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EN 954-1 and ten reasons NOT to use it

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Jon Severn, editor of MachineBuilding.net, suggests ten reasons not to use EN 954-1 for designing safety-related control systems for machinery, but rather to use EN ISO 13849-1 or EN (IEC) 62061.

EN 954-1 and ten reasons NOT to use itCEN has announced that the transition period during which machine builders can choose between EN 954-1 and EN ISO 13849-1 has been extended - see this article: EN 954-1 extension confirmed as two years. No doubt some machine builders will welcome this, as EN 954-1 is easier, simpler and cheaper to work with than either of the alternatives, EN ISO 13849-1 or EN (IEC) 62061. However, there are plenty of reasons for not using EN 954-1. And these views are not just those of a website editor - see, for example, EN 954-1 extension may delay advancements in machine safety (from Schneider Electric) and EN 954-1 extension - advice from Pilz.

1 - Machines designed to EN 954-1 may not be as safe

It is widely accepted that EN 954-1 is inadequate for use with complex or very hazardous machinery, so applying this standard instead of EN ISO 13849-1 or EN (IEC) 62061 could result in machinery that is potentially 'less safe.' Bear in mind also that EN 954-1 was first published in 1997 so by now it does not reflect the state of the art. Aside from the use of software within safety-related control systems, for example, EN 954-1 does not address the handling of common-cause failures or the adequate frequency of diagnostic tests on category 2 systems.

2 - Pressure from customers

Because of the inadequacies associated with EN 954-1, together with the recent uncertainty over the future of EN 954-1 (see this article: EN 954-1 final decision - transition extension confirmed) and the desire to 'future-proof' their machines (see below) machine specifiers may start to insist that EN 954-1 is not used. In particular, customers are likely to prefer machines with safety-related parts of control systems designed using EN ISO 13849-1 or EN (IEC) 62061, rather than those designed to a standard that does not reflect the state of the art.

3 - Compliance with the new Machinery Directive 2006/42/EC

EN ISO 13849-1 and EN (IEC) 62061 are both founded on the concept of functional safety - which EN 954-1 is not - and are better aligned to the new Machinery Directive 2006/42/EC. As such, the two newer standards are inherently better suited to the design of machines destined for the European market.

4 - EN 954-1 is not an international standard

Whereas both EN ISO 13849-1 and EN (IEC) 62061 are international standards and widely recognised in global markets, EN 954-1 is a European standard (EuroNorm). If machinery is destined for markets outside Europe, then EN 954-1 is unlikely to be applicable.

5 - EN 954-1 is no longer cited in Type C standards

While it is true that some Type C standards have not yet been revised in line with EN ISO 13849-1, many of them have and the remainder will be in time. Once amended, the standards will no longer cite EN 954-1, which could put machine builders in a difficult position when CE marking their machines. Although EN 954-1 is listed in the Official Journal of the European Union (see 'EN 954-1 harmonised to Machinery Directive 2006/42/EC'), if a Declaration of Conformity cites a Type C standard that refers to EN ISO 13849-1, then EN 954-1 cannot be used for the design of the safety-related parts of the control system.

6 - Customers want 'future-proof' machines

Machines often undergo modifications during their lifetime, which could be by the customer, OEM or a third-party. Depending on the nature of the modifications (for example, if the machine's performance is changed or there are alterations to the safety-related control system) it may be necessary to CE mark the machine again. If the machine was originally designed to EN 954-1 but has to be freshly CE marked after EN 954-1 has been withdrawn, parts of the control system might have to be redesigned to comply with the new standard. Customers - and OEMs - may therefore want to avoid the risk of this potentially costly situation arising by specifying that either EN ISO 13849-1 or EN (IEC) 62061 is used for the original design.

7 - EN 954-1 restricts the use of new technology

One of the major drawbacks of EN 954-1 is that safety-related control systems are effectively restricted to the use of relay logic. Modern configurable and programmable safety controllers offer machine builders and users considerable opportunities for cost savings. For example, complex logic can be more easily implemented using a configurable/programmable controller than by using relays, and the potential for wiring errors is greatly reduced. Furthermore, improved diagnostics can cut downtime and enable non-experts to troubleshoot machine stoppages. Note that safety devices such as laser are scanners typically run software on microcontrollers, so validation of the safety-related parts of the control system cannot be performed adequately using EN 954-1.

8 - EN 954-1 can waste money through over-engineering

The 'risk graph' in EN 954-1 tends to be used (incorrectly) as a risk assessment tool, leading users to designate a 'safety category' for a particular machine. For a machine on which there is one high-risk area, all too often the designer treats the entire machine as 'category 4' and therefore over-specifies much of the safety-related control system, including all of the guard switches. This results in excessive expenditure. In contrast, EN ISO 13849-1 can enable designers to create safety-related control systems that require fewer components and less wiring, with many of the components being to a lower specification and, therefore, less costly.

9 - Free software for the new standards

A complaint often levelled against EN ISO 13849-1 and EN (IEC) 62061 is that they require more complex calculations to be performed than when using EN 954-1. However, the SISTEMA software package can be downloaded free of charge from the German BGIA website and greatly assists the calculations required in EN ISO 13849-1. Alternatively, some machine builders have found that control systems for relatively simple machines can be designed with the aid of spreadsheets; creating the first spreadsheet is time-consuming, but subsequent designs for similar machines can be completed comparatively easily. Other software utilities are available for use with both EN ISO 13849-1 and EN (IEC) 62061: from Pilz, see PAScal safety calculator - a review by MachineBuilding.net and from IBF Automatisierungs und Sicherheitstechnik see this review: IBF Safexpert 5.4 CE marking software (NB newer versions of both packages are now available).

10 - Stop using EN 954-1 for peace of mind

If any one of the nine reasons above has sown a seed of doubt in your mind, switching from EN 954-1 to either EN ISO 13849-1 or EN (IEC) 62061 will give you peace of mind. And if you are in any doubt about how to proceed with the new standards, there are plenty of companies that can provide assistance through training courses, seminars, guidance documents, software, FAQs on their websites and facilities for asking questions of technical experts.

No doubt some people will read the above and decide to continue using EN 954-1, despite the arguments against. However, any comments on the above can be emailed to the author at .

Meanwhile, see this comment already received: 'Rockwell urges machine builders to use EN ISO 13849-1'.

 
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