‘SWeRF—A Method for Estimating the Relevant Fine Particle Fraction in Bulk Materials for Classification and Labelling Purposes’ by Pensis, Luetzenkirchen, and Friede

Abstract

The problem of realistically labelling minerals and other substances that contain crystalline silica is an old and difficult one. Pensis et al. (2014) describe a method intended for application under the European Classification and Labelling Regulation (EC, 2008), which in many respects is an advance on earlier methods. They point out that the classification is of hazard and that risk in particular applications must be determined separately, but hazard classification does take into account ‘the forms or physical states in which the substance is placed on the market and in which it can reasonably be expected to be used’ (EC, 2008, Article 5). The hazard from crystalline silica resides in the respirable fraction of the material after it has been made airborne. Pensis et al. propose a method for estimating this by tests without dispersing the material in air. In part of the method, the material is dispersed in a liquid and allowed to sediment for a period. The fraction of suspended material above a certain level is then removed, and on certain assumptions, the crystalline silica in this fraction represents the fraction of respirable silica if the material was dispersed in air. We see three major problems with the sedimentation component of the method (points 1–3 below), but in point 4, we present new results supporting the practicability of one aspect of the method.