– the underlying concepts of risk and the relationship of risk
to safety integrity (see Annex A);
– a number of methods that will enable the safety integrity
levels for the E/E/PE safetyrelated systems to be determined (see
Annexes C, D, E, F and G).
The method selected will depend upon the application sector and
the specific circumstances under consideration. Annexes C, D, E, F
and 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. Those intending to apply the methods indicated in these
annexes should consult the source material referenced.
NOTE For more information on the approaches illustrated in
Annexes B, and E, see references  and  in the Bibliography.
See also reference  in the Bibliography for a description of an
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 3.4.3
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
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. The
horizontal safety function of this international standard does not
apply to medical equipment in compliance with the IEC 60601
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 will not apply unless specifically referred to or
included in the publications prepared by those technical
Figure 1 shows the overall framework of the IEC 61508 series and
indicates the role that IEC 61508-5 plays in the achievement of
functional safety for E/E/PE safety-related systems.
Order online or call: Americas: +1 800 854 7179 | Asia Pacific: +852 2368 5733 | Europe, Middle East, Africa: +44 1344 328039