The ISA-18.2 and IEC 62682 alarm management standards provide recommended targets for average alarm rate and for alarm floods - a condition during which the alarm rate is greater than the operator can effectively manage (e.g., more than 10 alarm per 10 mins) Ref ISA-18.2. During alarm floods the chance of an operator missing an alarm or making a mistake is increased. The following table taken from IEC 61511 shows how the reliability of humans is impacted by stress.
|Human Performance||Probability of Failure (IEC 61511/ISA-84)|
|Trained, no stress||1.0% to .01%|
|Under stress||50% to 100%|
Consequently, alarm floods reduce the effectiveness of alarms used as safeguards or independent protection layers and increase the chances of process safety incidents.
Alarm rationalization is typically effective at reducing average alarm rate. To alleviate alarm floods, advanced alarming techniques such as alarm flood suppression may be required. SILAlarm™ provides the ability to define and document alarm flood suppression requirements so that they can be implemented in the control system. For DeltaV users, alarm flood suppression can be configured automatically in DeltaV via bulk edit from SILAlarm using new modules created by Emerson and exida.
SILAlarm provides the ability to define alarm flood suppression requirements systematically via a standard interface.
- Trigger conditions (required and / or voted) and associated logical expressions (for implementation in the control system)
- Maximum Suppression Time
- Unsuppression Behavior (Unsuppress all, Unsuppress none, Unsuppress Inactive alarms only)
- Common Alarm for annunciation to the operator (when other alarms are suppressed)
- Alarms to be suppressed*
- Suppressed priority (to change the alarm priority dynamically during a flood)
- Audit & Enforce changes detected in the control system configuration
- Management of Change
- Description text: Group, Required, Voted conditions for display on HMI faceplates and graphic screens.
*Display of priority, classification and use as a safeguard or IPL is shown to help assess whether the alarm can be suppressed