Simple to use and maintain. With only six moving parts, maintenance is easy. Fail-open design assures air supply for as long as the cylinder has air. Dual-flange silicone full facepiece comfortably fits a variety of facial sizes. This unit also features an oral/nasal cup to reduce lens fogging and a speaking diaphragm for clear, intelligible voice transmission. Hard coated polycarbonate lens provides over 200° field of vision. Harness assembly is flame resistant. Complies with NIOSH, MSHA and NFPA 1981, 1992 Edition.