Guidelines on Alarm Systems of Distributed Control System (DCS)

Some guidance on alarm settings, human interface (alarm presentation), alarm processing and system management controls for both safety related and other alarm systems include the following:

  • The alarm system should be designed to appropriate safety integrity level (SIL 1 or 2) with the designated reliability.

  • The alarm system should be independent from the process control system and other alarms unless it has also been designated safety related.

  • The operator should have a clear written alarm response procedure for each alarm which his simple, obvious and invariant, and in which he is trained.

  • The alarms should be presented in an obvious manner, distinguishable from other alarms, have the highest priority, and remain on view at all times when it is active.

  • The claimed operator workload and performance should be stated and verified.

Alarms which are not designated as safety should be carefully designed to ensure that they fulfill their role in reducing demands on safety related systems.

For all alarms, regardless of their safety designation, attention is required to ensure that under abnormal condition such as severe disturbance, onset of hazard, or emergency situations, the alarm system is remains effective given the limitations of human response.

The extent to which the alarm system survives common cause failures, such as a power loss, should also be adequately defined.