February 1, 2010

How to Avoid Alarm Overload with Centralized Alarm Management

Brandon Parker, Black & Veatch

Define Alarm Response

The EEMUA says that every alarm should have a defined response and that responses may be designed to be reactive, proactive, or cognitive:

• Reactive alarms require direct action to something that has happened.

• Proactive alarms, in contrast, ask operators to take action before something happens.

• Cognitive alarms don’t necessarily require direct action, but they do require operators to change their reference or frame of mind.

An example of a cognitive alarm would be the starting of a standby pump based on either a primary pump trip or on a process condition requiring the standby start. Even though no direct action is required by the operator, the operator may need to change his or her frame of reference in order to fully understand the present plant configuration and plan future actions accordingly. Such actions might include directing plant maintenance to correct the tripped equipment or having the plant technician evaluate a process transmitter for faulty calibration that might lead to a false start of the standby equipment.

It should be noted that cognitive alarms are very easy to abuse in quantities designed as well as true value for the operations of the plant. Therefore, most cognitive alarms may be best treated as a journal event or an alert.

The EEMUA states that "Adequate time should be allowed for the operator to carry out a defined response." Upon first look, this alarm design principle may appear to be pure common sense. However, based upon findings in the industry, this may not be the case. Each alarm should be evaluated with respect to the logic that drives the alarm as well as the process reacting behind the alarm. The alarm threshold developed must provide the operator enough time to adequately react to the alarm (process) scenario based upon the designed alarm response. For instance, it is common for tanks, sumps, and other vessels to have level alarms based purely off of a level value.

For most applications, this may be sufficient due to the volume of the vessel as well as the service of the process. However, for some processes, further evaluation of the rate of increase/decrease may also need to be applied so that in times of a higher rate of change, the normal alarm threshold limits are adjusted to provide the operator enough time to react accordingly.