Wishlist: how can rebreathers be improved to make them even safer ?

[Roger Hobden]

Design Failure Modes and Effects Analysis (DFMEA) is a standard part of any modern Product Development activity... IF properly implemented as part of the early PD process (esp Design Brief stage!) it should not lead to excessive development costs vs unexpected catastrophic failures or even just recalls. However I agree unless volume is shared with the military, unit costs are likely to be much higher... and of course the military would be unlikely to allow the release of the same model onto the civilian market!

Quite a good DFMEA summary here:
http://effectivefmeas.com/uploads/Failure_Mode_and_Effects_Analysis__FMEA__for_publication.pdf

Let me stress I am NOT a rebreather diver, but interested in these systems from a design and engineering POV.

According to a study by Dr Andrew Fock 'Killing them Softly':

With the caveat that they are “best guess numbers,” Fock concluded that rebreather diving is likely five to 10 times as risky as open circuit scuba diving, accounting for about four to five deaths per 100,000 dives, compared to about 0.4 to 0.5 deaths per 100,000 dives for open circuit scuba. This makes rebreather diving more risky than sky diving at .99/100k, but far less risky than base-jumping at 43 deaths/100k.

He found that there was no difference in fatality rates among manual or electronic units, or specific brands of rebreathers; accidents were roughly proportional to market share. Fock also pointed out that while the data suggests that deeper dives carry greater risks, a large number of rebreather fatalities occur in shallow depths within the recreational envelope.

As far as the causes or “triggers” that precipitated accidents, Fock concluded that the source of most problems was the human-machine interface, or so-called “pilot error,” involving assembly and pre-dive preparation, maintenance, training, and high risk behaviours that include ignoring checklists, carrying insufficient bailout and diving beyond one’s limits. “The question,” posed Fock,” is whether the risk can best be mitigated by training (reinforced by dive culture), or engineering out potential problems, or both.”​

Rebreather diving: ‘Killing Them Softly’ | DIVER magazine

Currently, one of the biggest safety issues surrounding rebreathers is the fact that divers become complacent and don’t rigorously adhere to a pre-dive checklist in assembling and preparing their unit for diving as they (presumably) learned in class, and also neglect required post-dive maintenance. (Some experienced rebreather divers don’t follow checklists either.) Even worse, some divers choose to dive knowing that there are problems with their unit such as a faulty sensor or small leaks.​

Creating A Safety Culture | DIVER magazine

So will creating new expensive high-end fully integrated 'fly by wire' rebreather technologies for the recreational dive market make the situation better or worse... if the diver then feels they can rely 100% on it?

Great post, that answers many questions that I had !

Thanks a million !

 

[Wookie]

I was thinking more about the near future ...

You know, you ask questions that have been asked here a thousand times, and a little research would keep you from asking them again. Then someone comes along and answers your questions, but you don't like their answers, you want answers to a different question.

A little advice I like to give to new members is to watch the interactions here. Do some searching. See if someone has already asked the question, and see if the answers are still valid. See if the answers are valid for your purpose. Then, come up with a well thought out question that gets to the root of what you want to know, instead of having to come up with 2 polls because you didn;t get the answers to the first one that you wanted. Or rejecting a well respected member's well thought answer because your question was not as well thought out.

We all like to see enthusiastic new members, and of course, you are welcome to come here and ask the same questions that have been asked and answered before, ad nauseam. But sometimes it is better to look and listen first.....

 

[Akimbo]

"Rechargeable" CO2 absorbent in a fixed matrix and didn't fail or turn costic when exposed to saltwater -- no channeling, packing, or buckets.

 

[Roger Hobden]

because your question was not as well thought out.

Point taken.

I am a teacher in my own area of occupation. I find that one of the common "problems" in many fields of knowledge, is that beginners often don't know which and how to frame pertinent questions in the first place.

Thank you for all of your comments, though.

I will keep them firmly in mind.

 

[Roger Hobden]

Also, 24-page thread discussions that seem to arrive at no conclusion, like the following currently ongoing one, make it pretty hard for a newcomer to SB to distinguish who's right and who's wrong, who's an authority, and who isn't ?

Why ‘everyone is responsible for their own risk-based decisions’ isn’t the right approach to take

 

[Wookie]

Also, 24-page thread discussions that seem to arrive at no conclusion, like the following currently ongoing one, make it pretty hard for a newcomer to SB to distinguish who's right and who's wrong, who's an authority, and who isn't ?

Why ‘everyone is responsible for their own risk-based decisions’ isn’t the right approach to take

No one is right, or wrong. Or in authority. Well, Pete owns the board, and his rule is “be kind to each other, and if you can’t be kind, at least don’t be a dick”. But the answer is that scuba diving is anarchy. Then when you die we all point our fingers and say “it was the split fins and spare air. We told him not to do that” regardless of the thousands of successful dives made every day with split fins and spare air.

 

[Roger Hobden]

But the answer is that scuba diving is anarchy.

OK, thanks again .

 

[lv2dive]

I read hundreds of posts before I even created a ScubaBoard account. There is a wealth of knowledge here and after reading dozens of threads, it’s easier to get a feel for the pontificators vs the people who know what they are taking about.

Also, 24-page thread discussions that seem to arrive at no conclusion, like the following currently ongoing one, make it pretty hard for a newcomer to SB to distinguish who's right and who's wrong, who's an authority, and who isn't ?

