Abstract: A closed circuit breathing apparatus for supplying breathable air to a facepiece to be worn by a user while working in an irrespirable atmosphere is disclosed. The apparatus includes an inhalation and an exhalation section connected to the facepiece. A CO.sub.2 scrubber and a rebreather bag are connected in series between the inhalation and exhalation sections. A motorized fan is disposed in the inhalation section for continuously pumping air from the rebreather bag to the inhalation section. A pressure reducing valve supplies make up air from a tank of pressurized oxygen enriched air to the inhalation section. The fan and pressure reducing valve are arranged to supply sufficient air flow (e.g., 10 to 150 LPM) to the facepiece to maintain a positive face piece pressure under the anticipated normal use of the apparatus. A demand valve supplies additional air from the pressure reducing valve to the inhlation section to maintain a positive pressure at the facepiece during periods of peak demand (e.g.