IEC 61508

IEC 61508 is the international standard that defines functional safety requirements for systems involving electrical, electronic, or programmable electronic technologies.

Purpose and Scope

IEC 61508, titled “Functional Safety of Electrical/Electronic/Programmable Electronic Safety-related Systems”, is an international standard developed by the International Electrotechnical Commission (IEC). It establishes a comprehensive framework for ensuring the safe operation of systems that incorporate electrical, electronic, or programmable electronic (E/E/PE) technologies.

The standard defines functional safety as part of the overall safety of a system that depends on the correct functioning of safety-related systems and external risk-reduction measures. IEC 61508 is technology-neutral and application-independent, making it suitable for use across industries such as manufacturing, transportation, and energy.

Safety Integrity Levels (SILs) are used to quantify the level of risk reduction, ranging from SIL 1 (lowest) to SIL 4 (highest).

Safety Lifecycle Approach

The standard introduces the concept of a safety lifecycle, which spans the entire lifespan of a safety-related system. Key phases include:

  • Hazard and risk assessment
  • Safety requirements specification
  • Design and engineering of safety functions
  • Validation and verification
  • Operation, maintenance, and modification
  • Decommissioning

This approach ensures that both random hardware failures and systematic errors are addressed through technical and procedural measures.

Systematic and Hardware Safety

IEC 61508 separates safety into two categories:

  • Systematic safety integrity – Focuses on processes, software, and human factors.
  • Hardware safety integrity – Involves probabilistic reliability, diagnostics, and fault tolerance.

Designers must apply appropriate techniques such as fault tree analysis and failure mode and effects analysis, along with rigorous quality assurance based on the intended SIL.

Relationship to Other Standards

IEC 61508 is the foundational standard for various industry-specific functional safety standards, including:

  • IEC 61511 – Process industry
  • IEC 62061 – Machinery
  • ISO 26262 – Automotive
  • EN 50126/8/9 – Railway applications
  • IEC 62304 – Medical device software

These standards adapt IEC 61508 principles to sector-specific needs and risk profiles.

References

  • IEC 61508:2010, Parts 1–7, International Electrotechnical Commission
  • IEC Functional Safety Portal
  • Smith, D. J., & Simpson, K. G. L. (2010). Functional Safety: A Straightforward Guide to IEC 61508 and Related Standards. Elsevier.

WinCC OA Safety Documents

WinCC OA is part of a safety-related overall system, and to assist integrators in working with the safety-related overall system, WinCC OA provides the following set of documents for download: