Where are Standards Headed?

The merging of EN ISO 13849 and IEC 62061 is underway. Navigate the path to unification and find out how it will be an opportunity for clarification, simplification and resolution of known issues.
By Derek Jones, Business Development – Safety, Rockwell Automation

What do you think about machinery safety standards? Are they a help or a hindrance?
There doesn’t seem to be much middle ground in answers to these questions. You either love machinery safety standards or hate them. If you have no real opinion, it’s probably because you never have to use them. However, if you’re reading this, you’re probably among the chosen ones who must use them, and you need to know what standards are out there and which changes are going to appear over the horizon.
That can be easier said than done, especially if you’re taking a global perspective. Trying to match different standards to various geographies can be frustrating and time-consuming. The increasing worldwide adoption of ISO and IEC standards certainly helps. For me, they‘re the first place to look when I’m trying to determine a globally acceptable solution for safety-related aspects of machinery.
Anyone who keeps abreast of what’s happening in ISO and IEC machinery safety standards will know the term “functional safety.” This is safety that depends on the way a machine functions. The biggest influence on the way a machine functions is its control system. So it’s no surprise that some of the most significant changes occurring in machinery safety standards are related to the safety-related aspects of their control.
We have moved from the relatively simple approach of the Categories of EN 954 to a more complex approach encompassing PL (Performance Level) of EN ISO 13849 and SIL (Safety Integrity Level) of IEC 62061. This hasn’t exactly been greeted with universal acclaim, but most people will accept that some sort of change was necessary. That change isn’t yet complete; work has now started on merging EN ISO 13849 and IEC 62061.
However, before we all throw our hands up in despair, let me say that it’s my contention that we have reached the summit in terms of difficulty and disruption. There should be no new methodologies or formulae. What we have, we should hold. Time and money have been spent getting us to where we are now, and this definitely isn’t the time for starting over. It’s the time to grasp opportunity for improvement.
Work has started in a joint ISO-IEC working group. The target date for completion was originally set at 2016, but that was determined to be too optimistic. 2018 might be more realistic.

How Did We Get Here?

What brought us to this point? To see where we should go in the future, we must first understand the lessons of the past.
Ten to 20 years ago, many of us were working with the “Categories” from the now-defunct “EN 954: Safety related parts of control systems.” The EN 954 approach required the use of basic safety principles, and either the use of simple, strong and well-tried components or fault tolerance and fault detection where necessary to prevent failure of the safety function.
Because the system seemed to achieve “Category 3,” for example, in pure structural terms posed a sometimes-irresistible temptation to invoke a much simplified tick-box approach.
Over time, users achieved an understanding of the full meaning of the standard as well as a reasonable consensus on how to interpret some of the “grey” areas. This was due in part to learning from experience of using it in practice and also because of the availability of instructive information such as the excellent guide produced by the IFA (formerly the BGIA) in Germany.

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As we approached the end of the 2000s, it became clear that the use of complex electronic and programmable technology for safety would become inevitable. It was evident that the provisions of this standard with its relatively simple approach couldn’t be counted on to cope with the next generation of machinery safety technology.
This situation lead to the publication in 2005 of “IEC 62061: Safety related electrical, electronic and programmable electronic control systems,” followed shortly by the fully revised EN ISO 13849. Both standards introduced a more complex approach that gives them both the possibility to deal with increasing complexity of safety technology and function.
In many cases, the safety function is no longer just a simple case of switching off the power. The advent of safety-capable logic, for example, has enabled intelligent safety functions that can react to different machine conditions and can assist productivity rather than obstruct it. However, the greater the flexibility of function, the greater the need for provisions against mistakes and faults.
ISO 13849 and IEC 62061 both include the necessary provisions, but at the cost of an increase in complexity including the requirement to do some calculation of the reliability. This, in turn, means that reliability data has to be sought for the parts of the system. The fact that this data is not always forthcoming creates some understandable frustrations. The upside is that we now have standards that can deal with complexity and which also cover some of the gaps in the old standard that could be an issue even for low complexity systems.

Merging Brings Opportunity

In summary, we have moved from a standard that was perceived as simple to use but was restricted in terms of the technology it enabled, to standards that are perceived as difficult to use but have enabled the confident use of new technology.
Merging IEC 62061 and ISO 13849 will remove the complication of having two standards. As part of the merging process, we need to make sure we don’t introduce any different or additional requirements. The merging process is as an opportunity for clarification and simplification. It’s also the chance for the resolution of some known issues such as the provision of reliability data.
I contend that we’ve made an overall gain, but without doubt there have been trade-offs along the way. It’s now time for some of the trade-offs to be re-examined with a view to getting the best of both worlds.
For more information, visit the Rockwell Automation Safety Resource Center at http://discover.rockwellautomation.com/safety and the Rockwell Automation Guardman Blog at www.guardmanblog.com.
Rockwell Automation Safety Solutions
www.rockwellautomation.com/go/tj10safety

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