TS EN 61508-6

TS EN 61508-6 is the guidance part of the functional safety series for electrical, electronic and programmable electronic safety-related systems, explaining how to apply IEC 61508-2 and IEC 61508-3. Rather than setting standalone design rules, it provides explanatory material and worked examples that help users interpret the core requirements and use them together in practice.

Application guidance for IEC 61508-2 and IEC 61508-3

Functional safety concerns the ability of a safety-related system to perform its required safety functions correctly and in a timely way. In the IEC 61508 family, IEC 61508-2 addresses hardware safety requirements, while IEC 61508-3 addresses software safety requirements. TS EN 61508-6 supports implementation by showing how these two parts are read together and how the functional steps in their application are typically approached.

The annexes included in this part provide practical guidance and example calculations. They cover an example technique for calculating hardware failure probabilities, a worked example for diagnostic coverage, a methodology for quantifying the impact of hardware-related common cause failures, and examples of applying the software safety integrity tables for safety integrity levels 2 and 3. In general technical context, these topics are central to safety integrity assessment because they link reliability data, diagnostic capability and failure-mode interaction to the overall safety argument.

• Annex A gives a brief overview of the requirements of IEC 61508-2 and IEC 61508-3.
• Annex B provides an example technique for calculating probabilities of hardware failure.
• Annex C gives a worked example of calculating diagnostic coverage.
• Annex D explains a methodology for quantifying the effect of hardware-related common cause failures.
• Annex E gives worked examples for applying the IEC 61508-3 software safety integrity tables to SIL 2 and SIL 3.

This second edition replaces the first edition published in 1998 and is described as a technical revision. It is most useful where hardware and software safety requirements must be aligned within a broader functional safety process.