Potential Safety Improvements in Rebreather Design

[gianaameri]

Equipment blamed for diver's death | Channel - ITV News

Lesson learned: rebreathers should be designed to minimise the risk of assembly error (or "blow bubbles for no troubles").

Anyone knows which make/model this was?

 

[gianaameri]

Tragic diving death | Bailiwick Express

A shallow water rebreather fatality - another pointless and unnecessary loss of life.

There was no reason to use a rebreather for a dive like this.

 

[gianaameri]

Yep, and the rebreather should be recalled (Hollis would, but there are not too many rebreather companies who can understand that).

And you're basing that brilliant deduction on...what?

Because a rebreather is "life-support" equipment and in case of failure, be that machine or human or both whichever comes first, the user is unable to self-rescue and will pass out and drown - including shallow, including in a pool.

As a consequence, a rebreather not being a tooth-brush which will generally fail safe for the user, it should be built by competent persons, with an adequate budget and R&D facilities, and based on sound engineering principles, as customary for life-support equipment (i.e. anaesthesia machines, space suits...).

This means that the machine should protect the user (as far as reasonably practicable) because the user cannot protect himself/herself (i.e. pass-out and drown is the best he/she can do).

Common sense, best practice, the norm - not intuition or deduction.

 

[gianaameri]

Still waiting for actual details on what the assembly error(s) was and when/how the diver built her gear for that dive.

You can ask the Coroner.

I have the exact details, but I prefer not to post them because Scubaboard censored (first locked, then "moved," and last they deleted) the prior thread I had started on the topic.

It must be a touchy subject.

Let's see how long before this thread is censored.

 

[tstormdiver]

You really hate rebreathers, don't you...

No, He just thinks that they can only be used below 150 ft. He doesn't realize they do have other uses in shallower water. While yes, there some increased risks,... if ones head is screwed on correct & they are paying attention, one can catch most any problem that would also present deeper.

As for possible failures, if the loop hoses &/ or DSV/ BOV are incorrectly assembled, it will show in unsuccessful moving of gas through the unit & in the positive & negative tests that are run. If the check lists are followed, this will be caught. If the canister is inserted upside down, air will not pass though the unit. The only way for CO2 bypass, is failing to insert the Sorb canister, incorrect packing of the sorb, loose or missing CO2 seal ring or malfunctioning mushroom valves (this should be caught on the stereo breathing & plugging 1 end the inhaling & exhaling then doing the same to the other side). All of this is in the pre- dive check lists. Mechanically, the unit is not that complicated. During my MOD1 training, I completely broke down, rebuilt & tested the machine over a dozen times before even getting it into the water.

 

[tstormdiver]

No I do not, I carry 2 AL 40's or 2 AL 80's for bailout. My instructor has one. It may help for a very short period of time, those small diluent cylinders won't last long, especially at depth,... now plumbed into a larger off- board gas source,... maybe, but also additional failure points.

 

[Jim Lapenta]

I've seen instructors who can't assemble a set of doubles or set up a bpw correctly. Instructor rating is meaningless. What is important is the training received and how well it was given and received. Then with that you still have to follow the checklist. To the letter. Problem is many recreational divers have never been taught to do that so it takes a while to get them in the habit of doing so. It's why I now teach use of them to ow students. Not acronyms that can be messed up. Actual written lists.

 

[gianaameri]

I've seen instructors who can't assemble a set of doubles or set up a bpw correctly. Instructor rating is meaningless. What is important is the training received and how well it was given and received. Then with that you still have to follow the checklist. To the letter. Problem is many recreational divers have never been taught to do that so it takes a while to get them in the habit of doing so. It's why I now teach use of them to ow students. Not acronyms that can be messed up. Actual written lists.

So, after a student does a course with you, they are no longer capable of making an assembly error (which in a rebreather will lead to loss of consciousness and drowning)?

