a room combining the use of air filters and continuous air circulation to produce levels of air borne particles that are lower, and typically much lower than normal atmospheric dust levels. Outdoor atmospheric dust levels are on the order of 400,000 particles/ft3 >0.5µm in size. Cleanroom cleanliness levels generally are agreed to begin at 100,000 particles/ft3 and extend down to 0.01 particles/ft3 or less! See also, Cleanroom Class.
