Potential Safety Improvements in Rebreather Design

[gianaameri]

If I were teaching the P2. I would consider improperly assembling the unit in this way and make my student remedy the problem pointing out all the things that just don't look right and fail a checklist in this condition. I do agree it is possible for this to happen again, but it seems like everytime the CCR manufacturer's builds a more idiot-proof machine...

Not really.

Fatalities due to incorrect assembly have only occurred on rebreathers which were poorly designed, that is they were non-compliant with Clause 5.1 of BS EN 14143: 2013 or BS EN 14143: 2003, which states:

“It shall not be possible to assemble or combine the components or parts in such a way that it can affect the safe operation and safe use of the apparatus, e.g. by incorrect connection of the hoses to the breathing circuit.”

At least that is true in this case.

 

[Brad_Horn]

Let's do this: let's go diving one day. Bring each of those rebreathers you believe to be foolproof. Let me assemble them, you dive them. I'd bet i could kill you with at least half of them. If i had more rebreather training, i could guarantee i could kill you with all of them. Nothing is sufficiently fool proof to a sufficiently exceptional fool.

I honestly can't believe certain people are still beating the same dead horse. It is impossible to design anything that is completely impossible to assemble incorrectly. It's not going to happen...ever. Not a rebreather, not an OC kit, not a firearm and hell, I'm a sailor...I've seen people that could assemble a damn hammer incorrectly. The CE standard that you keep referring to is unrealistic, kind of like the unrealistic student instructor ratios in most courses in ANY agency.
I challenge you to design and build anything that has more than 1 component...I will personally assemble it incorrectly.

Victor/Tom, Your challenge is off topic for this thread but I would be quite happy handing either of you my rebreather field stripped in a box; observe you figuring out how to build it and then I dive it! If you want to discuss it further go to PM.
If a rebreather can be misassembled by anyone in an unsafe fashion it fails the EN14143 criteria required to achieve CE cert! Namely “It shall not be possible to assemble or combine the components or parts in such a way that it can affect the safe operation and safe use of the apparatus, e.g. by incorrect connection of the hoses to the breathing circuit.”

 

[boulderjohn]

In reading both threads currently running related to this topic, as a middle of the road observer, I seem to see the regular recurrence of a certain theme in the discussions that mystifies me.

In my initial post, I suggested that what appeared to be two opposing points of view are actually saying the same thing. That is, "Rebreathers should be designed to the greatest degree possible to make it impossible to assemble them incorrectly through operator error."

As the discussions continue, I see some people strongly arguing against that by saying that it is impossible to make anything perfectly foolproof. It seems to me that saying that does not actually contradict that statement at all. "to the greatest degree possible" is not the same thing as "perfectly foolproof." More importantly, saying that it is impossible to make something perfectly foolproof implies an unstated corollary: "there is no point in trying." Does anyone really believe that if it is impossible to make something perfectly foolproof, then it is perfectly fine for equipment design to include potential error points that could have been eliminated with a different design? Does anyone really believe it is OK for designers to ignore the potential for such safety improvements in their design on the theory that it is solely up to the carefully trained user to spot the mistakes?

 

[Akimbo]

… More importantly, saying that it is impossible to make something perfectly foolproof implies an unstated corollary: "there is no point in trying." …

As a person involved in R&D and design most of my career I find that conclusion incongruous. Nothing is ever perfect but that does not imply that it can’t be improved. If humanity accepted your corollary then we would still be living in caves beating each other over the head with clubs… instead of using thermonuclear weapons.

 

[tomfcrist]

Victor/Tom, Your challenge is off topic for this thread but I would be quite happy handing either of you my rebreather field stripped in a box; observe you figuring out how to build it and then I dive it! If you want to discuss it further go to PM.
If a rebreather can be misassembled by anyone in an unsafe fashion it fails the EN14143 criteria required to achieve CE cert! Namely “It shall not be possible to assemble or combine the components or parts in such a way that it can affect the safe operation and safe use of the apparatus, e.g. by incorrect connection of the hoses to the breathing circuit.”

In the words of Barney Stinson...."Challenge Accepted!" Seriously, If you want me to think up a way to kill you while putting together your rebreather...I will. Hopefully you are smart enough to at least follow a post assembly checklist, find how bad I f-ed you up, and don't actually dive the $10000 unit that I just turned into a paper weight.

---------- Post added December 3rd, 2014 at 01:31 PM ----------

Not really.

Fatalities due to incorrect assembly have only occurred on rebreathers which were poorly designed, that is they were non-compliant with Clause 5.1 of BS EN 14143: 2013 or BS EN 14143: 2003, which states:

“It shall not be possible to assemble or combine the components or parts in such a way that it can affect the safe operation and safe use of the apparatus, e.g. by incorrect connection of the hoses to the breathing circuit.”

At least that is true in this case.

Although you are correct in this case, its only because you are correct by default.. However, what you still wont admit/own up to is that there is not one single rebreather on the damn planet that is compliant with Clause 5.1 of BS EN 14143: 2013 or BS EN 14143: 2003. Please provide some specific examples of units that you "Think" comply.

