This International Standard specifies requirements for the safety and essential performance of transportable liquid oxygen systems which are used as a supply source for oxygen therapy. These devices usually consist of a portable unit to be carried by or with the patient whilst in use and the vessel used to refill the portable unit. These devices are mostly used in home care applications and in health care facilities/institutions. These devices are often used without professional supervision. Liquid oxygen vessels used as a supply source for oxygen pipeline systems are excluded from this International Standard. The requirements of this International Standard which replace or modify the requirements of IEC 60601-1:1998 and its Amendments 1 (1991) and 2 (1995) are intended to take precedence over the corresponding general requirements.