Figure 7. A large-scale ventilated reactor enclosure used to contain production furnaces to mitigate particle emissions in the workplace (Used with permission from Flow Sciences, Inc.)
Lee et al. [2010] conducted personal, area, and real-time sampling in seven CNT plants. Results showed that nanoparticles and fine particles were most frequently released upon opening the chemical vapor deposition (CVD) furnace. Catalyst preparation and the opening of the CVD furnace resulted in the release of nanoparticles in the range of 20–50 nm. Lee et al. [2011] also evaluated workplace exposures to nanoscale TiO2 at manufacturing plants. In one TiO2 plant, the reactor was small and was placed in a fume hood; the entire process was conducted in that hood. Even though the reactor was located in the hood, high concentrations of nanoparticles were measured outside the hood. Worker exposure increased during product harvesting because the worker put his head into the hood to brush out the product powder. A second TiO2 plant isolated the large-scale reactor with a vinyl curtain and used a glove box for the harvesting of product from the reactor. Overall, airborne particle concentrations were fairly stable during production although increases occurred during both the operation of a process vacuum pump and welding conducted in the facility.
Yeganeh et al. [2008] evaluated a small facility producing carbonaceous nanomaterials including fullerenes. The process involved the production of materials in an arc furnace that was enclosed in a ventilated fume hood. This hood had a plastic front face shield and ports that allowed worker access during the process. The process involved placing graphite rods into the furnace, volatilizing the graphite in the furnace, producing raw soot, and using a scoop and brush to remove raw soot into a jar. At the beginning or end of each day, the reactors were completely cleaned by manual sweeping and vacuuming to remove residual soot. Real-time particle analyses showed that physical handling of material (sweeping of the reactor) resulted in the aerosolization of ultrafine particles. Measurements inside and outside the reactor enclosure (i.e., fume hood), however, showed that the hood was effective at containing particulates.
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Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes
