ASBESTOS REFERENCE STANDARDS—MADE AVAILABLE FOR ANALYSTS

Asbestos samples from insulation delagging operations are analysed, by light microscopy techniques, in their thousands in the U.K. each year. The Health and Safety Executive has produced a new publication to assist analysts (HSE, 1994). This draws together commonly used mineralogical techniques into one systematic method complete (for the first time in this series) with colour photographs. Any laboratory performing analyses using validated methods should have available reference material for comparison and calibration purposes. Certified reference standards (CRSs), preferably traceable to primary standards, are essential for analytical determinations. It is important that these CRSs have been produced and characterized in a technically valid manner, and that details of homogeneity trials, for example, used in certification s should be provided to confirm their acceptability. Producing reference material for asbestos is not straightforward, however. Asbestos is a term used for the fibrous forms of several naturally occurring silicate minerals. For regulatory purposes in the U.K., the Control of Asbestos at Work Regulations (CAWR) 1987, as amended by the CAWR (Amendment) regulations, 1992, define asbestos as any of the minerals chrysotile, crocidolite, amosite, fibrous anthophyllite, fibrous actinolite or fibrous tremolite. Natural occurrences of these minerals are found throughout the world, and there may be compositional variations in some of the types that lead to slightly different optical properties. The first three have had widespread commercial use, are much more commonly encountered than the others and there is general consensus that recently mined products are representative of the type. Chrysotile asbestos is defined as a fibrous mineral in the serpentine mineral group, while crocidolite asbestos is the fibrous variety of riebeckite. Amosite is really the trade name of fibrous grunerite. Distinguishing between the asbestos varieties of anthophyllite and tremolite can be difficult as they have similar optical properties. Also all asbestos amphiboles occur frequently as prismatic non-asbestos varieties. These can be fractured along cleavage planes producing fragments which resemble asbestos fibres. Actinolite asbestos does have more distinct optical properties, but is seldom seen in large concentrations in commercial materials.