Development of a Large Particle Aerosol Distribution System for Testing Manikin-Mounted Samplers

Personal samplers used to determine the inhalable fraction of workplace dust are tested while mounted on a manikin, which simulates a worker. To understand the mechanisms affecting the performance of such samplers, researchers must measure the airflow around the body where the samplers are mounted. Therefore, wind tunnel facilities to determine both airflow conditions around samplers and sampling efficiency are needed. A wind tunnel system was developed that was large enough to accommodate the top half of a life-sized manikin and employed a laser Doppler velocimeter for velocity measurements around the manikin. For generating particles up to 70 mu m, an aerosol generation system, using a two-dimensional scanning system to cover an extended area, was developed and tested. The generation system had carriages with linear bearings mounted on rod assemblies for scanning in the horizontal and vertical directions. Screw drives, powered by stepper motors under computer control, moved the carriages in a preprogrammed pattern. The generation system was characterized for its ability to generate uniform concentrations of aerosols over an extended area at wind speeds of 0.5 and 2 m/s and particle sizes of 7 and 70 mu m. Uniformity of concentration over the area studied, in the absence of the manikin, was 10% relative standard deviation (RSD) or better, except for 7 mu m particles at a wind speed of 0.5 m/s where some nonuniformity was observed. The uniformity under these conditions was improved by rearranging the distances between components in the wind tunnel.