The IEC 61511 revision: functional safety comes of age

Paul Boughton

The independent Safety Users Group has drawn together industry experts in a discussion about the revisions currently being made to IEC 615111. The resulting video offers practical insights into the proposals and is available free online. Sean Ottewell reports.

In light of revisions being made to IEC 61511, the independent Safety Users Group (SUG) has conducted an unprecedented round table discussion with members of the IEC 61511 standard committee to explore the maintenance of the functional safety standard and address common misconceptions.

In the resulting video, which is free online from the SUG website (see below), industrial safety trend setters from Shell Europe and DuPont USA are joined by experts from the UK's Health and Safety Executive (HSE), Emerson Process Management and IEC 61511 committee chairman Victor Maggioli to share their practical experience of the standard and its adoption in the chemical process, oil refining, tank storage and offshore industries.

Didier Turcinovic of the Safety Users Group says: "The safety community needs to share knowledge and ideas and the involvement of end users such as Shell, manufacturers such as Emerson Process Management and functional safety experts is essential to develop standards like IEC 61511 that meet their specific demands."

The IEC 61511 standard was first published in 2004 in order to provide specific guidance on the application of the IEC 61508 functional safety framework in the process industry. Trends in sustainable development, operational excellence (OP-EX) and quality control have driven growing interest in the standard.

In recent years, the recommendations from the Texas City oil refinery and Buncefield oil storage and transfer depot incident reports have accelerated the adoption of IEC 61511 to a point where it is widely accepted as the state of the art (Fig. 1).

IEC 61511 acceptance and adoption varies around the World, but in the UK the Health and Safety Executive (HSE) regards it as close to law. The HSE's IEC 61511 committee member Simon Brown explained: "IEC 61511 is becoming well accepted as the standard of good practice for safety instruments systems in the process sector. It's certainly not a legal requirement in itself, but the requirement to implement good practice is a legal requirement."

The 2007 Frost and Sullivan report "World Safety Systems Markets for Process Industries" stated that the safety systems market represented US$1 billion in 2006 and was expected to double by the year 2013. However, despite the boom in safety programmable systems and growing awareness within industry, the IEC 61511 standard is still misinterpreted whilst knowledge and competence gradually diffuses throughout international networks and supply chains.

IEC 61511 is currently under maintenance and the committee is working towards international acceptance on a number of important points that will be addressed in the revised standard. Key topics explored in the roundtable discussion include the effect of the revised IEC 61508 standard on its 61511 derivative, the clarification of "prior in use", as well as specific parts such as hardware fault tolerance (HFT), the safety manual, clause 12, SIL 4 and PFD calculations.

A new revision of the IEC 61508 'umbrella standard' is imminent which will have an immediate effect on the current IEC 61511 and its future revision.

The subject of 'prior in use' has been the root of enthusiastic debate within industry, and some parties argue that it is open to interpretation. This has important implications for end users, consultants and for manufacturers.

Aart Pruysen of Emerson Process Management commented: "There are many process conditions that are included in the prior use claim that can only be observed by the end user. It's also a matter of liability in case something happens, and who would be responsible. I think the standard, at this moment, makes it very clear that only end users can do that."

IEC61511 bridged many different areas of technology on a process plant (hazard and risk analysis, reliability engineering, quantitative analysis, instrumentation and testing). Committee chairman Maggioli explained: "The result was a new series of technological issues such as layer of protection analysis, safe failure fraction, and probability of failure on demand that has required further definition as the standard is revised."

The continuing evolution of technology, including wireless, safety fieldbus, safety software and SIL certified devices, has also impacted the standard.

In the video, Maggioli comments on the current status of the IEC61511 revisions, "I expect that you will see changes in the clause 12 software and hardware fault tolerance section. You may not see as many changes in SIL 4, the safety manual and PFD calculations."

o find out more about the topics discussed, the maintenance of the IEC 61511 standard and its application first hand visit and follow the IEC 61511 interview banner. The SUG's online knowledge base comprises more than 6000 pages of technical papers, white papers, video interviews, reports and training resources about intrinsically safe and explosion proof technology (ATEX), standards and regulations (such as IEC 61508 and 61511), risk management, safety lifecycle, process safety management and maintenance strategies. For more see http://www.safetyusersgroup.como