CCR Fatality (Feb 2013) - Australian Inquest Output

GLOC

GLOC

real name: Gareth Lock!
The report from the CCR fatality 2 years ago was recently heard and an excellent Coroner's report has been released. I can't find the original discussion thread on here but there was significant negative criticism over how could someone dive with cells 40 months old (cells 1 & 3) and 17 months old (cell 2). Similar discussions followed the fatality last year in the UK following the inquest 2 months ago where current limited cells were a contributory factor; it is a shame we don't get reports like this in the public domain.

As with any incident, it wasn't just technical issues at play (current limited cells, voting logic) but also a number of human factors involved.

The Coroner's report covers confirmation bias and anchoring as key human factors. I also think there was likely alarm blindness, maybe external pressures due to an inability to source reliable cells and the need to continue teaching, normalisation of deviance, inattention and/or selective attention blindness. I cover confirmation bias in some of the training I deliver have written about it here on my Cognitas blog.

Just because something didn't go wrong the last time a 'sub-optimal' decision is made, it doesn't mean the next time it won't go wrong. Forecasting the future based on past performance isn't a necessarily a great thing to practice when it comes to life support.

Diving has a level of risk which we can control and mitigate to a certain extent, as long as we are informed of the factors out there. I believe that reports like this are great because they go into significant detail identifying a number of non-technical factors at play. I also believe that when divers submit 'non-fatal' incident reports, they should consider go into a level which would allow someone unconnected to the incident to read it and determine what happened and why. Importantly, it isn't enough to know what happened, to improve we need to know why the diver made those decisions so that we are better prepared.

Regards
 
Yes it's a good report ,

I have a problem with Dr Fock, and his thinking on the diver not doing a dill flush cos diver needed to save gas , that s utter bollox ,
We don't need dill coming up from a dive ,
we also have wips on the bailout cylinders if we need to add more gas / volume , if having problems with inboard dill .
 
Last edited:
I didn't read the whole thing yet but I was interested and intrigued by the recommendations that a consistently high PPO2 voted out cell set off some kind of alarm. My questions are:

Do other rebreather manufacturers already have this capability and if not is anyone working on it?

and

If available would this be a desirable feature to prevent the case where either two cells are current limited and the voted out cell is accurately high?

Thanks,
Garth
 
Thanks for posting Gareth, that was a good read and very accessible.

Garth, if you read the whole report you might understand the alarms which were silenced and ignored. And realize that widespread adoption of these alarms by other manufacturers would not solve the problem(s) experienced on the fateful dive. The manner and frequency with which they were ignored is instructive to any CCR diver as "warning signs" can take many forms and the flashier and louder they are doesn't mean they are more likely to be understood or heeded.
 
The CCR Liberty can verify galvanic O2 cells by back-calculating expected PPO2 range using the Helium sensors (it can identify current limited cells). Implementation of appropriate alarms is under way.
 
lof said:
The CCR Liberty can verify galvanic O2 cells by back-calculating expected PPO2 range using the Helium sensors (it can identify current limited cells). Implementation of appropriate alarms is under way.
Click to expand...

:thumbsup:
 
lof said:
The CCR Liberty can verify galvanic O2 cells by back-calculating expected PPO2 range using the Helium sensors (it can identify current limited cells). Implementation of appropriate alarms is under way.
Click to expand...


That sounds like an excelent aproach to the issue

ATB

Mark
 
This was a tragic day here, and many divers were very shocked on hearing of Fil's death. On reading, there seems to be a few points glossed over, or misunderstood in this report. And yes, I HAVE read it...

1. Glosses over the use of old cells and how it reflects on safe work practices.

2. Glosses over the lack of calibration with regard to the same.

3. Glosses over cell check at 6m with regard to the same.

4. Doesn't understand that current limited cells would have responded to a partial dil flush. At least, it contradicts my understanding of current limiting, which is as those 2 cells were gradually producing less current during the dive (resulting in the one normal cell exceeding maximum read value) and would in a dil flush, even partial, result in those two current limited cells reading a much lower than expected value. Then one would expect to possible see one working cell at over 2.55 and the two failing ones far lower than possible for the dil being used. (I may have missed it in the report, but I use 15/55 on this dive, and it is a common gas here, available premixed, meaning anything less than a PO2 of 1.1 should raise BIG alarms in a diver's mind on a full flush) Therefore, this WOULD have shown up in the dive data.

