This International Standard is applicable to safety-related electronic systems (including subsystems and equipment) for railway signalling applications. The scope of this standard, and its relationship with other IEC standards, are shown in Figure 1. This standard is intended to apply to all safety-related railway signalling systems/subsystem/equipment. However, the hazard analysis and risk assessment processes defined in IEC 62278 and this standard are necessary for all railway signalling systems/subsystems/equipment, in order to identify any safety requirements. If analysis reveals that no safety requirements exist (i.e.: that the situation is non-safety-related), and provided the conclusion is not revised as a consequence of later changes, this safety standard ceases to be applicable. This standard applies to the specification, design, construction, installation, acceptance, operation, maintenance and modification/extension phases of complete signalling systems, and also to individual sub-systems and equipment within the complete system. Annex C includes procedures relating to electronic hardware components. This standard applies to generic sub-systems and equipment (both application-independent and those intended for a particular class of application), and also to systems/subsystems/equipment for specific applications. This standard is not applicable to existing systems/sub-systems/equipment (i.e. those which had already been accepted prior to the creation of this standard). However, as far as reasonably practicable, this standard should be applied to modifications and extensions to existing systems, sub-systems and equipment. This standard is primarily applicable to systems/sub-systems/equipment which have been specifically designed and manufactured for railway signalling applications. It should also be applied, as far as reasonably practicable, to general-purpose or industrial equipment (e.g.: power supplies, modems, etc.), which is procured for use as part of a safety-related signalling system. As a minimum, evidence shall be provided in such cases to demonstrate – either that the equipment is not relied on for safety, – or that the equipment can be relied on for those functions which relate to safety. This standard is applicable to the functional safety of railway signalling systems. It is not intended to deal with the occupational health and safety of personnel; this subject is covered by other standards.