Comprehensive list of all accidents

Gasman

Sorry Alex... you are obviously missing the point. This case and the cases described in Rebreather World archives do not constitute proof. Guessing and supposition do not constitute proof. There can be many other explanations or reasons for the events described. As I mentioned, when researchers have been looking for symptoms over thousands of military dives where the PPO2 is definitively known (because they are using O2 rebreathers) there has not been a single case described of convulsions at 1.3 ATA. You may be correct, but the evidence that you are using to support your case will not hold up against the large body of literature on the subject.

Don't get me wrong.... it's just if you are going in to support those widows and orphans we don't want your case to be so easily ripped to shreds by the first expert who has actually read the literature on the subject.

Andrew

AD_ward9

You are mixing up two separate things.

An individual accident investigation for a widow uses a great deal of data from a specific accident, including a complete review of all possible causes based on the generic FMECA (including in that are natural causes, marine hazards, normal SCUBA hazards such as stuck inflators etc). It includes computer modelling of the various plausible causes using the dive profile and specifics of the dive. It includes reviews by the best experts in the world in specific areas, that either party is able to muster. That end result may be useful to a widow, a manufacturer, or both.

The accident list does not have that objective at all. It is concerned instead with identifying plausible causes, on a statistical basis, so manufacturers, trainers and divers can avoid accidents. I cannot see how the summary accident reviews that this encompasses are in any way useful to a legal party concerned with one particular case.

Please could you describe the study of thousands of military dives. It clearly misses the fatal accident I mentioned which occurred to a military diver.

Sports divers are doing hundreds of thousands of dives a year. The scrubber may not be replaced as frequently as for a military diver, the depth will cause a higher WOB than for a military diver using a pure O2 rig, and in some cases the unit itself has a higher inherent WOB and hydrostatic imbalance.

Alex

solocavediver

Hi,

only a single example but, my cavediving instructor has seen a fatal O2 convulsion where the PPO2 was very carefully checked afterwards and was around 1.2. It was the Devils Ear cave system, on open circuit, depth ca. 90 feet, ca. 32% Nitrox. He was right next to the diver. He saw the convulsion but could not save the man because they were well into the cave. These things happen. Even without extra CO2 or WOB. They happen.

Dive safe,

Charles.

silent running

Hi Alex, I'm curious to know if you are aware of any divers on the list who either began diving on Rebreather straight away or switched to RB after less than 100 OC dives.

I noticed that slightly more than 10% of the divers on the list are classified as either trainee or novice, but there is no way of telling from the chart how much OC experience they had previous to switching to Rebreather.

Any insight on how people who move quickly from OC to CCR do safety wise? I am one of them-less than 100 dives before moving to SCR for 100+ hrs, then to ECCR. My guess is that I was better off switching to RBs sooner than later as my OC skills were not so ingrained, and the new Rebreather skills were thus easier to retain.

I also wonder if you have an opinion about whether diving Rebreather all the time is necessarily more risky than switching back and forth between OC and RB. I have done only 2 OC dives in the past 500hrs of RB diving-not counting BO practice. I am of the opinion that it is safer for me not to mix the skill sets and that the more I dive CCR, the more my setup routine becomes ingrained and the more I become familiar with how my unit behaves and it's capabilities. Your thoughts?

Thanks, -Andy

Freef

I doubt if ingrained skills would have as much of an effect as ingrained attitude. Just because you can do a dive as an experienced OC diver doesn't mean you can do it as a new CCR diver, and this is where people have come unstuck.

With the increased flexibility in depth on a CCR unit, planned or expected depths can be exceeded in a way they can't on OC. With computers like the VR3 that will calculate deco throughout the whole dive peope have the equipment to exceed their original dive plan by a wide margin. If that happens, insufficient bailout is carried and a serious problem occours then the diver risks making an appearance on Alex's list.

Attitude also plays a part in kit assembly and maintenance. CCR can't just be slung in the gatage the same way OC kit is and then put together in five minutes at the dive site. People have dived units with cells that just about squak by calibration, batteries on their last legs, dil tanks which are being used or bailout with 100 bar in them or less and a whole list of other 'minor' defects that could cause problems.

CCR is becoming the 'new twinset' in the world of diving. People who don't really use a unit to it's full potential buy one anyway so they can have boasting rights at the club or on the boat.

I would hazard a guess that most people on here have a better attitude to their unit, and dive it as a tool to get them where they want to go, than people who have bought one just to have a CCR.

__________________
David.

Diving the mahogany rebreather.

Gasman

Sounds like a most interesting case. Have you the autopsy findings, the gas analysis report and the dive computer download? If you do can you please pass these over to Petar Denoble at DAN so we can have a detailed look at it. If it all stands up to scrutiny then we will write it up for the medical journals.

