IEC 61508-5 ED3

Functional safety of electrical/electronic/programmable electronic safety-related systems - Part 5: Examples of methods for the determination of safety integrity levels

Scope

IEC 61508-5:2026 covers those aspects to be considered when electrical/electronic/programmable electronic (E/E/PE) systems are used to carry out safety functions.
A first objective is to facilitate the development of product and application sector international standards by the technical committees responsible for the product or application sector. This will allow all the relevant factors, associated with the product or application, to be fully considered and thereby meet the specific needs of users of the product and the application sector.
A second objective is to enable the development of E/E/PE safety-related systems where product or application sector international standards do not exist.
The scope of this document is the functional safety for E/E/PE safety-related systems but, apart from normative requirements in the hazard and risk analysis phase, this document does not itself provide normative requirements for malevolent action arising from a security risk.
NOTE 1 For requirements and/or guidance on security see the IEC 62443 series [4] and ISO/IEC 27000 series [5].
NOTE 2 For guidance on the coordination between safety and security, refer to IEC TR 63069 [6].
Considerations in this document
This document contains information on:
underlying concepts of risk and relationship of risk to safety integrity levels (see Annex A);
criteria in selecting the most appropriate methods for determining safety integrity level requirements (see Annex B);
methods that will enable the safety integrity levels for the E/E/PE safety‑related systems to be determined (see Annex C, Annex D, Annex E, Annex F and Annex G).
The method selected will depend upon the application sector and the specific circumstances under consideration. Annex C, Annex D, Annex E, Annex F and Annex G illustrate quantitative and qualitative approaches and have been simplified in order to illustrate the underlying principles. These annexes have been included to illustrate the general principles of a number of methods but do not provide a definitive account.
NOTE 1 Those intending to apply the methods indicated in these annexes can consult the source material referenced.
NOTE 2 For more information on the approaches illustrated in Annex B and Annex E, see references [7] and [8] See also reference [9] for a description of an additional approach.
This third edition cancels and replaces the second edition published in 2010. This edition constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous edition:
a) update of normative references;
b) alignment with the other parts of the IEC 61508 series.