Combining low cost and simple maintenance with high levels of comfort, the 3M™ Scott™ Sigma 2 positive-pressure self-contained breathing apparatus features an ergonomically designed lightweight backplate and fully adjustable harness. At the heart of the Sigma 2 set is a simple and reliable two-stage pneumatic system. A first breath-activated positive-pressure demand valve provides low breathing resistance and excellent dynamic performance – particularly at high flow rates. A first-stage pressure-reducing valve features only two moving parts and accepts cylinder pressures of up to 300 bar without adjustment. The system includes a shoulder-mounted combined pressure indicator with photo-luminescent face markings for low-light legibility and a robust stainless steel and polycarbonate case with a protective rubber shroud. A warning whistle has an operating pressure of 55 bar. Approved to EN 137:2006 Type 2, MED (Shipswheel approval), ISO 20269-2 and ISO 23269-3.