The SR 307 compressed air attachment is designed for connection to Sundström half masks and full face masks. This combination forms a breathing apparatus designed for continuous air flow, for connection to a compressed air supply. The SR 307 is an accessor y that enables a given facepiece to be used as either a filtering device or a protective device supplied with compressed air. The compressed air attachment is especially intended for applications involving heavy and sustained work in environments in which the pollutants have poor warning properties or are particularly toxic. The SR 307 is made of a material which is not liable to give rise to frictional sparking, which enables the attachment to be used in an explosive or flammable environment. The flow meter and warning whistle for temporary and continuous monitoring of the air flow rate are included. Control valve mounted on the user’s belt is included.