Quality control of airborne asbestos fibre counts in the United Kingdom – the present position

The United Kingdom Central Reference Scheme for asbestos counting has been expanded by initiating a series of regular interlaboratory counting exchanges (RICE) to minimize national within- and between-laboratory differences in asbestos fibre counts obtained by the membrane filter method. The scope of the present RICE operation is described and results are presented depicting current interlaboratory differences. National scatter is unacceptably large; up to ten-fold systematic differences occur between visual-counting laboratories, whilst random differences in counts of up to 100-fold occur on the same sample. For the reference samples evaluated, counts made by Magiscan automated image analysers are generally near the national mean and differences between Magiscans are usually small compared with differences between visual-counting laboratories.

Results obtained by an experienced group of laboratories relative to Magiscan have been used to derive a categorization procedure for assessing laboratory performance. Some details are given concerning future operation of RICE with a view to improving national reproducibility. A European-based scheme similar to RICE is needed to help ensure that the community asbestos directive applies uniformly in CEC countries.