Identification of asbestos fibres in mineral dusts

Status:

completed 11/1997

Aims:

The BGI 505-46 (formerly ZH 1/120.46) analysis method involving scanning electron microscopy is employed for measurement of respirable asbestos fibres in workplace air. The use of the REM-EDXA method permits measurement of the fibre concentration and provides information on the chemical composition of the particles. On the basis of this information, BGI 505-46 distinguishes four different fibre types: chrysotile asbestos, amphibole asbestos, calcium sulphate, and other inorganic fibres. Classification by this pattern is adequate for the majority of products for industrial use. During the identification of asbestos fibres in dusts created during the extraction, treatment and processing of mineral raw materials, the other mineral components of the rock concerned must also be considered. For rock mined in Germany, the incidence of asbestos is associated essentially with ultrabasic to basic igneous rocks and certain metamorphic rocks. Generally, it must be assumed that other minerals besides the asbestos minerals in these rocks release fibres of respirable dimensions. If the measures for identification of these fibres are limited to the provisions of the standard analysis method referred to above, a risk exists of confusion between certain mineral particles and asbestos fibres. Dissociation of asbestos from other inorganic fibres was to be enhanced by supplementary criteria for the identification of asbestos. The objective was to use uniform conventions for analysis in order to obtain comparable analysis results.

Activities/Methods:

The element contents of the asbestos minerals and typical minerals of rocks potentially containing asbestos were first gathered. Both the natural variability/mixed crystal formation of certain minerals and the limited accuracy of element analysis by EDX systems under the given analysis conditions had to be considered. From this information, a catalogue of criteria was drawn up by which the asbestos minerals may be dissociated from other minerals according to their chemical composition (EDX analysis with ZAF correction [software for consideration of element-specific parameters during quantitative analysis of the EDXA spectra]). The catalogue was tested against a selection of 25 typical minerals from rocks potentially containing asbestos. In order to assess whether the supplementary identification criteria still deliver comparable results when applied in different laboratories, two further laboratories assessed the same samples against the catalogue of criteria.

Results:

In the majority of cases, use of the supplementary criteria for fibre identification enables asbestos to be distinguished reliably from other fibres. An implementation of the catalogue of criteria is provided free of charge in the form of a table in the Microsoft Excel© spreadsheet format and enables the supplementary criteria to be applied efficiently. The Excel table is available for download, together with explanatory information, on the web site of the BG Institute for Occupational Safety and Health (BIA) under "Technical information/Software"

Further informations:

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