Tehran University of Medical Sciences International Journal of Occupational Hygiene 2008-5109 10 3 2018 08 30 124 134 JARED KHATTAK Department of Environmental and Radiological Health Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, 1681 Campus Delivery, Fort Collins, CO 80523 NARA SHIN Department of Environmental and Radiological Health Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, 1681 Campus Delivery, Fort Collins, CO 80523 WENDELL E. RHINE Aspen Aerogels, Inc., 30 Forbes Road, Northborough, MA 01532 GEORGE GOULD Aspen Aerogels, Inc., 30 Forbes Road, Northborough, MA 01532 CANDACE S.J. TSAI Department of Environmental and Radiological Health Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, 1681 Campus Delivery, Fort Collins, CO 80523 2018 10 26 2019 05 25 Fumed silica, due to the thixotropic properties and low thermal conductivity, is used in insulation products. Exposure to crystalline silica is of most concern and there is also evidence that exposure to nanometer-sized fumed silica may lead to adverse health outcomes. Workers’ exposure to aerosolized fumed silica and other potentially hazardous materials are commonly assessed using direct-reading instruments. These instruments often contain an aerosol pre-separator cyclone, which by dispersing agglomerated particles, may cause variations in the reading values. This study investigates the effect of these cyclones on the measurements by comparing three instruments for airborne fumed silica that was generated using manual and automatic manipulation methods of manual pouring and automatic stirring. The results from these experiments showed that the measured concentration of nano-sized fumed silica increased with the use of cyclone. This may attribute to the residual particles remained inside the cyclone or attached on its wall in the particle separation process, which needs to be considered in and the corresponding correction should be made when measuring the concentration of fumed silica with an instrument that uses a cyclone as a pre-separator. https://ijoh.tums.ac.ir/index.php/ijoh/article/view/379