Factory safety - Signing up for safety


There are now less than 12 months to go before machine owners and manufacturers are required to comply with the new Machine Safety Directive. Paul Considine of Wieland Electric suggests there are benefits to making the switch earlier

For the last year or so machine owners and manufacturers have had the choice of complying with the old Machine Safety Directive, based on EN 954-1, or the new Directive, in compliance with EN ISO 13849-1 or EN (IEC) 62061. Some have chosen to make the switch early, while others have opted to wait until the last minute – in this case 31st December 2011 – before adopting the new Directive.

As the deadline rapidly approaches, I would argue there are clear benefits to adopting the new Directive at the earliest opportunity – and the benefits offered by compliance with the new Directive outweigh any perceived disadvantages. The reasons for this lie in the fact the new Directive was introduced specifically to address inherent limitations in the old one.

The key issue here is EN 954-1 hasn’t kept pace with the changes in the industry. In particular, it focuses on calculated risk using a simple category system, whereby system behaviours are set against categories. The issue is the wider implementation of programmable electronics in safety systems means that such a simple system is no longer appropriate. Essentially the new Machinery Directive brings the regulations into line with what is already current practice and has the potential to improve safety.

So, for example, while EN ISO 13849-1 takes its core from the familiar categories in EN 954-1:1996 by examining complete safety functions, including all the components involved in their design, it takes things further. This is because it goes beyond this qualitative approach to include a quantitative assessment of the safety functions, based on a performance level (PL) that builds on the category approach.

The components and devices that make up the system require the following safety parameters:
s Category (structural requirement)
s PL: Performance level
s MTTFd: Mean time to dangerous failure
s B10d: Number of cycles by which 10% of a random sample of wearing components have failed dangerously
s DC: Diagnostic coverage
s CCF: Common cause failure
s TM: Mission time

In addition, EN ISO 13849-1 includes a description of how to calculate the PL that can be achieved when several safety-related parts are combined into one overall system, a very important factor in integrated safety systems. Any deviations from EN ISO 13849-1 are referred to IEC 61508.

Consequently, one of the major benefits of EN ISO 13849-1 is that it enables much wider use of programmable safety relays – enabling machine users to take advantage of the latest technologies. And it’s also worth noting the cost of these technologies has been greatly reduced in recent years, so if you’d felt they were too costly in the past you will find the situation has changed.

Programmable safety relays offer a number of time and cost savings and these begin at the early design stages and go right through to everyday operations. An obvious example is the ability to test safety circuits in the software before they are installed, which greatly reduces the time-consuming onsite testing and re-testing associated with stand-alone relays.

Similarly, working out the hard wiring feedback protocol is very complex using traditional methods whereas a flexible logic editor will flag up potential problems so they can be designed out.

Reductions in installation time are also possible because programmable safety relays are simply wired back to a central I/O point, so there is no need for the feedback loops and interconnecting terminals that go with stand-alone relays. Plus there is a reduction in the overall number of sub-systems – and the simpler a system is the less it is likely to develop faults.

Diagnostic functionality is also improved because programmable systems offer constant test outputs with full integrated fault diagnosis through the software – something that can’t be done with stand-alone systems. The upshot of this is less time is consumed carrying out manual fault tracing, as the diagnostics narrow down the search and allow engineers to home in on that problem area. In fact, it is often possible for such faults to be rectified without calling in specialist engineers. So downtime and disruption are minimised by faster fault tracing and rectification. And even when specialist input is required, at a hefty hourly rate, this will be minimised so expenditure on outside engineers is reduced.

Commissioning also benefits, as the software highlights any errors and helps to speed up the whole process, again saving time and money. And if the original settings are saved it is relatively easy to restore the system to its original settings if someone adjusts a parameter and finds it doesn’t work.

A further advantage is the full reporting structure, which enables reports to be generated automatically and added to the technical file, avoiding all of the time often dedicated to producing reports manually. These reports can also be used to focus maintenance resources in the areas that most need them.

As the new standards come in and facilitate the use of programmable safety relays, work by our company in this area has adopted a modular approach which also takes advantage of newer processing technologies. This has the effect of driving down costs down and producing highly affordable systems. As a rule of thumb, an ‘old style’ system using 3-4 stand-alone safety relays could be replaced by a programmable system for about the same cost, but with all the additional benefits. More extensive systems can be expected to deliver even greater savings, while paying a slightly higher price for smaller systems will often be worth it for the improved functionality.

EN 62061
It’s also important to note EN ISO 13849-1 will operate in conjunction with EN 62061, which is a sector-specific standard under IEC 61508. EN 62061, which is based on quantitative and qualitative examinations of the safety-related control functions, examines the overall life cycle from the concept phase through to decommissioning. It also describes the implementation of safety-related electrical and electronic control systems on machinery.

In describing performance level, EN 62061 uses the safety integrity level (SIL) and Probability of Dangerous Failure Per Hour (PFHD) parameters – and a number of safety sub-functions are derived from the risk analysis. This arrangement aligns to the sub-systems that make up a safety related control system, so that safety sub-function are assigned to the software or hardware devices that are sub-systems or sub-system elements.

Looking beyond safety
Safety is clearly of paramount importance and will be the overriding consideration. However, there are other benefits to early adoption of the new Machine Safety Directive to bear in mind as well. Not least of these is the awareness amongst end users that EN 954-1 is no longer suitable for many applications, even if they don’t understand the ins and outs of it. So there will be a concern that needs to be addressed by those with specialist knowledge, in providing accurate advice and explaining the options and their implications.

Such implications should also take account of other commercial issues, particularly for machine manufacturers or machine owners looking to sell their existing machines on the second-hand market. For example, compliance with the new Directive is likely to have broader acceptance throughout the European Union where machines may be moved between countries. Compliance is also likely to make CE marking more straightforward.

In fact the exchange or modification of machines is another factor that needs to borne in mind, as the Directive applies to any machine that is placed on the market – not just to new machines. In this respect, modifying a machine is regarded as placing it on the market so a new Declaration of Conformity may need to be issued, as would be the case with a brand new machine. The modified machine may also need to go through the CE marking process again. So compliance with the new Directive can be seen as a way of ‘future-proofing’ against difficulties that may arise in the future.

It’s clear some machine owners have delayed switching to compliance with the new Directive because they’ve been busy with other things and have felt they didn’t have the time to devote to getting to grips with the new Directive. There is also the possibility of a small increase in costs, which in the current climate could be another factor.

However, with the transitional period coming to an end there is no longer time for such luxuries and it will be necessary to bite the bullet and get to grips with the new Directive sooner rather than later. Here there is an ideal opportunity for electrical engineers, possibly working with companies that have particular expertise in this area, to play an important role in guiding end clients to the best solution. And, as outlined above, any such advice needs to take account of all of the factors, from the safety aspects right through to design advantages and the opportunity to cut life cycle costs through the application of the latest technologies.