Regarding the air flow, planners tend to focus on the controls of temperatures, humidity, air circulation and air cleanness. Generally speaking, temperatures ought to be 18 ± 2°C and humidity below 65%. According to Good Manufacturing Practice facilitated by Industrial Development Bureau, Ministry of Economic Affairs Taiwan, air cleanness in a general operating area is mandated below 100 CFU/5MIN/PLATE, pre-clean area below 50 CFU/5MIN/PLATE and clean area below 30 CFU/5MIN/PLATE. A clean processing area should have positive air pressure while a kitchen should have negative or slightly negative air pressure, allowing the air movement from a cleaner area towards less clean one. Furthermore, it is necessary to have proper air circulation during the work. The amount of air circulation is proportioned to air volume and size of the room. It also has to do with the size, the heigh, the position, the air supply method as well as the air quality of the room. Temperature difference determines the speed of exchange. The size of window screen mesh ought to be smaller than 1.5mm.
reference: Good Manufacturing Practice