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Practical Alarm Management for Engineers and

Technicians


Alarm Systems• Stand-alone Alarm

Annunciators with Lamps.• Alarm Systems within Process

Control Systems - DCS/SCADA

• Control Systems : Man-Machine-Interface (MMI).

• Alarm System is integrated part of Man-Machine-Interface.


Purpose of Alarms Alarms bring the following to the notice of the operator :

• Problems that need operator attention • Process changes that require corrective actions• Un-safe operating conditions before Emergency Shut-down of plant• Hazardous conditions• Deviations from desired/normal conditions


Functions of a Plant Operator• Safe and normal operation of plant /equipment• production at optimum levels• Identification of abnormal, hazardous and un-safe

plant / equipment conditions and take corrective actions

• Fault identification and communication of faults to maintenance


Functions of a Plant Operator

The functions and priorities of a plant operator change with the changing plant conditions, such as:

• During start-up, • Plant under stabilization,• During plant running in normal condition, • Plant in abnormal or up-set conditions, • Plant in emergency shut-down,• Plant in planned shut-down,• Mode of operation (Auto, Semi-auto, Manual)


Changing Plant Conditions & Functions of the Plant Operator

< Insert Figure 1-1 >


Functions of the Operator during plant Abnormal/Upset Conditions

< Insert Figure 1-2 >


Functions of Alarms

• To direct the attention of the operator towards the plant abnormal conditions which need timely assessment and/or timely corrective action(s).

• To guide the operator in an abnormal situation and help him to take timely corrective action(s) to bring the plant back to normal conditions.

• To provide feedback on the corrective actions taken by the operator in response to the alarms. (supplementary displays)


Key points for Designing an Effective Alarm System

• Present only relevant and useful alarms to the operator• Each alarm should have a defined response from the operator• Allow adequate time for the operator to respond to an alarm • Configure and present only good alarms


Present only Relevant & Useful Alarms

• Alarms that help an operator in monitoring and controlling the plant/equipment.

• Alarms should not be a nuisance or hindrance for the operator.• Operator’s time and attention should not be diverted on the

alarms which did not require any response or intervention from the operator and can be ignored.

• Otherwise, there is a possibility of the “Cry Wolf” effect with the operators feeling that they can afford to ignore alarms.


Each Alarm should have a Defined Response

• Response should be in the form of a Preventive and/or Corrective Action(s) or an Acknowledgement.

• At times the response to an alarm can be conditional. • Some alarms, such as "plant start-up sequence completed” or

“equipment stopped/tripped” inform the operator to change his response i.e. how he is monitoring or paying attention to the plant/equipment. (A mental response is all that is needed for the operator to make such a cognitive change.)


Allow Adequate Time for Response

• Adequate time for the operator to respond to the alarm.• The alarm should be given in advance to allow enough time for

corrective action in order to rectify the problem or fault.• Rate of alarms should not exceed the capability of the operator

to respond to the alarms.• Apart from responding to alarms, the operator also has various

other tasks/activities.• Alarm system design should be such that the overall functions

of an operator are manageable.


Average Workload imposed by the Alarm System on an Operator

W = R . T

Where: R – average rate of alarms presented T – average time taken to respond to the alarm

Note : While designing an Alarm System, Human Limitations

and Ergonomic Factors must be taken into account to make the Alarms System effective.


Configure & Present only Good Alarms

Characteristics of a Good Alarm :

• It must be relevant and not a spurious alarm• It must be presented on time, not in advance before the

operator response is needed, nor left too late, leaving no time for the operator to respond or take corrective action

• It must draw the attention of the operator towards important problems


Configure & present only Good Alarms

Characteristics of a Good Alarm:• It must clearly identify the problem and indicate the action(s)

to be taken.• It must be understandable. The alarm message should be clear

and easy to understand.• It must indicate the priority of the problem.• It must be unique. It should not be a duplication of another

alarm creating redundancy and increasing the alarm load on operator.


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