Characterization of current exposure to man-made vitreous fibres (MMVF) in the prefabricated house industry in Sweden

Abstract

The exposure to man-made vitreous fibres (MMVF) was investigated at 11 Swedish plants manufacturing prefabricated wooden houses. Current fibre levels were studied by monitoring personal exposure using the membrane filter technique. All samples were analysed by phase contrast optical microscopy (PCOM) according to Swedish standard rules; they were also analysed using a set of modified criteria for fibre counting, developed for this study, which in addition also required straight, parallel and/or convergent edges of the fibres. The objective of this alternating counting method, the modified fibre method, was to exclude fibres with appearance other than MMVF, that might be present in the wood industries. The method was validated by scanning electron microscopy (SEM). In all, 120 samples were taken and 273 analyses were performed. The mean exposure (GM), analysed by the standard method, was for insulators 0.10 f ml−1 (range 0.03–0.30 f ml−1) and for woodcutters 0.09 f ml−1 (range 0.05–0.19 f ml−1). Analysed by the modified fibre method the insuslators were exposed to 0.029 f ml−1 (range 0.013–0.077 f ml−1) and the cutters to 0.021 f ml−1 (range 0.014–0.033 f ml−1). A significant difference was observed between the exposure for near-field workers/job titles and far-field workers/job titles. Analysis of fibre levels by the modified fibre method indicated that only a minor proportion, around 25%, of the total airborne fibres were MMVFs. The reliability of the alternative modified counting method was high, and a high correlation (r = 0.94) with the SEM results was also achieved.