Potential Safety Improvements in Rebreather Design

[ScoobaChef]

Now to answer John's original question, I see the two sides in the argument a bit differently than his two choices.

- One side that is pushing for a rebreather design that is on par with recreational oc in simplicity, ease of assembly and general fail-safedness. Basically removing the user's discipline and attention to detail from the equation(or at least reducing it to the level required for OW)

-the other side that is supportive of improvements in reliability and safety, but still feel that there will never be a level of improvement that will remove the need for a trained diver with checklists and a high degree of care to ensure safe operating.

 

[HIGHwing]

I've hesitated to write something in this thread because I disagree the root cause to most accidents are generally design related. Fact is, rebreathers are beyond the average diver, and the training is fundamentally flawed. We need to look into how the divers get on the machines available and change the culture. Until the culture change happens, we'll continue to have threads like the other one.

 

[Brad_Horn]

The problem isn’t really a choice of where to put R&D money because the minute market size puts rebreather manufacturers at the mercy of outside technologies for breakthroughs. A reliable, robust, compact, and cost-effective CO2 sensor isn’t likely to be developed at a rebreather manufacturer.

Akimbo, Why not, that it the primary market! Especially considering one has already been designed, engineered, tested and certified. and it's now being produced (following upgrade and re-engineering of the auto-bailout trigger) so it can be shipped to (long suffering and very patient) customers. See
https://www.facebook.com/video.php?v=123144424405002&set=vb.151298954899613&type=3&theater
https://www.facebook.com/video.php?v=123147937737984&set=vb.151298954899613&type=3&theater

Same with a better CO2 absorbent (converter really) that resists channeling, has a much longer life per unit volume, is cost effective, and does not deliver a caustic cocktail when it get wet.

Available direct from Micropore. Cost effective is debatable as it is expensive but it certainly is efficient for its volume, and is the only CO2 scrubber media available that doesn't channel/dust and minimises caustic cocktail risk.
For comparison of EAC to flooded kitty litter see https://www.youtube.com/watch?v=JET2OdrjDlA
For more on the background see Micropore - Extendair on Vimeo
Technology which has evolved from the scuba rebreather market to the medical side SpiraLith?

Same with O2 sensors that don’t die with a few drops of salt water.

A lot of work has been done on that and freely published, have a read of http://www.deeplife.co.uk/or_files/DV_O2_cell_study_110107.pdf

Sure, manufacturers can make electronics housings that are less likely to flood. But they can’t make a major rebreather flood recoverable with today’s technology.

Why not? https://www.facebook.com/media/set/?set=a.623958114300359.1073741826.151298954899613&type=3 The water is purged direct from the CLs and scrubber whenever you want to recover from a flood. You just have to pick the right rebreather!

They also don’t have the resources to make the investments required to develop that kind of technology. If they did, they would probably get out of the rebreather business to sell the discovery to much larger industries.

They don't? Have a read through Deep Life Design Team: Functional Safety Design Services
The same technology is quite applicable to the wider diving market, see SUBA | The ultimate BCD and integrated dive computer that thinks and acts for you

 

[gianaameri]

giaameri,

You are talking about another human being, your dive buddy, as "...anything like that..." I thought even rebreather divers use weight belts, and in the 1950s we decided for obvious reasons that these should have quick release buckles. If the rebreather floods, and the diver then becomes negative, wouldn't dropping his/her weight belt be one way to achieve neutral/positive buoyancy? Or are they now using a harness which keeps the diver from dropping weights? If so, should this be revisited?

It sounds like the French Navy has figured out how to achieve "nil fatalities due to rebreather during training." Shouldn't rebreather divers start to look at this achievement?

SeaRat

The rebreather is rather permanently secured to the diver. It is very important that the counterlungs, wherever they are positioned, they stay very close to the body (technically the "Lung Centroid") or WOB can go well above the tested and safe limits, and cause CO2 retention (i.e. pass out and drown without warning due to hypercapnia as in this sad fatality). So, there is lots of straps, buckles...

In short, when the buddy you would be tethered to passes out, and loses the mouthpiece, the rebreather would flood.

A rebreather has an internal volume of maybe 10 - 15 liters. This fills with water, and the buddy suddenly becomes negatively buoyant (a lot negatively buoyant).

