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Steps in an Alarm Management Project
Our alarm management philosophy has five points.
The alarm philosophy decided on by the team was used in every step of the process from there on. Basically, it says that an alarm should be informative and help the operator do his/her job. It should not distract the operator’s attention from the alarms and conditions that do require action. In general, although there are some exceptions, if there is not a defined response for the operator that will help correct the situation, it shouldn’t be an alarm.
From this point on, if I use the word “alarm,” I mean an audible alarm—one that sounds a horn that an operator has to acknowledge to shut off. “Advisory” parameters in the control system cover those issues for which there is no defined response, and changing alarms to advisory or log events is one of the options for reducing alarms.
After we firmed up our alarm philosophy, we selected alarm metrics. Monsanto established a corporate-wide initiative to improve alarm system performance at all locations after an incident occurred that was partly due to a poor alarm system design. A corporate alarm team was chartered which agreed on a set of metrics. The average alarm rate metric was the one most used in the Soda Springs project.
Figure 3. The Six Sigma cause-and-effect fishbone diagram of Monsanto’s alarm issues.
Average Alarm Rate: Average number of alarms per hour per day
Operator Loading: Number of 10 minute periods per day with 10 or more alarms
We also report on
Standing Alarms—alarms lasting longer than 24 hours.
Alarms per console point count
Alarms per plant process area.
Initially the metrics decided upon by the Soda Springs team were the same as those defined by the corporate team. For our primary metric, we use ten-minute periods during the day and compare our performance to the EEMUA (Engineering Equipment & Materials Users Association) guideline: no more than ten alarms in a ten-minute period.
The metrics were calculated by dividing each day into 144 ten-minute periods. The number of alarms that occur in each ten-minute period is used to calculate the Average Alarm Rate. For this project we used four-hour averages. The threshold value was set at 10, so only those periods with 10 or more alarms are counted. These data were used for the initial analysis. Later in the project, the average alarm rate was used for evaluation of improvements, since it is the best indicator of the overall state of the alarm system. The advantage was that it included all time periods during the day regardless of the number of alarms, and analysis became much simpler. We assumed—and later found we were correct—that reducing the average alarm rate would reduce all other metrics as well.
In next month’s issue, we will cover the measurement, analysis and improvement phases of the Soda Springs alarm management project.
Brent J. Thomas is a manufacturing technologist at Monsanto.
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