collar or enclosure around the discharge point. These solutions have been used and evaluated in a variety of industrial settings and have been shown to effectively capture dusts when properly designed and implemented in the process.
Bag dumping/emptying. When raw, bulk nanomaterials receive further processing/refining, those materials are often dumped from containers such as drums or bags into hoppers that feed the downstream processing equipment. Ventilated bag dump stations have been in use in industry for many years and have been proven to be effective in controlling dusts. Several commercial vendors and sources of design guidance exist for these devices.
Large-scale handling/packaging. When nanomaterials are handled in quantities larger than those that can easily fit in a fume-type hood, a unidirectional flow booth can provide a suitable control to reduce worker exposure and mitigate a potential emission source. These booths are commonly used in the pharmaceutical industry and have also been employed for handling hazardous dye powders in industrial settings. They provide the flexibility for a variety of operations that require handling of nanomaterials from larger containers, such as drums. They can also be designed to provide local exhaust for specific operations that may occur inside the booths. These booths are available for a variety of commercial vendors or can be designed from sources of readily available guidance.
Machining of nanocomposites. When machining composite materials coated or impregnated with nanomaterials, good dust suppression techniques should be used. Guidance on dust suppression techniques from ventilation-based (woodworking-type) or mist/ water-based (silica/construction-type) controls may be adopted to reduce worker exposures. Exposures during machining should be carefully monitored and controlled. Standard engineering controls may need modification to properly control emissions. In addition to engineering controls, workers may need to wear appropriate respiratory protection.
3.4.4 Maintenance Tasks
Maintenance of the production facility and equipment can lead to exposures that are often overlooked. Demou et al. [2008] noted that maintenance procedures were a source of considerable particle emissions, specifically during the vacuuming of a reactor using a vacuum cleaner with a high-efficiency filter. However, other researchers have observed that cleaning the process area after CNT preparation reduced airborne particle concentrations [Lee et al. 2010]. Another typical activity not reported in the literature is the changeout of facility air filters. When local exhaust ventilation is used to contain nanomaterials and dusts, facilities will typically use air filtration prior to exhausting air from the building or recirculating into the work zone. When filters require change-out, the use of integral containment equipment and procedures can reduce maintenance worker exposure. Other general maintenance procedures, such as modifying ductwork or performing fan maintenance, will also require appropriate precautions to avoid exposing workers to nanomaterials settled in the equipment. In addition, general good housekeeping processes and written spill response procedures can help reduce the potential for worker exposure.
Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes
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