“Conduct any work that could generate engineered nanoparticles in an enclosure that operates at a negative pressure differential compared to the worker’s breathing zone. Examples of such enclosures include gloveboxes, glove bags, and laboratory bench-top or floor-mounted chemical hoods. In some cases, the air reactivity of precursor materials may make it unsafe to perate in a negative pressure glovebox and a positive pressures box may be used if it has passed a helium leak test. If a process (or subset of a process) cannot be enclosed, then use other engineered systems to control fugitive emissions of nanomaterials or hazardous precursors that might be released. For example, use a local exhaust system like a “snorkel hood.”

• Do not exhaust effluent air reasonably suspected to contain engineered nanoparticles whose hazards are not well understood. Whenever practical, filter it or otherwise clean (scrub) it before release.
• HEPA filtration appears to effectively remove nanoparticles from air, at least to particles as small as 2 nanometers in diameter. Below that size, data suggests that filter performance degreades as particles experience ‘thermal rebound’ and reaerosolization from the filter matrix.
• Minimize the dispersal and environmental release of nanomaterials. Carry out all manipulations of engineered nanoparticles in a glove box, glove bag, chemical fume hood, or other airborne contaminant control system. Whenever practical, remove (scrub or capture) the contaminant from the effluent from such a control system before the effluent is released into the general environment. If it is not practicable to handle dispersible nanoparticles in such a containment system, conduct a document the results of a hazards analysis before using alternative hazard controls.
• Exhaust the effluent from ventilated enclosures outside the building whenever feasible. Filters, scrubbers or bubblers appropriately used to treat unreacted precursors and may also be effective in reducing nanomaterial emissions. If using portable bench top HEPA filtered units, exhaust them through ventilation systems that will carry the effluent outside the building whenever possible.
• If it is not feasible to duct HEPA-filtered treated exhaust air outside the building:
  • Follow the guidance in ANSI Z9.7, American National Standard for Recirculation of Air from Industrial Process Exhaust Systems.
  • Conduct a hazards assessment and implement appropriate engineering controls. (Examples of such controls include periodic air monitoring, and an accurate warning/signal capable of initiating corrective action or process shutdown before nanoparticles could be exhausted or re-entrained into the work area).
• Do not use horizontal laminar-flow hoods (“clean benches”) that direct a flow of HEPA-filtered air into the user’s face to control exposure to nanomaterials.
• Consider exhausting Type II biological safety cabinets, in which free nanomaterials are handled, directly to the exterior (hard ducted) or through a thimble connection over the cabinet’s exhaust. Air from inside the cabinet, even if HEPA-filtered, should not be recirculated within the laboratory except as provided for in ANSI Z9.7, American National Standard for Recirculation of Air from Industrial Process Exhaust Systems.
• Maintain and test the effectiveness of exhaust systems and components as specified by the manufacturer. Evaluate equipment previously used to synthesize, handle or capture nanoparticles for contamination and incompatibility before reusing or disposing of it.
• Evaluate equipment previously used to synthesize, handle or capture nanoparticles for contamination and incompatibility before removing, remodeling, repairing, reusing, or disposing of it. Due to the potential for residual contamination use appropriate cleaning methodologies (i.e., wet wiping).”¹

1. U.S. Department of Energy, Nanoscale Science Research Centers, “Approach to Nanomaterial ES&H,” 6-7 (Rev. 3a May 12, 2008) .