With the exception of my trip to LCBR, I rarely dive OC. When I do, I normally fill my own tanks. If I am out of the area, I will analyze my tank unless I watched it being filled and know for a fact what the content is. LCBR was the exception, I didn't watch them fill every tank but I did check out where they fill the tanks and how they sort them. I was comfortable that the air tanks had air and the Nitrox tanks had Nitrox.
When diving CCR, analyze everything or watch it being analyzed after a fill.
When diving CCR, analyze everything or watch it being analyzed after a fill.