[Microscopic quality control--numeric representation of asbestos fiber concentration in environmental air of the workplace].

The study aimed at assessing the reliability of determinations of respirable asbestos fibre concentration which were performed by selected laboratories of the Work Hygiene Departments of the Regional Sanitary Epidemiological Stations (RSES). Two rounds of microscopic specimen exchanges were organized, the specimens containing from 20 to 700 asbestos fibres per 1 mm2. The results of specimen density determinations performed by RSES analysts were compared with reference determinations (i.e. average density determinations performed by 7 workers of the Institute of Occupational Medicine, Lodz, checked by two international tests). During the first exchange, the RSES determinations were found to be significantly lower than the reference determinations. At the second exchange, they exceeded the reference values. The poor precision of determining asbestos fibre concentration by the majority of the RSES analysts makes it necessary to provide additional training for that group, apart from that a survey of the quality of RSES laboratory equipment should be carried out and a system of internal quality control for the RSES laboratories should be developed and implemented.