Historically the methodology for monitoring of aerosols containing fibres has been rather different to that for other aerosols. The standard method (the membrane filter method) for determining occupational exposures to asbestos in most countries in the EU is based on the European Asbestos Workers Protection Directive. For man-made mineral fibres, the WHO-EURO method applies. In these methods, fibres are collected, using cowled sampling heads, onto filters and counted using phase contrast optical microscopy. Decisions on whether or not fibres are "countable" are based on assessments of fibre geometry. This contrasts with other workplace aerosols where assessment relates to penetration to various regions of the respiratory tract and depends on the aerodynamic diameter of the aerosol. New conventions (inhalable, thoracic and respirable) have now been agreed between CEN, ISO and ACGIH and there is now a recognition that it may be more appropriate to also classify fibres according to their aerodynamic properties and in particular according to the thoracic convention (which defines the fraction of airborne material penetrating below the larynx). This would limit analysis to those fibres most closely associated with disease and would prevent large (non-thoracic) particles and fibres from obscuring the fibres of interest on the filter surface.
The objective of this study is to provide a basis for harmonising these approaches by development of the membrane filter method to include selection of the thoracic fraction of fibrous aerosols. The project will investigate the suitability of the current method and four new methods based on personal thoracic aerosol samplers, for a range of fibre types.
As of 1 January 1998, Phase 1,2 and 3 have been completed and Phase 4 begun. The samplers selected in Phase 1 were (in addition to the standard cowled sampler) the GK2-69 sampler, a SIMPED variant cyclone, the CATHIA sampler and the IOM thoracic foam sampler. In Phase 2, it was found that all samplers matched the convention (in terms of bias) for some size distributions, the best being GK2-69 (biases 0.03 to 0.08) and the poorest, the CATHIA (0.04 to 0.70). In Phase 3, the distribution of aerosol across the collection substrate of each was found to be satisfactory. First samples have been produced and distributed for Phase 4. Work continues.
The project involves seven main phases to be carried out by a consortium of eight partners. These are; Phase 1, Preparatory phase; 2, Validation of the samplers against the thoracic convention using spherical particles; 3, Assessment of the distribution of the filter deposit with spherical particles; 4, Laboratory evaluation of the selection characteristics of the samplers as a function of aerodynamic diameter using fibrous aerosols and comparison with the thoracic convention; 5, Review of the laboratory studies; 6, Field studies in workplace environments and 7, Report and recommendations.
Funding SchemeCSC - Cost-sharing contracts
53754 Sankt Augustin
S3 7HQ Sheffield
6700 EV Wageningen
171 84 Solna