This document specifies common requirements for transportable liquid oxygen systems and specific requirements for base units. Base units are used as a store for liquid oxygen for refilling portable units. They can also, if fitted with a flow outlet and flow control, be used as a source for the supply of oxygen direct to the patient. Stationary liquid oxygen systems used for oxygen pipeline supply systems are excluded from this document. NOTE 1: Throughout this document the term units is used where the requirement applies to both base units and portable units. NOTE 2: ISO 18777 Part 2 specifies those requirements specific to portable units.