Potential Safety Improvements in Rebreather Design

[tstormdiver]

You are applying reverse logic.

Not at all. I am saying, somewhere,.... Training, attention to details & common sense has to play a roll. As I have heard before, "you can idiot- proof things all you want, God will always create the better idiot to get around it".

 

[Wookie]

The concept of ALARA or ALARP (As Low As Reasonably Achievable or Practicable) was designed for the nuclear industry regarding radiation exposure. The concept assumes that every radiation worker will receive some exposure to radiation, so the industry uses a reasonable approach to lowering that exposure as much as possible utilizing the concepts of time, distance, and shielding, either permanent or temporary. I have worked hot spots in reactor compartments literally with lead aprons shielding my whole body to limit my exposure to extremities, which have a much higher tolerance for ionizing radiation than the trunk of the body.

I'm not sure the concept applies in rebreathers. How many fatalities are too many? I see Claudia and Brad and others familiar with the APOC watching this thread. The APOC was conceived with the thought that no rebreather fatalities was the only acceptable number, and I've seen an APOC in use, it isn't widely available, if at all. Other manufacturers make units IAW ISO or CE standards and have big fat liability policies. I've heard stories of one manufacturer taking his unit apart underwater and completing the dive. I believe there is a video to go along with this.

My point is, there is very little in life without inherent risk. Scuba diving is a higher risk sport, and if you don't believe me, you should take a look at my life insurance premiums. Rebreathers can be dived safely, but rarely are. If I've seen a thousand rebreather divers on my boat, I've only seen 25 checklists used start to finish. Yes, everyone prebreathes and everyone does a positive and a negative loop pressure check, but a checklist is (to me, coming from the nuclear industry) proof you LEAVE BEHIND when something bad happens. I don't believe that any court has found that there has been a failure of a rebreather when properly assembled and used, only when it has been incorrectly assembled in some fashion, or used by someone unqualified. A properly filled out and completed checklist for every rebreather assembly would prevent this, every time.

But as Jim Lapenta points out, doing checklists is hard.

 

[gianaameri]

The concept of ALARA or ALARP (As Low As Reasonably Achievable or Practicable) was designed for the nuclear industry regarding radiation exposure. The concept assumes that every radiation worker will receive some exposure to radiation, so the industry uses a reasonable approach to lowering that exposure as much as possible utilizing the concepts of time, distance, and shielding, either permanent or temporary. I have worked hot spots in reactor compartments literally with lead aprons shielding my whole body to limit my exposure to extremities, which have a much higher tolerance for ionizing radiation than the trunk of the body.I'm not sure the concept applies in rebreathers. How many fatalities are too many? I see Claudia and Brad and others familiar with the APOC watching this thread. The APOC was conceived with the thought that no rebreather fatalities was the only acceptable number, and I've seen an APOC in use, it isn't widely available, if at all. Other manufacturers make units IAW ISO or CE standards and have big fat liability policies. I've heard stories of one manufacturer taking his unit apart underwater and completing the dive. I believe there is a video to go along with this. My point is, there is very little in life without inherent risk. Scuba diving is a higher risk sport, and if you don't believe me, you should take a look at my life insurance premiums. Rebreathers can be dived safely, but rarely are. If I've seen a thousand rebreather divers on my boat, I've only seen 25 checklists used start to finish. Yes, everyone prebreathes and everyone does a positive and a negative loop pressure check, but a checklist is (to me, coming from the nuclear industry) proof you LEAVE BEHIND when something bad happens. I don't believe that any court has found that there has been a failure of a rebreather when properly assembled and used, only when it has been incorrectly assembled in some fashion, or used by someone unqualified. A properly filled out and completed checklist for every rebreather assembly would prevent this, every time. But as Jim Lapenta points out, doing checklists is hard.

From the HP2 manual (short for Hollis Prism 2):

6. Attach Counterlungs To Yoke
A. Insure inhale counterlung is on right side (with bladder & yoke face-up).
B. Clip Fastex buckles in place
C. Line-up Velcro parts and compress

You insure inhale counterlung is on "right side"... and put a check-mark on check-list.

BUT - oh s., you did not notice you reversed the counterlungs by MISTAKE.

You believed you did it correctly, but you did not, and yet you gave yourself a PASS on the check-list.

How does a check-list help you in this case?

P.S. I don't use check-list - they do not work for me as per the above example and give a false sense of security (but adopt other and better means which work for me).

 

[Dr. Lecter]

In 2014 though, is it acceptable for a woman in her prime and in the western world to die for just making a mistake and this for a recreational activity for a 14 meter dive?

It's no more or less acceptable than any other logical consequence of one's own actions. Step off a curb in right in front of a bus and physics takes over - whether it's "acceptable" or not is irrelevant, because we need both busses and curbs. It's up to us to look before we step, and in this case someone chose to go diving on a CCR after training without doing any looking. It's very sad, but it's not a problem with the CCR's design.

As to your checklist point, note that there are some relevant sections you skipped over:

9. Assemble DSV/BOV + Hoses, Check + Install

a. open/close, purge, mouthpiece
B. check mushroom valve seals and flow direction.
c. install hoses onto dsV/BoV
d. Perform a mushroom valve sealing test (stereo check)
e. install dsV/BoV onto counterlungs paying attention to flow direction arrow.

