A respiration system includes a regulator including an inlet for connection to a source of pressurized gas and an outlet for delivery of the gas to the user, and a respiration facepiece for use in connection with the regulator including an interface removably attachable to the regulator, at least one seal system adapted to form a sealing engagement with the face of a user, an inhalation port in fluid connection with the regulator interface and with the facepiece interior, an inhalation check valve in fluid connection between the inhalation port and the facepiece interior; an exhalation port in fluid connection with the facepiece; an exhalation check valve in fluid connection with the exhalation port; and an ambient port separate from the inhalation port and from the exhalation port, which is in fluid connection with the facepiece interior without an intervening check valve.