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IEC 61508 – The Functional Safety Basic Standard

Functional Safety Basic Standard IEC61508

The Functional Safety Basic Standard IEC61508 is often referred to as the mother of all functional safety standards. This standard was introduced in 1998 with the intention of defining cross-industry processes and methods to be used for safety-relevant electrical, electronic and programmable electronic systems. IEC61508 is applied if no industry-specific standards are available for this area.

Scope of the Functional Safety Basic Standard IEC61508:

With ISO26262, EN50128 and DO178, the automotive industry, the railway industry and also the aerospace industry have their industry-specific standards, so that IEC61508 is not applied in these industries.

IEC61508 is mainly used in industrial automation. Here, too, specific standards such as IEC62061 and ISO13849 are usually used to determine the Safety Integrity Level (SIL) or the Performance Level (PL) of the system, for example. For the methods and measures to be applied in software and hardware development, however, reference is made to IEC61508 at various points in individual standards.

From a legal point of view, the Product Liability Act in Germany forms the legal framework for compliance with functional safety in all industries.

Structure of the Functional Safety Basic Standard IEC61508:

The IEC61508 comprises the following 7 parts. It covers all product life cycle phases, from product idea to decommissioning and also defines requirements for organization, responsibilities, management and overall safety culture.

  • Part 1: General requirements (including overall safety life cycle, management and assessment of functional safety, assignment of safety requirements to the E/E/PE system)
  • Part 2: Requirements for electrical/electronic/programmable electronic safety-related systems
  • Part 3: Software requirements
  • Part 4: Definitions and abbreviations
  • Part 5: Examples and methods for the determination of safety integrity levels
  • Part 6: Guidelines on the application of IEC61508-2 and IEC61508-3
  • Part 7: Overview of techniques and measures

Application examples of the Functional Safety Basic Standard IEC61508:

The following examples are given in the standard itself:

  • Emergency shutdown system in a hazardous chemical plant
  • Overload warning device of a crane
  • Interlocking safety devices and systems for stopping machines in an emergency case
  • Variable speed motor drive for use of speed reduction as a protective measure

Restrictions of the Functional Safety Basic Standard IEC61508:

The standard expressly declares itself not responsible for the following areas:

  • Environmental conditions which a system must comply with (e.g. EMC, heat, shock etc.)
  • Any kind of security considerations
  • Nominal performance of a system and other functional requirements
  • Non-electrical/electronic safety measures (e.g. mechanical protection of a system)

IEC61508 focuses on functional safety considerations, i.e. dangers are systematically determined which can arise from the (hardware and software) function of a device. Procedures and measures appropriate to the risk are then established for each of these hazards.

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