The RICE and AFRICA schemes for asbestos fibre counting

The Regular Interlaboratory Counting Exchanges (RICE) and the Asbestos Fibre Regular Informal Counting Arrangement (AFRICA) were initiated as U.K. and international schemes, respectively, to improve standards of counting asbestos fibres using phase contrast optical microscopy. In both schemes, reference samples are evaluated by participating laboratories in rounds of sample exchanges, and counting performance is assessed by comparing laboratory counts with reference counts. Their development is summarized from inception to the present day. This summary includes descriptions of the scope and scale of membership, the nature of reference samples and reference counts, and their main operational features. Criteria for classifying laboratory performance as satisfactory or unsatisfactory, based on performance ratings of counts in a single round and categories of counts over four consecutive rounds, are described.

In the first round of RICE, systematic differences up to 150-fold occurred between mean laboratory counts, with 300-fold differences being observed for single samples; 77 laboratories were rated 1 (the best performers; i.e. those laboratories providing counts closest to the reference values), 48 laboratories were rated 2, and 50 laboratories were rated 3 (the worst performers; i.e. those laboratories providing counts furthest from the reference values). Performance improved appreciably in the next round; of the 175 original participants, the numbers of laboratories rated 1, 2 and 3 were 125, 44 and 6, respectively. Further improvements were achieved and maintained in subsequent rounds. Similar patterns of both short- and long-term improvement also occurred in AFRICA.

Progress in developing both schemes further is described, particularly in relation to the nature of the reference samples and reference counts.