So, you are attached to a weight. You cannot remove the rebreather easily or quickly from the buddy because it is designed to stay put and tight (no quick release as a weight belt).

If the buddy is semi-conscious or struggles, that raises the risk for you even further.

Tethering can do good, but also has the potential for a dual fatality.

It is somewhat safer in our application, to be good buddies and stay at arm's lenght and be vigilant, and for each rebreather diver in the buddy team do like the French military do and wear a Draeger Crown Strap.

Then, as explained earlier, if you can get hold and control your buddy, you will need some means to remove him/her from the rebreather loop poisoning him/her, and give fresh gas - and that is where the BOV comes in.

You can see how actually the Crown Strap sits on the diver at minute 1:47 here:

https://www.youtube.com/watch?v=j4VcSduUJbY#t=108

I train with these people and they are some of the finest divers and they have top instructors (they are between Russia and Germany, a rock and a hard place).

The BOV instead you can see and hear its safety use described here at about minute 06:20:

[video=vimeo;2311128]http://vimeo.com/2311128[/video]

So, not so much tethering, but a Crown Strap and a BOV could have helped to prevent this fatality (and good training from qualified ex-military instructors rather than the average rebreather instructor could have helped too - strict adherence to protocol and good knowledge of what actually works and does not and how to teach).

 

[mmadiver]

Brad Horn what is your association with Deep Life?

 

[Dr. Lecter]

"auto-bailout"..."thinks and acts for you"

 

[KevinNM]

While I don't own or use a rebreather, the concept of automating this makes me think about Air France Flight 447.

 

[HIGHwing]

As a pilot, I've studied AF447 in depth. That plane crashed IMHO because fear gripped the left seat pilot. All he had to do to save that aircraft was put his hands in his lap.

 

[bowlofpetunias]

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A ScubaBoard Staff Message...

I have moved the posts that related primarily to Rebreather design issues from the Rebreather blamed for Jillian Smith's death thread here. Posts related to the incident have been merged with the original thread on the topic in A & I. Many posts were deleted for being off topic and breaching the special rules of A & I Bowlofpetunias

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On a personal note I have found the discussion to be quite informative regarding Rebreathers. Hopefully now the general discussion on Rebreather safey issues will remain in the correct forum and separate from the A & I discussion.

 

[Omisson]

The rebreather is rather permanently secured to the diver. It is very important that the counterlungs, wherever they are positioned, they stay very close to the body (technically the "Lung Centroid") or WOB can go well above the tested and safe limits, and cause CO2 retention (i.e. pass out and drown without warning due to hypercapnia as in this sad fatality). So, there is lots of straps, buckles...

In short, when the buddy you would be tethered to passes out, and loses the mouthpiece, the rebreather would flood.

A rebreather has an internal volume of maybe 10 - 15 liters. This fills with water, and the buddy suddenly becomes negatively buoyant (a lot negatively buoyant).

So, you are attached to a weight. You cannot remove the rebreather easily or quickly from the buddy because it is designed to stay put and tight (no quick release as a weight belt).

If the buddy is semi-conscious or struggles, that raises the risk for you even further.

Tethering can do good, but also has the potential for a dual fatality.

It is somewhat safer in our application, to be good buddies and stay at arm's lenght and be vigilant, and for each rebreather diver in the buddy team do like the French military do and wear a Draeger Crown Strap.

Then, as explained earlier, if you can get hold and control your buddy, you will need some means to remove him/her from the rebreather loop poisoning him/her, and give fresh gas - and that is where the BOV comes in.

You can see how actually the Crown Strap sits on the diver at minute 1:47 here:

https://www.youtube.com/watch?v=j4VcSduUJbY#t=108

I train with these people and they are some of the finest divers and they have top instructors (they are between Russia and Germany, a rock and a hard place).

The BOV instead you can see and hear its safety use described here at about minute 06:20:

[video=vimeo;2311128]http://vimeo.com/2311128[/video]

So, not so much tethering, but a Crown Strap and a BOV could have helped to prevent this fatality (and good training from qualified ex-military instructors rather than the average rebreather instructor could have helped too - strict adherence to protocol and good knowledge of what actually works and does not and how to teach).

A crown strap would not have helped here. It would merely have kept the mouthpiece in. If she died of drowning in seawater yes. She drowned on her own gastric fluids.