One dead, one missing (since found), 300 foot dive - Lake Michigan

[doctormike]

Is it just me, but it sure seems there are a lot of fatalities for no more people that use rebreathers? I know they are used in a riskier environment but I know about two fatalities basically on the surface using them.

The surface is the riskiest place to be. Any issues with O2 delivery and the loop PO2 drops quickly. Buoyancy issues become much more challenging in shallow water as well, with an extra gas space to manage, especially as the CCR or the operator adds gas to the loop to maintain a setpoint.

They are much easier to dive in deeper water.

 

[Clayton122]

Don’t let this deter you from diving with DA. They are top notch. I’m a local regular. If they were sketchy, I would not be diving with them at all.

I can concur with this. I dive with Double Action at least several times a year, and to date, have had nothing but safe and wonderful experiences with them.

 

[DandyDon]

The husband's body was recovered.
Body of missing diver in Lake Michigan recovered - WTMJ

 

[Marie13]

Just saw this. From the ROV operators who found Jim Winn. I’m told he’s with Wazee Sports dive shop in WI.

Search Up-date for missing diver - Bruce's Legacy

 

[RainPilot]

If it’s your wife you might stop thinking rational and both end up dead.

I agree with your premise, but it may not be irrational to act in this way. One of the never-ending debates about technical rescue, is how far do you risk yourself in order to assist your buddy? Every dive team has to figure this out for themselves, basically doing a cost-benefit analysis without necessarily thinking of it in those terms.

If it is a friend? I may take on a certain amount of risk but really, they are on their own beyond a certain point. My son? He will get the last breath of gas from my tank. This is not irrational, this is a careful analysis on my part of what I am prepared to live with during and, more importantly, after the dive. In the case of this dive, children on the shore also change the picture dramatically.

@tbone1004 and @victorzamora have, I believe, even had this discussion with each other's SO as they are a pretty constant team.

 

[John C. Ratliff]

For those of you who are saying that "diver error," or "human error" are the cause of these rebreather accidents and fatalities, I'd like you to look at the following accident model. This is David DeJoy's Human Factors Model for Accident Causation, which was published in the early 1990s by the American Society of Safety Professionals. Note that all accidents are shown as "human errors." But, also note that there are many factors which go into those errors. These include "Person Machine Communications," the "Environment," and "Decision-Making." I have used this model since it was published to analyze accidents and determine the factors which go into them, and have published internationally with this model.

The situation with rebreathers is that the individual can be more easily overcome by the complexity of the "Micro-Task" and "Macro-Task" environments. Far from making the environment safer, the rebreather technology demands much more attention than many divers can give in certain environmental conditions. This is part of the answer about why we have very highly qualified divers die using rebreather technology, IMHO.
Toward a Comprehensive Human Factors Model of Workplace Accident Causation - ProQuest

SeaRat

 

[RainPilot]

Is this something specific with the rEvo or rebreathers as a whole? I know little about RB.

It varies. rEvo are inherently negative even before the counter lungs flood (amount depends on the frame size and SS vs Ti), this makes them nice in the sense of less weight on a belt but it can lead to being overweighted easily depending on your exposure suit / bioprene levels.

My Poseidon unit, in a jacket BCD with AL tanks needs about 3 lbs to sink it with empty counterlungs, the counter lungs are pretty hard to fully flood in that unit. When I dive drysuit with it, I have a steel plate and steel tanks, that makes it around 5-10lbs negative depending on gas weight and plate thickness. Some of the SM CCR units are pretty close to neutral by design.

Generally, most units on the market will be negative if you manage to fill them completely with water, some more than others.

 

[John C. Ratliff]

A CCR works by circulating a single breath for most of the dive, and removing the CO2 that your body generates. There are two small tanks - one maintains a set PPO2 by adding O2 at a rate sufficient to match what the diver metabolizes. The other adds a diluent - air or some other gas - to maintain the loop volume as you descend and ambient pressure increases. Diluent can contain helium for deeper dives, to keep the END in an acceptable range, but it isn't added continually once you are at depth.

When you ascend on CCR, ambient pressure drops and so does your PO2. This is one of the challenges of diving a rebreather, and a fast ascent from depth can indeed result in hypoxia, so O2 is added to the loop on ascent.

In an emergency swimming ascent (CESA), I believe that the diving equipment is irrelevant - OC or CCR. It is no longer supplying gas to the diver. The ascent results in gas continually venting from the lungs, so the only FIO2 that is in the equation is what was in your lungs when you started the ascent.

Dr. Mike,

Looking at this, it appears that an emergency swimming ascent is not achievable using CCRs. Is it in the training protocol that the diver cannot make such an ascent, as it may be beyond the CCR's ability to add enough oxygen to make the ascent achievable without blackout. I saw on the CCR website that at a depth of some 220 feet, the oxygen level is at about 10% (from memory). This is in safety terms an IDLH environment (Immediately Dangerous to Life and Health) for oxygen levels is anything below 19.5% (NIOSH and OSHA) or 18% (ACGIH) at the surface. How much is taught in rebreather courses about this?
https://www.acgih.org/docs/default-source/presentations/2004/aihce_slides_4.pdf?sfvrsn=f6fadf0d_2

SeaRat

 

[RainPilot]

John, a CCR does not present the same need for an ESA as OC does. On a 300' plus tech dive, OC and CCR divers would not even contemplate an ESA. there would be gas sharing (OC) or separate bailout (CCR) protocols in place.

Even then, a CCR doesn't present a "loss of gas" situation like OC would. If you are out of diluent, an ascent is normal since diluent is not needed for ascent. If you are out of O2, then a PPO2 drop would occur on the ascent but then you would be bailed out onto an OC tank, or even a second CCR, or you could plug in your OC deco tank into the unit to manually add O2, or you could breathe your diluent in SCR mode until it got too lean, or....

There are many ways to deal with issues in a CCR but ESA is almost never one of them.

 

[John C. Ratliff]

John, a CCR does not present the same need for an ESA as OC does. On a 300' plus tech dive, OC and CCR divers would not even contemplate an ESA. there would be gas sharing (OC) or separate bailout (CCR) protocols in place.

Even then, a CCR doesn't present a "loss of gas" situation like OC would. If you are out of diluent, an ascent is normal since diluent is not needed for ascent. If you are out of O2, then a PPO2 drop would occur on the ascent but then you would be bailed out onto an OC tank, or even a second CCR, or you could plug in your OC deco tank into the unit to manually add O2, or you could breathe your diluent in SCR mode until it got too lean, or....

There are many ways to deal with issues in a CCR but ESA is almost never one of them.

RainPilot,

What features of CCR will warn the diver of PPO2 drop, other than a blackout? PPO2 drop physiologically has no warning. Again, going to the DeJoy diagram, what are the Person (Diver) Machine Communications that would indicate such a failure? If a diver is preoccupied by environmental factors, can this communication overcome the distraction?

SeaRat