Determinants of workplace exposure and release of ultrafine particles during atmospheric plasma spraying in the ceramic industry

Abstract

Atmospheric plasma spraying (APS) is a frequently used technique to produce enhanced-property coatings for different materials in the ceramic industry. This work aimed to characterise and quantify the impact of APS on workplace exposure to airborne particles, with a focus on ultrafine particles (UFPs, <100 nm) and nanoparticles (<50 nm). Particle number, mass concentrations, alveolar lung deposited surface area concentration, and size distributions, in the range 10 nm – 20 μm were simultaneously monitored at the emission source, in the worker breathing zone, and in outdoor air. Different input materials (known as feedstock) were tested: (a) micro-sized powders, and (b) suspensions containing submicron- or nano-sized particles. Results evidenced significant UFP emissions (up to 3.3x106/cm3) inside the projection chamber, which impacted exposure in the breathing zone outside the projection chamber (up to 8.3x105/cm3). Environmental release of UFPs was also detected and quantified (3.9x105/cm330 ). Engineered nanoparticle (ENP) release to workplace air was also evidenced by TEM microscopy. UFP emissions were detected during the application of both micro-sized powder and suspensions containing submicron- or nano-sized particles, thus suggesting that emissions were process- (and not material-) dependent. An effective risk prevention protocol was implemented, which resulted in a reduction of worker UFP exposure in the breathing zone. These findings evidence the potential risk of occupational exposure to UFPs during atmospheric plasma spraying, and raise the need for further research on UFP formation mechanisms in high-energy industrial processes.