evaluated the downflow booth with a ventilated collar added. The ventilated collar surrounded the interface between the drums and exhausted air at a rate of 425 ft3/min. During this test, the initial drum was inverted and the powder materials were emptied by gravity with the operator massaging the materials into the final product drum. The operator’s breathing zone concentration averaged 0.03 µg/m3 during this process. This study showed that the use of a downflow booth significantly reduced operator exposure during powder transfer processes and that adding a second level of LEV, the ventilated collar, further reduced the exposure by two orders of magnitude.
HSE Control Guidance Sheet 202, Laminar Flow Booth, presents a design for powder-handling processes called a horizontal- or cross-flow design [HSE 2003b]. The concept behind the design is similar to the downflow booth except that air enters the booth from the booth face. Air moves across the back of the worker toward the back of the booth. An issue with the cross-flow design is the secondary airflow patterns caused by the presence of the operator in the booth. Additionally, if purity or cleanliness of the product is important, sweeping of the air across the operator could be problematic. These patterns may cause turbulent dispersion of dust in the booth and result in higher operator exposure or potential leakage, compared to the downflow booth, but may provide a reasonable control for some processes.
3.4.3.4 Nanocomposite Machining
Initial studies have shown that machining some nanocomposite materials can result in the release of nanoscale particles to the work environment. Engineering controls when machining materials are available for most common processes. They range from ventilation of handheld tools using a high velocity-low volume (HVLV) system to the use of wet cutting techniques commonly adopted for silica control during construction activities. The use of standard dust controls such as those described by the HSE for woodworking as well as those identified in the ACGIH Industrial Ventilation Manual for machining processes provide a source of guidance that can be used to identify controls for machining processes. Bello et al. [2009] showed that the use of wet suppression techniques during sawing of nanocomposites reduced exposures down to background levels.
3.4.3.5 Summary
Processing nanomaterials involves a variety of steps. Following the production process, bulk unrefined materials may be packaged and shipped for use or may be subject to further processing. These processes require handling and manipulation of nanomaterials and have been shown to be a point of exposure for workers. These processes typically are composed of a limited number of tasks that may result in exposure of workers to nanoparticles or their agglomerates.
Product discharge. When processes empty into a large container, there is a potential for exposure especially when removing the full drum. Several engineering controls are available for this process/task. Nonventilation controls, such as inflatable seals and continuous liner systems, reduce the possibility of exposure. Ventilation-based options include the ventilated
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Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes
