PERSPEC: A Personal Sampler with Size Characterization Capabilities

Abstract

The recommendations recently proposed by the International Standards Organization (ISO) and the American Conference of Governmental Industrial Hygienists (ACGIH) on particle-size definitions have stressed the importance of gathering information on a larger size interval than previously used and, specifically, in three size fractions defined by smooth collection efficiency curves with 50% cut-points at 10 µm and 3.5 µm. A personal sampler is proposed based on the inertial size separation of airborne particles and on the subsequent deposition on a 47- or 50-mm diameter membrane filter. The sampler operates with a standard rechargeable battery personal pump in a sealed circuit with a suction flow rate of 4 Lpm through the filter. Of this, 2 Lpm are recirculated into the inlet nozzle on the axis as a filtered air core of 4-mm diameter. A flow rate of 2 Lpm of external air is drawn through the surrounding ring of equal area. While proceeding through the nozzle, larger particles penetrate deeper into the clean air and are deposited closer to the center of the filter. There is a unique relationship between size and radial deposition distance from much above 10 µm to below 2.5 µm. Therefore, three concentric zones are easily determined with boundaries at 10 µm and at 3.5 µm (or, alternatively, at 2.5 µm). The sampler inlet can be made to follow the inspirability curve, with 50% point at around 30 µm. The deposit can be evaluated as total particulate mass, and in case it exceeds an action level, the three zones can be cut and separately analyzed. As an alternative, the filter can be scanned by nondestructive techniques or by optical and electron microscopy.