Page:Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes.pdf/57



Figure 17. A ventilated bag-dumping station that reduces dust emissions when emptying product from bags into a process hopper (Contains public sector information published by the Health and Safety Executive and licensed under the Open Government License v1.0.)

Research into the effectiveness of these types of devices has shown that worker exposure to dust and vapors can be reduced. A review of commercially available units showed that their use with a variety of materials—including limestone, carbon black, and asbestos—controlled particle concentrations to acceptable levels [Heitbrink and McKinnery 1986]. However, particle contamination on the surface of the bag and handling/disposal of bags caused increased worker exposure. An integral pass through to a bag disposal chute/compactor can help reduce dust exposure resulting from bag handling. Further studies in mineral processing plants showed that the use of an overhead air supply also significantly decreased worker exposure [Cecala et al. 1988]. The ACGIH Industrial Ventilation Manual also has two designs that are applicable to the control of powder materials during bag dumping [ACGIH 2013]. Design plate VS-15-20, Toxic Material Bag Opening, is similar in design to the HSE station described above but recommends a slightly higher control velocity of 250 fpm at the face of the station opening. In addition, Design plate VS-50-10, Bin and Hopper Ventilation, requires a hood face velocity of 150 fpm. In general, higher velocities are specified to adequately capture dusts in a plant environment. While the materials used in the studies discussed above were not nanoscale, the application of the dust control concept is still relevant. However, the capture velocities specified in the Industrial Ventilation Manual may be excessive when attempting to contain nanomaterials; lower velocities may be warranted. 42

Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes