Development of respirable aerosol samplers using porous foams

Workplace aerosols must be sampled to assess the degree of health hazard caused by the particulate matter. By adjusting the sampling flow rate, most of the samplers can match the 50% cutoff size, but not the slope of the respirable convention defined by the American Conference of Governmental Industrial Hygienists, the International Organization for Standardization, and the European Committee for Standardization (CEN). Combinations of foams (or other porous material) of different nominal sizes (10-100 ppi) and thicknesses (5-35 mm) were employed to overcome this bias. A foam disk 25 mm in diameter was placed in an asbestos sampling cowl. Dioctylphthalate was the liquid test agent. An aerodynamic particle sizer and an Aerosizer were calibrated against a settling chamber and were employed to measure the aerosol number concentrations and size distributions upstream and downstream of the foams. The sampling efficiency data showed that the 50% cutoff size could be met for foams in series, but that the slope remained sharper than the new definition. Foams in parallel showed great flexibility and many of the parallel combinations flattened the slope, closer to that of the new international respirable convention. For instance, when the total flow rate is set at 10.1 L/min the aerosol penetration through foams in parallel (100 ppi, 20 mm thick, diameter 25 mm + 10 ppi, 20 mm thick, diameter 13 mm) nearly matched the new international standard for respirable fraction. This sampler can be further miniaturized for smaller sampling flow rates to fit the capacity of personal sampling pumps.