The increasing global adoption of alarm management standards (ISA-18.2 and IEC 62682) is bringing the importance of alarm rationalization to the forefront. Rationalization is defined as the “process to review potential alarms using the principles of the alarm philosophy, to select alarms for design, and to document the rationale for each alarm.” (ISA-18.2 / IEC 62682)

Admittedly this definition may not be very understandable unless you already know what rationalization is. I define rationalization as the work process that determines which alarms are necessary, establishes their settings (e.g., priority, limit, classification), and documents their basis (cause, consequence, corrective action, time to respond) in a master alarm database. 

Even more helpful is to think about the definition of an alarm:

Alarm: An audible and/or visual means of indicating to the operator an equipment malfunction, process deviation or other abnormal condition requiring a timely response. (ISA-18.2 / IEC 62682)

Rationalization can be thought of as the process of reviewing potential alarms to verify that they meet the definition of an alarm. Parsing the definition above allows us to create the criteria below to assess whether an alarm is justified or not. Pretty simple and powerful.

  1. Must be targeted at the operator (understandable and actionable by the operator)
  2. Must indicate a problem or unexpected situation that is outside of normal process conditions (something is wrong)
  3. Must require a timely response from the operator to correct the abnormal situation (acknowledging the alarm or silencing the alarm horn don’t count) 

More than 80% of alarm management performance issues can be traced to alarms that don’t meet the definition (or criteria) above. 

Alarm rationalization is THE technique for eliminating the resultant alarm management issues. Performing a successful rationalization will improve all of the recommended performance metrics in ISA-18.2 / IEC 62682 as shown below. To see how, check out the webinar link included at the bottom of this post.

Alarm Management Issue

Solution Technique

ISA -18.2 / IEC 62682 Metric

Alarm Overload (Steady State)


1 – 2 alarms / 10 mins

Alarm Floods (After an Upset)

Rationalization, Advanced Alarming

< 1% of the time (≤ 10 alarms / 10 mins)

Chattering Alarms

Apply Deadband, On / Off Delays as part of Rationalization


Standing / Stale Alarms

Rationalization, Alarm Setpoint Determination

< 5 at any one time

Bad Actors / Frequently Occurring

Bad Actor Knockdown, Rationalization,

Top Ten makeup <5%

Redundant Alarms

Rationalization, Conditional Alarming

Impacts other metrics

Alarms with no Response

Rationalization, Alarm Response Procedures

Impacts other metrics

Alarm Priority not meaningful


Annunciated Priority distribution:  5% / 15% / 80%

So, alarm management problems really can be rationalized away!

To learn more about how alarm rationalization can eliminate the most common alarm management issues, check out this exida webinar.

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