ISO 7919-4:2009 establishes provisions for evaluating the severity of in-situ, broad-band shaft vibration measured radial (i.e. transverse) to the shaft axis at, or close to, the main bearings. These are in terms of

- vibration under normal steady-state operating conditions;

- vibration during other (non-steady-state) conditions when transient changes are taking place, including run up or run down, initial loading and load changes;

- changes in vibration which can occur during normal steady-state operation.

ISO 7919-4:2009 is applicable to heavy-duty gas turbine sets used in electrical and mechanical drive applications, with fluid-film bearings, outputs greater than 3 MW and an operating speed range under load between 3 000 r/min and 30 000 r/min. This includes gas turbines coupled to other rotating machinery either directly or through a gearbox. In some cases, ISO 7919-4:2009 is not applicable to the evaluation of the vibration of the coupled equipment.