The ideal time to develop a PtD strategy is during the development phase of a process, material, or facility. As the nanotechnology field is still in its relative infancy, there are numerous opportunities to implement PtD in the early stages. The manner in which these materials are handled and processed can largely affect the overall safety of the process, and the health and safety of workers may be significantly improved through the implementation of a PtD strategy.
1.3.2 OELs as Applied to Nanotechnology
Occupational exposure limits (OELs) are useful in reducing work-related health risks by providing a quantitative guideline and basis to assess the worker exposure potential and the performance of engineering controls and other risk management approaches. Currently, no regulatory standards for nanomaterials have been established in the United States. However, NIOSH has recently published two current intelligence bulletins (CIBs) regarding occupational exposures to nanomaterials. In a CIB on titanium dioxide (TiO2), NIOSH recommends exposure limits of 2.4 mg/m3 for fine TiO2 and 0.3 mg/m3 for ultrafine (including engineered nanoscale) TiO2, as time-weighted average (TWA) concentrations for up to 10 hours per day during a 40-hour work week [NIOSH 2011]. In a CIB on carbon nanotubes and nanofibers, NIOSH recommends that worker exposure be limited to no more than 1 µg/m3 [NIOSH 2013].
Other countries have established OELs for various nanomaterials. For example, the British Standards Institute recommends working exposure limits for nanomaterials based on various classifications such as solubility, shape, and potential health concerns as related to larger particles of the same substance [BSI 2007b]. Germany’s Institut für Arbeitsschutz der Deutschen Gesetzlichen Unfallversicherung, an institute for worker safety, has published similar guidelines [IFA 2009].
In the absence of governmental or consensus guidance on exposure limits, some manufacturers have developed suggested OELs for their products. For example, Bayer has established an OEL of 0.05 mg/m3 for Baytubes® (multiwalled CNTs) [Bayer MaterialScience 2010]. For Nanocyl CNTs, the no-effect concentration in air was estimated to be 2.5 μg/m³ for an 8-hr/day exposure [Nanocyl 2009].
Another approach that may be taken when OELs are absent is the ALARA concept, As Low As Reasonably Achievable. While ALARA is generally the goal for all occupational exposures, this concept is particularly useful when OELs are absent or in the case of contaminants with unknown toxicity.
1.3.3 Control Banding
Control banding is a qualitative risk characterization and management strategy, intended to protect the safety and health of workers in the absence of chemical and workplace standards. Control banding groups workplace risks into hazard bands based on evaluations of hazard and exposure information [NIOSH 2009b]. Note that control banding is not intended to be a substitute for OELs and does not alleviate the need for environmental monitoring or industrial hygiene expertise.
Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes 7
