Oxygen concentrators and nitrox sticks

[nickbutcher]

...
as @grantctobin said, these are really only removing the N2 from the atmospheric gas and you're left with all of the trace gases with Argon being the primary offender. If you're diving OC then you have nothing to worry about and just pretend it doesn't exist. If using it as a "100% O2" deco bottle, you're still creating a near pure gradient on the issues for the N2 and/or He to come out, you're just pushing some Ar in but it's not really significant. If using that gas for the O2 bottle on a CCR then the Ar accumulates and as it is both very dense and extremely narcotic then you want to dil flush fairly regularly to prevent it from building up, every ~10-15mins or so seems to be an accepted interval but if you're on OC it truly doesn't matter.

This came as an unexpected kick in the arse when I first dived Bikini. The O2 generator on the boat was delivering 93% and it didn't occur to me that the remaining 7% was almost entirely argon until I got down past about 30m for the first dive.

Then it took me a while to realise why, even with around 50% helium in the diluent, I was narked off my tits.