A summary of asbestos fibre counting experience in seven countries

The membrane filter method for the evaluation of airborne concentrations of asbestos in the work place, is now used in many countries. In order to ensure uniform protection for the worker and internationally comparable exposure data it is important that different laboratories can reproduce fibre counts with reasonable accuracy. The results of an international counting trial of fibre by centres in nine countries were published recently in this journal. This current report summarises the results of internal exchanges of membrane filters for asbestos counting in seven of these countries. Observations from these several countries indicate the need for regular comparisons of counts between laboratories, regular contact with experienced observers, proper training in the use of the phase contrast microscope, standardisation of the methods of counting agglomerates, attention to the types of samples used for internal and external comparisons, choice of microscope, and separate training for counting chrysotile and amphibole fibres. An improved method of producing standard asbestos samples for counting purposes is required.