While I have no doubt that the convulsion occurred and was observed, there are a myriad of other reasons why it may have happened which need to be excluded before we go on line and post that the "the cause was X". Once these have been excluded then the information should be available to all.
To give you a few examples of possible reasons for convulsions underwater :

• Gas embolism
• Medication
• Subarachnoid haemorrhage
• Stroke (CVA)
• Hyperoxia secondary to incorrect gas mixture

This is just a very quick list off the top of my head and not meant to be comprehensive but should give you some idea that while we might think we know the cause there are often many other possibilities that must be considered.

Andrew

hrdubwd

On CNS toxicity ... (apropos several posts above)

When I started rebreather training, I spent a long time trying to understand how it was all supposed to work, but even after a lot of searching could find no scientific basis for the NOAA table, which appears to be the root of all 'rules'. Eventually, I got this forwarded (courtesy of Dave Dinsmore) from Dr J Morgan Wells, "the person directly involved with establishing NOAA's PO2 exposure limits back in the early 1990s":

"The NOAA Diving Man. is an operations manual, not a scientific publication. The info. has its basis in science, but reflects operational and admin. considerations as well. This is the case with the oxygen limits. The info. in the table includes a consideration of both central nervous system, and pulmonary oxygen toxicity. As Dr. Darvell points out, this may not look "systematic" when plotted as a function of time and pO2 on a single graph, but it is really a plot composed of the two curves of pul. and CNS O2 tox. Some operational considerations were also included. To fully understand the basis of the current O2 limits, one would need to study the rather large body of literature on both pulmonary and cns O2 toxicity, and to take into consideration the effects of exercise, temperature and the unanticipated events which occur during diving operations. The Dive. Man. tables were composed from the above, and are thus an end product of the above. You can not backtrack from them and expect to be able to reconstruct the scientific data used to construct them."

[emphasis supplied]

Try as I might, I could not find the "the rather large body of literature" that actually establishes this, and still have not - although many seem to believe it exists. Dr Wells declined (by silence) to explain any further. Read into that what you will. You may, however, find it odd, as I do, that it is claimed to be a composite - which I do not think is said anywhere else - and certainly not in the NOAA manual editions that I consulted. This is doubly odd because we are taught to deal with pulmonary and CNS as separate issues!

Kevin Gurr is under the impression they are separate issues. This has been the basis of the BSAC teaching all the way through the nitrox grades - there are separate tables, and with IANTD trimix, for example. If I understand JMW properly, the OTU calc is entirely redundant - it cannot mean anything extra in the face of the NOAA table. If it does, the NOAA table is insufficient as stated, if it doesn't - why are we taught it? The NOAA manual does not make any of this clear.

BTW: the only work that I could find that was cited as "scientific" was on a handful of US Navy underwater cyclists following orders to pass out. It is a study so awful in its design (and the statistics so appalling) it would not get published today - and the conclusions bear no relation to the 'results' (so please do not cite that one for me).

What prompted some of my concern was the inconsistency of the limit curve:



Note the upward turn at 1.1? - it is seemingly better (more 'generous') at pO2 > 1.1 until one exceeds 1.5. This makes no sense. (Although it could arise from the 'composite' nature, it is still inconsistent on the wrong side of safety.) I also failed to get any help from Carl Edmonds, who seemed to think the whole thing was meaningless because pre-term babies are put in hyperbaric O2 ...

However, the problem is even worse than it appears because if is a composite of two graphs, then logically the minimum of the pair has to be taken as limiting, and that cannot be derived from the trends that the two main segments show (unless the individual curves have very funny shapes!). In other words, it is not even a conservative 'worst case' plot (even allowing for rounding to tidy numbers).

(Incidentally, there are a number of other supposedly-NOAA tables out there with many more data points: they are simply crude interpolations from those in the original table, they do not represent better data.)

So, the question stands, as has been asked several times in various ways: where is the basis for this table? I don't think it is any more than guesswork. What is more worrying is that I can find no evidence that designers of deco software, computers, or training courses - anywhere - are aware of any of this. It is taken as gospel - do not question what you do not (and we do not) understand. What is worrying is that I could not find anyone who was prepared even to think about it.

This is not to say that I am questioning the existence of O2 toxicity, but clearly we are going to have a very hard time understanding what happens in incidents when the basis of the entire edifice is so awfully shaky - and apparently indefensible.

Sigh.

BWD

hrdubwd

If so, sounds fair. I for one, then, do not know enough. Where is this explained or taught, please? I have never encountered anything like it in my reading or training.

Ta,

BWD

Nailer99

Mel Clarke talks about this in her CCR trimix manual, available through the RBW store on this site. I've read about it elsewhere, but can't remember just where, right now.

hrdubwd

OK, thanks.

BWD