Do You Know What Your Oxygen Cells Do When Water Blocked?

[Brad_Horn]

"Deep Life Ltd have updated their study on "Characterisation of Oxygen Cells for Diving Rebreather Applications: Sourcing, Performance, Safety and Reliability" that has now spanned 16 years.

Despite it being a fundamental element of rebreather design and critical to the safe operation of any eCCR. Deep Life Ltd found that highlighting the explanation of how galvanic oxygen cells actually work was urgently required. After discovery that some recreational rebreather manufacturers were not aware of the simple fact that Oxygen must flow in and out of the cells freely in order for the diver to know their PPO2, and if the cell face was to be blocked by water, then the cell will continue to show the same PPO2 as before the water block occurred. See Sections 9.1.1, 9.1.2 and 10.1.8."
http://www.deeplife.co.uk/or_files/DV_O2_cell_study_E4_160415.pdf

Nothing new, just seems like some haven't done their research! Oops... Documentation of this issue goes back to the '90s.... http://johnclarkeonline.com/2012/12/...xygen-sensors/

Identification of the manufacturers who haven't considered this issue in the design of their eCCR is pretty easy: just check to see that it is covered in your units manual, published FMECA or unmanned testing documentation.

 

[The Chairman]

Your first link gives me a 404 error, but the second link was pretty interesting.

Why not make a list of CCRs that pass and those that don't.

 

[Brad_Horn]

Link to the DL article should be fixed.

I think it might just be better that folk read their own user manuals or CCR documentation and identify where this oxygen cell fault mode is covered and review the implicit issues. Just cause your displays are displaying a particular PPO2 might not mean that is what is in the loop.

 

[Dr Simon Mitchell]

Brad,

Would you care to substantiate your "discovery" that "some manufacturers" were not aware that oxygen needs to be able to diffuse freely across the cell membrane in order for the cell to work properly? That sounds as plausible as claiming to discover that some car manufacturers didn't know you have to start a car's engine in order to drive it. I'm sure you have some sort of convoluted reason for making the claim. I would be interested in hearing it.

Simon M

 

[Brad_Horn]

Simon, not my discovery. Per the link to John Clarks work this has been known about for some 25years as a cell fault and issue that needs to be factored into Rb design and oxygen control. You yourself have been aware of it for quite some time pg 233 http://media.dan.org/RF3_web.pdf and pg 254-58 Technical Diving Conference Proceedings.
That certain rebreather manufacturers were still not aware of this issue (more importantly, they did not understand the implications) - in particular that the PPO2 freezes at the point the cell is water blocked, before gradually decaying - was enlightening! An example of this is shown at Rebreather Todo lo referente a los recicladores de buceo - LANDIVE

As to substantiation, all will be revealed in time, I am sure. If they choose to reveal their ignorance to you directly, cool. In the interim what the various manufacturers have published about this cell fault in their respective units documentation provides sufficient information for discussion and self awareness. I am sure identification and rectification, of water blocked cells during a dive, is fully covered in eCCR training classes....

DL and therein OSEL became aware of it being a real issue only recently (post accident investigation) from the fact that at least one rebreather manufacturer has their cells collocated, in a place where they all flood at the same time. As a result at least one cell manufacturer is updating its data with this information: it was in their original sheet, but it became apparent that not everyone understood the grammar and how it was worded.

Kind regards
Brad

 

[rjack321]

DL and therein OSEL became aware of it being a real issue only recently (post accident investigation) from the fact that at least one rebreather manufacturer has their cells collocated, in a place where they all flood at the same time.

Even the OSEL O2/M CCR's cells will all flood at the same time, they are ~1cm apart in the same carriage like every other CCR on the market except maybe a few vintage things.

 

[Brad_Horn]

Even the OSEL O2/M CCR's cells will all flood at the same time, they are ~1cm apart in the same carriage like every other CCR on the market except maybe a few vintage things.

Yes they will, if your diving inverted. Not typically recommended. Otherwise under normal diving conditions they are at the highest point of the loop. As the POD is at 45', usually any moisture on the cell faces clears, rather than being trapped. As it is an mCCR you continue to be supplied O2 at 0.7lpm independent of the PPO2 monitoring....
www.facebook.com/151298954899613/photos/pb.151298954899613.-2207520000.1461051907./852630848099750/?type=3&theater

 

[Dr Simon Mitchell]

Simon, not my discovery. Per the link to John Clarks work this has been known about for some 25years as a cell fault and issue that needs to be factored into Rb design and oxygen control. You yourself have been aware of it for quite some time pg 233 http://media.dan.org/RF3_web.pdf and pg 254-58 Technical Diving Conference Proceedings.

This is exactly my point. It is ludicrous to suggest that manufacturers do not know this. This thread is just another example of your insatiable need to bash competitors under the guise of providing authoritative information.

As to substantiation, all will be revealed in time, I am sure.

How many times has the diving community heard this from you? Brad, if you and Alex think you have discovered some issue of high relevance to the technical diving community and you want to disseminate in a credible manner, why don't you do what real scientists do and submit your work to a properly peer reviewed scientific journal.

Simon M

 

[DA Aquamaster]

It's something I considered on out KISS Sidekicks. The three cells are oriented perpendicular to the horizontal axis of the rebreather and are spaced 120 degrees apart. In that regard, in any attitude no more than one cell would ever "hold" water.

However, there is also surface tension in play that might prevent a drop from running off the face of a cell anyway, but that's an issue of cell design, not the rebreather and I'm happy with the specifications of the cells I use in it,

 

[rjack321]

Yes they will, if your diving inverted. Not typically recommended. Otherwise under normal diving conditions they are at the highest point of the loop. As the POD is at 45', usually any moisture on the cell faces clears, rather than being trapped. As it is an mCCR you continue to be supplied O2 at 0.7lpm independent of the PPO2 monitoring....
www.facebook.com/151298954899613/photos/pb.151298954899613.-2207520000.1461051907./852630848099750/?type=3&theater

Highest point of the loop and ~1cm apart, so how are they not flooding at the same time? Besides if the unit is flooded who cares? You can't breath through water.

Also not sure why molex connectors are inadequate and only coax connectors are acceptable? At least according to this pdf... I do appreciate the temperature testing, I think its great you did that bit.