Adopt machinery safety standards now says Pilz
As the Machinery Directive EN 13849-1 standards better reflect state of the art in Machine Safety System design, machine builders should adopt these standards sooner rather than later, says Kevin Ives, Machinery Safety Consultant at Pilz Automation Technology.
Ever since the first Machinery Directive, the recommended method of meeting all of the Essential Health and Safety Requirements (EHSR's) was to follow the advice in the 'Harmonised Standards'. These are standards that have been written in support of the directive.
As with the directives, the standards are being improved/upgraded with new versions being announced as being harmonised against the relevant directive. In 2007, the long awaited replacement for Safety of Machinery - Design of safety related control systems EN 954-1 was printed. This standard, EN 13849-1, has the same title and seeks to achieve the same ends but uses a risk-based approach. The standard introduces new criteria such as Diagnostic Coverage (DC) and Mean Time To Dangerous Failure (MTTFd), which need to be taken into consideration when designing the system.
The normal situation, when a standard is rewritten, is to allow a two-year 'change over' period. This is provided to enable manufacturers to modify their design and documentation to align with the new require-ments. Using this rule, EN 954-1 should have been revoked and replaced by EN 13849-1 in late 2009. But at this point, problems started to emerge. There were a few complaints made to the commission claiming that two years did not allow sufficient time for some manufacturers of components to provide the information and data needed to calculate failure rates, as required by the latest standard.
The commission agreed and therefore delayed revoking EN954-1 until the end of 2011. The latest list of harmonised standards that can be used to demonstrate compliance with the directive, does not list EN 954-1. This clouds the issue further. In theory, manufacturers cannot use standards that are not harmonised to claim compliance with the directive, but EN954-1 will not be revoked until the end of 2011. All of the machine-specific standards (C standards) that were written before the introduction of EN 13849-1 list EN 954-1 as an appropriate standard to use for the design of the safety-related controls. This raises even more confusion.
As the newer standards better reflect state of the art in Machine Safety System design, Pilz recommends that machine builders adopt these standards sooner rather than wait until the end of the transition period. Why? Because Pilz believes the future of automation and machinery lies in flexible, modular architectures, which will provide users with the high level of availability and adaptability required for agile, lean manufacturing plants. Modern plant and machinery will therefore require intelligent safety systems.
The new standard reflects this increased tendency to use electronic and programmable systems for safety rather than traditional electro-mechanical devices that were used when EN-954 was published. EN 13849-1 provides requirements for the design and integration of safety-related parts of control systems, including software. It has wide applicability as it applies to all technologies, including electrical, hydraulic, pneumatic and mechanical.
While acknowledging the decision of the EU, Pilz believes that the prob-abilistic approach of the new standards provides machinery designers and users with many advantages when assessing the reliability of safety systems. While there is an increased complexity in requirements to make design calculations, tools such as Pilz's PAScal Safety Calculator are available to calculate the required Performance Level (PL) and Safety Integrity Level (SIL). This software also evaluates a safety system design and then generates the necessary documents to be included in the machine's technical file. Training courses are also available on the new Machinery Directive 2006/42/EC.
Furthermore, those companies designing and manufacturing new machinery who apply one of the new standards now will not incur additional costs of design, validation, and documentation when the transition period ends in December 2011.
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