This part of ISO 15859 specifies limits for the composition of breathing air and establishes the sampling and test requirements applicable for the verification of the breathing air composition. This part of ISO 15859 is applicable to sampling and test methods for breathing air intended for purging and pressurization of space systems as well as flight hardware and ground support facilities, systems and equipment. This part of ISO 15859 may be applied to influent breathing air. This part of ISO 15859 is applicable to any sampling operation required to ensure that, when the fluid enters the launch vehicle or spacecraft, the fluid composition complies with the limits provided hereafter or with any technical specification agreed to for a particular use.