Drying a head, water ingress in O2 cells

[BlueTrin]

Hi, I was told during my MOD1 class to try to avoid putting my head in a position where the O2 cells were upside down after diving.

This was so that the water condensation wouldn’t fall into the opening of the O2 cells.

But I was wondering, are the O2 cells damaged by more exposure to water?

Is there any basis for this? Some of the people I dive with say that they never heard of such advice.

/ asking for a friend

 

[nickbutcher]

...
Is there any basis for this? Some of the people I dive with say that they never heard of such advice.
...

My MOD1 instructor advised me to leave the JJ head in an orientation that would allow any water on the cell membranes to drain off.

Seems sensible; however as I understand it, rebreather cells have hydrophobic membranes (hence reacting slightly slower than the cells made for O2 analysers).

If I'm diving regularly, I tend to only remove the head when I change the scrubber and then I dry the cells by leaving the head in a place where it's most secure from other divers, rather than worrying about what direction the cells are facing - they dry pretty quickly regardless.

Don't forget that a CCR loop will at 100% humidity within minutes of breathing on it. I've never had a cell fail from water ingress.

 

[Capt Jim Wyatt]

I think it is wise to try and keep moisture away from the tops of the cells. When I remove my head I position it upside down so gravity helps move the moisture away from the cell top membranes. Overnight I leave it with cell tops up and a small fan blowing air over the top of the head. YMMV.

The Analytical Industries flier entitled "Galvanic Oxygen Sensors applied to CCR's" has a blurb about liquid/moisture and it states: Condensation on the sensing surface of the sensor reduces the signal output by blocking the diffusion of O2 into the sensor and is mistakenly categorized as a sensor defect. The reality, there is no damage to the sensor, simply remove the liquid and the signal output returns".

 

[Brad_Horn]

Refer highlighted Yellow sections https://www.opensafetyglobal.com/Safety_files/DV_O2_cell_study_E4_160415.pdf

 

[BlueTrin]

I read quickly, will re read later at home.

Am I correct to say that it looks like that water condensation ingress does not damage the cell if dried but should absolutely avoided before diving?

 

[Capt Jim Wyatt]

Am I correct to say that it looks like that water condensation ingress does not damage the cell if dried but should absolutely avoided before diving?

That is my understanding.

 

[mr_v]

When cells get really wet, you'll have PPO2 disco on you monitor as mV readings and the subsequent conversions to humand-friendly PPO2 reading will be out of wack.

When you get the unit of water, ensure that you position it in a way that prevents any water ingress. Then dry the unit. rEvo is an oddball in this sense, as rEvos don't have typical heads. I take lid off the unit, wipe the lungs with a spare shammy, drain the loop and position the cell tray so that water drips out/off. If there is breeze, it usually takes ~15 mins for the unit to become relatively dry(ish). Put all back together and drive home.

 

[Capt Jim Wyatt]

I was a rEvo guy for several years and I did the same thing with the cell tray as I do now.