Differences between eCCR’s and mCCR’s design that may effect mortality rates

silent running · 14th February 2007, 07:42

Quote: (Originally Posted by Gill Envy)

Andy, thanks for bringing it back around...that line sounds like a thread tittle begging a post, perhaps you could do the honors as i'm guessing it might bring in some new input. In any case it really has boiled down to this question for me. I wish we could answer it definitively. Talking it over with some folks last night, it's hard to get a solid answere...are there really cases where shared cells caused the back up to fail as well?

On another angle, i'm wondering if having a totally independent system to compare to, rather than another rendition of the same three cells might help word off the "auto pilot effect" which in and of it'self would be worthwhile and perhaps more KISS like.

Hi Gill, I'm trying to get some more people I've talked to about electronics to post about the isolation issue. It's going to require a good layman's explanation of EE and a solid knowledge of ECCR electronics failure modes to write up something worth while. Hopefully I can get at least one of my contacts to post and start another thread....

I understand the compare 4th to the other 3 angle possibly making the checking habits better, probably true. But in the end, it still comes down to how you were trained. And if there's anything I've become convinced of in my time diving RBs, it's that there's many benefits to keeping things simple. Adding another set of seals, cells, cables and a computer certainly has benefits, but if the electronics can be properly isolated from allowing high current to feedback into the sensors, I would much prefer the simplicity of a properly isolated 2dry. Still wondering if it's really possible.

Mike · 14th February 2007, 08:59

Quote: (Originally Posted by silent running)

Is a 4th cell really the only way to insure redundancy in an ECCR?

Still wondering...

Probably.
Theoretically, anyway.
Dave S mentioned one example where a Mk 15 secondary was effected by an electronics pod failure, so it's even been seen in the real world.

However, I personally don't believe that the prism type setup will ever fail in such a way that it both gives false information AND doesn't make it obvious that there is a failure somewhere.

As I have decided that I'm going to carry enough bailout, then I don;t care if it fails as long as I can see that it has failed. Either the system will be working, or broken and known broken and I'll be following a bailout plan.

However, if I stick with the Prism, I'll probably get one of the subsea digitals so I can see all three cells at once... and for robustness.

Mike

silent running · 14th February 2007, 13:38

Quote: (Originally Posted by Mike)

Probably.
Theoretically, anyway.
Dave S mentioned one example where a Mk 15 secondary was effected by an electronics pod failure, so it's even been seen in the real world. Mike

Hi Mike, if you notice, the incident Dave S is refering to occured in an MK unit whose potting was cracked, which allowed for ingress into the electronics and which then affected the 2dry. This is obviously not a likely failure mode. From what I'm hearing and from going back and looking at Alex's post about O2 isolation, I don't see how flooding the battery compartment on the Prism will interfere with the sensors...

AD_ward9 · 15th February 2007, 20:57

Quote: (Originally Posted by jptaylor9)

Yep, seems a reasonable expectation! (To Mark Chase: some people expect people to just pick up something and for it to work). Like new cars, somethings need fixing under warranty.

1. EN61508 requires not just a billion hours between critical failure, it requires the system have availability of better than 100k hours. If manufacturers met that legal requirement, then in all the dives a year by all divers on eCCRs, only 1 would be aborted because the equipment was not working in predive checks.

2. The bath tub curve you posted is very well known. The front end of the curve can be avoided by decent manufacturing process control and soak testing.

The bottom line is that it is not unreasonable to expect a life critical system to actually work when you want it to, and any system that does not is flawed in more ways than one.

Alex

silentscuba · 15th February 2007, 22:10

Quote: (Originally Posted by silent running)

Hi Gill, I'm trying to get some more people I've talked to about electronics to post about the isolation issue. It's going to require a good layman's explanation of EE and a solid knowledge of ECCR electronics failure modes to write up something worth while. Hopefully I can get at least one of my contacts to post and start another thread.....

Sure would like to here more about this subject!!!!!

bletso · 15th February 2007, 22:20

Quote: (Originally Posted by AD_ward9)

The bottom line is that it is not unreasonable to expect a life critical system to actually work when you want it to, and any system that does not is flawed in more ways than one.

Alex

Funny, if I purchased a CCR, I would expect it to work all the time. I wouldn't consider that an unreasonable expectation. My homebuilt doesn't, but I don't get irate when it doesn't, just upset I missed a dive.

I have to admit though that everytime it hasn't work as expected, it was diver error, not equipment.

