Simplified safety: embracing performance-level risk assessment

Like it or not, new standards requiring quantifiable, statistical safety analyses are coming…and they will change forever how you evaluate hazards in your plant.

06/14/2011


There’s no avoiding it any longer. Performance level risk assessment is here. Unquestionably, it is not the most popular option for measuring and mitigating hazards, but thanks to new global-based standards, it is the method most manufacturing will have to use.

Why? And what has brought U.S. industry to this point? A number of factors: principally a twice-postponed international machine safety standard known as EN ISO 13849-1, which will finally—yes, really—take effect on January 1, 2012. Companies selling abroad will have to comply with this standard if they want to market overseas. And compliance means performance-level-based risk assessment. Despite sharp criticism from most U.S. sources about the complexities and difficulties of applying this standard and standards like it, the performance-level assessment methodology it requires does, in many ways, help better define statistically weighted hazards. According to Scott Krumwiede, manager of manufacturing solutions at RWD Technologies, a division of General Physics Corp., it essentially removes subjectivity from the analysis.

Why performance-level assessment?

Performance-level assessments have their roots in SIL (safety integrated level) designations. “We used to use category assessments and then SIL assessments,” said Krumwiede, “with SILs the broader, more in-depth and refined approach. Performance-level-based assessment goes yet a step farther, applying a more comprehensive level of scrutiny to everyday control systems. It will have a positive impact on safety overall.”

Among the most difficult aspects of performing standard risk assessments was assigning a hazard weight to an assessed outcome. “For instance,” Krumwiede went on, “if I decide it’s a Category 3 hazard, how did I arrive at that conclusion? How much weight did I to assign to each issue? Earlier systems required interpretation. Perhaps it was a Category 3 hazard, perhaps not.”

In Krumwiede’s estimation, performance-level risk assessment offers a more refined and accurate look at a hazard. “It helps put the cause of a hazard into statistical balance,” he explained. “If it is an electrical hazard, for example, we look at all the components, at failure rates, at other factors that change the way the end result is weighted. A performance-level process takes us through all the components and assesses each one. Older methods rely more heavily on the experience of the person making the assessment.” Everything in a performance-level-based standard, including and especially the process of weighting hazards, is based on statistical calculations. Essentially EN ISO 13849-1 requires component manufacturers proactively define product performance, thereby helping OEMs and end users with the assessments and calculations outlined in the standard. “Manufacturers must develop performance-level ratings for their products and give them to their customers,” said Krumwiede. “Those values can be plugged into the risk assessment equation, eliminating the need to weigh a hazard based on experience. It takes a large part of the decision-making process out of the hands of those using a component and places the burden on the manufacturer to define product performance.”

Why all the fuss?

What then are the drawbacks of this approach? First, noted Krumwiede, any discussion about the pros and cons of the standard or its methodology are beside the point. “There will be no more delays. We have no choice. EN ISO 13849-1 will take effect in 2012. No matter what you think about it, if your company wants to sell abroad, it will have to comply with the standard.”

Complexities and complaints aside, the new way carries discernable benefits. MTTF (mean time to failure) ratings on equipment and components give OEMs and end users selectivity in what they put in their equipment. “When a system is designed,” said Krumwiede, “its components will now carry these ratings. Some will have a longer MTTF than others. If a project has a 2-year lifecycle, you wouldn’t necessarily have to select components with 100-year lifecycles, even if they were available. Based on MTTF, a more economical selection could be made with reasonable confidence.”

Further, performance-level assessments are forcing component manufacturers to categorize components in terms of how long it will take for a component to fail. “If I pick relay A,” Krumwiede continued, “I know it will cycle, for example, 100,000 times before reaching its predicted failure. If I pick relay B, it will cycle a million times before its predicted failure. Relay B may cost $60 while relay A may cost $6; both will do the job. Is the failure of the relay critical to the process? If it is, spend the extra money. If not, select the less expensive one and consider it a consumable.”

Krumwiede noted we have not yet seen performance-level-based assessments change how facilities economically justify projects, but admitted they may impact ROI calculations down the road. “If you have hard numbers to plug in, these ratings could become a requirement in an OEM specification. For example: ‘I want a machine with such-and-such a performance level.’ I haven’t seen anyone put out RFQs with that kind of information yet, but it certainly is something that could happen.”

What lies ahead?

U.S. manufacturers need to be aware that compliance with EN ISO 13849-1 is required only if they do business overseas. “If you only operate in the U.S.,” said Krumwiede, “this standard won’t affect you until and unless a U.S. standards-setting body incorporates or adopts it—and that’s not likely to happen anytime soon. However, so much manufacturing is global today that, in reality, very few companies are unaffected.”

Those faced with conducting performance-level assessments might find coping with the rigors of EN ISO 13849-1 a bit easier by turning first to another standard: ISO TR 14121 2007, Safety of Machinery—Risk Assessment. “It offers guidance for moving from frequency and severity to basic performance-level assessment, but at a less complicated level,” suggested Krumwiede. “It introduces manufacturers to other standards that use performance-level estimation and forms a kind of bridge to the thinking put forth in EN ISO 13849-1. It is not an end in itself, but may be a helpful stepping stone.”

What is the bottom line? “Saddle up!” smiled Krumwiede. “Get to know EN ISO 13849-1 really well. It admittedly presents a significant challenge, one that may lead to redefining acceptable risk. The bad news is there is no way to avoid it. If you sell abroad, you must comply; you will have to do performance-level risk assessment. The good news is that mathematical analysis is probably a better, more efficient methodology. The new standard just may be a better way to do things…and it won’t be so hard once you get the hang of it.”

Contact Scott Krumwiede at SKrumwiede@gpworldwide.com or visit his company website at us.gpworldwide.com. For more on risk-assessment-related safety products, visit Siemens Industry at www.siemens.com. More information on the standards is available on the International Organization for Standardization website at www.iso.org.

For more information on safety automation products, visit the Siemens Industry website at www.siemens.com. www.usa.siemens.com/safety This article was submitted for the Siemens Simplified Safety custom newsletter. See other articles in the Siemens Simplified Safety newsletter. www.controleng.com/newsletter/siemens-simplified-safety.html



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