Fit-for-purpose risks in conformity assessment of a substance or material – A case study of synthetic air

•A fit-for-purpose Bayesian approach to conformity assessment is described.•The developed technique is based on comparison of the risks of false decisions.•The technique considers measurement uncertainty, correlation and mass balance.•Fit-for purpose risks are calculated for industrial medicinal synthetic air.•Such risks in conformity of air as a standard gas mixture of an NMI are evaluated.