Report on the Training Exercise to help RICE laboratories prepare for the change to the new counting scheme

The fibre counting method for measuring concentrations of airborne asbestos will change with the introduction (scheduled for October 2006) of the revised Control of Asbestos at Work Regulations. The change affects the counting of fibres touching-particles; currently, they should be excluded (if the particle diameter is > 3 �m) whereas they will be included under the new rules. The training exercise focussed analysts� attention on this aspect of the method. A high proportion of the analysts and laboratories in the RICE scheme participated. The analysts counted the fibres specified by the current (MDHS 39/4) rules, and noted how many extra fibres (on the same fields of view) would be counted under the new rules. This gave a direct estimate of the increase in count. A few expert laboratories had produced initial estimates of the percentage increase in count for each slide. These estimates were consistent with consensus (median) values from the laboratories in this exercise. Conversion factors, derived from expert laboratories� data, will be used to convert reference values for RICE slides to values appropriate to the new rules. Most laboratories produced results consistent with those from expert laboratories and satisfactory counts by the usual RICE proficiency testing criteria. However, a significant minority (about 25%) of laboratories produced more poor counts (relative to the normal RICE criteria) than usual. The implications of this finding are discussed and advice offered for laboratory managers.