ISO 15859-12:2004 specifies limits for the composition of carbon dioxide (CO₂) and establishes the sampling and test requirements applicable for the verification of the carbon dioxide composition.

ISO 15859-12:2004 is applicable to composition, sampling, and test methods for carbon dioxide intended for purging and pressurization in both space systems flight hardware and ground support facilities, systems, and equipment. ISO 15859-12:2004 may be applied to carbon dioxide influents. Carbon dioxide may be of the gaseous or liquid type.

ISO 15859-12:2004 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.