I went diving this past weekend and, as I have been doing for a while know, I took my CO analyser with me. I was diving with an OP I trust and did not expect to find any trace of carbon monoxide. Still, I went on and tested the tanks.
First, it was my buddy's tanks (doubles) that were analysed. No carbon monoxide found. Then I went for mine. The device started to beep and indicated 18 ppm. I repeated the tests on both sets of doubles, with the same results. I talked to the OP manager and tested two other sets. The first red 7 ppm and the other, 0. The manager apologised and asked for my analyser to check other tanks. Some time later, he came back to me and said he believes the contaminated tanks were a group of five that had been on lent for another OP. Still, he promised to go over the OPs procedures regarding CO control.
What really surprised me that day was my experience with another diver setting up beside me, who I believe to be and instructor. When I detected CO in my tanks, I told him that and offered my analyser for him to check his gas. He told me he couldn't smell anything strange in his tanks and said he did not want to use the analyser.
edit: spelling