Pompano Beach Fatality Sunday April 16th

[doctormike]

Yes, your PO2 rises on descent...and because pressure on descent is increasing, gas volume in your loop decreases, necessitating the addition of diluent to compensate. Therefore, even with a lean dil, the possibility of going hypoxic on descent is unlikely because you are constantly adding gas with more O2 even if it's a "lean dil" and even with O2 supply off (which is unlikely given additional info below).
I will add that I know the individual in question, having dived with him regularly for 20 years, 15 years of which was on CCR. And it was standard practice for us to only add O2 while on the surface preparing to dive. This was a standard practice as it was used as a backup check that our O2 was on while pre-breathing and checking cell integrity, etc. Therefore, the loop PO2 on the surface upon splashing in would typically have been around 0.60-0.80. Using 10/50 trimix as diluent would also be typical. While considered a "lean dil", I am sure folks can work out the math to determine the shallow depth straight 10/50 would support life for an extended period of time.
I will also add that the incident occurred in the water column, at around 160 fsw and before reaching the wreck, and at around 2 minutes into the dive.
While not ruling out hypoxia, I wouldn't be looking at it as a primary, secondary, or even tertiary scenario given the above.

Right, but the point of my post is that many people reading accident analysis threads are trying to learn about failure modes and avoiding the next accident. It's not a legal deposition trying to determine precisely what happened in this particular case to this particular diver.

You have added specifics which I didn't know before. Furthermore, I didn't know Joe, but simply stating that LOC on CCR raises the question of hypoxia isn't meant to be a slight against his skils or reputation. I hope you don't take it that way.

Maybe I read too much into the last two posts. But I do think that implying that hypoxia is not something to be considered isn't helpful.

 

[aue-mike]

Right, but the point of my post is that many people reading accident analysis threads are trying to learn about failure modes and avoiding the next accident. It's not a legal deposition trying to determine precisely what happened in this particular case to this particular diver.

You have added specifics which I didn't know before. Furthermore, I didn't know Joe, but simply stating that LOC on CCR raises the question of hypoxia isn't meant to be a slight against his skils or reputation. I hope you don't take it that way.

Maybe I read too much into the last two posts. But I do think that implying that hypoxia is not something to be considered isn't helpful.

I have not taken anything you posted in here as a slight against Joe. And I did not state nor imply hypoxia is not something to be considered. I considered hypoxia, but based on the information I posted (and additional information not for public dissemination) and my lengthy personal experience with Joe, considered it to be unlikely over other scenarios.
Over the past 3+ years, Joe had focused on diver education. Over that time he instructed numerous technical divers, be it for cave diving classes, CCR classes, etc. I know Joe would want to know what happened, and would want to educate other divers on the accident circumstances for their benefit. Which is why I opted to now wade into this to try to provide some useful context and information.
The universe of potential CCR failure modes and diving accident/incident causes is well documented. If one wants to simply consider/conclude the cause of death was due to either: 1) hypoxia; 2) hyperoxia; 3) hypercapnia; 4) medical issue; 5) gear issue; 6) human error; 7) some combination of the above; 8) etc., -- especially before any detailed gear analysis or coroner report (which 99/100 are unhelpful) has been conducted or released -- then we don't need to have this forum as it will always be covered by something within this spectrum. And per your statement: "It's not a legal deposition trying to determine precisely what happened in this particular case to this particular diver." If we are not trying to determine the particulars of the incident, just what is the point of this forum?

The best way to learn about failure modes and how to avoid the next accident is to take quality diver training and surround yourself with solid, like-minded, safety-conscious divers. It's that simple.

 

[mderrick]

Mark-
You are a rebreather diver. Please think about your statement above and why your scenario is fundamentally problematic.
Mike

Mike,
I believe you are thinking that as the diver descends on CCR, the loop PO2 will normally increase and can even spike high during a rapid descent typical of technical dives. However, my statement is not at all "problematic". I've investigated several accidents and personally observed one where LOC occurred during or shortly after descent. While descent does cause a relative increase in the PPO2, at the same time the diver is burning oxygen out of the loop if oxygen is not being replaced by the rebreather.

