MDW - 11/01/2018 1:09 PM
CGA, DOT, and OSHA require O2 cleaning for any tank with 23.5% or higher O2 content (yes, NOT 40%).

As for regulators, I would think the same limit should apply, at least to first stages where the same high pressures are present. Maybe I could see a little slack on the second stage where the pressure is lower and the volume and flow is restricted.

That said, I keep everything O2 clean (tank, valve, hose, reg, BC) if it will be used with Nitrox. And that said, it’s not rocket science to O2 clean stuff (BTW, speaking of rocket science, NASA requires O2 cleaning for anything over 21% O2).