Potential Safety Improvements in Rebreather Design

[rongoodman]

Including safety improvements is obviously a Good Thing, and in this particular case, I don't see any downside to Hollis using different threads or fittings to keep divers from putting the counterlungs on backwards. The real issue, though, is that it's just one more example of a diver not using the safety equipment provided--there's no way that she could have built that unit the way she did had she just used the supplied checklists. The surprising thing to me is that she was a recent student--you usually read about divers taking a little more time to become that complacent.

 

[Steve_C]

The surprising thing to me is that she was a recent student--you usually read about divers taking a little more time to become that complacent.

Ah, but she was an instructor of some flavor. Not saying that was her case, but more than one instructor is dead due to over confidence.

 

[descent]

Ah, but she was an instructor of some flavor. Not saying that was her case, but more than one instructor is dead due to over confidence.

That is a common theme in this forum and over on RBW.

 

[Akimbo]

Making it difficult to connect devices incorrectly has been a basic design principle long before I was born. Data and power connectors should never be the mechanically interchangeable for example. High and low pressure quick disconnects should not be compatible. That said; there is no limit to the oversights that end users can uncover. Unfortunately, discovering them often costs lives in any industry.

Manufacturers will endeavor to eliminate human error for many good reasons. Depending on training alone is never the best choice. I can’t remember who wrote this but the best design principle I ever read was “manuals are list of human interface failures”.

 

[C Dub]

A rebreather is something I'm interested in, way down the road when my experience and skills are appropriate.

I think every fitting should fit into one, and only one, matching counterpart.

 

[descent]

... “manuals are list of human interface failures”.

Hah! I haven't heard that one before, and I have been in software for a while!

When I am writing new code (or debugging someone else's), I watch for required human interactions. Those sections of code where interactions with the user have become concentrated are some of the buggiest messes I have ever seen.

Why? Because the device (or the code) has 'state'.

For the interaction to be good under all circumstances, the user should be able to immediately perceive the state of the system before making any inputs. Ideally, the user input makes one single atomic modification to the state of the device.

As you can imagine, almost everything made by the hand of man is horribly deficient in this regard.

 

[gianaameri]

Side One: Although it is impossible to make rebreather design 100% foolproof in setup, the design should be as foolproof as possible in order to minimize the possibility of operator error.
Side Two: It is impossible to make rebreather design 100% foolproof in setup, so there is always the possibility of operator error.

This being an internet forum, I should disagree with both sides.

However, I agree with both, but only about half for each side.

Side 3: "The design should be as foolproof as possible in order to minimize the possibility of operator error. So there is always the possibility of operator error."

 

[boulderjohn]

This being an internet forum, I should disagree with both sides.

However, I agree with both, but only about half for each side.

Side 3: "The design should be as foolproof as possible in order to minimize the possibility of operator error. So there is always the possibility of operator error."

How is that different from side one?

 

[gianaameri]

How is that different from side one?

A lawyer would argue the three statements are different, but we are all saying the same thing, but from different perspectives and beliefs.

The better way to express the concept is what the manufacturers agreed in EN14143 (the EU wide norm):

“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.”

 

[Akimbo]

Hah! I haven't heard that one before, and I have been in software for a while!...

Human interface doesn’t just apply to software. I believe the term was used in the aircraft industry during WWII. However, the book the quote is from was written by an interface designer, not programmer, from Sun Microsystems if memory serves.

That quote has guided my designs of mechanical and electrical systems since reading it… but the manuals are still too damn big!