Functional Safety: A Straightforward Guide to IEC61508 and Related Standards

The need to specify quantitative safety targets for overall systems, and for their separate protection sub-systems, has grown rapidly over the last ten years. This feature has become known as Functional Safety and numerous standards and guidelines have emerged, most of which incorporate the idea of safety-integrity levels (SILs).

The quantified target (either a failure rate or a probability of failure on demand) determines which of four target SILs is called for. The higher the SIL then the more onerous the qualitative requirements to be observed during the life-cycle.

Thus safety-integrity is addressed from two points of view:

Meeting the numerical failure rate target

Meeting the qualitative requirements for the SIL in question

The IEC Standard 61508, Functional Safety, has become the umbrella document under which most other guidelines are now regarded as "2nd tier guidance".

Functional Safety: A Straightforward Guide to IEC 61508 and Related Standards is based primarily on understanding that standard and provides a straightforward guide to the essentials.


Dr David J Smith BSc,PhD,CEng,FIEE,HonFSaRS,FIQA,MIGasE has been directly concerned with reliability, safety and software quality for 30 years. He has written a number of books on the subject as well as numerous papers. His PhD thesis was on the subject of reliability prediction accuracy and common cause failure. He chairs the IGasE panel which develops its guidelines on safety-related systems (now in its third edition). He has also made contributions to IEC 61508.

Kenneth G L Simpson MPhil,FIEE,FInstMC,MIGasE has been associated with safety-related systems design and also with their assessment for 25 years. He is a member of the IEC 61508 drafting committee and also of the I Gas E panel which writes the gas industry guidance. Following a career in aerospace, Ken has spent 20 years in the control system industry and is a Director of Silvertech International plc, a leading designer of safety and control systems. He has written a number of papers on the topic and gives frequent talks.

Explains the practical and management issues raised by the important new international standard for safety-critical systems

Guidance on self-assessment could save you thousands in consultancy fees

BSc, PhD, CEng, FIEE, HonFSaRS, FIQA, MIGasE., Independent Consultant, Technis, Tonbridge

Ken Simpson, MPhil, FIEE, FInstMC, MIGasE., Managing Director of Silvertech, a major supplier of safety systems, and a member of the IEC 61508 committee structure.