5. I thought Inspo style electronics included a high PO2 alarm that could not be suppressed. That means the coroner misunderstood the nature of the alarms Fil suppressed (cell warnings) and his recommendation to AP to change their high PO2 alarm to one that cannot be suppressed shall have been aimed at not being able to suppress a cell warming alarm.

cheers

Andy
 
Hi.
I haven´t read the report yet but here you have a short post about a similar experience:

I had the exact same thing happen to me in a mine here in Sweden on my Meg a few years back. Two cells where limited at 1.27 and the third that showed the correct value was voted out.
The cells acted fine on calibration and 6m check on the way down. After about 35 minutes on SP 1,3 i see that my HUD is flashing a bit strange. I look at my handset and see:

Cell #1: 1,27
Cell #2: 1,7 (voted out)
Cell #3: 1,27

I quickly bailed and did a diluent flush.
All cells acted as normal and dropped to 0,85 (21/35 diluent at 30 meters). I went back to the loop and watched as the machine took the PO2 back up towards the setpoint.
Cell #1 & #3 stopped at 1,27 again but I could still hear the solenoid firing. I did a flush again when Cell #2 reached 1,45.
I aborted the dive and told my partner that the Cells where acting up.
I flew the machine manually on 1,0 on the way back and did a prolonged Deco just to be on the safe side since I didn´t trust the cells anymore.

All cells where under 12 months old and should have been fine.
After that incident my partner told me that if it would have been her she would probably have toxed and it would have gone from a small incident to a major one quickly.
She then sold her Meg and quit CCR diving.

I had spare cells and changed them and everything has been fine since. But I still don´t trust the machine and cells and monitor their values more often than others during a dive..
My conclusion is that cells can be fine at the beginning of the dive and diminish during the dive under constant high PO2.

Thanks for reading.

Best regards

Jonas Roos
 
Maybe we all should buy Narkedat90 pressure pots and test our cells to around 2.0 for at least 30 minutes monthly.
Expensive sure, but what is your life worth to you?
I can't imagine a toxing diver thinking "I'm glad I saved 300 or 600GBP by not buying a cell checker that would have prevented my imminent death"

Michael
 
Andy Del said:
.

4. Doesn't understand that current limited cells would have responded to a partial dil flush. At least, it contradicts my understanding of current limiting, which is as those 2 cells were gradually producing less current during the dive (resulting in the one normal cell exceeding maximum read value) and would in a dil flush, even partial, result in those two current limited cells reading a much lower than expected value. Then one would expect to possible see one working cell at over 2.55 and the two failing ones far lower than possible for the dil being used. (I may have missed it in the report, but I use 15/55 on this dive, and it is a common gas here, available premixed, meaning anything less than a PO2 of 1.1 should raise BIG alarms in a diver's mind on a full flush) Therefore, this WOULD have shown up in the dive data.
Click to expand...

Andy if I am understanding you correctly you are saying that if he did a dil flush the 2 bad cells would read lower than the PO2 of his dil at that depth?
This is not necessarily true and more likely if the unit was not calibrated correctly. The more likely scenario during a dil flush of current limited cells is that they would all read an accurate PO2 at lower PO2s (during a dil flush). If they all read correctly during a dil flush this tells you that the cell reading a high PO2 COULD be the correct one and the loop is not safe at the higher PO2 levels because you do not have a verified accurate means of monitoring it.


Sent from my iPhone using Tapatalk
 
michael_fisch said:
Maybe we all should buy Narkedat90 pressure pots and test our cells to around 2.0 for at least 30 minutes monthly.
Expensive sure, but what is your life worth to you?
I can't imagine a toxing diver thinking "I'm glad I saved 300 or 600GBP by not buying a cell checker that would have prevented my imminent death"

Michael
Click to expand...

I thought cell testers were not that accurate in predicting a cells life due to having no humidity, and have a cool ambient environment.
 
cathal said:
I thought cell testers were not that accurate in predicting a cells life due to having no humidity, and have a cool ambient environment.
Click to expand...

That my be true that you can't trust a cell 100% just because you tested it in the pressure pot.

