Inhalability of large solid particles

Large particles (10–150 μm) with systemic toxicity pose a health risk if inhaled regardless of where they deposit. This research seeks to better define particle inhalability, the fraction of airborne particles that are inhaled as a function of particle size. Measurements of inhalability were made for solid particles using a 1.6×1.6×5-m wind tunnel. Tunnel air velocities were 0.4, 1.0, and 1.6 m/s. A full-size, full-torso mannequin was used to collect dust entering either the mouth or nose for breathing at minute volumes of 14.2, 20.8, and 37.3 l. The mannequin either faced the oncoming wind or rotated slowly (0.06 rpm) during sample collection. At the test section, air velocity was uniform to within 10% and aerosol concentration was uniform to within 15% over the central 80% of the cross section. Orientation-averaged inhalability for mouth breathing was higher than the inhalable particulate mass (IPM) sampling criterion for particles smaller than 35 μm and lower than the criterion for larger particles, leveling off at about 30% for particles >70 μm. Facing-the-wind mouth inhalability showed the same trend as the IPM sampling criterion, but the measured values were 25% higher. Wind velocity and breathing pattern had little effect on inhalability for the range of conditions examined here. Orientation-averaged inhalability for nose breathing dropped quickly with particle size reaching less than 10% at 60 μm. Facing-the-wind nose inhalability was slightly increased for particles smaller than 60 μm compared to orientation averaged inhalability for nose breathing.