Nano-scale materials have different physical and chemical properties than the same materials in larger sizes. So the methods you would use to protect workers against those materials in larger sizes won’t always work for nanomaterial exposures. In fact, in some cases, you may need to protect workers against materials that pose no hazard in larger forms.
The good news is that because their size is the thing that makes them hazardous, many of the control strategies are the same for all nanomaterials. NIOSH has issued recommendations for engineering controls that should be useful in controlling a broad range of nanoparticles.
Controlling Nanomaterial Exposures
“Nanomaterials” are defined as particles with at least one primary dimension that is less than 100 nanometers (nm). Some are deliberately created to be small: These are called engineered nanoparticles. Others are not engineered, such as the nanoparticles found in diesel exhaust.
In November 2013, NIOSH addressed this emerging worker health issue with the publication of a 1,000-page guidance document, Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes (available at http://1.usa.gov/1eivjQx).
NIOSH recommends that employers consider controlling worker exposures by using the following methods:
- Limit process inventories. Producing nanomaterials as they are consumed in the process reduces the potential for exposure.
- Operate a process at a lower energy state. Lower temperatures and pressures create lower “fugitive,” or escape, emissions and, in turn, lower exposures.
- Use fail-safe devices. If a system that uses or produces nanomaterials has a problem, a fail-safe device ensures that the system reverts to a safer condition. NIOSH cites the example of a valve controlling a reagent for a reaction. If the safe condition for the system requires the valve to be closed, the fail-safe valve would automatically close in the event of a failure.
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- Automate product transfer. Workers who don’t handle powdered or vaporous materials will not be exposed to them. Therefore, processes should be designed so transfers between operations do not involve manual handling.
- Closed-system handling. Again, screw-fed or pneumatic handling of powdered or vaporous materials in a closed system minimizes worker exposures.
- Use local exhaust ventilation. A well-designed local exhaust ventilation is essential, especially considering that nanoparticles are more likely to leak than larger particles. Ducts should be maintained under negative pressure, which will prevent particles from leaking out of the ducts. Both ducts and pipes containing nanomaterials should be connected using flanges with gaskets that prevent leakage.
- Use continuous bagging. The intermediate output from various processes, as well as the final products, should be bagged using a continuous process. A continuous bag that is heat-sealed after loading will eliminate dust exposures caused by powder handling.
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- Minimize container sizes. Whenever nanomaterial must be handled manually, container size should be minimized to limit the potential release of materials and prevent workers from placing their faces close to the materials (as can happen when they bend over to reach into a barrel). NIOSH recommends a maximum container depth of 25 inches.
- Use long-handled tools. If the combination of large containers and manual handling is unavoidable, a long-handled tool can help workers put some distance between themselves during manual handling and transfers. NIOSH also recommends additional engineering controls to provide a barrier between the container and the worker’s breathing zone.
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