That being said I think I have only ever had a cell go bad underwater once (it was not a nice cell). I always test mine in the pressure pot before a dive trip and have found a few bad ones in the pressure pot. We also use one at SubGravity to test cells of customers heads sent in for repair and fairy often we find an old cell that is current limited that they hadn't noticed by using the pressure pot. So in short I think pressure pots are very useful.


Sent from my iPhone using Tapatalk
 
Michael Thornton said:
That my be true that you can't trust a cell 100% just because you tested it in the pressure pot.

That being said I think I have only ever had a cell go bad underwater once (it was not a nice cell). I always test mine in the pressure pot before a dive trip and have found a few bad ones in the pressure pot. We also use one at SubGravity to test cells of customers heads sent in for repair and fairy often we find an old cell that is current limited that they hadn't noticed by using the pressure pot. So in short I think pressure pots are very useful.


Sent from my iPhone using Tapatalk
Click to expand...

As you said. Important being just beacause they passed the pot there's no guarantee they'll be ok during the dive. You still have to use the old bag of tricks during the dive.

The fine thing about the pot is that it will let you spot a cell that is bad already. Which then means you don't have to put all your gear together, pack it in to your car, travel for miles, gear up, get in the boat, get in to the sea, get to 6 m depth only to find out that one or more cells are current limited before doing all the previous in reverse. In this perspective the N@90 mini pot isn't all that expensive...
Now, while your still at it, and if you have (access) to a Petrel EXT (or similar) you can also watch all three cells at the same time. N@90 offers a special cable for this purpose. This feature lets you see very clearly all three cells response time and thereby spot a cell that's lagging, although it eventually reaches the correct value. A sign that this cell may be going south in the near future and perhaps needs closer attention during the dive ahead. How many divers manage to do this on the way to the 6 m mark?


/nils
 
the solution is so simple...

just change one sensor every 6 months, or even if you think the absolute max duration of use is 12 months, well then just change one sensor every 4 months in your 3-sensor rebreather;
you will NEVER have 2 sensors that show current limitation the same way during the same dive

paul
 
cathal said:
I may be mistaken but is that not what happened in this incident?

Cathal
Click to expand...

2 cells were 40 months old and current limited.
1 cell was 17 months old and read accurately (or thereabouts) but was voted out.

This is the fourth or fifth fatality I have read about in the past 6 to 8 months due to using cells way beyond the recommended replacement date which were current limited.
 
paulraymaekers said:
the solution is so simple...

just change one sensor every 6 months, or even if you think the absolute max duration of use is 12 months, well then just change one sensor every 4 months in your 3-sensor rebreather;
you will NEVER have 2 sensors that show current limitation the same way during the same dive
Click to expand...

Thanks Paul :)

cathal said:
I may be mistaken but is that not what happened in this incident?
Click to expand...

No because the two cells that became current limited at the same time were changed at the same time (same age).

Current limitation happens because the amount of lead in the cell (or, more specifically, the area of lead) is insufficient to react with a certain flow of oxygen diffusing in. If the flow exceeds that, the current will stay the same (broadly).
As the cell consumes oxygen, it consumes lead, so the area gets smaller, so the ppO2 at which the cell becomes current limited gets lower. For a given cell design, that ppO2 will depend on how much oxygen it's been exposed to (and at what temperature too).

If new cells are put in one at a time, regularly spaced, each cell will have consumed very different amount of oxygen. So, assuming manufacturing is reasonably consistent, they won't become current limited in the same way at the same time.

Cheers,

Matthieu
 
emmbee said:
Thanks Paul :)



No because the two cells that became current limited at the same time were changed at the same time (same age).

Current limitation happens because the amount of lead in the cell (or, more specifically, the area of lead) is insufficient to react with a certain flow of oxygen diffusing in. If the flow exceeds that, the current will stay the same (broadly).
As the cell consumes oxygen, it consumes lead, so the area gets smaller, so the ppO2 at which the cell becomes current limited gets lower. For a given cell design, that ppO2 will depend on how much oxygen it's been exposed to (and at what temperature too).

If new cells are put in one at a time, regularly spaced, each cell will have consumed very different amount of oxygen. So, assuming manufacturing is reasonably consistent, they won't become current limited in the same way at the same time.

Cheers,

Matthieu
Click to expand...

Many thanks for your explanation, so both cells that were current limited during the dive were off a similar age - 40 months but had different current limitations. Am I correct?

Cathal
 
You must log in or register to reply here.
Back
Top