Safety expert urges machine builders to adopt latest standard

Machinery Directive 2006/42/EC has now been with us for some time. It was introduced in 2006 and published in the Official Journal (OJ) in September 2009; the publishing of any article, directive or notification of a standard in the OJ is the point at which the use of the document becomes mandatory.

Ever since the first Machinery Directive, the recommended method of meeting all of the Essential Health and Safety Requirements (EHSRs) has been to follow the advice in the Harmonised Standards. These are standards that have been written in support of the directive. A list of the standards applicable for use against the directive is printed in the OJ following the ratification of the directive.

As with the directives, the standards are being improved/upgraded with new versions being announced in the OJ as being harmonised against the relevant directive. In 2007, the long-awaited replacement for EN 954-1 Safety of Machinery - Design of safety related control systems was printed. This standard, EN ISO 13949-1 (and BS EN ISO 13849-1 in the UK), 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.

Transition confusion

The normal situation, when a standard is rewritten, is to allow a two-year changeover period. This is provided to enable manufacturers to modify their designs and documentation to align with the new requirements. Using this rule, EN 954-1 should have been revoked and replaced by EN 13849-1 in late 2009. The inclusion of EN ISO 13849-1 as a harmonised standard against 2006/42/EC was announced in the OJ in September 2009.

At this point, the problems started to emerge. There were some complaints made to the European Commission (EC) 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 EC agreed and therefore delayed revoking EN954-1 until the end of 2011 [see EN 954-1 extension confirmed as two years - Ed]. The latest list of harmonised standards that can be used to demonstrate compliance with the directive does not list EN 954-1. This list was printed in the OJ dated 20th October, 2010. 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 [see EN 954-1 harmonised to Machinery Directive 2006/42/EC - Ed].

All of the machine-specific standards (C standards) that were written before the introduction of EN ISO 13849-1 cite EN 954-1 as an appropriate standard to use in the design of the safety-related controls. This raises even more confusion.

Change for the better

As the newer standards better reflect the 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? Pilz believes the future of automation and machinery lies in flexible, modular architectures that 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 electromechanical devices that were used when EN 954 was published. EN ISO 13849-1 provides requirements for the design and integration of safety-related parts of control systems, including software. It has wide applicability as it is suitable for use with all technologies, including electrical, hydraulic, pneumatic and mechanical.

While acknowledging the decision of the EU, Pilz believes that the probabilistic approach of the new standard provides machinery designers and users with many advantages when assessing the reliability of safety systems. Although there is an increased complexity in requirements to make design calculations, tools such as the Pilz PAScal Safety Calculator are available to calculate the required Performance Level (PL) and Safety Integrity Level (SIL). This software also evaluates safety system designs 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, including one-, two- and four-day City & Guilds Machinery Safety Courses, Safety Design and CE Marking.

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.