The purpose of an alarm is pretty straightforward - to draw the operator’s attention to an abnormal situation that requires action in order to prevent an undesired consequence. Alarms that don’t meet this principle often become nuisance alarms. A nuisance alarm is defined as:

“an alarm that annunciates excessively, unnecessarily, or does not return to normal after the correct response is taken (e.g., chattering, fleeting, or stale alarms). – ISA-18.2”

In many process plants, operators get a large number of nuisance alarms (you may recognize these as the alarms that are “permanently” displayed on the alarm summary screen). Nuisance alarms are bad because they desensitize the operator, causing them to ignore, and potentially miss, critical alarms. This is sometimes called “The Boy Who Cried Wolf” phenomenon.

To see a video of the Boy Who Cried Wolf adapted to nuisance alarms in a process plant, please watch the video “The Story of the Sump Pump Nuisance Alarm”

Developing a thought process that it is OK to ignore alarms is dangerous. This is not the operator’s fault; it is an alarm management failure. The operator’s job is to interpret a myriad of data, understand what is happening to the process now, and project the impact of current events to the future (situation awareness). Nuisance alarms give false indications of what is going on, impact the operator’s ability to concentrate, and hurt situation awareness.

Once operators start to ignore alarms, how do they know when to stop? How do they determine what is a real alarm and what is a false indication that can be ignored? Are they always right? Does the set of alarms that can be ignored without consequence change based on process conditions?

How can we count on operators to respond reliably to an alarm that is used to reduce risk (e.g., as an independent protection layer or safety (related) alarm) if they learn that it is not necessary to respond to all alarms? These questions go to the heart of alarm system integrity.

Stay tuned as future blogs take on the subject of how to address nuisance alarms in greater detail.

Tagged as:     Todd Stauffer     Nuisance Alarm     ISA-18.2     Alarm Management  

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