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Alarms and events
Reducing unnecessary alarms through good design and alarm rationalization
Good alarm design through effective alarm rationalization is considered a best practice
strategy for dealing with excessive alarms resulting either from alarm floods or high numbers
of standing alarms.
Effective alarm rationalization removes alarms that do not meet the criterion of a necessary
alarm. It does this by ensuring that:
Only those events or states that require specific operator action within a short time (for
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example, 15–30 minutes) are configured as alarms.
If no operator action is required, then that event or state should either:
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Not be annunciated to the operator, or
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Be configured as an alert or notification rather than an alarm.
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The attributes of the remaining true alarms (for example, the trip point, priority, dead-
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band, alarm on/off delay and range extension) are set to provide the best compromise
between enabling quick operator action and avoiding nuisance alarms.
One approach to alarm rationalization is to use controller logic to reduce standing alarms and
flooding. For example, you might use controller logic to:
Combine multiple similar alarms into a single robust alarm (for example, by using logic
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to combine alarms from temperatures on the side of a tank), or
Cover changing equipment modes, or
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Suppress consequential alarms.
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On the other hand, you might consider using Alarm Configuration Manager (ACM) and
Dynamic Alarm Suppression (DAS) as more effective alternatives to customized controller
logic.
Despite best efforts to rationalize alarms, alarm systems can still suffer from alarms that are of
no immediate operational relevance. This might happen, for example, when the documented
operator action may not apply due to some circumstance not accounted for in the alarm design
process. Rationalization can therefore not entirely prevent excessive standing alarms or alarm
floods. Nevertheless it is a key component of (and indeed the very foundation of) a well-
designed and effective alarm system.
Dealing with alarms related to maintenance and repair
Often, operators put the point into the Disable or Journal-only state when this occurs, or
manipulate some other alarm attribute, such as alarm priority. However, putting an alarm into
"maintenance" means that this alarm will no longer protect the process.
The site alarm strategy should therefore identify a work process to:
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