scope:

This part of IEC 61508 contains information and guidelines on IEC 61508-2 and IEC 61508-3.

- Annex A gives a brief overview of the requirements of IEC 61508-2 and IEC 61508-3 and sets out the functional steps in their application.

- Annex B gives an example technique for calculating the probabilities of hardware failure and should be read in conjunction with 7.4.3 and annex C of IEC 61508-2 and annex D.

- Annex C gives a worked example of calculating diagnostic coverage and should be read in conjunction with annex C of IEC 61508-2.

- Annex D gives a methodology for quantifying the effect of hardware-related common cause failures on the probability of failure.

- Annex E gives worked examples of the application of the software safety integrity tables specified in annex A of IEC 61508-3 for safety integrity levels 2 and 3.

IEC 61508-1, IEC 61508-2, IEC 61508-3 and IEC 61508-4 are basic safety publications, although this status does not apply in the context of low complexity E/E/PE safety-related systems (see 3.4.4 of IEC 61508-4). 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 IEC/ISO Guide 51. IEC 61508 is also intended for use as a stand-alone standard.

One of the responsibilities of a technical committee is, wherever applicable, to make use of basic safety publications in the preparation of its publications. In this context, the requirements, test methods or test conditions of this basic safety publication do not apply unless specifically referred to or included in the publications prepared by those technical committees.

NOTE In the USA and Canada, until the proposed process sector implementation of IEC 61508 (i.e. IEC 61511) is published as an international standard, existing national process safety standards based on IEC 61508 (i.e. ANSI/ISA S84.01-1996) can be applied to the process sector instead of IEC 61508.