Why ‘everyone is responsible for their own risk-based decisions’ isn’t the right approach to take

 

[KevinNM]

Then when you die we all point our fingers and say “it was the split fins and spare air. We told him not to do that” regardless of the thousands of successful dives made every day with split fins and spare air.

It’s just a matter of time if you do that. Unless you can back kick in the split fins, then it’s Ok.

 

[DA Aquamaster]

Design Failure Modes and Effects Analysis (DFMEA) is a standard part of any modern Product Development activity... IF properly implemented as part of the early PD process (esp Design Brief stage!) it should not lead to excessive development costs vs unexpected catastrophic failures or even just recalls. However I agree unless volume is shared with the military, unit costs are likely to be much higher... and of course the military would be unlikely to allow the release of the same model onto the civilian market!

Quite a good FMEA summary here:
http://effectivefmeas.com/uploads/Failure_Mode_and_Effects_Analysis__FMEA__for_publication.pdf

Let me stress I am NOT a rebreather diver, but interested in these systems from a design and engineering POV.

According to a study by Dr Andrew Fock 'Killing them Softly':

With the caveat that they are “best guess numbers,” Fock concluded that rebreather diving is likely five to 10 times as risky as open circuit scuba diving, accounting for about four to five deaths per 100,000 dives, compared to about 0.4 to 0.5 deaths per 100,000 dives for open circuit scuba. This makes rebreather diving more risky than sky diving at .99/100k, but far less risky than base-jumping at 43 deaths/100k.

He found that there was no difference in fatality rates among manual or electronic units, or specific brands of rebreathers; accidents were roughly proportional to market share. Fock also pointed out that while the data suggests that deeper dives carry greater risks, a large number of rebreather fatalities occur in shallow depths within the recreational envelope.

As far as the causes or “triggers” that precipitated accidents, Fock concluded that the source of most problems was the human-machine interface, or so-called “pilot error,” involving assembly and pre-dive preparation, maintenance, training, and high risk behaviours that include ignoring checklists, carrying insufficient bailout and diving beyond one’s limits. “The question,” posed Fock,” is whether the risk can best be mitigated by training (reinforced by dive culture), or engineering out potential problems, or both.”​

Rebreather diving: ‘Killing Them Softly’ | DIVER magazine

Currently, one of the biggest safety issues surrounding rebreathers is the fact that divers become complacent and don’t rigorously adhere to a pre-dive checklist in assembling and preparing their unit for diving as they (presumably) learned in class, and also neglect required post-dive maintenance. (Some experienced rebreather divers don’t follow checklists either.) Even worse, some divers choose to dive knowing that there are problems with their unit such as a faulty sensor or small leaks.​

Creating A Safety Culture | DIVER magazine

So will creating new expensive high-end fully integrated 'fly by wire' rebreather technologies for the recreational dive market make the situation better or worse... if the diver feels they can then rely 100% on it?

A couple thoughts...

First let me also stress that you are not a rebreather diver, and thus might be missing some of the subtle nuances that are involved.

Second, Fock based this statement on some very broad generalizations:

"With the caveat that they are “best guess numbers,” Fock concluded that rebreather diving is likely five to 10 times as risky as open circuit scuba diving, accounting for about four to five deaths per 100,000 dives, compared to about 0.4 to 0.5 deaths per 100,000 dives for open circuit scuba. This makes rebreather diving more risky than sky diving at .99/100k, but far less risky than base-jumping at 43 deaths/100k."

Beyond "best guessing" Fock also makes the assumption that all OC diving carries equal risk. That is not the case. As a result to get accurate numbers you have to parse the OC data to get a subset that translates well to CCR use, which for the most part is still strongly biased in the technical and cave diving end of the spectrum. Then within technical and cave diving you have to look at the risks in various types of dives. 300' deep dives are dangerous in both CCR and OC, as are dives with extreme linear penetration . The risks can be different, but depending on the dive OC can be more or less safe than CCR.

Interestingly Fock identified 43 deaths per 100,000 base jumps. What isn't mentioned is that the accident rate per 100,000 people per year is a nearly identical 42.7 per 100,000 people. In other words, just surviving a year is statistically as dangerous as making 1 base jump per year.

Let's also quantify 4 or 5 deaths per 100,000 CCR dives. Few divers, OC, SCR, or CCR, have 5,000 dives period. But lets assume a diver has 5000 dives and that ALL of them are SCR or CCR dives. That carries just 1/20th the risk 100,000 dives and similarly the "4 to 5" deaths per 100,000 dives, equates to a .20 to .25 probability of dying in the course of 5,000 rebreather dives.

Then we also have to consider that the average CCR dive is a lot longer than the average OC dive, especially when we consider the average 20 to 40 minute pretty fish dive. We average about 240 minutes per dive on CCR, compared to about 90-120 minutes per OC dive in some of the same caves. In other words we make one dive on CCR when we used to make 2 dives on OC. That increases the OC risk for us by a factor of 2 - just based on our OC versus CCR dive numbers per day, and if we compare our 240 minute dive time figure to an average 40 minute open water OC pretty fish dive, the corrected OC risk is 6 times greater.

Again the risks are different but OC divers dies because they did something stupid - and so do CCR divers. But the way Fock presents the risk is in very general numbers with no consideration for context and differences in conditions and relative dive time.