Page:Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes.pdf/52

 Many options are available to facilities that require worker protection during small-scale material handling operations. The best option for a given process depends on several factors including scale of handling operations, physical properties of materials being handled (size, density, wet or dry formulation), work environment (lab versus plant, cross drafts, nearby activity), equipment requirements (size of equipment/operation being enclosed), and level of protection required. Independent of the control selected, users should also adopt good work practices, such as using the smallest possible quantities of materials. Other procedures, such as wiping down and sealing containers before they are removed from the enclosure, are recommended. In addition, using care when working with powders, such as refraining from dropping dust from height, helps to prevent dust generation and to reduce operator exposure. The proper positioning of these workstations away from doors, windows, air supply registers, and aisleways will help to reduce the impact of cross drafts.

3.4.3 Intermediate and Finishing Processes

Exposures resulting from the manual handling of powdered materials are common in industry. Reduction in worker exposure through implementation of careful work practices and appropriate engineering controls would benefit these operations. Dumping bags of powdered materials has been commonly reported in the literature for production and processing. Typically, a worker dumps the ingredients for one process into a hopper and then compacts or disposes of the empty bags. Ventilated bag-dumping stations have been used successfully in a variety of industries and applications. The transfer of large quantities of nanomaterials requires different solutions adapted to the particular process. However, a few controls that are applicable to these common processes are available and have been evaluated for similar industrial operations.

After the completion of production, many nanomaterials are sent for further processing. The powder product may be refined through a common process such as spray drying [Lindeløv and Wahlberg 2009]. Other studies have documented collection of fugitive emissions of nanomaterials from the process reactors using devices such as baghouse air filters [Evans et al. 2010]. In both of these operations, the nanomaterials are collected in a barrel or drum following the completion of these production steps. Several examples of engineered drum or bag filling solutions have been described elsewhere and could be implemented to reduce such releases [ACGIH 2013; Hirst et al. 2002]. These engineering controls consist of enclosing the product off-loading process by temporarily sealing the drum/bag to the filling vessel above and/or overbagging through a continuous liner type bagging system. The addition of a local exhaust ventilation hood near the drum/bag opening could also be used to capture airborne nanomaterials.

Evans et al. [2010] studied nanoparticle concentrations in a facility that manufactured and processed carbon nanofibers (CNFs). The authors discussed four discrete events that resulted in elevations in airborne particle concentrations. The largest increases in particle concentration measured within the plant were related to manual handling processes, such as dumping product into lined drums and manual change-out and closing bags of final treated CNF product. Increases in particle concentrations were the result of the change-out and closing of the collection bag containing approximately 15 lbs of CNFs. Emissions from this event were almost entirely due to aerosolized CNFs. Tamping of the bag to settle contents (so Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes

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