Dale

14th February 2007, 07:42	#211 (permalink)
silent running Mature mouth breather Current Rebreather/s: Prism Topaz Other Rebreather/s: Join Date: Jun 2005 Location: U.S.A. Brooklyn, New York Posts: 1,873	Re: Differences between eCCR’s and mCCR’s design that may effect mortality rates Quote: (Originally Posted by Gill Envy) Andy, thanks for bringing it back around...that line sounds like a thread tittle begging a post, perhaps you could do the honors as i'm guessing it might bring in some new input. In any case it really has boiled down to this question for me. I wish we could answer it definitively. Talking it over with some folks last night, it's hard to get a solid answere...are there really cases where shared cells caused the back up to fail as well? On another angle, i'm wondering if having a totally independent system to compare to, rather than another rendition of the same three cells might help word off the "auto pilot effect" which in and of it'self would be worthwhile and perhaps more KISS like. Hi Gill, I'm trying to get some more people I've talked to about electronics to post about the isolation issue. It's going to require a good layman's explanation of EE and a solid knowledge of ECCR electronics failure modes to write up something worth while. Hopefully I can get at least one of my contacts to post and start another thread.... I understand the compare 4th to the other 3 angle possibly making the checking habits better, probably true. But in the end, it still comes down to how you were trained. And if there's anything I've become convinced of in my time diving RBs, it's that there's many benefits to keeping things simple. Adding another set of seals, cells, cables and a computer certainly has benefits, but if the electronics can be properly isolated from allowing high current to feedback into the sensors, I would much prefer the simplicity of a properly isolated 2dry. Still wondering if it's really possible.
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14th February 2007, 08:59	#212 (permalink)
Mike Prism 'prentice Current Rebreather/s: Prism Topaz Other Rebreather/s: Inspiration Classic Evolution Join Date: Feb 2005 Location: Melbourne Posts: 332	Re: Differences between eCCR’s and mCCR’s design that may effect mortality rates Quote: (Originally Posted by silent running) Is a 4th cell really the only way to insure redundancy in an ECCR? Still wondering... Probably. Theoretically, anyway. Dave S mentioned one example where a Mk 15 secondary was effected by an electronics pod failure, so it's even been seen in the real world. However, I personally don't believe that the prism type setup will ever fail in such a way that it both gives false information AND doesn't make it obvious that there is a failure somewhere. As I have decided that I'm going to carry enough bailout, then I don;t care if it fails as long as I can see that it has failed. Either the system will be working, or broken and known broken and I'll be following a bailout plan. However, if I stick with the Prism, I'll probably get one of the subsea digitals so I can see all three cells at once... and for robustness. Mike __________________ Open ....... Closed Mind ........ Loop
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14th February 2007, 13:38	#213 (permalink)
silent running Mature mouth breather Current Rebreather/s: Prism Topaz Other Rebreather/s: Join Date: Jun 2005 Location: U.S.A. Brooklyn, New York Posts: 1,873	Re: Differences between eCCR’s and mCCR’s design that may effect mortality rates Quote: (Originally Posted by Mike) Probably. Theoretically, anyway. Dave S mentioned one example where a Mk 15 secondary was effected by an electronics pod failure, so it's even been seen in the real world. Mike Hi Mike, if you notice, the incident Dave S is refering to occured in an MK unit whose potting was cracked, which allowed for ingress into the electronics and which then affected the 2dry. This is obviously not a likely failure mode. From what I'm hearing and from going back and looking at Alex's post about O2 isolation, I don't see how flooding the battery compartment on the Prism will interfere with the sensors...
(Offline)

15th February 2007, 20:57	#214 (permalink)
AD_ward9 RBW Member Current Rebreather/s: Other CCR Other Rebreather/s: Other CCR Join Date: Jun 2005 Location: Scotland Posts: 2,011	Re: Differences between eCCR’s and mCCR’s design that may effect mortality rates Quote: (Originally Posted by jptaylor9) Yep, seems a reasonable expectation! (To Mark Chase: some people expect people to just pick up something and for it to work). Like new cars, somethings need fixing under warranty. 1. EN61508 requires not just a billion hours between critical failure, it requires the system have availability of better than 100k hours. If manufacturers met that legal requirement, then in all the dives a year by all divers on eCCRs, only 1 would be aborted because the equipment was not working in predive checks. 2. The bath tub curve you posted is very well known. The front end of the curve can be avoided by decent manufacturing process control and soak testing. The bottom line is that it is not unreasonable to expect a life critical system to actually work when you want it to, and any system that does not is flawed in more ways than one. Alex
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15th February 2007, 22:10	#215 (permalink)
silentscuba rEvo CCR Driver Current Rebreather/s: Classic Kiss rEvo Other Rebreather/s: Inspiration Classic rEvo Join Date: Jun 2005 Location: Mill Creek, WA USA Posts: 612	Re: Differences between eCCR’s and mCCR’s design that may effect mortality rates Quote: (Originally Posted by silent running) Hi Gill, I'm trying to get some more people I've talked to about electronics to post about the isolation issue. It's going to require a good layman's explanation of EE and a solid knowledge of ECCR electronics failure modes to write up something worth while. Hopefully I can get at least one of my contacts to post and start another thread..... Sure would like to here more about this subject!!!!! __________________ Curt McNamee rEvo CCR Diver KISS CCR Diver www.silentscuba.com
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15th February 2007, 22:20	#216 (permalink)
bletso An independent diver. Current Rebreather/s: Dolphin Home Build Other Rebreather/s: Dolphin Home Build Join Date: May 2006 Location: Louisville, KY, USA Posts: 263	Re: Differences between eCCR’s and mCCR’s design that may effect mortality rates Quote: (Originally Posted by AD_ward9) The bottom line is that it is not unreasonable to expect a life critical system to actually work when you want it to, and any system that does not is flawed in more ways than one. Alex Funny, if I purchased a CCR, I would expect it to work all the time. I wouldn't consider that an unreasonable expectation. My homebuilt doesn't, but I don't get irate when it doesn't, just upset I missed a dive. I have to admit though that everytime it hasn't work as expected, it was diver error, not equipment. Dale
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