2. Use of a Master Alarm Database (MAD) to facilitate control and management of changes to the alarm configuration parameters;
3. Improvements to the Human Machine Interface (HMI), such as better graphics design for alarm management and easy access to alarm help;
4. Mode-based alarming;
5. Testing of alarms; and
6. Alarm suppression technology.
Let's now consider these separately, with the understanding that some may not apply everywhere.
1. Full rationalization. A considerable effort is required to rationalize all of the alarms configured for a particular plant area. The number of alarms that can be rationalized by an experienced team is often quoted at around 100 per day.
The benefits of full rationalization are that alarms activated during incidents are better designed and, thus, less likely to contribute to unnecessary alarm floods. One aspect of rationalization that deserves special attention is the use of appropriate dead-bands and debounce timers (when alarms are activated or cleared). An ASM Consortium project confirmed that more extensive use of debounce timers can be particularly effective when some alarms otherwise would chatter during alarm floods . The ASM study found that the use of debounce timers and other configuration changes reduced the 10-min. alarm rate by 45% to around 90%. However, many plants don’t use this functionality very extensively even when it’s readily available on the distributed control system (DCS) and known to be effective.
Most sites currently don’t have fully rationalized alarm systems — so this opportunity for improvement has considerable potential.
Figure 1 - MAD’s Role: Use of a Master Alarm Database
2. Use of a Master Alarm Database. A MAD is the master repository for the alarm configuration parameters (Figure 1). Some vendors (e.g., Honeywell) now include operating envelope data in an expanded database known as the Master Boundary Database. The addition of operating envelope information is significant because well-designed alarms often relate to one or more of the many limits that define the operating envelope for safe and efficient operation.
Use of a MAD facilitates several different functions:
• Enforcing alarm parameters. This activity overwrites alarm parameters on the DCS when these are found to differ from the values stored in the MAD. It prevents the alarm system from being used when operators (or others) have changed the values of parameters (such as alarm priorities or alarm limits) — perhaps on a temporary basis — and not restored the as-designed values afterwards;
• Tracking enforcements. This enables identifying alarm parameters regularly being changed and updating them, if needed, to more appropriate values;
• Logging all changes to the MAD. This clarifies why and when changes were made and who made them;
• Providing online operator help. Information can include the likely cause of an alarm, the consequences of no action, the action itself, and the time available for operators response; and
• Linking alarms to the relevant operating-envelope values. Reasons for the alarm limits become much more transparent, making any changes in alarm values that violate the operating envelope — which could have serious implications — less likely.
The benefits of using a MAD are that the plant continues to operate using the parameters agreed upon during rationalization. If some parameters are changed on a regular basis for justifiable reasons, the alarms can be reviewed again and the MAD updated to include the modified values.