March/April 2012
The Final Say

EN ISO 13849-1 emerging as key global machine safety design standard

By Richard Harris

The dawn of 2012 provided an appropriate time to look closely at the EN ISO 13849-1 standard. As of 1 January, the extended transition period for moving from EN 954-1 to EN ISO 13848-1 expired, with EN ISO 13849-1 obviating EN 954-1. Ironically, the original extension for the transition took effect on the same date that the new Machinery Directive became the governing document for safety and supply of machinery across the European Economic Area (EEA).

EN ISO 13849-1 was so closely associated with the Machinery Directive that many design engineers thought the standard was just applicable for machine builders exporting to Europe. While it is essential for those builders, the continuing development of global business and machine standards has made EN ISO 13849-1 a key one for machine builders everywhere, not just those exporting to the EEA.

Increasingly, large multinational enterprises are requiring a single machine design that can be shipped to any of their facilities. Designing machines to meet the EU Machinery Directive is the most practical way to meet this requirement; using EN ISO 13849-1 to demonstrate compliance with the directive is the easiest way to verify the design of the safety system.

A more rigorous approach

EN ISO 13849-1 provides safety requirements and guidance on the principles for the design and integration of safety-related parts of control systems (SRP/CS), including the design of software. For these parts of SRP/CS, it specifies characteristics that include the performance level required for carrying out safety functions. It applies to SRP/CS, regardless of the type of technology and energy used (electrical, hydraulic, pneumatic, mechanical, etc.), for all kinds of machinery. It does not specify the safety functions or performance levels that are to be used in a particular case.

Unlike EN 954-1, EN ISO 13849-1 addresses the programmable electronic safety devices increasingly specified in modern machines. The standard provides a quantitative approach to risk assessment and safety validation, whereby Performance Levels are used to evaluate the risk for a given safety function, as opposed to the Categories of EN 954-1. Performance Levels quantify the required and achieved level of safety in probabilistic terms, providing greater confidence that the required levels of safety yielded by risk assessments are accurate.

Under EN ISO 13849-1, safety system evaluation is based on the following factors:

  • Control Architecture, Category B, 1, 2, 3, or 4
  • Mean time to dangerous failure (MTTFd) of the parts
  • MTTFd of the system
  • Diagnostic coverage for the system in relation to its parts
  • Addressing common cause faults

EN ISO 13849-1 builds on the architectures of the earlier standards EN 954 and EN 1050 to create a more functionally reliable safety implementation. The process enhancements of the new standard include a risk assessment to define the basic architecture and category, a device selection process that prioritizes the inherent reliability of each component MTTFd, evaluation of MTTFd for the entire system, a process of diagnostic coverage, and final evaluation of common cause faults.

New windows of opportunities

The new standard will motivate manufacturers to re-evaluate their safety control systems. Components may need to be re-selected. Circuits and architectures may be simplified. The integration of safety PLCs will increase as they provide better diagnostic coverage and simplification to enable higher MTTFd.

With EN ISO 13849-1 taking full effect, an opportunity has emerged for machine builders to meet the growing need for "single machine design" on a global basis. Compliance with the Machinery Directive effectively creates the documentation necessary for this single global standard, and EN ISO 13849-1 will be the dominant standard used to document safety system design for the directive.

Further impetus for the standard is being provided by the Robotics Industry Association; their adoption of the ISO 10218-1 robot safety standard is driving use of EN ISO 13849-1 as a means to demonstrate design compliance.

"You do things when the opportunities come along," Warren Buffett once said. For those designing safety systems as part of machines, the formal arrival of EN ISO 13849-1 represents an excellent opportunity to leverage a standard for the new requirements of today's increasingly borderless marketplace.

ABOUT THE AUTHOR

Richard Harris is Channel Relations Manager with Omron STI. He has more than 15 years of experience with the company and more than 30 years in the automation industry.