Air pressure, or atmospheric pressure, atm, is a pressure unit of 101.325 kPa, which roughly corresponds to the average normal atmospheric pressure at sea level.
Positive pressure is the pressure within a system that is greater than the environment surrounding the system. If there are openings that allow a leak from a pressurized room, the air will escape into the surrounding environment. To prevent airborne microorganisms such as bacteria etc. from entering the room, an overpressure of purified air prevails in clean rooms where the air is allowed to escape from the room in a controlled manner.
