

So here is a quote and I would like to see how far do rebreather divers agree with it.

"Fock concluded that rebreather diving is likely five to 10 times as risky as open circuit scuba diving, accounting for about four to five deaths per 100,000 dives, compared to about 0.4 to 0.5 deaths per 100,000 dives for open circuit scuba. This makes rebreather diving more risky than sky diving at .99/100k, but far less risky than base-jumping at 43 deaths/100k."

Rebreather diving: ‘Killing Them Softly’ | DIVER magazine

See the paper itself. http://dhmjournal.com/files/Fock-Rebreather_deaths.pdf The summary above is a bit of an over simplification.

Using analysis of the BSAC numbers over the same period gives a four fold increase. Really you need to read the discussion of diver behaviour.

My favourite bit:

Despite more than a decade of warnings, the dangers of overconfidence do not seem to have been taken to heart by many new CCR divers. Furthermore, there have been a number of near misses reported on RBW forums that seem to arise from misinformation promulgated via the internet. These issues continue to be a challenge to those who wish to promote safety in this area.

 

[tbone1004]

the biggest risk is sensors. O2 sensors are inherently wonky, and CO2 sensors aren't really available that work. If we had rock solid O2 sensors that didn't drift, get limited, or just sh!t the bed *hopefully the Poseidon sensors prove to fix this*, and we also had CO2 sensors that worked in the environment that we dive in, then you would be able to trust the O2 readings from the sensors, and know if there was breakthrough. If that was the case, the safety would likely get significantly better.
As mentioned above, in OW diving, the difference in say normoxic depths may not be significant because you can carry 2x al80's and get up from anywhere you are with little issue so you are buying some time ability due to gas consumption of OC, but you aren't really getting much of a benefit outside of gas consumption.
In cave diving, the time factor is something that has saved several of my friends who would have died if they were on OC. Carrying enough gas is impractical for a lot of those dives so it saves a lot of logistic concerns.

The big thing about the statistics above are to look at who is doing what kind of dives and whether the dives that are killing CCR divers are still being conducted on OC *they largely aren't*, what the incident rate would be if they were on OC *probably pretty comparable*. It's important to be able to differentiate if it was the CCR that killed them *Wes Skiles*, or they died, and happened to be on CCR but they probably would have died whether they were on CCR or on OC

 

[CAPTAIN SINBAD]

Makes sense. On a second note, how do rebreathers behave in ice conditions? Open circuit is prone to free flow (piston regulators more than sealed diaphragms but sealed diaphragms are also not completely reliable.) Are rebreathers affected the same way? Thanks.