Rebreather Question

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I think the argument is whether or not current limited cells are the cause of the hyperoxia incidents, or if it's just lack of awareness by the diver, or some other malfunction (stuck solenoid, etc.). Not simply hyperoxia itself.
 
Hypoxia for any reason over hyperoxia by reason of current limited cells.

I think you had that one backwards. Limited cells cause the rebreather/diver to inject more O2 into the loop thinking their ppO2 is low. Particularly dangerous on deco stops below 30ft where you are trying to get to 1.6 and can actually exceed it by quite a bit.

@JohnnyC I think there are some documented deaths on hyperoxia both by current limited cells, and cells with poor linearity. @Bobby likely has examples of both
 
@JohnnyC I think there are some documented deaths on hyperoxia both by current limited cells, and cells with poor linearity. @Bobby likely has examples of both

I'm sure there are. I think everybody is just playing at semantics now.
 
I think you had that one backwards. Limited cells cause the rebreather/diver to inject more O2 into the loop thinking their ppO2 is low.

I've heard about an order of magnitude more incidents about hypoxia for any reason than I have about hyperoxia due to current limited cells. How is this backwards?
 
I've heard about an order of magnitude more incidents about hypoxia for any reason than I have about hyperoxia due to current limited cells. How is this backwards?

ahh, I think I read it backwards then. I read it as more incidents about hypoxia due to current limited cells, that makes more sense now
 
This is not CCR-specific data. It doesn't look like the CCR causes are broken out but I may have missed it.

There were 64 CCR specific incidents in that time frame. Not all were investigated but the US ones have 13 summary vignettes discussed. And the range of issues is far broader that hypoxia is 10x more responsible than hyperoxia. The only other dataset is pre 2007 and cells (and training) have changed quite a bit in 11 yrs. Its behind a paywall so I cant see much
Title: Fatalities in divers using rebreathers
Authors: Denoble PJ, Ellis J, Vann RD
Publication: Undersea and Hyperb Med.
Volume: 34(4)
Pages: 282-283
Year: 2007
 
What davehicks posted isn't wrong, it's just incomplete.

I'm sorry but you're wrong. In davehicks post he claimed:
If your sensors are that far off in the middle of a dive, then end the dive. Don't put yourself in a critical deco situation if things are square. Back on the surface Recalibrate at 100% o2 and check that they read 21% in air. Then you will know if your sensor is failing or just had an intermittent wet connection.

a calibration in response to a wet cell or faulty connector will mask the problem, NOT fix it. This is a common misconception but one that needs to be corrected because it is dangerous!

If you record the millivolts in O2 at the beginning of the dive and they are different at the end of the dive you have a cell problem not a calibration problem. Cell failure seldom shows up during calibration because current limiting commonly occurs above 1ATA.
 
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I'm not trying to be an a##hole, but as a CCR instructor, my question for Jordan D is why wasn't all of covered in your training? Diluent flushes, oxygen flushes at 20 fsw, current limiting of oxygen sensors, etc. are basic concepts for rebreather diving.
 
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