Here is a specific example, one of many possible: The CCR diver has properly prepped their unit including a pre-rebreathe during the transit to the dive site. During the transit, the oxygen valve is 'rolled off' as the rebreather bounces against a tank rack and bench designed for AL-80's. The loop PO2 is stable at the expected set point, say 0.7 ATA from the pre-breathe and indicated pressure on the SPG is as expected as well (from the charged hoses, which may be quite long on some units and hold a surprising amount of oxygen).

Once the dive boat reaches the site the diver dons the CCR, runs an abbreviated pre-jump list, then enters the water and makes a very rapid descent. In our area, this is a typical occurrence especially if the diver is "smart bombing" the wreck. While the loop PO2 is initially increasing, and the solenoid initially injects some oxygen (from the hose residual), eventually the loop PO2 will begin to drop and will more rapidly drop if the diver pauses their descent for any reason. The first diver jumping on a technical wreck dive in our area often has the task of chaining in a descent/ascent line for others to follow. That diver is exceptionally task loaded with navigating to the wreck and tying in. If the task loaded diver fails to notice their setpoint is not being maintained (the usual concern being a brief hyperoxic spike, not hypoxia), then LOC follows.

Note, this isn't a hypothetical example, it's has happened to me personally exactly as I described and I was lucky enough to notice dropping PO2 before it became dangerously low. I've caught two more roll offs over the years, but before gearing up as I now always manually check the valve immediately before gearing up. I've also personally observed several CCR divers actually perform their pre-breathe and then close the valve as a result of a deeply ingrained OC habit. Just to be clear, I'm not proposing the circumstance I've just described above as what happened in the case of the accident being discussed. I'm simply describing my findings in more than one case where LOC on CCR happened during or very shortly after rapid descent. If setpoint is not being maintained, a rapid descent quickly after entry will delay LOC rather than occurring at or near the surface.

 

[aue-mike]

Mike,
I believe you are thinking that as the diver descends on CCR, the loop PO2 will normally increase and can even spike high during a rapid descent typical of technical dives. However, my statement is not at all "problematic". I've investigated several accidents and personally observed one where LOC occurred during or shortly after descent. While descent does cause a relative increase in the PPO2, at the same time the diver is burning oxygen out of the loop that is not being replaced if oxygen supply has failed.

Here is a general example, one of many possible: The CCR diver has properly prepped their unit including a pre-rebreathe during the transit to the dive site. During the transit, the oxygen valve is 'rolled off' as it bounces against a tank rack and bench designed for AL-80's. The loop PO2 is stable at the expected set point, say 0.7 ATA from the pre-prebreathe and indicated pressure on the SPG is as expected as well (from the charged HP hose, which is quite long on some units and holds a surprising amount of oxygen).

Once the dive boat reaches the site the diver dons the CCR, runs an abbreviated pre-jump list, then enters the water and makes a very rapid descent. In our area, this is a typical occurrence especially if the diver is "smart bombing" the wreck. While the loop PO2 is initially increasing, and the solenoid initially injects some oxygen (from the hose residual), eventually the loop PO2 will begin to drop and will rapidly drop if the diver pauses their descent for any reason. The first diver jumping on a technical wreck dive in our area often has the task of chaining in a descent/ascent line for others to follow. That diver is exceptionally task loaded with navigating to the wreck and tying in. If the task loaded diver fails to notice their setpoint is not being maintained (the usual concern being a brief hyperoxic spike, not hypoxia), then LOC follows.

Note, this isn't a hypothetical example, it's has happened to me personally exactly as I described and I was lucky enough to notice dropping PO2 before the loop became seriously hypoxic. I've caught two more roll offs over the years, but before gearing up as I now always manually check the valve immediately before gearing up. I've also personally observed several CCR divers actually perform their pre-breathe and then close the valve as a result of an OC habit. Just to be clear, I'm not proposing the circumstance I've just described above as what happened in the case of the accident being discussed. I'm simply describing my findings in more than one case where LOC on CCR happened during or very shortly after rapid descent.

