This part of this European Standard defines the terms, definitions, quantities, symbols and units that are used throughout the EN 13445. It also contains instructions on how to use the standard (Annex A) as well as an index which covers the whole standard (Annex B). This information is aimed to aid the user of the EN 13445. This European Standard applies to unfired pressure vessels with a maximum allowable pressure greater than 0, 5 bar gauge but may be used for vessels operating at lower pressures, including vacuum. The selection, application and installation of safety related accessories intended to protect pressure vessels during operation are covered in EN 764-7.