Structure of IEC 61508

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IEC 61508, “Functional Safety of Electrical /Electronic/Programmable Electronic Safety-Related System”, is the basic reference for Functional Safety.

What IEC 61508 aims at

IEC 61508 provides safety equipment suppliers and users with a common framework to design products and systems for safety-related applications.

It consists of 7 parts:

  • IEC 61508-1 Generic Requirements: defines the activities, documentation, management and validation related to each phase of the safety lifecycle;
  • IEC 61508-2 Requirements for E/E/PE systems: specifies how to define the specification of the safety requirements and the activities to be carried out during the design and implementation of the product;
  • IEC 61508-3 Software Requirements: Same as Part 2 but applied to software;
  • IEC 61508-4 Definitions and abbreviations: provides definitions and abbreviations of terms used in the standard;
  • IEC 61508-5 Examples of methods for the determination of SIL: provides methods for the calculation of SIL levels for E/E/PE safety systems;
  • IEC 61508-6 Guidelines for the application of Parts 2 and 3: provides mainly a guideline for quantitative analysis;
  • IEC 61508-7 Overview of techniques and measurements: provides descriptions of techniques used in safety engineering and software.

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Some features of IEC 61508

IEC 61508 has the following features:

  • Provides a method by which to implement and manage a process for safety systems.
  • Safety Management: not only hardware and software engineering, but also managing every aspect of the system, from Concept to Decommissioning.
  • Does not define who should be responsible for the various phases;
  • Does not include specific design or engineering validation parameters. This is a generic, multi-sector standard.
  • Not a mandatory standard but a voluntary one.
  • Deals mainly with failures that could affect people or the environment. May also be used for economic impact.
  • Defines qualitative, quantitative and semi-quantitative requirements to achieve a specific level of Safety Integrity.


Other Functional Safety standards

IEC 61508 defines the minimum requirements that equipment and systems must follow in order to be used in each specific industrial sector.

The other standards define the rules on how to correctly implement/extend these minimum requirements to specific sectors.

  • ISO 13849 Machine Safety
  • EN 50126/8/9 Railway
  • IEC 61800-5-2 Electrical Drivers
  • IEC 61513 Nuclear Sector
  • EN 60601 Medical Devices
  • IEC 50156 Furnaces
  • IEC 61511 Process Industry
  • IEC 62061 Machinery
  • ISO 26262 Automotive
  • IEC 61131-6 PLC


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