Scanning Electron Microscope (SEM) news
The WHO fibre counting rules described in HSG 248 (HSE 2005) came into effect on 13th November 2006. The counting rules have changed from those contained in the European Reference Method (ERM) to new rules based on the World Health Organisation (WHO) method previously only used for Machine Made Mineral Fibre (MMMF) evaluation.
The change in the new method which has the greatest potential to affect results is the inclusion of fibres that are in contact with particles >3µm diameter. In order to reflect the new optical method, IOM has decided to incorporate this significant change into our fibre counting analysis by Scanning Electron Microscope (SEM).
Following a non discriminatory count the new HSG 248 method still allows for a discrimination count to be carried out using the optical methods detailed in MDHS 87, however, in order for this analysis to be carried out, it is now a requirement to hold UKAS accreditation for this technique. The method described in MDHS 87 may be suitable for discriminating between certain fibre types of larger (>1µm) diameter but the limitations of the method are such that, at this time, IOM does not intend to extend our UKAS accreditation to include this method.
IOM will continue to provide a comprehensive discriminatory analysis of airborne samples by SEM without the limitations of the optical method and have incorporated the major change in the new optical counting rules into our SEM method. This analysis will continue to be conducted under our UKAS accreditation