Definition - What does Positive Pressure mean?
Positive pressure refers to pressure that exceeds the surrounding pressure of any room, chamber or confined space. Positive pressure is maintained in a closed zone to ensure no outside contaminated gaseous or liquid substance can get into that protected zone.
Safeopedia explains Positive Pressure
Positive air pressure clean rooms are used by electronics, aerospace, optics, military and defense applications and researchers. In these rooms, the air escaping from doors, ceilings or walls, due to the positive air pressure is not harmful.