Appreciate the response Mark. Yes, these scenarios can happen as described. And I am aware of incidents where divers have gone hypoxic and perished on the bottom due to O2 valves being turned off. But IMHO this speaks of poor training, experience, and practices.

EDIT:
"While the loop PO2 is initially increasing, and the solenoid initially injects some oxygen (from the hose residual), eventually the loop PO2 will begin to drop and will rapidly drop if the diver pauses their descent for any reason."
I don't think I would agree with your assertion that the PO2 would "rapidly drop if the diver pauses their descent for any reason." During our CCR training, our instructor had us set our PO2 at a safe level (can't remember the specifics, but let's say, e.g., 0.50) and then shut off our O2 to monitor the rate of our PO2 drop while our instructor observed/monitored the situation. During our course, we even kicked against the side of the pool to see how fast one could burn (metabolize) through O2. It was definitely not "rapid" in our experience. But perhaps I am misunderstanding your point.

I know we could easily delve into semantics and "chicken versus egg" discussions, and will concede these scenarios would ultimately be considered hypoxic fatalities, but that is not, nor should not, be the real trigger. It's clearly human error.

 

[doctormike]

I have not taken anything you posted in here as a slight against Joe. And I did not state nor imply hypoxia is not something to be considered. I considered hypoxia, but based on the information I posted (and additional information not for public dissemination) and my lengthy personal experience with Joe, considered it to be unlikely over other scenarios.

Right. But a brief cryptic comment suggesting that considering hypoxia is "fundamentally problematic" with no context works against the process of accident analysis. Especially if that comment is based on information that is not available to other members of the thread. Not everyone here is a rebreather diver.

I'm not trying to be difficult or give you a hard time. I appreciate your expertise (and of course, offer my condolences). I just think that it would have been better to just explain why you felt hypoxia was unlikely in this case based on whatever information you feel comfortable sharing.

Over the past 3+ years, Joe had focused on diver education. Over that time he instructed numerous technical divers, be it for cave diving classes, CCR classes, etc. I know Joe would want to know what happened, and would want to educate other divers on the accident circumstances for their benefit. Which is why I opted to now wade into this to try to provide some useful context and information.
The universe of potential CCR failure modes and diving accident/incident causes is well documented. If one wants to simply consider/conclude the cause of death was due to either: 1) hypoxia; 2) hyperoxia; 3) hypercapnia; 4) medical issue; 5) gear issue; 6) human error; 7) some combination of the above; 8) etc., -- especially before any detailed gear analysis or coroner report (which 99/100 are unhelpful) has been conducted or released -- then we don't need to have this forum as it will always be covered by something within this spectrum. And per your statement: "It's not a legal deposition trying to determine precisely what happened in this particular case to this particular diver." If we are not trying to determine the particulars of the incident, just what is the point of this forum?

Sorry, I disagree. The point of the forum is - in my opinion - NOT to determine what happened in a particular case. With few exceptions, we rarely can do this because of concerns about liablity, the limits of any formal investigation, and other factors (especially in US cases, where there is no formal reporting mechanism). The point of this forum is to use these cases as a springboard for discussion so that people can learn from tragedy and become better divers. Even if the lesson that they learn may not be what actually happened in the case.

The best way to learn about failure modes and how to avoid the next accident is to take quality diver training and surround yourself with solid, like-minded, safety-conscious divers. It's that simple.

Yeah, but this helps too. Sometimes things don't come up in training, and the only way you think about them is through accident analysis.

 

[aue-mike]

Right. But a brief cryptic comment suggesting that considering hypoxia is "fundamentally problematic" with no context works against the process of accident analysis. Especially if that comment is based on information that is not available to other members of the thread. Not everyone here is a rebreather diver.

