Are rebreathers getting safer over time?

[PfcAJ]

As you stated in your first sentence.
I like having the Shearwater running 3 cells and my hud running an independent cell or two. For us, heading for the surface may not be the most desired option. I strongly feel that having the ability/option to add cells is an advantage for certain dives. We did not have the option on old units. Likewise, the divecan system allows for my hud to be independent of my controller, independent of my computer....So the chance of going "blind" is reduced.

The paradigm the Poseidon runs on is interesting, but it is not a unit I would do technical dives with - irrespective of what the manufacturer claims.

if the things not workin right staying at depth is a better option?

 

[Dr. Lecter]

What about the Se7en? They seem to think you only need two, and the argument for their verification system is compelling.

I don't think adding more sensors, going to five, six, seven, or whatever, does much except to make an already complex system more complicated. I would expect a five sensor system to have the same human element issue, complacency in cell verification and replacement cycles, if not more so.

The Se7en's approach is possibly ideal for a recreational eCCR, where if anything goes wrong with the sole pO2 monitoring/addition system the response is to bail and surface. For diving where going off a functional loop to complete a substantial deco and/or other overhead obligation is not a riskless decision, the ability to independently validate your impression that some number of cells have failed and fly the unit manually with backup pO2 monitoring is a definite improvement.

---------- Post added May 24th, 2015 at 03:05 PM ----------

In my mind, it doesn't matter if you have 2,3,5, or however many cells. If one is reading something abnormal ....

Keep calm, dil-flush, and apply brain to the situation.

 

[PfcAJ]

Dat brain might be the broke part. We've already established that it's the weakest link.

 

[Dr. Lecter]

Dat brain might be the broke part. We've already established that it's the weakest link.

True, but we're talking cell validation. If you dil flush and find yourself unable to figure out whether/which cells are invalid, then by all means GTF off the loop because the brain *and* the cell(s) are broken.

 

[kr2y5]

Are sensor failures believed to be correlated? How likely is it that 2 sensors simultaneously fail? How about 3 sensors at once? Would you trust a rebreather with 7 sensors and a voting logic? Is there some point where you could just trust the single majority value that comes out of it, or would you still want to see all sensor outputs, no matter what, and to verify them manually, as it was described above?

 

[KevinNM]

I've seen this suggested by multiple people as a good intro to O2 sensors.
http://www.revo-rebreathers.com/uploads/downloadsitems/Understanding_oxygen_sensors.pdf

 

[Dr. Lecter]

Are sensor failures believed to be correlated? How likely is it that 2 sensors simultaneously fail? How about 3 sensors at once? Would you trust a rebreather with 7 sensors and a voting logic? Is there some point where you could just trust the single majority value that comes out of it, or would you still want to see all sensor outputs, no matter what, and to verify them manually, as it was described above?

Why would you want to tie all your cells into a single monitoring system?

 

[ajduplessis]

Why would you want to tie all your cells into a single monitoring system?

Like the man said, he does not know breathers. He is asking questions to try and better understand the system, why then as an informed CCr diver are you answering his questions with a question? Stop being "clever" and rather explain and educate with the knowledge you. Is this not why you post here??

 

[Dr. Lecter]

Like the man said, he does not know breathers. He is asking questions to try and better understand the system, why then as an informed CCr diver are you answering his questions with a question?

 

[kr2y5]

Why would you want to tie all your cells into a single monitoring system?

I guess one presumed benefit of having a computer to collect all outputs, and spit out just one number or communicate via alarms would be, for a diver to have less stuff to have to constantly eyeball, and experience less task loading as a result of that. Maybe this is a non-issue? Since I don't have any experience diving a rebreather, I cannot tell. Since many people in this thread seemed to be pointing to task loading as one of the biggest (perhaps the biggest?) area of concern, I am just trying to understand to what extent this is a solvable problem. Ultimately, my question is, to what extent it may be OK to not ingest all signals, to place some trust in the electronics, let go, and let the computer do some of that work.

I take it from your post that you're more concerned about the failure of that electronic system as a whole than the burden of having to process multiple sensor inputs. I wonder how likely this is, given current technology? I don't know how electronic in rebreathers works, but fault-tolerant hardware has been used in a number of places for decades... From earlier posts, it didn't sound like most folks were viewing rebreather electronics as a weak link nowadays, but maybe I misread the responses.

What if you had two independent circuits connected to all those sensors. Or, what if you always had an option to switch back to "full manual" and see all sensor outputs through some alternate means if your computer failed. Would it be somewhat more acceptable under those, or any other circumstances, to just "run on autopilot" much of the time, or would you still be concerned about having to deal with an unfamiliar display during a stressful situation? Is it inevitable that you have to manually keep track of everything?