Safety Certification Demand Grows

Wednesday, March 7, 2012 @ 07:03 PM gHale


By Nicholas Sheble
“IEC 61508 applies to electrical, electronic, and programmable electronic safety-related systems, but does it also apply to mechanical products? Indeed it does,” said certified functional safety expert Chris O’Brien.

O’Brien spoke Wednesday during an exida webinar, “Mechanical Product IEC 61508 Certification.” He discussed the certification process for simple mechanical products like valves, actuators, and solenoid valves.

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O’Brien and engineers at exida developed a technique for calculating classified failure rates for electronic and mechanical devices according to the requirements of EN/IEC 61508-2 20 years ago, which was even before 61508 came out.

The tool is FMEDA (Failure Modes Effects and Diagnostic Analysis). It’s a systematic analysis technique to obtain subsystem/product-level failure rates, failure modes, and diagnostic capability.

In the early 2000’s exida concluded products working in safety critical applications had mechanical components and an FMEDA done without considering these mechanical components was incomplete and possibly misleading.

The fundamental problem in using the FMEDA technique was the lack of a mechanical component database that included part failure rates and failure mode distributions.

Using a number of published reference sources, the organization began development of a mechanical component database in 2003. Following several years of research and refinement, they were able to leverage FMEDA for use on combination electrical/mechanical components and purely mechanical components.

According to one of O’Brien’s charts during the webinar, there has been a six-fold increase in the safety certification of products in the last ten years. “We expect that trend to continue,” O’Brien said.

This only illustrates the rush to be compliant with the standard as means of protecting not only the public but also the viability and future of the vendors, original equipment manufacturers (OEMs), and end-users themselves.

IEC 61508 is the international standard for electrical, electronic-and-programmable electronic safety related systems. It sets out the requirements for ensuring that systems are designed, implemented, operated, and maintained to provide the required safety integrity level (SIL).

There are four SILs, which reflect the risks involved in the system application. SIL4 is to protect against the highest risks. The standard specifies a process that we can follow such that information about the system uses common terminology and system parameters.

Click here to listen to Wednesday’s webinar. Specifically, it describes the certification process for simple mechanical products like valves, actuators, or solenoid valves.

Topics include:
• IEC 61508 requirements for these certification projects
• The ability to get random failure rates for each failure mode, proof test coverage, and useful life via the FMEDA technique
• A comparison between “Cycle Test” results and FMEDA results
• There is also a discussion of design process issues and an explanation of user documentation requirements

Engineers who specify valves, actuators, and other mechanical devices for safety functions may find this webinar beneficial as will those interested in IEC 61508 certification for their mechanical products.

Nicholas Sheble (nsheble@isssource.com) is an engineering writer and technical editor in Raleigh, NC.



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