10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Characterization of Airborne Fibrous Particle Deposition on Screens with Different Configurations
BON KI KU, G.J. Deye, Centers for Disease Control and Prevention, NIOSH
Abstract Number: 405 Working Group: Health Related Aerosols
Abstract Understanding transport characteristics of workplace aerosol particles is important in assessing their fate in the respiratory system of workers who are potentially exposed to nanomaterials such as cellulose nanomaterials. In this context, inhalation of airborne nanomaterials and their deposition in the respiratory system is getting more attention during the process-related workers’ activities in the workplace because it may cause toxicological responses. In order to estimate the toxicity of fibrous particles as a function of length, it is required to separate fibers by length and understand mechanisms related to fiber separation for use in toxicology studies. For nonspherical particles with high aspect ratios, such as aerosolized fibers and cellulose nanomaterials in the workplace, their deposition can be very different from spherical particles. In this study, we used screens with different mesh sizes to characterize deposition of fibrous particles on them and measured screen collection efficiency of fibrous particles as a function of aerodynamic diameter to better understand the deposition of the fibrous particles. Three screen configurations [i) without a laminar flow entrance length, ii) with the laminar flow entrance length (about 23 cm), and iii) centrally blocked screen] were tested to investigate the effect of screen pore size (10, 20, and 60 µm) and screen configuration on collection efficiency of fibers. Screen collection efficiency was obtained based on measurements of upstream and downstream concentrations of a test chamber either without or with a screen.
Test material was glass fiber powder used as a surrogate of asbestos, supplied by the Japan Fibrous Material Research Association (JFMRA) (Kohyama et al., 1997). This same material has been used in our recent studies for aerosolization of airborne fibers (Ku et al., 2013), fiber alignment in electric field (Ku et al., 2018) and classification of airborne fibers by length using screens (Ku et al., 2014).
The results showed that screen collection efficiency increases as screen mesh size decreases from 60 to 10 µm for both cases with and without entrance lengths. For the screen configuration without entrance length, higher collection efficiency was obtained than the case with entrance length probably due to increased impaction or self-filtration caused by the close proximity of inlet to screen. In addition, the difference between the collection efficiencies for the different configurations was small in the aerodynamic size range below 3 µm while it increased in the size range from 3 to about 7 µm, indicating that as large aerodynamic diameter is associated with longer fibers, some differential selection of fibers is possible.
Acknowledgements This work was funded by the National Institute for Occupational Safety and Health through the Nanotechnology Research Center (NTRC) program (CAN 93908N0).
References Kohyama, N., Tanaka, I., Tomita, M., Kudo, M., Shinohara, Y. (1997). Preparation and characteristics of standard reference samples of fibrous minerals for biological experiments. Ind Health 35: 415-432. Ku, B.K., Deye G, and Turkevich LA (2018). Direct Measurement of Aerosol Glass Fiber Alignment in a DC Electric Field. Aerosol Science and Technology, DOI:10.1080/02786826.2017.1387640 (in press). Ku, B.K., Deye, G., and Turkevich, L.A (2013). Characterization of a Vortex Shaking Method for Aerosolizing Fibers. Aerosol Science and Technology, 47:12, 1293-1301, https://doi.org/10.1080/02786826.2013.836588. Ku, B.K., Deye, G.J., & Turkevich, L.A. (2014). Efficacy of screens in removing long fibers from an aerosol stream - sample preparation technique for toxicology studies. Inhal Toxicol, 26, 70-83.
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