Workplace Exposure to Nanoparticles during Thermal Spraying of Ceramic Coatings

Thermal spraying is widely used for industrial-scale application of ceramic coatings onto metallic surfaces. The particular process has implications for occupational health, as the high energy process generates high emissions of metal-bearing nanoparticles. Emissions and their impact on exposure were characterized during thermal spraying in a work environment, by monitoring size-resolved number and mass concentrations, lung-deposited surface area, particle morphology, and chemical composition. Along with exposure quantification, the modal analysis of the emissions assisted in distinguishing particles from different sources, while an inhalation model provided evidence regarding the potential deposition of particulate matter on human respiratory system. High particle number (>10(6) cm-3; 30-40 nm) and mass (60-600 µgPM1 m-3) concentrations were recorded inside the spraying booths, which impacted exposure in the worker area (10(4)-10(5) cm-3, 40-65 nm; 44-87 µgPM1 m-3). Irregularly-shaped, metal-containing particles (Ni, Cr, W) were sampled from the worker area, as single particles and aggregates (5-200 nm). Energy dispersive X-ray analysis confirmed the presence of particles originated from the coating material, establishing a direct link between the spraying activity and exposure. In particle number count, 90% of the particles were between 26-90 nm. Inhaled dose rates, calculated from the exposure levels, resulted in particle number rates (n˙) between 353 × 10(6)-1024 × 10(6) min-1, with 70% of deposition occurring in the alveolar region. The effectiveness of personal protective equipment (FPP3 masks) was tested under real working conditions. The proper sealing of the spraying booths was identified as a key element for exposure reduction. This study provides high time-resolved aerosol data which may be valuable for validating indoor aerosol models applied to risk assessment.