This document specifies minimum requirements for breathing sets and breathing tubes intended to be used with anaesthetic breathing systems, ventilator breathing systems, humidifiers or nebulizers. It applies to breathing sets and breathing tubes and patient end adaptors supplied already assembled and to those supplied as components and assembled in accordance with the manufacturer’s instructions.This document is applicable to breathing sets which include special components (e.g. water traps) between the patient end and machine end.Provision is made for coaxial and related bifurcated, double-lumen, or multiple-lumen breathing sets and breathing tubes suitable for use with patient end adaptors.