This International Standard specifies the characteristics of unused triaryl phosphate ester fluids for turbine governor controls and other hydraulic systems in electrical power stations. NOTE Fluids used in this application are classified under category TCD of ISO 6743-5:—[1]. These fluids are difficult to ignite and show little tendency to propagate flame, but cannot be considered nonflammable. Such fluids should only be filled into systems designed for their use and where recommended by the equipment manufacturer. Regular maintenance of these fluids is important. Detailed information on their maintenance and associated safety procedures is given in IEC 60978[3] or should be obtained from equipment manufacturers and fluid suppliers.