Here's how it starts: you're a hazmat responder and you have a four gas detector from one of the major manufacturers. Let's say that manufacturer recommends the following calibration gas mixture: 10 ppm hydrogen sulfide / 250 ppm carbon monoxide/ 2.5% methane/ 17% oxygen/ balance nitrogen. So you purchase that mixture from a calibration gas vendor. The gas vendor doesn't use the same monitor that you're using to analyze and certify your mixture. Perhaps they use a flame photometric gas chromatograph or an FTIR for the H2S . Their analysis is accurate because there are no cross sensitivities involved in their analysis of the other gases.
You, on the other hand, are using a quad gas detector whose H2S cell has a cross sensitivity to high concentrations of carbon monoxide. The H2S may read a few parts per million high because of this. Does your instrument compensate for that cross sensitivity or do you have to take take that into account manually?
Do you know the answer?
What other cross sensitivities does your gas detection equipment have? You might be surprised. Our next posting will fill in a few of these answers for you.