Considerable activity has been expended in the process industries to improve plant alarm systems. An underlying assumption has been that an alarm system could be created that had certain inherent characteristics (i.e., the system is either good or bad). Research by Meyer and Bitan into alarming for intensive care situations shows that such an assumption is likely invalid (Meyer, J. and Bitan, Y. "Why better operators receive worse warnings". Human Factors, Vol 44, No. 3, Fall 2002, P343-353.)
It has been proven that low validity/unreliable alarms (cry-wolf alarms) degrade alarm system effectiveness and operator performance. The work of Meyer and Bitan shows that the capabilities of the operator can and do interact with the alarm system to alter its predictive value. Surprisingly, good operators are more likely to have their performance levels drop, because they can anticipate process changes and thereby expect alarms to occur. As a result, the predictive information provided to the good operator is of less value than that provided to the poor operator. The net effect, unfortunately, is a less valid alarm system (lower predictive value) for the better operators. Other research has shown that as the predictive value of alarms decreases, operators are less likely to respond, respond more slowly, and/or assign less weight to the alarm information.
The authors' primary thrust is that an operator's performance alters the value of the alarm system, but what are the implications for control of hazardous processes? At a minimum, there are two major implications. First, we can no longer judge an alarm system independent of the individuals using it. Second, the variance in board operator performance will need to be minimized such that the alarm system can be configured for a narrower, and higher, level of expertise.
RELATED EXTERNAL MEDIA
|Consortium Reports New Findings on Alarm Rates||Automation World|
|How Many Alarms Can An Operator Handle||Chemical Processing|
|Impact of Alarm Rates and Interface Design on Operator Performance||Automation World|
|Operator Interfaces: Moving from Comfortable to Most Effective||Automation World|
|Operator Performance as a Function of Alarm Rate and Interface Design||Mesa.org|
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