Bobby
Contributor
Dave,
You may call ******** on whatever you would like. I have friends that have taken your same attitude and have paid with their lives. I would guess that you either don't notice it because you don't do the math or haven't been diving CCR long enough to have the experience or both. Yes cells can have linear drift and in many ways. They can be just about spot on up to 1.0 then go far out without being completely limited, most of the time linear drift is a fairly constant curve however not always. Limiting and Linear Drift are mechanically the same failures just in a bit of a different way.
I've used cells with more than 10% linear drift, that drift was maintained and stable up to and just past 1.6. When diving remotely with limited supplies sometimes that is the choice that I have made however I've kept my PO2's down even with deeper deco until I reached 20'/6m where I know my PO2 is limited. Not to side track the discussion however that is also a reason that I do deco gas switching, on a CCR, when doing dives that require deeper decompression stops. I setup my decompression gases in order to have a 1.6 set point with the gas switch then do a solid flush to see what I can actually get from the cells.
There is also humidity limiting. Do long enough dives and cells will become saturated with water causing them to read considerably lower or even be limited. Bump your set point up too high with this condition and tox is a likely result.
Maybe you will have more faith in Wikipedia. If your CCR cells show 0.21 in air and 1.0 in O2 then you need to go down to 20'/6m and check the output with O2, otherwise you are still flying blind unless you are diving a 0.7 set point. You can also check the mv in air and mv in O2, do a little math and know that the cells are linear to 1.0. Do just a bit more math, go down to 20'/6m and check mv again with O2 and know for sure that your calibration and cells are good. It is simple division and multiplication.
Your Gibson guitar won't result in your death if you play it out of tune or incorrectly. There is a better safer way to handle O2 cells on CCR's, that is simply do the math and know the health of your cells. No doubt or assumption, simply knowing that when your start the dive that your cells are in good health. I also check my cells at 20'/6m at the end of every dive. It gives me an idea of where they are with humidity and time on them. Different dive times will show different humidity limiting and by doing this I build a knowledge of how my cells are affected over varying dive time.
