Three dead in Poland last week

[tarponchik]

@rolanddiver , @Kay Dee With the caveat that they are “best guess numbers,” 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. And, of course, Dr. Fock is ignorant and does not know what he's talking about. Or maybe he's a troll.

 

[rjack321]

@rolanddiver , @Kay Dee With the caveat that they are “best guess numbers,” 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. And, of course, Dr. Fock is ignorant and does not know what he's talking about. Or maybe he's a troll.

He's not that far off. But didn't correct or standardize for depth and decompression.
There are millions of shallow (<30m) air dives done every year which weight the open circuit denominator. CCRs allow people to do dives that are impossible on open circuit due to depth, duration, or remoteness and those dives are going to be more risky for sure.

 

[Jack Hammer]

And, of course, Dr. Fock is ignorant and does not know what he's talking about. Or maybe he's a troll.

More likely that people fail to understand what he wrote and how to interpret the numbers and tend to cherry pick what makes for a great headline.

Rebreather dives tend to be more on the technical side of diving. Lumping in statistics from the recreational side skews those numbers. A better assessment would be rebreather incidents compared to similar OC technical incidents.

 

[lowwall]

@johndiver999 (and to a lesser extent @lowwall), given your self admitted lack of knowledge of rebreathers I suggest you take a good hard read and a deep think about all what both Dr Mitchell and @rjack321's had to say in their posts, especially the intricacies / variables involved, as both are experienced rebreather divers.

And given all the intricacies / variables involved, I also agree Diver 1 did the 'right thing'. Unfortunately 'doing the right thing' can still end tragically, but better than two dead divers.

I read them and I appreciate both of them taking the time to explain the issues involved.

Now I'm trying to wrap my head around why so many people with families willingly take on what appear to be the large additional risk factors of RB diving. Here's my thinking... Accident analysis normally uncovers a chain of decisions or events that led to the ultimate outcome. Changing any of these would have avoided the outcome. For OC fatalities, these chains almost always start before you enter the water with some combination of pre-existing health or condition issues, extremely poorly maintained or known-faulty equipment, lack of planning and/or knowingly entering conditions that greatly exceed your training. In other words, simply following the basic rules makes the sport extremely safe.

None of these seem to be factors here. Indeed, the accident chain appears distressingly short: a poor (but not completely unreasonable or fatal by itself) choice of bailout gas given the max depth and loss of contact with a buddy. As a father and husband, I would not partake of an activity where death is a not unusual outcome even if I do nearly everything right. This looks to me a bit like Himalayan expedition climbing on the spectrum of risk, where even the best and most prepared climbers have a non-negligible chance of dying every day on the mountain due to non-controllable factors.

 

[ScubaAl]

When number of deaths are said to be X/per 100,000 dives, where does the 100,000 dive number come from? When people dive their dive isn't uploaded into some master data base, so that if someone does died there is a number of dives to work with.
When someone does pass away while diving that's a known number, but total of dives done around the world isn't known.
So when deaths per 100,000 dives is thrown out there is just made up data.
Al

 

[lowwall]

Rebreather dives tend to be more on the technical side of diving. Lumping in statistics from the recreational side skews those numbers. A better assessment would be rebreather incidents compared to similar OC technical incidents.

You don't have to wait for enough deaths to provide a p < .05 to examine relative risks. In other activities (not sure about diving) this is called fundamental analysis.

In this case, we clearly see there is at least one large additional risk factor compared to making the same dive as an OC technical dive: buoyancy issues when changing depth due to the need to compensate for the counterlung gas. As @rjack321 put it, "Controlling 3 sources of buoyancy (wing, drysuit, counterlungs) while also controlling 3 sources of buoyancy in a bailed out buddy is pretty much not going to happen. (even on BO the counterlungs need to be vented). Perhaps with 2 buddies or a mooring/anchor line."

 

[Dan]

When number of deaths are said to be X/per 100,000 dives, where does the 100,000 dive number come from? When people dive their dive isn't uploaded into some master data base, so that if someone does died there is a number of dives to work with.
When someone does pass away while diving that's a known number, but total of dives done around the world isn't known.
So when deaths per 100,000 dives is thrown out there is just made up data.
Al

Maybe this article helps in determining number of dives: Participation in recreational scuba diving

 

[ScubaAl]

My point is no one knows how many dives are done. fatality, yes but in any give day, week, month no one knows how many dives were done around the world.

Al

 

[fsardone]

I read them and I appreciate both of them taking the time to explain the issues involved.

Now I'm trying to wrap my head around why so many people with families willingly take on what appear to be the large additional risk factors of RB diving. Here's my thinking... Accident analysis normally uncovers a chain of decisions or events that led to the ultimate outcome. Changing any of these would have avoided the outcome. For OC fatalities, these chains almost always start before you enter the water with some combination of pre-existing health or condition issues, extremely poorly maintained or known-faulty equipment, lack of planning and/or knowingly entering conditions that greatly exceed your training. In other words, simply following the basic rules makes the sport extremely safe.

None of these seem to be factors here. Indeed, the accident chain appears distressingly short: a poor (but not completely unreasonable or fatal by itself) choice of bailout gas given the max depth and loss of contact with a buddy. As a father and husband, I would not partake of an activity where death is a not unusual outcome even if I do nearly everything right. This looks to me a bit like Himalayan expedition climbing on the spectrum of risk, where even the best and most prepared climbers have a non-negligible chance of dying every day on the mountain due to non-controllable factors.

