To date, no studies have been conducted to quantify exposure to nanoscale particles from the use of amorphous silica and carbon black in tire manufacturing.  Because both carbon black and amorphous silica are nanostructured materials, with primary particles in the nanoscale and aggregates and agglomerates of much larger size (up to 100 microns), exposure to nanoscale particles of these materials during tire manufacturing is expected to be negligible.  However, because of the strong sheer forces imparted by the mixer during rubber compounding, there is a potential to break apart the agglomerates.  In the absence of data to understand this hypothesis, we developed a methodology to determine if and to what degree workers were exposed to nanoscale particles of amorphous silica and carbon black during the tire manufacturing process.  In this study, we collected air samples using the Dekati Electrical Low Pressure Impactor (ELPI) in a tire manufacturing facility and developed a methodology to analyze the size-fractionated samples for carbon black and amorphous silica, using scanning transmission electron microscopy, coupled with electron dispersive spectroscopy.  This methodology allowed us to predict what percentage of particles were carbon black, amorphous silica, or "other" in an effort to semi-quantitatively understand the potential for worker exposure to these materials in the nanoscale.  Coupling this information with size-specific particle counts from the particle counting function of the ELPI, we were able to estimate size-specific air concentrations for carbon black and amorphous silica.  Based on the results of this analysis, we determinded that workers had potential exposure to nanoscale particles of carbon black and amorphous silica, previously determined to be improbable due to aggregation and agglomeration that naturally occurs with these materials.  However, the magnitude of nanoscale (d50 between 17 and 94 nm) exposure was low and unliely to represent a health risk, with nanoscale carbon black air concentrations ranging from approximately 8,900 to 77,600 particles/cm³ and nanoscale amorphous silica air concentrations ranging from approximately 400 to 22,200 particles/cm³.  With pending development of occupational exposure estimates for nanoscale materials, this methodology will allow occupational health and safety practitioners to estimate worker exposures to specific materials, even in scenarios where many particle types may be contributing to total particulate exposure.   Presented by Marisa Kreider, Managing Health Scientist, Cardno ChemRisk.