This study initially was designed to provide a baseline assessment of potential sources of ENM emissions during a variety of handling/process operations. As a result of the initial assessment, the reactor cleanout operation was determined to be an uncontrolled source of ENM emissions, apparently due to technicians brushing and scraping unwanted buildup from the inside of the reactor. This finding prompted an effort to minimize potential worker exposure, mainly through the use of PPE as well as consideration of other measures such as LEV. By expanding the baseline assessment strategy, NIOSH was able to evaluate the LEV system and determine its effectiveness in controlling ENM emissions. By changing the existing reactor cleanout work practice (vigorously brushing and scraping in multiple directions during the February survey) to a more targeted brushing/scraping (toward the inlet of the LEV during the July survey), emissions (both number and mass concentrations) were dramatically reduced. Despite the large reduction in emissions observed in this study, it is not appropriate to make a determination regarding personal exposures. The air samplers were deliberately placed at a location near the potential source of ENM emission thereby creating a worst case scenario. Therefore, all data collected provide information on process-specific concentrations and should not to be construed as representative breathing zone concentrations. In addition, there are no accepted occupational exposure criteria specific to the engineered nanometer form of a material against which to compare the findings of this survey. The occupational exposure limits for the larger particulate from each metal could serve as a minimal guide. Despite the limitations imposed on this survey by these factors, it can be concluded that the potential for release of ENMs does exist during reactor cleanout operations. However, based on the analysis of the filter-based air samples and the direct-reading instrumentation, it is clear that a properly maintained LEV can be highly effective in controlling ENM emissions. This finding, coupled with the current use of PPE, appears to be an acceptable method of reducing the potential for worker exposure.