The Uni-Guard™ DOF (diffuser outlet filtration) is an individual room air filtration system. The company says the system combines its Valid Air® high-performance ceiling air diffusers with built-in Filtrete™ technology from 3M to protect building occupants from recirculated airborne contaminants. According to the manufacturer, this product traps particles that accumulate inside a building’s ducts in a filter located inside the ceiling air vent. Efficiencies range from MERV 8 to MERV 16, depending on the application, with low static pressure drop. Carbon- and zeolite-impregnated filters are available.