- Exposure potential to the nanomaterials from the task/operations
- The facility that houses the operation
The steps taken to perform PHAs for specific operations should be documented to let others know what was done and to help others understand what works. PHAs are frequently conducted as initial risk assessments to determine whether more sophisticated analytical methods are needed and to prepare an inventory of hazards and control measures needed for these hazards. One or two individuals with a health and safety background and knowledge of the process can perform PHAs. As part of the assessment, the health and safety professional should evaluate the magnitude of the emissions (or potential emissions) and the effects of exposure to these emissions. PHAs are an important first step toward developing control measures that can be considered during the planning stage. Essentially, hazard control should be an integral component of facility, process, and equipment design and construction. This includes design for inherent process safety. The use of engineering controls should be considered as part of a comprehensive control strategy for hazards associated with processes/ tasks that cannot be effectively eliminated, substituted for, or contained through process equipment modifications.
The standards for an occupational health and safety management system, as outlined in ANSI/AIHA Z10 [ANSI/AIHA 2012] and BSI 18001 [BSI 2007c], promote a continuous improvement cycle (plan, do, check, act), which does not have an exit point and is the basis for worksite analysis. Figure 2 illustrates how control measures are incorporated into an occupational safety and health management system. The continuous improvement loop is applicable to all hazards in a process/facility (e.g., airborne contaminant exposures, ergonomic, combustible dusts, fire safety, and physical hazards). The hazard assessment should be reviewed during each cycle described by Figure 2 and periodically updated when major changes occur. Although the optimal time to undertake a PHA is during the design stage, hazard assessments can also be done during the operation of a facility and have the benefit of using existing data.
After the PHA is complete, the nanomaterial risk management plan is designed to avoid or minimize hazards discovered during the assessment. The following options should be considered:
- Automated product transfer between operations. A process that allows for continuous process flow to avoid exposures caused by workers handling powdered or vaporous materials.
- Closed-system handling of powdered or vaporous materials, such as screw feeding or pneumatic conveying.
- Local exhaust ventilation. Steps should be taken to avoid having positive pressure ducts in work spaces because leakage from ducts can cause exposures. Ducts or pipes should be connected using flanges with gaskets that prevent leakage.
- Continuous bagging for the intermediate output from various processes and for final products. A process discharges material into a continuous bag that is sealed to eliminate dust exposures caused by powder handling. Bags are heat sealed after loading.
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Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes
