'Clinically dead' rebreather diver dragged from quarry - and then revived

[doctormike]

I do believe that people are often using data from "do more people die (per dive) on rebreathers than on OC?" to answer "Is, for a given dive, a rebreather much more likely to have me die?". And that makes a difference imo. I'm not trying to "reclassify" deaths on rebreathers, I'm trying to get comparable data.

An excellent point. I agree with you that the important question is "for this specific dive profile and this specific diver, what is the risk of death on OC vs the risk of death on CCR?". And to understand why that's an unanswerable question, you need to consider the scientific method.

The only way to know that for sure would be a prospective randomized study. If you want to know if surgery is better than medical management of coronary artery disease, and there is no clear answer to that question, then it's ethical to randomize people with CAD into a group that gets a bypass operation, another group that gets meds, and then look at survival a few years down the road.

You can't do that with OC vs CCR for a number of issues. Issues related to ethics (signing up people to possibly die for a hobby), study design (how would you control for experience? Would you need both groups to be equally proficient in CCR and OC? Would that accurately model the real world question?), and logistical (you would need a huge number of divers to show a statistically significant difference).

I don't want to speak for Dr. Mitchell, but I'm assuming that the reclassify comment referred to the problem of trying to extract underlying factors from historical data. You would have to decide what to do with deaths that were ON rebreathers, but not necessarily CAUSED by the rebreather. And that very decision brings bias into the analysis.

So yes, rebreathers have their own unique risks and challenges, and yes the death rate per diver-hour is greater than OC. But I don't think that you can just take that 10x multiplier as the answer to the very important question that you are asking, based on that published database analysis. Like most things, the truth is more complicated than that...

 

[Cowfish Aesthetic]

The accident was a near fatal rebreather accident. You don't think that a discussion of rebreather fatalities is remotely related to that?

Or are we supposed to wait for the "official report" to discuss it, so we know exactly what happened?

Please help me out then: what lesson should I take from the last five pages of discussion that could help me or any other diver avoid the accident in question?

 

[RockiesFan]

The lesson to take is pay very close attention to detail when diving in general, but especially so in CCR because errors are less forgiving. The other aspect is when giving aid to possible drowning victims, oxygenation is just as important as compressions.

 

[doctormike]

Please help me out then: what lesson should I take from the last five pages of discussion that could help me or any other diver avoid the accident in question?

Well, since we have no idea what the cause was of the accident in question is, or any relevant medical or dive details, there is nothing that anyone can contribute to this discussion that could help you or any other diver avoid the accident in question. But as psibar said, we have already learned two good lessons from the thread, imperfect as it is.

What do you want to talk about...?

 

[infieldg]

I'm pretty sure the only dangerous part of my kit is ME Risk management is the foundation of both OC and CCR training - you don't wreck dive or breath non-normoxic gases without training nor do you dive CCR without being certified - and it seems to me that we OC guys regularly screw up our gas planning and management in situations where a CCR would have more than enough contingency time out of the box (on non-extreme dives) to accommodate.

I often wonder (usually when "CCRs are deadly" comes up again) how many OC fatalities from OOA or toxicity (too deep or grabbing the wrong reg) or even narcosis related stupidity would have been prevented with a CCR. A friend recently almost drained a tank of bottom gas not noticing his reg free flowing due to using a scooter, something that's happened to me before... we ALL need to be attentive, even us OC divers need to be self-aware enough to feel CO or CO2 starting to incapacitate us albeit to a lesser extent perhaps, but unlike CCR don't always have a completely different breathing gas to switch to. Rebreathers are one of dozens of things waiting to punish a casual attitude underwater I think.

I'm actively saving for an SF2 even though by the time I can afford one AND the training it'll be obsolete lol

 

[rjack321]

I do believe that people are often using data from "do more people die (per dive) on rebreathers than on OC?" to answer "Is, for a given dive, a rebreather much more likely to have me die?". And that makes a difference imo. I'm not trying to "reclassify" deaths on rebreathers, I'm trying to get comparable data.

RE: your first question
100m dives are far more dangerous than 20m dives
CCRs allow far more divers to do 100m+ dives
CCRs are roughly associated with 10x more fatalities than open circuit dives.