6. Negative Pressure Test (hold for 1 minute minimum) a. open dsV/BoVB. inhale from dsV/BoV in cc mode, exhaling through nose until counterlungs are fully collapsed c. close dsV/BoV d. allow to sit for one minute; watch for signs of leaks.
7. Positive Pressure Test (hold for 1 minute minimum) a. close oPV
B. Fill loop fully with oxygen using manual oxygen addition valve until oPV vents
c. allow to sit for one minute, watch for signs of leaks d. open dsV/BoV, evacuate loop contents

 

[Wookie]

From the HP2 manual (short for Hollis Prism 2):

6. Attach Counterlungs To Yoke
A. Insure inhale counterlung is on right side
(with bladder & yoke face-up).
B. Clip Fastex buckles in place
C. Line-up Velcro parts and compress

You insure inhale counterlung is on right side... and put a check-mark on check-list.

BUT - oh s., you did not notice you reversed the counterlungs by MISTAKE.

You believed you did it correctly, but you did not, and yet you gave yourself a PASS on the check-list.

How does a check-list help you in this case?

P.S. I don't use check-list - they do not work for me as per the above example and give a false sense of security.

The beauty of the checklist that doesn't work is that it can be easily modified by the manufacturer so that it does work. Look, this isn't teaching 17 year old sailors to run a reactor plant, this is teaching adults who presumably want to be there to dive a bit of scuba gear. So if what you infer by your reading of the coroners report is that the loop was assembled backwards, the counterlungs were put on the wrong side, and the unit still passed positive and negative, a concept I find a stretch, but then, I'm not certified on a Hollis, nor will I be, then a simple checklist modification may be in order, and Hollis should be able to do that by sending out a notice to all P2 users. Namely, step 6A would further identify the inhale counterlung with a description of what it looks like. Tammy says that the counterlungs don't look the same at all.

It's fine that you don't use a checklist. I've had a number of conversations with Leon regarding checklists, and our common ground is that they work if properly done, but most folks get too smart for them very quickly. Sadly, I had a very good friend and crewmember die on his meg. A checklist would have saved him, because he couldn't possibly have passed the negative pressure test with his particular problem. He installed his O2 selenoid incorrectly.

 

[gianaameri]

It's no more or less acceptable than any other logical consequence of one's own actions. Step off a curb in right in front of a bus and physics takes over - whether it's "acceptable" or not is irrelevant, because we need both busses and curbs. It's up to us to look before we step, and in this case someone chose to go diving on a CCR after training without doing any looking. It's very sad, but it's not a problem with the CCR's design.

Subway or Underground example then.

Easy to fall under one - but the newer ones have access doors both on train and platform.

What is acceptable in Sierra Leone now, may not be acceptable in the EU, and what was acceptable in the UK in the Middle Ages, may not be acceptable now.

What is acceptable now in our application is the safety standard which the rebreather industry gave itself - and it was not met according to the Coroner and HSL.

So, let me add to the failure by manufacturing and training, also the failure by Supervision:

1. The Notified Body who certified the unit and gave it a PASS on its check-list.
2. The Authorities who are supposed to supervise Notified Bodies and Manufacturers.

BUT Yes, the user was at fault big time in this case.

---------- Post added November 29th, 2014 at 01:20 PM ----------

As to your checklist point, note that there are some relevant sections you skipped over:

We do not know if she skipped over the check-list or that if assembled the way she did the unit would pass or fail pos. or neg. pressure tests.

The information I have say nothing as to check-list.

BUT any rebreather diver that does not do a pos. and neg. check pre-dive is skipping a very important check (I do those tests and don't use a check-list).

We do not know if she did or skipped pos. and neg. test from the information available.

 

[tstormdiver]

You (I understand you are a HP2 diver) ain't dead because you did not make the same mistake she did, which was preventable if the unit had been designed such that it cannot be assembled incorrectly.

Because I had adequate training as how to properly assemble the unit using checklists & have the attention to detail to immediately notice the night & day difference in the lungs.

 

[Brad_Horn]

Odd,... Since it has been shown that nearly all rebreather fatalities have been shown to be the result of operator error, not machine design, whether, because of being a inexperienced or careless or such.

Tammy, could you help me out and point to the evidence or analysis that shows this for a fact? My understanding is that most rebreather fatalities have insufficient detail about the root cause to form a conclusion, which would point to a rather critical flaw in your proof.
If you haven't already perhaps it's worth emailing the Jersey coroner and reading in full what he says, as this incident appears to be one of the known exceptions to your statement....

 

[Wookie]

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A ScubaBoard Staff Message...

removed reference to deleted post bowlofpetunias

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Just to be clear. You contention is that a rebreather shouldn't physically be able to be assembled wrong, regardless of any administrative or training steps that are standards in the industry that would immediately show that the unit was assembled wrong? So, if, for instance, I were able to install an empty O2 or Dil or fail to pack my scrubber, and choose not to do a checklist (as you yourself claim) that should be the manufacturers fault?

I don't want to dive your perfect rebreather. Sounds like you need a MkVI. Bring extra batteries.

 

[Wookie]

Just to be clear. You contention is that a rebreather shouldn't physically be able to be assembled wrong, regardless of any administrative or training steps that are standards in the industry that would immediately show that the unit was assembled wrong? So, if, for instance, I were able to install an empty O2 or Dil or fail to pack my scrubber, and choose not to do a checklist (as you yourself claim) that should be the manufacturers fault?

I don't want to dive your perfect rebreather. Sounds like you need a MkVI. Bring extra batteries.

I have seen all 3 happen. I have seen RB divers put on an empty (or nearly so) O2, Dil, and assemble the unit and forget to pack sorb. All were caught on pre-dive checks. The worst accident we've had on board was a diver who made a dive with a not full dil cylinder. She thought she had plenty. Turns out she didn't for her particular situation, and she learned how to breath O2 at 50 feet. She was lucky to have survived.