Characterisation of Stone Airborne Dust Populations by Opto-Digital Microscopy

The problem of the production of airborne dust emission during several industrial processes (i.e. dry stone working actions) was taken into account. In order to find new methods to reduce dust emissions, the proposed approach was the dimensional and morphological dust characteristics according to different working tools and materials. In this perspective, two different methods have been investigated: the size class distribution analysis of dust particles based on a laser diffraction system (LD) and the 2D fractal analysis of airborne dust populations acquired as digital images. The first approach (dust size class distribution through laser based diffraction system) permitted to directly characterise particle dust size class distribution in respect of the ornamental stone processed and the working action applied. The second one (2D fractal analysis method) allowed the study of dust image structure and texture by evaluating statistical fractal parameters (“fractal dimensions” and their precision), to quantify the efficiency in space or surface covering by dust particles. The 2D fractal analysis method appeared to be an interesting approach providing information on particles spatial disposition and on the structure of the disposition itself permitting this way to derive information concerning the overall characteristics of dust particles and, as a consequence, about the behaviour of the working process. The study was developed with reference to several materials resulting from ornamental stone dry working. Interesting correlation have been found between fractal parameters and the parameters deriving from the size class distribution analysis by LD, supporting the validity of the proposed approach. An application of the proposed method to other dust populations (i.e. wood-working airborne dusts) is straightforward.