Where to buy the IEC61508 standard
As with everything to do with standards for the electricity and electrical industries, IEC61508 is published by the International Electrotechnical Commission itself. It can be bought from the organisation’s website directly either on CD or as a download; see the link below.
The IEC describes itself as “the world’s leading organization that prepares and publishes International Standards for all electrical, electronic and related technologies - collectively known as electrotechnology. Wherever you find electricity and electronics, you find the IEC supporting safety and performance, the environment, electrical energy efficiency and renewable energies.”
The IEC also manages conformity assessment systems that certify that equipment, systems or components conform to its International Standards.
Buy the IEC61508 standard online directly from IEC
Isolator suitable for use in SIL2 circuits
New versions of R Stahl’s type 9170 switching repeater and the type 9175 digital output provide increased safety while transferring intrinsically safe binary signals: for the first time, they ensure complete, consistent error monitoring of every channel from the field to the control level despite an isolator in between.
The new modules, which complement R. Stahl’s ISpac model range, allow users to detect cable errors between isolator and process control units and also to identify interferences in the field which are then reported to the control system via signal channel. Applications with safety-oriented signals according to IEC EN 61508 / 61511 - e.g emergency stops using magnetic valves - will benefit from reliable monitoring of the complete circuit. Safety is increased for the plant, operating staff and the time spent on error detection is minimized. The new modules are suitable for Ex i signals in zones 0 and 1 and, at the same time, for use in SIL 2-compliant signal circuits.
Certification Body to guide you through IEC61508
Baseefa, the UK based certification body, can offer a service to help customers to assist get an understanding of IEC 61508 as well as provide them with a certified data set according to the standard.
The company points out that IEC 61508 is written on a cradle-to-grave approach for complete safety systems, but has often been misused to award spurious “SIL” numbers to individual items of hardware. It is keen to reiterate that a Safety Integrity Level (SIL) can only be applied to a complete system and not to a component of such a system. By using the CASS Methodology approved by the UK experts who work with IEC 61508 systems, Baseefa says it can produce an authenticated meaningful data set for any component of a system, so that a system designer can justify the SIL for the complete system.
Further information on how Baseefa can help with IEC61508 certification
Functional Safety Book - Second Edition available
Functional Safety, A Straightforward Guide to Applying IEC 61508 and Related Standards is now available as a second edition. This fairly easy-to-read guide by David Smith and Kenneth Simpson has been expanded and improved.
IEC 61508 may be complex, but the book claims to overcome that complexity. It introduces the standard in the context of safety in general, then moves on to give practical advice about implementation and obtaining certification. It also explains how IEC 61508 relates to second tier standards and related guidance, such as IEC 61511, 61513, UKOOA, ISA S84.01 and DIN standards, among others. The authors illustrate their explanations with examples, and four case studies with exercises set the information in context. Templates and checklists for drawing up your own implementation plan and information on self-certification are also provided.
The publishers say that as Functional Safety is applicable to many industries, Functional Safety in its previous edition proved to be an invaluable reference for professionals from a variety of industries, such as project, instrumentation, design and control engineering as well as the oil and gas, chemical, rail, power generation, nuclear, aircraft, and automotive sectirs.
The new edition includes a new chapter on IEC 61511, the process sector standard, published since the first edition. The text has been updated throughout in light of the authors recent experience and two case studies have been added.
Review of the previous edition: “As a straightforward guide to IEC 61508 this book will be difficult to surpass. I can’t remember recommending a book to my peers and colleagues with so much enthusiasm; it really is a reference book worth having” - Malcolm Warren in Measurement and Control.
More details on Functional Safety: A Straightforward Guide to Applying IEC 61508 and Related Standards
More details on Functional Safety: A Straightforward Guide to Applying IEC 61508 and Related Standards
Introduction to Functional Safety - Free Application Note
Here’s a very nice explanatory guide to IEC61508 which again, goes back a while, but has some good material in it. MTL’s An introduction to Functional Safety and IEC 61508 points out that the benefits to users are that a more scientific, numeric approach to specifying and designing safety systems is possible; the nature of the risk can be quantified; and a protective system appropriate to the risk can be designed. It means that under- or over-specifying of protective systems is less likely and, in many cases, a less expensive solution can be shown to provide adequate protection.
The Application Note is intended to provide a brief introduction to the IEC61508 standard and to illustrate how it is applied, although it does not claim to be a complete interpretation of the standard - not in just 16 pages!
Download your free Functional Safety Application Note
CASS: improving your IEC61508 certification
CASS (Conformity Assessment of Safety-related Systems) is a certification scheme designed to offer “a rigorous and internationally acceptable structure under which consistent certification of safety related systems can take place”. It has been created as a not-for-profit company, managed by an elected board. Members include associations representing manufacturers, designers, installers, users, certifiers or regulators of safety related systems.
CASS covers all industry sectors including process, aerospace and transport and the scheme is operated through independent third-party certification bodies, accredited to the European and International accreditation standards.
CASS says it is an initiative “designed to provide an overall safety framework, which includes the use of recognised safety standards and competent assessors”. Its objective to develop a conformity assessment scheme meeting the requirements of IEC 61508, enabling the safety systems industry (manufacturers, integrators and end users) to collaborate in order to improve its competitive position.
For further information and to see if the CASS certification scheme might improve your IEC61508 certification, start at About The CASS Scheme where there’s also a free introductory brochure to download.
Launch of New Safety Annunciator
RTK Instruments has recently launched an annunciator which the company says is the first SIL2 annunciator certified to IEC61508 to appear on the market.
The SIL725 Safety Annunciator has been designed and manufactured to provide a high safety integrity for critical alarm applications and for use as a component part of a safety instrumented system. The unit is third party certified by SIRA using the CASS methodology to a safety integrity level of SIL2.
With a modular construction, units can be constructed from one to 128 channels with a choice of two window sizes and six colours. RTK says: “Whatever the size and complexity of your alarm scheme, the SIL725 can be configured to provide the best solution. With a field proven multi-redundant ASIC design this annunciator gives the best in reliability, flexibility and programmability for all applications and industries.”
More information on the RTK Instruments IEC61508-certified SIL725 Safety Annunciator
An introduction to IEC61508: free brochure
For a very general introduction to IEC61508, there’s a long-serving but decent enough downloadable brochure on the IEC website. Simply titled Functional safety of electrical/ electronic/ programmable electronic safety-related systems, the 12-page document is a good management-level backgrounder and lists all the full IEC61508 specification documents. You can download a copy of the IEC61508 brochure here (PDF, 524kB).
