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ALL CHANGE - A RESPONSE TO EN ISO 13849-1

23 November 2012

The most common way of classifying safety related systems on machinery, Standard EN 954-1 ‘Safety related parts of control systems’, was withdrawn at the end of 2011 and replaced by EN ISO 13849-1:2008

For many years the most common way of classifying safety related systems on machinery has been to use the categories of the standard EN 954-1 ‘Safety related parts of control systems’. This standard was withdrawn at the end of 2011. After this date, EN 954-1 can no longer be used to provide a presumption of conformity with the European Machinery Directive. A new standard to replace EN 954-1 has already been published and is available for use: EN ISO 13849- 1:2008, or ‘Safety of machinery - Safety related parts of control systems’.

In some circumstances it may be possible to use alternative standards such as EN (IEC) 62061. However, the majority of designers will turn to EN ISO 13849-1 because the standard has been specifically drafted to provide a transition path for those who design systems to Categories per EN 954-1. It covers all control system technologies (electrical, mechanical, pneumatic and hydraulic) and can be used either for a complete system or for a subsystem. For the next few years EN ISO 13849-1 is likely to become the most commonly used standard for machine safety systems.

ISO 13849 is a globally recognized standard that was originally released in 2006 and adopted by the European Union as a required standard in 2009 as EN ISO 13849. The standard categor - ises safety levels, helping designers identify the level of safety necessary to effectively mitigate risk. It provides a transition path from the previous five ‘Categories’ (B, 1, 2, 3, 4) to the new classification of five ‘Performance Levels’ (a, b, c, d, e).

MORE RIGOROUS

Traditional machine safety standards are prescriptive, providing only guidance on structuring controls to meet safety requirements. With these older standards, a designer may have had difficulty understanding - or explaining - why a costly or seemingly sophisticated safety system was needed for a particular application. The newer international safety standards are more rigorous in their design requirements and provide quantifiable methodologies for machine builders to identify and document the potential hazards associated with a machine and the risk levels to users: To comply with ISO 13849-1, a machine builder must define and document the statistical probability of an unwanted occurrence or dangerous failure, or the calculated mean time to dangerous failure as part of the overall performance level (PL). To comply with IEC 62061, a machine builder must describe the amount of risk to be reduced and the ability of a control system to minimize that risk in terms of a safety integrity level (SIL).

TO COMPLY WITH ISO 13849-1, A MACHINE BUILDER MUST DEFINE AND DOCUMENT THE STATISTICAL PROBABILITY OF AN UNWANTED OCCURRENCE OR DANGEROUS FAILURE

Although a European standard, the implications of this change are global. Machine builders who proactively migrated to the international standards before the deadline have a competitive edge when serving global or multinational customers.

Increasingly, manufacturers – especially global or multinational ones – buy machines adhering to internationally accepted standards.

The standards are designed to assess risk over prolonged periods and boost long-term safety-system predictability – so operators gain confidence in the machine and increase productivity. Ultimately, a more predictable machine is a safer machine, and safer machines are more productive.

The newer international safety standards are more rigorous in their design requirements and provide quantifiable methodologies for machine builders to identify and document the potential hazards associated with a machine and the risk levels to users.

To comply with ISO 13849-1, a machine builder must define and document the statistical probability of an unwanted occurrence or dangerous failure, or the calculated mean time to dangerous failure as part of the overall performance level (PL).

To comply with IEC 62061, a machine builder must describe the amount of risk to be reduced and the ability of a control system to minimize that risk in terms of a safety integrity level (SIL). This documentation helps machine designers demonstrate actual risk reduction and justify the value of safety, including the costs of upgrades.

The SISTEMA software utility (Safety Integrity Software Tool for the Evaluation of Machine Applications) provides developers and testers of safety-related machine controls with comprehensive support in the evaluation of safety in the context of ISO 13849-1. The tool (available from http://www.dguv.de/ifa/en/ pra/softwa/sistema/index.jsp) enables modelling the structure of the safetyrelated control components based upon the designated architectures, thereby permitting automated calculation of the reliability values with various levels of detail, including that of the attained Performance Level (PL). The SISTEMA program is now available with selection of English language. SISTEMA may be downloaded and distributed to third parties free of charge.

Relevant parameters such as the risk parameters for determining the required performance level (PLr), the category of the SRP/CS, measures against common-cause failures (CCF) on multi-channel systems, the average component quality (MTTFd) and the average test quality (DCavg) of components and blocks, are entered step by step in input dialogs. Each parameter change is reflected immediately on the user interface with its impact upon the entire system. Users are spared time-consuming consultation of tables and calculation of formulae, since these tasks are performed by the software.

The final results can be printed out in a summary document.

Two resources have been created to use as an aid in determining the PL specs for a wide array of Rockwell Automation safety products. Data is now available in the form of an electronic library or PDF datasheet. Each can be used with IFA’s SISTEMA based on EN ISO 13849-1.

The availability of the electronic library and/or datsheet is evidence of the recognition by Rockwell Automation of the impact of EN ISO 13849-1 and other functional safety standards on industry. It is one of a number of activities and tools launched to provide help and guidance on how to deal with changes in legislation and standards in an ever more competitive environment.

The IFA SISTEMA software utility used with the Rockwell Automation SISTEMA libraries or PDF datasheet will provide machinery and system designers with comprehensive support in the evaluation of safety in the context of EN ISO 13849-1.

Key Points

  • EN ISO 13849-1:2008, or ‘Safety of machinery - Safety related parts of control systems’ replaces EN 954-1
  • New standards are designed to assess risk over prolonged periods
  • The SISTEMA software utility provides developers and testers of safetyrelated machine controls with comprehensive support in the evaluation of safety

 
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