Nanoscale silver particles are some of the most widely used nanomaterials in commerce. Workers who produce or use silver nanomaterials are potentially exposed to those materials in the workplace. Previous assessments of occupational exposure to silver did not account for particle size. The National Institute for Occupational Safety and Health (NIOSH) assessed potential health risk from occupational exposure to silver nanomaterials and derived a recommended exposure limit (REL) for silver nanomaterials (<100 nm primary particle size) of 0.9 micrograms per cubic meter (μg/m3) as an airborne respirable 8-hour time-weighted average (TWA) concentration.