DEVELOPMENT OF A METHOD FOR THE DETERMINATION OF LOW CONTENTS OF ASBESTOS FIBERS IN BULK MATERIAL

Asbestos is a category 1 carcinogen under the EU classification, but i n the absence of a method to quantify asbestos in a matrix at the 0.1% level, there has been a delay in implementing relevant directives to asbestos, An analytical scheme for identification and quantification o f asbestos using polarised light microscopy (PLM) and phase contrast o ptical microscopy (PCM) has now been developed. When used on artificia l mixtures by an experienced laboratory, it achieved the required targ et performance, at 0.1% asbestos concentration by mass in a bulk sampl e, to obtain a result, which with 90% probability, is correct within a factor of two. The method of identification by PLM and quantification by PC:M has been assessed by interlaboratory comparisons, The method begins with an initial identification using PLM, and depending on asbe stos type and matrix a combination of preparation procedures are used to produce the analytical filter. A gentle comminution method was used which reduces the risk of overmilling, The asbestos mass percentage o n the filter is quantified using PCM in combination with a PLM attachm ent for identification of possible non-asbestos fibres, The final meth od is supported by efficient methods for fibre identification for size determination and calculation of total fibre volume. A statistical an alysis of mass concentration estimates was made and the effect of pref erred orientation of fibres on the analytical filter was quantified.