Functional safety and IEC 61508

Functional safety and IEC 61508

IEC 61508 is a basic standard that define two kinds of requirements

1) requirements in terms of "safety life cycle" and in terms of "documentation"

2) technical requirements both for hardware and software

  • First :
    • Qualitative requirements in terms of architecture are based mainly on Hardware fault tolerance - HFT and are defined in tables 2 and 3 of IEC 61508-2). Based on theses tables : 
      • the manufactured can define a products that realize the safety functions
      • the end user define its architecture that fullfill the technical hardware fault tolerance of the standard
    • Quantitative requirements in terms of PFD AND / OR PFH
  • Second : requirements of IEC 61508-3 for Software. 

For this purpose IEC 61508 standards comprise 7 parts : 

–   IEC 61508-1 part includes general requirements that are applicable to all parts. 

–   parts 2 and 3 provide additional and specific requirements for E/E/PE safety-related systems (for hardware and software);

–   part 4 gives definitions and abbreviations that are used throughout this standard;

–   part 5 provides guidelines on the application of part 1 in determining safety integrity levels, by showing example methods;

–   part 6 provides guidelines on the application of parts 2 and 3;

–   part 7 contains an overview of techniques and measures.

IEC 61508-1, IEC 61508-2, IEC 61508-3 and IEC 61508-4 are basic safety publications, and as basic safety publications, they are intended for use by technical committees in the preparation of standards in accordance with the principles contained in IEC Guide 104 and ISO/IEC Guide 51. IEC 61508-1, IEC 61508-2, IEC 61508-3 and IEC 61508-4 are also intended for use as stand-alone publications.

IEC 62061 that is the publication for machoinery sector is based on this IEC 61508 standard.