Double Fatality in June 2014 (UK) - Inquest and Media Reports

rjack said:
The meg diver started the dive with at least 1 cell which was 4 yrs old and the youngest cell (of the 3) was 19 months old. Then he toxed.

How can this fatality be blamed on anything other than the diver's use of (failed) cells way past their recommended replacement date?
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Easy

I jumped in with three brand new APD cells and i had two curret limited and one total failure

So what?

Why didnt I die when I suffered this and the dozon or more other cell failures & wireing issues i have had in the last decade?

Surely if cell failure was the cause of death every one whos ever had a cell go down would be dead?

ATB

Mark
 
Chett. L said:
Hi Mark,

The likelyhood of 3 New cells all failing at the same time far lower than 19 months 3 and 4 cells failing, you know that...

Best regards,
Chett
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Chett i really dont know that

The only time I have ever suffered multiple cell failure was on new cells

And they sure as hell didnt fail in a uniform way that could go unnoticed.

The old cells in this unit were totaly diferent batches and vastly diferent ages.

You as an experianced CCR diver are trying to convince me that they failed in a totaly uniform way all current limited to show a 1.3pp02 when the unit PP02 was in fact much higher

Just how likley do you think that is?

ATB

Mark
 
GLOC said:
In fairness Brad, that isn't all of the Poseidon-related fatalities nor do they contain much data in terms of causality and lessons learned. I remember seeing Martin Parker's presentation of the Aquarius Project fatality using unit data to recreate the incident and determine what happened. That is the sort of thing that should happen but that cost money...
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Fair point Gareth, with the June 13 and May 14 fatalities it appears Poseidon have joined others and put public incident reporting in the too hard basket. Appears a bit of a pity as looking at those reports they started off well and they have certainly published lessons learnt as applicable for their kit for the earlier incidents.

Unfortunate for their test diver but agree that that was a good accident investigation presentation; however, out of the 300 plus rebreather related fatalities that appear to be recorded and I have to admit I haven't looked to see how many more you are tracking over what DL publish, but there are what, maybe what 10? of them that you can link to a decent published accident investigation report that is sufficient to give lessons learnt. The 3 or 4 public NEDU accident investigation reports on CCR incidents including at least a couple from military dives are excellent.

Is this incident only the 3rd? acknowledged one from current limited cells or have there been more that have gone unreported?
 
GLOC said:
I think Mark's point is that failures are predominately a concern when they are undetected failures, especially when you have two cells fail in the same manner when a systems uses voting logic to determine the correct cell - see the presentation from the Parks diver at Eurotek for another example of OxTox.

It boils down to the argument that IF all of the cells were reading below 1.0 before getting in the water, then the fact that they were old (or new) makes no difference because they have failed in a detectable manner.

Using 'new' cells means that you are less likely to have a double undetected current-limited failure causing the loop to be Hyperoxic. This is a different failure mode to getting in the water with cells which are 'known' to not be operating correctly.

Regards




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This is my boan of contention.

I am never more vigulent on my CCR than when I fit new cells.

Its new cells that give me the most greif especialy in the first few dives

Its removing old cells and fitting new ones thats the time when you can dammage the loom & get wireing issues that look like cell failures

I have reduced the cell error rate on new cells by soaking them in a bag of 02 for at least a couple of hours before use, but prior to this I often found new cells were reading high by mid way through a dive.

Most people wouldn't notice but I do dill flush check cells and I run pure 02 at 6m at the end of a dive so cell errors show up more

And we realy need to stop saying that cell errors on old cells are undetectable but some how cell errors on new cells show up just fine?

Why? How? what are you basing this on?

In (very) recent years we have started intorducing new cells on a rota and avoiding batches of cells but in the good old days it was three cells out three new ones in (As per my trainig course) QED batch failures ment it was more likley all three cells would fail.

ATB

Mark

PS I also get suspiscious when i can run 1.6 at the end of a dive at 6 as I normaly find it a struggle to do so
 
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Is there really much point to the debate over old v new? Cell failures (like pretty much everything) will follow a form of bathtub curve, with the end dip of the curve starting at xx months (probably 18-24). I dont have the exact data and frankly I dont care, since as mark says you have to assume that any cell can fail at any time and start acting accordingly.

The problem with all the statistical analysis is twofold;

1. it may only be a 1% risk, but if you're in that 1% the impact is 100%!
2. People modify how vigilant they are based upon the level of risk ("Oh I'll be alright, these cells are all changed in the latest clever idea every other 3-6 months").
 
