Clean rooms are classified by the particulate count measured in the air. The extremely sterile atmosphere is achieved significantly by controlling the airflow strictly (out vents in the ceiling and in vents in the floor). You still will accumulate dirt in nooks and crannies which are difficult to clean properly, which doesn’t actually cause the room to fail particle counts.
Clean rooms are classified by the particulate count measured in the air. The extremely sterile atmosphere is achieved significantly by controlling the airflow strictly (out vents in the ceiling and in vents in the floor). You still will accumulate dirt in nooks and crannies which are difficult to clean properly, which doesn’t actually cause the room to fail particle counts.