Would you feel more comfortable, despite your teaching skills and your student learning abilities, if, ultimately, the student at a later date would not be able to make an assembly error because the diving equipment (i.e. rebreather) rather than being designed as a Lego, it is designed such that:

“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.”

???

Every diver makes mistakes (that should be the safest assumption... invincibility is for teens).

 

[Jim Lapenta]

That is not what I said. Given the proper circumstances and the talent of the average person to screw something up, no matter how well you engineer "one way assembly only", someone will find a way to put a square peg in a round hole. I see this at times in my day job. Usually proceeded by "here's a hammer" try that.

Would it be the ideal situation where it could not be messed up? Yes. But as long as "some assembly required" is on the box it just isn't going to happen. While it is tragic that people die from their mistakes, it is also a fact of life. The only way to completely avoid that is to not live in the first place.

Rebreathers are complicated yet simple pieces of equipment when it comes down to it. I've only been on one and that was just a rebreather experience. One where we completely disassembled the rig, followed a tear down check list, reassembled it according to the assembly checklist, tested it, and got in the water for a planned one hour or so dive. Mine lasted 20 minutes and I had to bail out to my OC slung 40. Even following the list right after entering the water and descending the mouthpiece split on the side and every breath started filling one of the counter lungs. Had I been just a little more aggressive twisting and pulling on some things like the mouthpiece I may have caught that and caused the failure on the surface.

I keep that mouthpiece and use it as a reminder when it comes to the importance of following procedures and not being tentative. Such a small thing that is now on my assembly checklist for OC. Just in case.

You can't engineer total safety. Even if you made a unit that was sealed and could only be opened and closed at the factory. It will sometime fail, the user will fail to operate it correctly, or any number of other things.

Diving can kill. Plain and simple. Personally I make that crystal clear to every student. We all should. But more importantly we, as instructors, need to remember that ourselves. There are a number of dead instructors who seem to have forgotten that and got in over their heads. They paid for it, dearly.

 

[gianaameri]

That is not what I said. Given the proper circumstances and the talent of the average person to screw something up, no matter how well you engineer "one way assembly only", someone will find a way to put a square peg in a round hole. I see this at times in my day job. Usually proceeded by "here's a hammer" try that.

Would it be the ideal situation where it could not be messed up? Yes. But as long as "some assembly required" is on the box it just isn't going to happen. While it is tragic that people die from their mistakes, it is also a fact of life. The only way to completely avoid that is to not live in the first place.

Rebreathers are complicated yet simple pieces of equipment when it comes down to it. I've only been on one and that was just a rebreather experience. One where we completely disassembled the rig, followed a tear down check list, reassembled it according to the assembly checklist, tested it, and got in the water for a planned one hour or so dive. Mine lasted 20 minutes and I had to bail out to my OC slung 40. Even following the list right after entering the water and descending the mouthpiece split on the side and every breath started filling one of the counter lungs. Had I been just a little more aggressive twisting and pulling on some things like the mouthpiece I may have caught that and caused the failure on the surface.

I keep that mouthpiece and use it as a reminder when it comes to the importance of following procedures and not being tentative. Such a small thing that is now on my assembly checklist for OC. Just in case.

You can't engineer total safety. Even if you made a unit that was sealed and could only be opened and closed at the factory. It will sometime fail, the user will fail to operate it correctly, or any number of other things.

Diving can kill. Plain and simple. Personally I make that crystal clear to every student. We all should. But more importantly we, as instructors, need to remember that ourselves. There are a number of dead instructors who seem to have forgotten that and got in over their heads. They paid for it, dearly.

We are only talking about engineering the unit so that it cannot be assembled incorrectly and harm the user.

That is easy.

Many rebreathers come with that feature out of the box, but evidently not all.

Reliability and dependability and safety of a correctly assembled unit is another topic in itself (not the topic in this thread insofar in this case "incorrect assembly" was the root cause of the fatality).