It's one of those arguments reminiscent of the old classic GI3 how far can you shove a baseball bat up your arse thread on Techdiver.

Anything can fail but anything that consumes fuel is going to fail most as time passes and fuel is used up. That is a simple, inescapable fact. Obviously a cell that doesn't fail early is going to fail late, giving the appearance that cells have a high likelihood of early failure if you have to wait and the cell gets cycled out before it is allowed to die. Simple observation bias.

You can run old cells. I'd bet most drunk driving incidents go undetected, no accidents, no arrests. But for an individual doing it repeatedly, what are your cumulative chances when that is a regular behaviour?

The cells were not the failure. Behaviour including deliberately getting in the water with a 4 year old cell, a 3 year old cell and a mix of cells including the shittest brand ever produced was the failure. What happened was inevitable. Maybe not on that dive but inevitable all the same.
 
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IMHO, the issue of cell date/life/date, is a side bar to the issue of whether or not current best practices are being taught and followed.

In my small corner of the world divers and instructors are not changing out their cells in a timely manner.

Despite the efforts of many there is not concensous as to what is best practice in this matter. I would also contend that there is too little time spent in training teaching and re enforcing how to measure cell health mid dive.

The drive for technological fixes and recreational rebreathers is all very fine and well but it seems to me a distraction from the need to instill the basic skills needed to run a rebreather with O2 cells. I do not feel that this is currently effectively taught. I will go further and suggest that it does not even occupy an appropriately prominent part of the curricculum of the major training agencies.

My experience with cells in my four years at this is that the ones I now can purchase are excellent and very reliable. No doubt this feeds complacency.

Peter
 
lizardland said:
The cells were not the failure. Behaviour including deliberately getting in the water with a 4 year old cell, a 3 year old cell and a mix of cells including the shittest brand ever produced was the failure. What happened was inevitable. Maybe not on that dive but inevitable all the same.
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Totally agree here.

PeterN said:
IMHO, the issue of cell date/life/date, is a side bar to the issue of whether or not current best practices are being taught and followed.

In my small corner of the world divers and instructors are not changing out their cells in a timely manner.

Despite the efforts of many there is not concensous as to what is best practice in this matter. I would also contend that there is too little time spent in training teaching and re enforcing how to measure cell health mid dive.

The drive for technological fixes and recreational rebreathers is all very fine and well but it seems to me a distraction from the need to instill the basic skills needed to run a rebreather with O2 cells. I do not feel that this is currently effectively taught. I will go further and suggest that it does not even occupy an appropriately prominent part of the curricculum of the major training agencies.

My experience with cells in my four years at this is that the ones I now can purchase are excellent and very reliable. No doubt this feeds complacency.

Peter
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I'm in this corner of the world :)

And I concur. People are using cells past the CCR manufacturer's recommended limits. Which at least for the Vandergraphs which are individually tested to 1.7 by ISC before shipping to Meg customers (although I think they will sell their cells to anyone), are 12 months of use, 18 months total age. Rotating cells to stagger their ages and batches is no longer recommended.

If I were forced to use AI cells I think I'd probably revert to OC honestly. Those things are just crap.
 
rjack said:
Totally agree here.



I'm in this corner of the world :)

And I concur. People are using cells past the CCR manufacturer's recommended limits. Which at least for the Vandergraphs which are individually tested to 1.7 by ISC before shipping to Meg customers (although I think they will sell their cells to anyone), are 12 months of use, 18 months total age. Rotating cells to stagger their ages and batches is no longer recommended.

If I were forced to use AI cells I think I'd probably revert to OC honestly. Those things are just crap.
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I've been using AII Mk15 cells for six years and not had a single failure. Dont know if there is something different inside but they are significantly better than any AII R22D equivalents I had in my KISS.
 
lizardland said:
I've been using AII Mk15 cells for six years and not had a single failure. Dont know if there is something different inside but they are significantly better than any AII R22D equivalents I had in my KISS.
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That's good to hear.

I guess I really don't understand Mark's point about the diver who toxed. His cells were ancient and I can't see how they could all calibrate within specs being that old - even if they might have been completely unused. He chose to use ancient cells = unknown loop ppO2 = toxicity, seems pretty straightforward causality to me.
 
Richard, the point is as per the post above.

