This document provides guidelines for the use of hydrogen in its gaseous and liquid forms as well as its storage in either of these or other forms (hydrides). This document identifies the basic safety concerns, hazards and risks, and describes the properties of hydrogen that are relevant to safety. Detailed safety requirements associated with specific hydrogen applications are treated in separate International Standards. Hydrogen in this document means protium (the most common isotope of hydrogen) (1H2), not deuterium (2H2) or tritium (3H2).