Mineral fibre sampling and size selection

Potential health hazards due to fibre inhalation are only evaluated in a limited way by simple optical microscopy examination of the membrane filters on which the fibres have been collected. One must consider the amount of fibres deposited and persisting in the most vulnerable organ compartments. Exposure evaluated in this way must take account of the deposition efficiency and relative clearance efficiency of different regions of the respiratory tract, which depends mainly on the diameter and length distribution of the fibres. The fibre diameter roughly indicates the deposition site in the respiratory tract, while the length is mainly connected with toxicity. For these reasons, at international level, special samplers have been recently proposed, capable of distinguishing the fibre sizes, in order to separate the so-called 'thoracic fraction' (the total fibres which penetrate beyond the larynx) and the 'respirable fraction' (only the fibres reaching the non ciliated respiratory area), which represent the most interesting sizes as far as health effects are concerned. Our purpose in this context is to explore the feasibility of using the Inertial Spectrometer (INSPEC) as a sampler that separates the fibres according to their aerodynamic diameter. The optical and electron microscope observations of the samples demonstrate a satisfactory size separation of the fibres and alignment along the flow lines. Therefore, INSPEC is successful in restricting the microscopic analyses to the potentially noxious fibres and in assessing specific concentrations for each diameter interval.