Defines requirements for inhalational anaesthetic breathing systems for adults, supplied either assembled by the manufacturer or for assembly by the user according to the manufacturer's instructions. Also covers circle absorber assemblies, exhaust valves, inspiratory and expiratory valves and, in some designs, those parts of an anaesthetic breathing system that are incorporated within an anaesthetic workstation, including the expiratory gas pathway of an anaesthetic ventilator and any parts of a non-operator-detachable anaesthetic-gas scavenging system (AGSS).