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Continued participation in an asbestos fiber-counting proficiency test with relocatable grid slides.

The effect of using relocatable reference slides of chrysotile and amosite in asbestos fiber counting proficiency testing was examined for volunteer analysts from laboratories in the USA. Results of participation in one round have been published; two more rounds are reported here. In the first round, participants were asked to draw what they saw, allowing identification of error type by comparison to the reference. In later rounds only the number of fibers per field was reported since the number of errors per field has been shown to be a reasonable estimate of proficiency. The third round included a training exercise. The total number of participants stayed reasonably constant with some reduction over time. More restricted numbers participated from round to round. Those who dropped out had lower average scores than those that remained in the program; from 2006 to 2007 this difference was significant, but for 2007 to 2008 it was not. The overall results for amosite were generally good compared to an arbitrary proficiency score of 60, and continued to improve further over time. The results for chrysotile were better in rounds 1 and 3 than round 2, so that both attention to detail (drawing the fibers in round 1) and training (round 3) may improve performance, which is consistent with the major type of error being oversight of fine fibers. However, the results are still poor, even by round 3, and no analyst achieved a score of 60 in all three rounds. Further improvement is preferred since chrysotile is the most commonly encountered type of asbestos in the USA. Depending on the adopted score for proficiency many laboratories or analysts may be labeled as poor performers and this may be a deterrent to voluntary participation in this type of exercise, especially for those in most need of assistance. Participants have tested new relocatable reference asbestos proficiency counting slides in three rounds of chrysotile and three rounds of amosite. Performance for amosite was good. Poor performance for chrysotile appears to be improved by greater attention and training.