 

[boulderjohn]

As a person involved in R&D and design most of my career I find that conclusion incongruous. Nothing is ever perfect but that does not imply that it can’t be improved. If humanity accepted your corollary then we would still be living in caves beating each other over the head with clubs… instead of using thermonuclear weapons.

It is not my corollary--it appears to be the corollary I see implied in some of the arguments being made. To me it is inconceivable that anyone would think that, yet it seems to be the unstated implication of some posts.

 

[gianaameri]

Although you are correct in this case, its only because you are correct by default.. However, what you still wont admit/own up to is that there is not one single rebreather on the damn planet that is compliant with Clause 5.1 of BS EN 14143: 2013 or BS EN 14143: 2003. Please provide some specific examples of units that you "Think" comply.

The Meg is.

The Draeger Dolphin would as well.

The POS7 is.

The APD Evolution/Inspiration would (if you discount the o-ring and spacer which goes in the scrubber and which if omitted would cause CO2 by-pass).

I am certified on all of the above.

The only caveat is the scrubber.

If you consider that the user filling a scrubber with granular sorb is non-compliant to the Clause, then some units fail, leaving possibly only those rebreathers which use a EAC or a pre-packed disposable granular scrubber as compliant.

If we have a big debate on this though, I suggest you start another thread because as a one-off your and my post are no big deal, but if we engage in a big discussion we are going to end-up way off-topic and we will be told off.

 

[Akimbo]

It is not my corollary--it appears to be the corollary I see implied in some of the arguments being made...

I never interpreted these posts that way. Although it is a broad generality, the two camps seem to me as saying that improvements are fine but it won’t solve the root problem, which is true. It is likely that rebreather technology will never reach the same level of imperfect reliability and simplicity as open circuit Scuba for example. Some people argue that training and discipline is the only answer while others see the solution more incrementally. Discussions like this are part of the continuum in the product design trade.

 

[tomfcrist]

The Meg is.

The Draeger Dolphin would as well.

The POS7 is.

The APD Evolution/Inspiration would (if you discount the o-ring and spacer which goes in the scrubber and which if omitted would cause CO2 by-pass).

I am certified on all of the above.

The only caveat is the scrubber.

If you consider that the user filling a scrubber with granular sorb is non-compliant to the Clause, then some units fail, leaving possibly only those rebreathers which use a EAC or a pre-packed disposable granular scrubber as compliant.

If we have a big debate on this though, I suggest you start another thread because as a one-off your and my post are no big deal, but if we engage in a big discussion we are going to end-up way off-topic and we will be told off.

The meg is NOT in compliance....http://www.swiss-cave-diving.ch/PDF-dateien/NEDU-Report_1-4.pdf

The evo/inspo is not in compliance.

Can you install a valve backwards? Can you "forget" to install an o-ring?....then its not in compliance.

The scrubber caveat is not a caveat....it is the centerpiece of a rebreather....if it can be packed incorrectly...its not compliant. Even those rebreathers that use prepacked scrubber cartridges are non compliant, because you can fail to freaking use one.(Has happened by the way....More than once).

The whole situation of this fatality sucks. It sucks that she died, it sucks that she didn't use a single checklist properly, it sucks that none of the other CCR divers noticed the ClusterBomb that she was wearing when she got in the water. When push comes to shove, she either didn't have the knowledge and experience to earn the Certification she held on that unit, or she was just flat out reckless. The unit was NOT the root cause of her demise.

As far as being told off for having a conversation that is relevant to the thread itself "Rebreather Blamed for...." I'm not particularly worried about it. Wouldn't be the first time a Mod has told me to disengage...probably wont be the last.

 

[gianaameri]

The meg is NOT in compliance....http://www.swiss-cave-diving.ch/PDF-dateien/NEDU-Report_1-4.pdf

The evo/inspo is not in compliance.

The scrubber caveat is not a caveat....it is the centerpiece of a rebreather....if it can be packed incorrectly...its not compliant. Even those rebreathers that use prepacked scrubber cartridges are non compliant, because you can fail to freaking use one.(Has happened by the way....More than once).

As far as being told off for having a conversation that is relevant to the thread itself "Rebreather Blamed for...." I'm not particularly worried about it. Wouldn't be the first time a Mod has told me to disengage...probably wont be the last.

Let us start with the Meg.

The report identifies faulty O2 Sensors and incorrectly assembled solenoid.

The faulty O2 sensor is a fault inherent with a component and not its assembly by the user.

So, it does not count.

The solenoid assembly is a factory technican approved job, not an end-user assembly task.

So, it does not count.

Equally, there is a solenoid in the HP2. Incorrect assembly by the factory (or the user tampering with it) cannot count towards non-compliance with the Clause.

Same goes with the O2 Sensors if they develop a fault intrinsic to one of the failure modes of the O2 Sensor.

The Clause is only concerned with user assembly of the rebreather (not factory assembly of user non-serviceable parts, or failure of components like O2 sensors).