US Patent 7152602 Mask apparatus

A face mask comprises a sealing collar (1) extending around the mouth with a shelf (4) extending under the nose supporting a gel insert (7) that makes sealing contact between the nostrils and a passage (6) through the shelf. A curved, rigid window (30) is a push fit in a central opening (2) of the collar (1) and has a gas inlet (33) attached with it so that the window can be removed or connected with the sealing collar as necessary. The collar (1) supported on the head by a harness (20) having two triangular portions (21) on opposite sides encircling respective ears.