A Low Velocity Wind Tunnel to Evaluate Inhalability and Sampler Performance for Large Dust Particles

Abstract

Workers in occupations such as mining, wood working, spray painting, pesticide application, and metal grinding are exposed to large particles in the 10 to 150-μm particle size range. For sampling large particles such as these, the American Conference of Governmental Industrial Hygienists has recently adopted criteria for inhalable particulate mass (IPM) sampling. Measurements of inhalability and IPM sampler performance are sensitive to the direction and velocity of the ambient air motion as well as particle size. Because of the complex flow field around a person, these measurements are best made under simulated industrial conditions in a large, low velocity wind tunnel where particle size, wind velocity, and direction can be carefully controlled. An 11,000 ft³/min, open-cycle, closed-jet wind tunnel with a cross-section of 1.6 × 1.6 m has been constructed for IPM studies. It can produce wind velocities from less than 0.1 to 2 m/s (20 to 390 ft/min). It can accommodate a full-torso mannequin. The mannequin has been modified to collect the dust entering the nose or mouth. It can rotate at 0.1 to 1 rpm and is connected to a mechanical breathing machine to simulate human breathing over the usual range of work rates. Three gear-feed, aspirating dust feeders deliver narrow-distribution aluminum oxide dust to a reciprocating dust distribution manifold. A wooden lattice induces controlled turbulence in the test section. Turbulence intensity from 3 to 14 percent can be produced. Air velocity is uniform within 10 percent and dust concentration is uniform to within 15 percent at the test section. The tunnel meets the European Economic Community's guidelines for testing indoor IPM samplers and shows good performance over the particle size range of 10 to 145 μm.