The Keys to Operator Performance

Operator Error Rates Double on the Ninth Day of Work After Eight Days of Consistent Performance

By Aaron Hand

If you want to keep plant operators performing at optimal levels, how many alarms should you try to hold your system to? What's the best way to present procedures to those operators so they know what to do when they do face an alarm situation? And what's the best way to train them how to follow those procedures?

There's no shortage of anecdotal evidence to provide suggestions for these and other questions related to target alarm rates, worker fatigue, training, display colors and graphics, information hierarchy, and any number of factors that could contribute either to operators' ability to keep a plant running, or the likelihood of them bringing it to its knees, noted Dave Strobhar, principal human factors engineer at Beville Engineering. But hard research can be harder to come by, so several players in the petroleum industry joined forces about five years ago to get the research done.

Strobhar presented several interesting findings from the open industry-academia collaboration, the Center for Operator Performance , at ABB Automation & Power World last month in Houston. The group has found, for example, that the alarm-per-minute average isn't as magic a number as some might believe; that providing procedures that span several units improves performance over per-unit procedures; and that operator error rates do not rise linearly as one might believe, but instead double on the ninth day of work after eight days of consistent performance.

Driven by operating companies, the center also counts among its members three of the major DCS suppliers. The group was founded by Wright State University and Beville Engineering, which specializes in the analysis of operator performance issues.

An ongoing project with Penn State University is exploring the best way to present procedures, which are growing ever-more voluminous. Procedures tend to be organized by unit, each unit with its own set of procedures. "The problem is that in some cases I might have responsibility for more than one unit," Strobhar said. "I've seen console operators that have three sets of procedures in front of them because alarms are going off on three different units at the same time."

Modularizing those procedures instead could help companies tailor procedures to an individual instead of a unit, mixing and matching procedures that occur across several units.

With Louisiana State University, the center also has researched the ideal alarm frequency within an operating system. The group ran university students through a series of controlled experiments—with rates of one, two, five, 10 and 20 alarms per 10-minute period—to see how operator response time would measure up. "For one, two, five and 10 alarms in 10 minutes, performance was flat," Strobhar said. "But at 20 in 10 minutes, you see the alarms starting to queue up."

The first study ran the experiments in 10-minute bursts, so they then wanted to see how the numbers would be affected in one-hour time spans. In this case, they looked at 15, 20, 25 and 30 alarms per 10 minutes. Although there was a slight increase across the timeframes, it wasn't until 30 per 10 minutes that alarms started really queuing up more.

The conclusion was that 10 alarms in 10 minutes is in fact a very conservative number. "A lot of companies are beating themselves over their heads trying to reach that number," Strobhar said, noting that with better operators, better displays and other positive factors, that number could be more like 20–25 alarms per 10 minutes.

Of course, everyone wants to know the best way to make a "better operator." In a study with Klein Associates, the center looked into whether they could adapt the military's decision making exercises (DMX) to process plants. What they found was that it could be done easily with very short training sessions—one hour on occasion at the start of a shift, for example.

"You need to practice making decisions," Strobhar emphasized. "It's a skill like anything else." Through relatively simple, low-cost training sessions, companies have been able to keep their operators' skills honed, identify knowledge gaps and lost practices, and help build mental models.

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