Cost-effective compliance for machine safety
05 January 2010
Despite rumours to the contrary, the new EU Machinery Directive came into force, as originally planned, at the end of last year. Paul Considine explains the implications and charts a course for easy compliance
There has been considerable discussion about the EU Machinery Directive in recent months, including moves to delay its implementation. At the time of writing, however, these moves seem to have been unsuccessful and the Directive remained on schedule to come into force on December 29 2009. In fact, even if there had been a last-minute change of plans, this would only have been a delay, and anyone involved in supplying, designing or installing safety systems for machinery would still have needed to understand the implications of the new Machinery Directive.
The main impact of the new Directive will be to change the ways in which machine safety is managed. It’s also important to note that requirements of the Directive apply to any machine modifications as well as new machines – and both require a Declaration of Conformity.
The reason for introducing a new Directive (2006/42/EC) is to address the limitations of its predecessor (Directive 95/16/EC), which achieved compliance though EN 954-1 but hasn’t kept pace with changes in technology. Most notably, EN 954-1 was based on calculated risk and aimed to set an appropriate system behaviour, or control class, against a category.
However, as a result of the increased use of programmable electronics in safety technology, it is no longer feasible to measure safety purely in terms of simple categories.
Furthermore, EN 954-1 did not provide information on the probability of failure. Directive 2006/42/EC will address these issues and achieve compliance through two standards – EN ISO 13849-1 and EN 62061.
The first of these will be quite familiar. EN ISO 13849-1 incorporates the categories from EN 954-1:1996 and examines complete safety functions, including all the components involved in their design.
In bringing machine safety up to speed, though, it goes a step further to include a quantitative assessment of the safety functions, based on a performance level (PL) that builds on the category approach. It also describes how to calculate the PL that can be achieved when several safety-related parts are combined into one overall system.
Any deviations from EN ISO 13849-1 are referred to IEC 61508, which includes the sector -specific standard EN 62061 – the other element of the new Directive.
In EN 62061, the performance level is described through the safety integrity level (SIL) and the safety functions identified from the risk analysis are divided into safety sub-functions. As a safety-related control system is made up of several subsystems, these safety sub-functions are assigned to the actual devices (hardware or software) that are the subsystems or subsystem elements. The safety-related characteristics of these subsystems are described through the SIL and Probability of Dangerous Failure per Hour (PFHD) parameters.
There is no doubt that the new Directive is more complex than its predecessor, so it’s fortunate that there are new, cost-effective technologies that can be deployed to make safety management easier. For example, integration of functions can ensure that all levels, or sub-functions, of safety operations area addressed through the same system, making the whole process more efficient as well as more convenient.
These systems can also play a major role in minimising downtime when a fault occurs and, crucially, are available at a lower cost than the older monitoring systems that readers may be familiar with – so they are also more cost-effective.
For instance, by integrating fault diagnosis into the safety control system, a great deal of time can be saved in tracing the location of the fault prior to repairing it. These same systems can also be put to good use in the early design stages of a machine safety system, by using simulation technology for a ‘dry run’. Clearly, flagging up potential problems before the system goes live is far better than discovering them once the system has gone live.
All of which highlights the benefits of a fully integrated system that brings together all of the key functions. These can include the monitoring of every aspect of safety - from post-top emergency buttons to light beams on conveyors – as well as facilitating fast location and diagnosis of faults. Furthermore, they operate from a centralised computer so that all of the information is readily accessible at any time.
Just as importantly, this is an approach that takes advantage of the latest technologies at a sensible price with no compromise to safety. And as the new Machinery Directive is a fact of life, and non-compliance isn’t an option, it makes perfect sense to choose the most cost-effective option.
Paul Considine is with Wieland Electric
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