Was that because they were deeper and longer dives? or because of the equipment choices? Or some other factor like differences in training? Or perhaps younger fitter divers with less financial resources tend to dive OC and older more established divers with age related latent medical issues tend to have adopted CCRs later in their (employment/family/financial) careers?

The "comparable data" standardizing for all these factors does not exist. Its unlikely that the reasons for the differences have even stayed the same over the last 20+ years of recreational CCRs given changing designs, training, and understanding of risk factors.

Re: your second question
For this particular incident, hypoxia to the point of passing out can be caused by a few things:
1) O2 shut off or empty; 2) diluent leaking in the loop (especially if hypoxic); 3) CCR turned off or dead battery. On OC, hypoxia is pretty much limited to breathing the wrong gas or failing to analyze your gas - which is inherently limited/unlikely because not many OC divers bring a hypoxic gas to a quarry in the first place. It is safe to say that on any given dive you (one person, whatever age they happen to be) are more likely to die on CCR. Its also safe to say that there are many dives you can't do on open circuit so you either need to accept the CCR's risks or just not do the dives.

 

[KenGordon]

Please help me out then: what lesson should I take from the last five pages of discussion that could help me or any other diver avoid the accident in question?

Always know your PPO2.

Dive with buddies that know how to rescue and revive you.

Don’t do 100m dives OC.

 

[Patoux01]

The "comparable data" standardizing for all these factors does not exist.

But that doesn't mean we should use a different dataset. The number of deaths per car accident at 200 km/h is likely a poor predictor of the number of deaths per car accident at 30 km/h.


I am not sure which second question you are talking about. If you mean this "Is, for a given dive, a rebreather much more likely to have me die?", then that answer you give is not the right answer. I could also answer it with "well, it is cold (quarry in the UK in january), so a rebreather keeps you warmer, therefore safer", or "A rebreather has no reg freeze issue, so you're safer".
It's a lot more complicated than looking at one particular issue (hypoxia) that is unlikely to happen on OC. Or else we're gonna end up saying to all incidents where a freeflow happened "you should have been on a rebreather, you'd have been safe".

It is safe to say that on any given dive you (one person, whatever age they happen to be) are more likely to die on CCR.

Well, is it really safe to say? It has been told and repeated and repeated some more, but I can't seem to find a real reason (and heck, I don't even have a rebreather).
If we take data from https://www.divegearexpress.com/pub/media/tektipspdf/Fock-Rebreather_deaths.pdf we get that 33% of the accidents happened in "benign" conditions, ie where scuba is usually performed. I am purposefully excluding caves and wrecks (might not be correct). The problem then becomes to know how many dives are made on ccr in those conditions. Assuming all rebreather dives, then we get a risk of about 1.5 whereas scuba is given at 0.5, should that be only half the dives, we'd be around 3.
So I guess the conclusion is "it's more dangerous", but does it warrant "death traps", "order of magnitude" and that kind of scary statements? I'm confident however that quite a few of the people calling rebreathers with those names are diving air beyond 40m depth, and interestingly, there is actual data to show that is likely not the smartest thing to do. Gas density guidelines

 

[rjack321]

I'd love to see the CCRs that has no regulators...

And which unit(s) are you certified and diving on?

 

[KenGordon]

I'd love to see the CCRs that has no regulators...

And which unit(s) are you certified and diving on?

He said ‘no reg FREEZE issues’ not no regs. He also says he doesn’t have one.

For the benefit of others, gas is added only now and again. O2 at about 1l/minute and dil mostly not at all. Throughout a 60 minute dive only maybe 200l of gas will be used. So the cooling and then freezing issues do not happen. Indeed, on mine I have unsealed regs I would never dive OC.

The CC issues are different to OC. No free flows but a solenoid can stick, etc. Generally though time is not a big problem, and time pressure leads to mistakes and panic.

If we look at numbers... in some years there are no deaths in the UK of CC divers. Sometimes as many as 3. This is out of maybe 8 to 15 diver deaths each year. They are over represented, however if they all changed back to a twinset and stages I am not sure the numbers would suddenly improve overall as some of those twinset divers would be doing complicated dives and pushing limits.