An undetected double failure is a different failure mode to choosing to dive cells which don't calibrate. Other than the information posted by Martin, I don't have information to say whether or not the cells were calibrated before the dive. If I find out, I will update the report accordingly.

The fact that the outcome is (unfortunately) the same doesn't necessarily mean that the in human factors terms the causality was the same.


Regards
 
rjack said:
That's good to hear.
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I dont know if it applies to all AII cells but the R10D equivalents are rock solid in my experience. Dont know if it makes a difference but they are made to order.

I've got an old set of civilian cells, an old set of non-magnetic Navy issue cells and a dead AII R22d equivalent knocking around. If I get a chance this weekend I'll cut them open and see what the differences are. The Mk15 cells are, however, a LOT heavier than KISS type cells.
 
GLOC said:
The fact that the outcome is (unfortunately) the same doesn't necessarily mean that the in human factors terms the causality was the same.
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See I would not categorize a 4yr old cell as viable regardless of calibration or if it rose to 1.6 at 6m on descent etc. Its "failed" before it even got to that point. As lizard pointed out, the error was not the cell it was the diver choosing to use a cell that old in the first place. Its rejected based on date before mV output is even considered. (to me at least)
 
Randy Thornton said:
The amazing thing to me is that there are still several members on this forum that openly admit to diving O2 cells well past their expiration date and do so as though they are wearing a badge of honor!
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Peter L said:
If anything please learn but don't deride or pretend that you would be any better on the day. Please make sure that you swap out a cell every 3-6 months and don't dive any that are beyond 18 months from manufacture.

Chris was a top bloke that was task loaded to the point of breaking, there was no other lesson to be learnt.
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I don't think there is much more to say than these two comments.

I cannot figure the diving with old cells argument - the probability of old cells failing is higher than new ones, but new ones do fail so you have to check every before and during dive the cell health.

I can fully appreciate how the emotion of the situation compounded with a simple kit failure would be enough to cause the second death.

Adding more technology to solve the issue isn't the way to go in recreational diving, IMHO.

All very sad.

Matt.
 
Mark Chase said:
Chett i really dont know that

The only time I have ever suffered multiple cell failure was on new cells

And they sure as hell didnt fail in a uniform way that could go unnoticed.

The old cells in this unit were totaly diferent batches and vastly diferent ages.

You as an experianced CCR diver are trying to convince me that they failed in a totaly uniform way all current limited to show a 1.3pp02 when the unit PP02 was in fact much higher

Just how likley do you think that is?

ATB

Mark
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Hi Mark,

Just like you don't know, I don't know either. And I'm certainly not trying to convince you of anything pertaining to this case because there's too many unknown variables particularly to what their dive set up procedures were before entering the water.

Best regards,
Chett
 
rjack said:
That's good to hear.

I guess I really don't understand Mark's point about the diver who toxed. His cells were ancient and I can't see how they could all calibrate within specs being that old - even if they might have been completely unused. He chose to use ancient cells = unknown loop ppO2 = toxicity, seems pretty straightforward causality to me.
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My point is simple.

The diver did not die because of old cells he died because he didnt check or monitor his cells

Cells either calibrate or they dont

WHen i had my three cell failure dive my brand spankig new cells refused to calibrate in my Hammer head

Martin parker blamed it on my Hammer Head and said my Classic head would calibrate OK

It did calibrate just fine and all three cells failed on the first dive.

Old or new calibration is no test of cell health and infact it can and does cover up cell failures.

Thats why I NEVER calibrate my unit unlless after a PP02 in air and PP02 in 02 passive test has been done. If my cells are significantly out from my last dive I will want to know why.

Cells are very stable till they start to fail.

Generaly if i do 50 dives in a year I may have to recalibrate 2 maybe 3 times in that year

I see divers calibrate at home recalibarte on the boat and recalibrate imediatly before kitting up and I wonder what cell failure they are trying to cover up?


Calibration is where the unit sees a cell is not reading corectly and re jigs the compensation to get that cell back in range. Thats prety much all it is. The cell not tested under stress and whilst calibration will reject cells that fall outside X Y milivolt range its is blatently obvious that it will let through cells that cant perform during dive conditions.

ATB

Mark
 
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Mark Chase said:
Sorry my senile dementure obviously kicking in.

Fec me mate C02 and a Tox on the same dive!!!!!

Golf is a nice hobby you know :D
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Just listened to a very interesting presentation from Simon Mitchell showing that high levels of CO2 and OxTox are closely related.

Regards
Larry


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