A new proficiency testing scheme for occupational hygiene laboratories undertaking the analysis of diesel engine particulate emissions

We report details of a proficiency testing (PT) scheme for laboratories undertaking the analysis of diesel engine particulates (DEP) collected on workplace air filter samples. Within this occupational hygiene setting, the established approach is to measure the elemental carbon (EC) content within DEP as a specific marker of workers’ exposure to engine emissions. Measuring EC is undertaken in laboratories using combustion-based analysers. To date six, PT rounds have been completed with participation ranging between thirteen and twenty-three laboratories. In each round participants received four quartz fibre filter samples (plus blank filters) loaded with DEP with indicative EC mass loadings in the range 9–204 µg/filter. Round assigned values and standard deviation for performance assessment values were calculated by consensus from returned participant data following outlier removal. On this basis, it was determined that on average 81 % of the returned data was deemed satisfactory, i.e. returning a z (or z’) score ≤ 2. The use of two operationally defined analytical protocols, namely NIOSH 5040 and EN 16909, now dominate but they give different EC values so the preparation of reference air filter samples with preordained EC values determined using both protocols for use in future interlaboratory comparisons is therefore recommended.