OCFA Self-Contained Breathing Apparatus (SCBA) Practice Exam

The key idea is that the facepiece is kept slightly above the surrounding air pressure. This positive pressure pushes inside air outward through any small gaps in the face seal, so when the seal is imperfect, air leaks out rather than contaminant air leaking in. The regulator continuously supplies air to maintain that slight overpressure, which helps keep inhaled air clean even if the seal isn’t perfect. It’s not about creating a vacuum, and the goal isn’t to reduce regulator flow; it’s to use the internal overpressure to prevent inward flow of contaminants.