Basic SARs are most commonly used in either one of two modes: continuous flow (the breathing air flows into the facepiece at a standard, steady rate) or pressure demand (the facepiece is continually pressurized with breathing air, and additional air is drawn in based upon the wearer’s breathing requirements). Pressure demand SARs require a high pressure supply source due to their performance requirements.The basic SAR is comprised of a respirator facepiece—which could be a tight fitting half mask or full face mask, or a loose-fitting hood or helmet assembly—connected via an air supply hose to a source of breathing air.