International Standards and Conformity Assessment for all electrical, electronic and related technologies
Functional Safety and the IEC

IEC 61508

Functional Safety


Edition 1.0

B) International Standards framework


B1) How will the standard be published internationally?

The standard is already published by the IEC and is available from the IEC Webstore.

B2) What is the international status of IEC 61508?

Adoption of IEC International Standards by any country, whether it is a member of the IEC or not, is entirely voluntary. IEC National Committees undertake to apply IEC International Standards transparently to the maximum extent possible in their national and regional standards. Any divergence between the IEC International Standard and the corresponding national or regional standard shall be clearly indicated in the latter.

B3) How does IEC 61508 fit together with application sector or product standards?>

The standard sets out a generic approach for all safety lifecycle activities for E/E/PE safety-related systems that are used to perform safety functions. This unified approach has been adopted in order that a rational and consistent technical policy is developed for all E/E/PE safety-related systems, irrespective of the application sector. A major objective is to facilitate the development of product and application sector international standards based on the IEC 61508 series. For this reason the first four parts of the standard are basic safety publications.

B4) What is a basic safety publication?

Parts 1, 2, 3 and 4 of IEC 61508 are designated as IEC basic safety publications. This means that IEC Technical Committees will have to use these parts in the preparation of each of their own product or application sector international standards that has E/E/PE safety-related systems within its scope. IEC 61508 will therefore have far reaching implications across all IEC application sectors.


Note that basic safety publication status does not apply in the context of low complexity E/E/PE safety-related systems or where the required safety integrity of the E/E/PE system is less than the lowest safety integrity level in IEC 61508.

B5) What product or application sector international standards based on IEC 61508 are there?

The following product and application sector standards have been published:


Reference, Edition, Date, Technical Committee, Title
IEC 61513 ed1.0 (2001-03)
SC 45A
Nuclear power plants - Instrumentation and control for systems important to safety - General requirements for systems
IEC 61511-1 ed1.0 (2003-01)
SC 65A
Functional safety - Safety instrumented systems for the process industry sector - Part 1: Framework, definitions, system, hardware and software requirements
IEC 61511-2 ed1.0 (2003-07)
SC 65A

Functional safety - Safety instrumented systems for the process industry sector - Part 2: Guidelines for the application of IEC 61511-1

IEC 61511-3 ed1.0 (2003-03)
SC 65A

Functional safety - Safety instrumented systems for the process industry sector - Part 3: Guidance for the determination of the required safety integrity levels

IEC 62061 ed1.0 (2005-01)
TC 44
Safety of machinery - Functional safety of safety-related electrical, electronic and programmable electronic control systems
IEC 61800-5-2 ed.10 (2007-07)
SC 22G

Adjustable speed electrical power drive systems - Part 5-2: Safety requirements - Functional.


Other standards may also be under development. (If you are aware of any such standards, please let us know using the feedback facility)


In addition to the development of product and application sector international standards based on IEC 61508, there are many standards which reference IEC 61508.

B6) How do safety integrity levels 1 to 4 in IEC 61508 convert or relate to the categories described in EN 954-1?

Because of the different technical criteria used in IEC 61508 and EN 954-1:1996 (also published as ISO 13849-1:1999 and which has now been superseded by IS0 13849-1: 2006), these two standards do not provide a sufficient technical basis for directly linking a measure of safety performance based on the requirements for categories in EN 954-1:1996 with a similar measure of performance based on the requirements for safety integrity levels in IEC 61508.


However, in the context of safety performance, a pragmatic view is that an E/E/PE safety-related system capable of supporting safety integrity level 1 (SIL1) safety functions (according to IEC 61508) broadly satisfies the requirements for a category 1 or a category 2 system (according to EN 954-1:1996). Likewise, SIL2 can be said to satisfy category 3 and SIL3 can be said to satisfy category 4.


It is essential to note that there is no equivalent correlation in the reverse direction. For example, it cannot be said that any category 3 E/E/PE safety-related system is capable of supporting SIL2 safety functions. This is because many of the requirements of IEC 61508 do not have an equivalent in EN 954-1:1996.


Further details are available in IEC 62061.

B7) Can I use IEC 61508 as a standalone standard?

Yes. A major objective of the standard is to enable the development of E/E/PE safety-related systems where product or application sector international standards do not exist.


Many requirements of IEC 61508, particularly in IEC 61508-2 and IEC 61508-3, are not repeated in the application sector or product standards but are referenced instead. The result is that most users of product or application sector international standards will also need IEC 61508.

B8) Will IEC 61508 be revised?

As part of the normal IEC maintenance cycle, the standard has been revised. Amendments were based on comments received from national committees.


Two international maintenance teams were responsible for revising IEC 61508. Maintenance Team MT 61508-1/2 was responsible for IEC 61508-1, IEC 61508-2, IEC 61508-4 and IEC 61508-5 and Maintenance Team MT61509-3 was responsible for IEC 61508-3. The other two parts, IEC 61508-6 and IEC 61508-7, contained informative text in support of IEC 61508-2 and IEC 61508-3, and responsibility was divided accordingly between MT61508-1/2 and MT61508-3.


IEC 61508 Edition 2.0 was published in April 2010 and will not be replaced by a new edition before 2014.


Note: For the FAQs for IEC 61508 ed2.0 see question B8 in FAQ - Edition 2.0