To qualitatively assess whether exhaust re-entrainment may be an issue, smoke can be released within each hood in the production room while a researcher observes the emission of the smoke through the exhaust stack. This qualitative test will help to evaluate the potential for re-entrainment of exhaust into any air intakes or roof openings. The behavior of the exhaust plume is dependent on varying environmental conditions such as wind speed and direction; therefore, this test should be repeated to capture the potential for re-entrainment under a variety of conditions. In addition, air velocity measurements should be taken at the center of the exhaust duct opening to evaluate the discharge velocity of the hood exhaust. These readings should be evaluated, along with the physical design and installation of the exhaust stack, against guidance from consensus standards organizations such as ASHRAE, ACGIH, or AIHA.
4.1.5 Facility Sampling and Evaluation Checklist
When evaluating a facility that manufactures or uses nanomaterials, it is important to first assess what engineering controls are in place in the facility. The initial assessment should involve looking at the processes and equipment as well as the general plant environment, the effective use of the engineering control by the operator(s), and the overall performance of the control equipment. Checklists are useful tools for helping to identify the process and facility factors related to nanomaterial production, use, emissions, and exposure. A checklist as shown in Table 4 may help for collecting basic process information (e.g., capacity, location, and usage) and control operation and maintenance parameters to ensure effectiveness of exposure control.
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Current Strategies for Engineering Controls in Nanomaterial Production and Downstream Handling Processes
