Here to stay
By Mike Miller, FS TÜV Expert, Global Safety Market Development, Rockwell Automation
Reprinted with permission from The Journal from Rockwell Automation and Our Partners, copyright 2011 by Rockwell Automation, Inc. and Putman Media, Inc.
Compliance with international safety standards gives US (United States) machine builders a competitive advantage, while providing manufacturers with more reliable machines.
Satisfying global customer demands for greater safety and reliability
International safety standards are reshaping how global machine builders approach machine safety system design. Do machine builders in the United States need to comply?
The answer depends on the machine builder's competitive goals and customer base. For those serving or seeking to do business with global customers, the answer is a definitive "yes". For those aiming to satisfy customer demands for safer, more reliable machinery, the answer also is "yes".
Machine builders who currently serve the needs of North American end users alone should also follow International Standards as a guideline for best practice — not only to gain a competitive edge domestically, but also as a preparatory measure in case they later expand to pursue global customers.
What are the relevant standards?
Increasingly, global and multinational manufacturers around the world are moving towards following internationally accepted machine-safety system standards to improve flexibility, reduce liability and take advantage of technologies supported by updated standards.
The European Union standards bodies CEN (Comité Européen de Normalisation, the European Committee for Standardization) and CENELEC (Comité Européen de Normalisation Electrotechnique, the European Committee for Electrotechnical Standardization) elected to mandate two of the most rigorous machine safety standards: ISO (International Organization for Standardization) 13849, Safety of machinery – Safety-related parts of control systems, Part 1: General principles for design, together with Part 2: Validation, and IEC 62061, Safety of machinery – Functional safety of safety-related electrical, electronic and programmable electronic control systems. This means that any machines shipped into or out of Europe must comply with one of the two standards following the final withdrawal of EN 954-1 in 2011.
This also means the many machine builders in the United States who design machines destined for Europe will need to comply with the European adoption of these International Standards. They also must continue to meet a variety of US standards, such as ANSI (American National Standardization Institute), ASSE (American Society of Safety Engineers), ASME (American Society of Mechanical Engineers) and OSHA (Occupational Safety and Health Association).
Increasingly, manufacturers, especially global ones, are seeking machine builders that understand how to design machines in line with these International Standards. In some cases, it's mandated to do so in order to be able to manufacture in these countries.
More and more, manufacturers follow internationally accepted standards to provide streamlining of their global plants. Such manufacturers can be assured they're investing in safe machinery that helps protect workers and equipment and that displays excellent reliability. They understand the business value inherent in investing in contemporary machine safety systems and standardizing their plants worldwide. These upfront investments help reduce incidence, minimize training and maintenance costs, and often increase productivity.
"As a global manufacturer with over 180 locations worldwide, we focus on international safety standards to ensure that machine operators in all locations have the same level of confidence in the machine's safety system," says Mike Douglas, General Motors' senior manager and consultant, Global Health & Safety, Design, Standards and Technologies.
"International safety standards represent the highest confidence level in achieving machine safety, resulting in more predictable, reliable machines," he notes.
New elements of time and risk help justify costs
Historically, machine control-system safety standards were prescriptive in nature, simply providing guidance on the structure of control systems to help ensure safety requirements were met. The newer international safety system standards are more rigorous in their design requirements and provide a more quantifiable methodology to help ensure overall safety system performance and integrity.
The International Standards add two very important elements to the definition of the reliability of the machine's safety function: time and risk. These two elements help machine builders take advantage of a more methodical approach to safety system design.
Both International Standards require machine builders to identify and document the potential hazards associated with a machine and the risk levels the hazards present to users.
The safety system is then designed to the level of risk associated with the hazards present on the machine. This allows the machine designer to design the safety system to the correct functional level.
Appropriate documentation proves a machine's level of safety, designers can better justify a need for a safety system upgrade, and operators can be more confident in the reliability of a machine's safety system.
To comply with ISO 13849-1, a machine builder is required to define and document the statistical probability of an unwanted occurrence or dangerous failure, or MTTFd (the calculated mean time to dangerous failure). A machine builder must also define and document the machine's structure, or hardware configuration (often called categories), and its ability to detect dangerous failures, called diagnostic coverage.
Each component in a safety system must have an assigned probability of, or mean time to, dangerous failure. By adding the "time" element and the ability to detect dangerous failures to the existing safety structure approach, the ISO 13849-1 standard forces the designer to validate that the control system does what is required of it.
This standard applies beyond electric/electronic systems to include mechanical, hydraulic and pneumatic safety-related parts of the control systems.
To comply with IEC 62061, a machine builder is required to describe the amount of risk to be reduced and the ability of a control system to reduce that risk in terms of SIL (safety integrity level).
The machinery sector uses three SILs; SIL 1 is the lowest and SIL 3 is the highest. A SIL applies to a safety function. The subsystem making up the system that implements the safety function must have an appropriate SIL capability. Conducting a risk assessment helps a designer define the amount of risk to be reduced and the SIL claim limit that safety-related control function must meet.
Both the documentation process and the performance-based approach help make it easier for designers to quantify and justify the value of safety.
Previously, a designer might have had difficulty understanding – or explaining – why a costly or seemingly sophisticated safety system was needed for a particular application. Now, with the ability to quantify circuit reliability through specific performance and system integrity calculations, the designer can show the value in terms of actual risk reduction and thereby more easily justify the value of safety.
Furthermore, machine designers can leverage the required documentation to cost-justify a system upgrade that includes a more effective safety solution.
Requiring designers to document risks and the control system's ability to reduce those risks also increases a machine builder's confidence in the reliability of the safety components. Because the standards are designed to assess risk over a prolonged period, a machine's safety system can be more predictable in the long term. This can help enhance a machine operator's confidence while operating a machine and, in turn, can help increase protection and productivity on the job.
Ultimately, a more predictable machine is a safer machine, and a safer machine is a more productive machine.
Help from automation suppliers
In support of the industry's move toward internationally accepted standards, automation suppliers are taking measures to help machine builders understand fully the benefits and to meet the requirements of machine safety control systems standards. These include getting safety products certified and offering education, training programs and tools.
For example, Rockwell Automation provides a product library file designed for use with the SISTEMA calculation tool from Germany's IFA, and a PDF file designed for manual calculation. Functional safety data, including the SISTEMA calculation tool and library, can be downloaded at the Rockwell Automation Safety Solutions Portal.
Also available on the Rockwell Automation Safety Solutions Portal are white papers, animations on safeguarding techniques and technologies, and archived versions of a functional safety webinar series.
Global standardization is here to stay
The machine safety world continues to change, and the European Union's mandate of rigorous international safety standards represents the global trend toward standardization. Ultimately, this will provide more flexibility to achieve and cost-justify designs, safer machine control systems and more consistency across plants.
While machine builders who plan to serve the needs of North American end users alone don't need to comply with the requirements of International Standards, they should consider following International Standards as a guideline for best practice, enabling them to gain a competitive edge domestically.
Find out more
- IEC 62061Safety of machinery - Functional safety of safety-related electrical, electronic and programmable electronic control systems
- ASME American Society of Mechanical Engineers
- ANSI American National Standards Institute
- ASSE American Society of Safety Engineers
- CENCEN The European Committee for Standardization
- CENELEC The European Committee for Electrotechnical Standardization
- ISO 13849-1Safety of machinery -- Safety-related parts of control systems -- Part 1: General principles for design
- ISO 13849-2Safety of machinery -- Safety-related parts of control systems -- Part 2: Validation
- OSHAOccupational Safety and Health Association