When a process is heated, the use of canopy hoods (Figure 8) may be another reasonable alternative as long as the design meets the operational and facility exposure control requirements [ACGIH 2013; McKernan and Ellenbecker 2007]. Even if the process does not involve heat, contaminant capture velocities suitable for gas/vapor contaminants (rather than coarse particulates) may be sufficient, as ultrafine and nanoparticles possess negligible inertia and follow the flow stream well.
When controlling exposures during operations such as product harvesting and reactor cleanout, solutions such as spot LEV systems (e.g., a fume extractor) or containment may be acceptable alternatives. Manual harvesting of product materials may be better suited for higher-level enclosure controls such as a glove box or a specially designed enclosure to provide good capture while minimizing loss of product materials. The use of a commercially available fume extractor has been shown to be effective in reactor cleanout and provides a flexible solution that may meet facility needs across a range of operations [Methner 2008]. Selection of any control should be evaluated to ensure worker acceptance and use as well as verifying that it meets the exposure control objectives.
3.4.2 Small-scale Weighing and Handling of Nanopowders
Small-scale weighing and handling of nanopowders are common tasks; examples include working with a quality assurance/control sample and processing small quantities in downstream industries. During these operations, workers may weigh out a specific amount of nanomaterials to be added to a process such as mixing or compounding. The tasks of weighing out nanomaterials can lead to worker exposure primarily through the scooping, pouring, and dumping of these materials. Many different types of commercially available laboratory fume hoods can be employed to reduce exposure during the handling of nanopowders. Other controls have also been used in the pharmaceutical and nanotechnology industries for containment of powders during small-quantity handling and manipulation. They include glove boxes, glove bags, biological safety cabinets or cytotoxic safety cabinets, and homemade ventilated enclosures.
Methner et al. [2007] evaluated a university-based research lab that used CNFs to produce high-performance polymer materials. Several processes were evaluated during the survey: chopping extruded materials containing CNFs, transferring and mixing CNFs with acetone, cutting composite materials, and manually sifting oven-dried CNFs on an open benchtop. Real-time monitoring did not identify any process as a substantial source of airborne CNF emissions; however, weighing/mixing of CNFs in an unventilated area resulted in elevated particle concentrations compared to background. Other studies have shown that benchtop activities such as probe sonication of nanomaterials in solution can also result in emission of airborne particles [Johnson et al. 2010; Lee et al. 2010]. Producing dispersions by sonication is a primary operational step, and the industrial hygiene assessment should address the sound level exposure as well as the potential exposure to aerosols of nanomaterials from the sonication. Maintaining the sonicator/dispersion process within an enclosure such as a hood can be an effective means for mitigating the noise and aerosol exposure.
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Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes
