The use of measurement uncertainty and precision data in conformity assessment of automotive fuel products

• The automotive fuels should comply with strict legislative requirements.
• Conformity assessment should minimize the risk of making the wrong decision.
• The use of uncertainty estimates and precision data can support reliable decisions.
• Using these approaches acceptance limits can be calculated.
• The two approaches are compared using the results of 769 diesel samples.

In order to use a test result to decide whether it indicates compliance or non-compliance, it is necessary to take into account the dispersion of the values that can be attributed to the measurand. When dealing with conformity assessment of automotive fuel samples against European Union specification limits, this dispersion may be represented by uncertainty estimates based on either standard method precision data (ISO 4259 approach) or within laboratory precision data (intermediate precision approach). The present work presents possible decision rules based on these approaches and directly related to the required or acceptable level of probability of making a wrong decision. Acceptance limits for 95% and 99% confidence levels are calculated for all the properties of automotive fuels. Moreover, the effect of different approaches for defining guard bands, different levels of confidence or different number of replicate measurements is investigated using the results of the analyses of 769 diesel fuel samples for the determination of sulfur mass concentration.