[The respirable fraction: measurement and characterization]

A definition is first of all made of the fractions of airborne dust that can deposit in the various regions of the respiratory apparatus, according to the aerodynamic size of the particles. Since the "respirable" fraction is the most important fraction from a medical point of view, instruments have always been developed that were designed to sample this portion of dust. The author describes the evolution of the criteria for sampling the "respirable" dust fraction and the contribution to research in this field made by the group of industrial hygienists of Milan, under the leadership of Prof. Zurlo, in particular with the development of the aeolian classifier. The results are reported of a comparison made between the four respirable dust selectors most widely used in European Community countries, that was carried out in a pyrite mine in Tuscany. The mean values obtained were practically identical, thus demonstrating that sampling techniques have now achieved proven homogeneity.