If the alarm list in a control room keeps scrolling, the problem is often not the process but the alarm system itself. When an operator must acknowledge dozens of alarms an hour, the one that really matters gets lost in the noise. Alarm management rebuilds alarms around the question “what will the operator do about this?” rather than “how many can we configure?”.
Every alarm should require an action from the operator. Anything that does not is not an alarm; it should be information, an event record or an indicator.
Why do alarm floods happen?
An alarm flood is usually hundreds of related alarms sounding in quick succession as a result of a single process event. Standards such as ISA-18.2 define an alarm flood as more alarms in a short window (typically ten minutes) than an operator can manage. Common sources are:
- Default limits: high/low alarms generated automatically for every analog point at commissioning, never reviewed against process knowledge.
- Repeating alarms: chattering signals, and alarms with no hysteresis or on-delay.
- Status counted as an alarm: normal operating events such as “pump stopped” or “valve closed” remain in the alarm list.
- Consequential alarms: the consequences of one root cause (for example flow, pressure and level alarms after a feed loss) all sound separately.
- Equipment under maintenance: alarms of out-of-service equipment are not suppressed and keep sounding (stale alarms).
How is alarm management done?
Guidelines such as ISA-18.2 and EEMUA 191 treat alarm management as a lifecycle: writing the philosophy, identifying and rationalizing alarms, detailed design, implementation, operation, maintenance, monitoring and assessment, management of change and audit. In practice the cycle becomes these steps:
- Write the alarm philosophy. What is an alarm, which priorities map to which colour, sound and response time, and who may change an alarm and when? Even a one-page document makes a difference.
- Measure the current state. Average alarms per hour, the ten most frequent alarms, flood events, average acknowledgement time and alarms active for more than 24 hours give a first snapshot.
- Rationalize. For each alarm, record the purpose, the likely consequence if it is violated, the operator’s expected action and the time allowed for it. An alarm with no answer is removed or turned into information.
- Prioritize. Priority is derived from the severity of the consequence and the response time; most alarms should be low/medium and only a few at the highest priority.
- Improve the design. Apply hysteresis, delays, state-based suppression (for example suppressing related alarms when equipment is stopped) and grouping of consequential alarms.
- Monitor and manage change. Report the indicators regularly and require an approved change process for adding alarms or changing limits.
Which indicators should track performance?
| Indicator | What it tells you | Commonly cited target (indicative) |
|---|---|---|
| Average alarm rate per operator | Steady workload | A few alarms per hour; EEMUA 191 cites about one alarm per ten minutes on average as “manageable” |
| Time in alarm flood | Overload moments | A small percentage of time; ideally close to zero |
| Top 10 most frequent alarms | The source of the noise | Only a small share of total alarms (e.g. 20–30%) |
| Number of stale alarms | Forgotten or unsuppressed alarms | Very few; method: alarms active for more than 24 hours |
| Priority distribution | Whether priorities are meaningful | Few high, mostly low/medium |
Target values are given in standards and industry guidance as indicative; they should be assessed together with your plant’s process risk and number of operators. The number should show the direction of the trend, not be the goal itself.
Think of alarms and operator graphics together
Reducing the alarm count alone is not enough; operator graphics should show an alarm in process context. Being able to see which equipment the alarm belongs to, what to do and the related trend or procedure in one click shortens response time. That is why alarm projects often run together with DCS/PLC programming and graphics improvement.
Alarm events should be backed up regularly along with maintenance and change records (automation backup and restore). On an existing system, your history data can be reviewed for alarm analysis within ASP Otomasyon’s service and consulting offerings.
Frequently asked questions
What is an alarm flood?
It is when more alarms sound in a short interval than an operator can manage. It typically results from the consequences of a process event or from poorly configured alarms.
Does reducing the alarm count reduce safety?
No; done properly it increases it. Rationalization leaves only alarms that need action and raises the chance that important alarms are noticed. Safety functions are protected separately.
How long does an alarm management project take?
It depends on scope. An initial measurement and a clean-up of the most frequent alarms deliver gains quickly; full rationalization proceeds unit by unit.
