BS EN 61508-2:2002 - Page 2

This part of IEC 61508:

• is intended to be used only after a thorough understanding of IEC 61508-1, which provides the overall framework for the achievement of functional safety
• applies to any safety-related system, as defined by IEC 61508-1, which contains at least one electrical, electronic or programmable electronic based component
• applies to all subsystems and their components within an E/E/PE safety-related system (including sensors, actuators and the operator interface)
• specifies how to refine the information developed in accordance with IEC 61508-1, concerning the overall safety requirements and their allocation to E/E/PE safety-related systems, and specifies how the overall safety requirements are refined into E/E/PES safety functions requirements and E/E/PES safety integrity requirements
• specifies requirements for activities that are to be applied during the design and manufacture of the E/E/PE safety-related systems (i.e. establishes the E/E/PES safety lifecycle model), except for software, which is dealt with by IEC 61508-3 (see figures 2 and 3) – these requirements include the application of techniques and measures, which are graded against the safety integrity level, for the avoidance of, and control of, faults and failures
• specifies the information necessary for carrying out the installation, commissioning and final safety validation of the E/E/PE safety-related systems
• does not apply to the operation and maintenance phase of the E/E/PE safety-related systems – this is dealt with in IEC 61508-1 – however, IEC 61508-2 does provide requirements for the preparation of information and procedures needed by the user for the operation and maintenance of the E/E/PE safety-related systems
• specifies requirements to be met by the organisation carrying out any modification of the E/E/PE safety-related systems.

NOTE 1 This part of IEC 61508 is mainly directed at suppliers and/or in-company engineering departments, hence the inclusion of requirements for modification.

NOTE 2 The relationship between IEC 61508-2 and IEC 61508-3 is illustrated in figure 3.