I am not going to say that rebreather diving is safer than OC diving, it is not. But this mishap started well before entering water.
Diver had been not diving for several months, yet dive was planned and executed in challenging conditions.
Choice of gas was hardly adequate: wob in CCR mode is more critical the OC, so the diluent was 19/48 while the bailout was air.
They decided to dive in cold dark and limited visibility, all conditions that lead to narcosis.
Switched from helium warm humid mix to very cold, dry air.
So all of these conditions are easily seen in hindsight, but why the decision of the diver made sense at the time? What are the right antidotes to avoid making the same mistakes?

After the COVID lockdown I went for a dive, decided minimum/no deco same profile as the mishap dive, experienced buddy. We descended to 47 meters, turned the dive and ascended following the bottom of the lake, cold, dark and low viz.

We were lucky? Nothing did happen. What was the plan?
Plan was to come back already decompressed, we only had 5’ deco by the time we came up at 6mt and we would have followed the bottom in case of problem, as the mishap (appropriately, in my view and for the reason stated by others) team did. The only difference was we knew 2 things:
1 the whole dive there was an available guideline and we are cave trained solo divers, plan was to stay on the line;
2 at 39 mt there is a direct line anchored to a big boulder leading to a submerged buoy up to 3/4 meters.
So our plan had an escape route from almost maximum depth and it is well marked by a permanent guideline.
We had a risk assessment plan a contingency plan and an emergency plan. Was all of this well thought over in the mishap dive? Or was a dive in which they went through the moves of having a plan (remember wrong bailout gas for depth) but it was incorrectly planned?
When you deviate from procedures and you get away with it, or you become complacent and you do not pay the price for it, you deviate more and you become more complacent until you pay the ultimate price (normalization of deviance). Did ever the mishap divers bailed out to air at 45 meters? Did they know the effect?

In this case, probably, the dive was well within the capability of the divers when they were current and recent, within their training and capabilities. But, probably, a problem even when current and recent would have taxed their capabilities to solve it smoothly.

After a long hiatus from diving, probably this as a shakedown dive was a bit too much. Add the wrong gas for bailout and a minor problem (you feel disorientated because dark, cold and low viz and start doubting of you scrubber and bailout to the wrong gas) you are adding rings to the chain of events leading to the accident. Chain of events that started when you decided to dive, in that place, in those conditions, with those gases, with a profile including deco.

Are we realistic in evaluating our capabilities to handle issues underwater? How wide is our safety margin? Should we increase it after a period of inactivity? Are we accepting eccessive risks? How can we assess our risk?

I developed a risk assessment matrix, and a small article, which, I do not have here, it has been posted on the now defunct Technical Diving Magazine Issue 24 page 15.
I will dig it up and repost it. I do have the entire magazine and will try to attach it.

Edit: it worked. So with the information available try to fill the risk management matrix and see how it comes out in term of risk.

Cheers

 

[Dr Simon Mitchell]

Hello again,

I'm was initially surprised that losing contact with a distressed buddy (after watching him switch to his bail out and have difficulty working an inflator) would be considered "doing the right thing". I now accept that conclusion from the experts, but initially it sounded like losing contact was a terrible, unfortunate mistake to me.

This is a slightly disingenuous interpretation of my comment about "doing everything right". For clarity, I was not suggesting that losing contact was "doing the right thing" and nor was rjack. I was primarily addressing your concern about the decision between direct ascent and returning up the slope. In relation to the separation, yes, of course that was not good, and yes, you could perhaps characterize it as a mistake. But as any experienced diver knows all it takes to lose contact with a buddy in 1m visibility is taking your eyes off them for a few seconds to attend to something important in your own space. Seen through that lens, the loss of contact could equally be characterized as extremely bad luck. I don't believe this is a point upon which Diver 1 should attract a lot of criticism.

This looks to me a bit like Himalayan expedition climbing on the spectrum of risk, where even the best and most prepared climbers have a non-negligible chance of dying every day on the mountain due to non-controllable factors......and........Now I'm trying to wrap my head around why so many people with families willingly take on what appear to be the large additional risk factors of RB diving.

This is a very reasonable statement, though if we went into specifics I believe estimates of risk in many Himalayan climbing scenarios exceed those for rebreather diving. The principle you are articulating is nevertheless entirely correct. Rebreather diving (and the deeper / longer diving that rebreathers make possible) is comparatively high risk. A good instructor will always make this clear to prospective rebreather divers who in turn should involve other affected "risk acceptors" in their lives (such as a spouse) in discussions about whether to participate or not. I have seen and done things in diving that I never would have done were it not for rebreathers, but I have exposed myself to significant risks in doing so. I have always had clear vision of this balance between risk and benefit which started with KayDee on this thread who was my original instructor.

And, of course, Dr. Fock is ignorant and does not know what he's talking about. Or maybe he's a troll.

Andrew is none of those things of course, and it is highly relevant that he is an active rebreather diver - which speaks to my point about balancing risk (which he clearly understands) and benefits.

Anyway, more or less everything that has been said about his paper (which I have attached for anyone interested) in the above comments is correct. Its obvious weakness is the lack of an accurate denominator which was estimated from some relatively hard data on new rebreather diver certifications and survey data on average numbers of dives typically performed by rebreather divers. This is obviously imperfect, but no better method exists even today seven years after his paper was published. The criticism that he does not correct for the type of diving undertaken with rebreathers (deeper, longer) is valid, but one must remember that if it is rebreathers that make this sort of diving possible / accessible, then the deaths that occur under these circumstances are still "rebreather deaths".

Simon M