“While there are clearly defined GMP requirements for particulate and microbial air cleanliness for the sterile manufacturing area, there are no concrete requirements for air cleanliness for the non-sterile manufacturing area. In pharmaceutical practice, terms such as "cleanroom Grade E or F", "grey or black area" and, more recently, the terms "CNC" (classified not controlled) and "NC" (not classified) have become common for non-sterile manufacturing“, explains GMP Senior Expert Christine Oechslein.