I can see that. But I made that comment to allow folks to engage their brains to hopefully recognize the concerns about the referenced conclusion/scenario. And the points I raised (depth/pressure effects on PO2 and gas volume) are fundamentals of all diving, not just CCR.
While I again appreciate your input about basing comments on information that is not available to other members of the thread, that does cut both ways. That is, coming to conclusions or offering scenarios without knowing all the particulars of an incident may also work against the process of accident analysis. And therein lies the rub...

 

[doctormike]

I can see that. But I made that comment to allow folks to engage their brains to hopefully recognize the concerns about the referenced conclusion/scenario. And the points I raised (depth/pressure effects on PO2 and gas volume) are fundamentals of all diving, not just CCR.
While I again appreciate your input about basing comments on information that is not available to other members of the thread, that does cut both ways. That is, coming to conclusions or offering scenarios without knowing all the particulars of an incident may also work against the process of accident analysis. And therein lies the rub...

Right, i think that we are pretty much on the same page, and it may be semantics. Accident Analysis really isn't what we are doing here - that implies a formal investigation to figure out exactly what happened in a particular case. Like the FAA process.

I really don't think that's why this forum exists. In fact, in many cases, online fourms work against that process, by giving the weight of expert opinion to scenarios that don't accurately reflect what happened. Sort of like what happened with my dive buddy's loss of her instabuddy last year in Newfoundland.

Obviously, people get different things out these forums. Personally, I find the discussion helpful and interesting, and i have learned a lot, even from "off topic" threads!

So I'm fine with conjecture and hypothetical scenarios, as long as all of the discussants understand the nature of those posts, and don't conclude that the opinion of the loudest voices here represent the truth.

 

[L13]

...
Over the past 3+ years, Joe had focused on diver education. Over that time he instructed numerous technical divers, be it for cave diving classes, CCR classes, etc. I know Joe would want to know what happened, and would want to educate other divers on the accident circumstances for their benefit. Which is why I opted to now wade into this to try to provide some useful context and information.

Given this, why is there:

(and additional information not for public dissemination)

Any accident relevant information should be public. And based on your statement about Joe and what he would want, he would agree.

It is rather hard for anyone to evaluate any statements by anyone hiding the truth about what happened.

It is hard to "educate other divers on the accident circumstances for their benefit", if relevant "accident circumstances" are "not for public dissemination."

 

[aue-mike]

Given this, why is there:


Any accident relevant information should be public. And based on your statement about Joe and what he would want, he would agree.

It is rather hard for anyone to evaluate any statements by anyone hiding the truth about what happened.

It is hard to "educate other divers on the accident circumstances for their benefit", if relevant "accident circumstances" are "not for public dissemination."

Because it is speculative and from personal conversations not supported by follow-up analysis of gear, which won't be available until it's released by the authorities. Furthermore, other bits are opinions based on personal experience with the deceased, and obviously may conflict with actual circumstances so it would obviously be considered anecdotal to those not familiar with the individual.
If you want to focus on that, so be it.

 

[Seaweed Doc]

Because it is speculative and from personal conversations not supported by follow-up analysis of gear, which won't be available until it's released by the authorities. Furthermore, other bits are opinions based on personal experience with the deceased, and obviously may conflict with actual circumstances so it would obviously be considered anecdotal to those not familiar with the individual.
If you want to focus on that, so be it.

Will any relevant details be released by authorities? In other accident scenarios, often we hear nothing. (At least in the US, barring litigation and even there the information will be one-sided.) Occasionally we get "lucky" in that the deceased was diving for a federal agency and there will be a very thorough, balanced public report. The last one of these I read pointed out that a very skilled, very experience diver made at least 3 mistakes. (This was the NOAA diver in Alaska.) That said, from comments made so far I'd lean toward medical event. But we may never know for sure.

I think there's educational value in knowing what MIGHT have gone wrong even if it's not what DID go wrong. We're not a court determining liability or guilt, just a bunch of folks wondering out loud.