The use of a MAD is often regarded as critical to maintaining the alarm system’s integrity. This demands its implementation as an integrated part of the alarm system as well as robustness because its enforcement and operator-help functions must have high availability. It’s not simply an offline tool with DCS access but needs integrated functionality that can limit the loading on the DCS. Most sites currently don’t utilize a MAD — so this means for improvement again has considerable potential.
3. Improvements to the Human Machine Interface. Human factors issues have often been neglected. However, the whole control center environment affects operator effectiveness. At a more detailed level, the HMI can significantly impact alarm management .
Figure 2 - HMI Improvement: Right clicking on
The quality of graphics and the style of alarm presentation on graphics vary widely. Some sites primarily rely on the standard DCS vendor “alarm summary” and “groups” — without any detailed graphics. Other sites also utilize very effective alarm presentation and operator help integrated into detailed operating graphics. Figure 2 shows a right-click contextual menu including functionality to acknowledge the alarm and obtain operator help for it from a MAD.
The potential for performance improvement by enhancing the HMI clearly depends on the quality of graphics (from an alarm presentation perspective) currently in use at a particular plant.
There’s also the possibility of utilizing a graphic designed specifically to be effective during alarm floods. The ASM Consortium has recently tested a graphic that might serve to replace the traditional list-based alarm summary, a format that isn’t usually effective when large numbers of alarms occur. Tests showed that the new style has considerable potential for giving operators a better understanding of the true abnormal situation — thereby allowing them to act more effectively.
Because floods are still the most significant alarms problem in many plants, this enhancement clearly has considerable potential for performance improvements.
4. Mode-based alarming. Many plants have multiple operating modes (startup, normal running, shutdown, cold standby, regeneration, etc.). The alarm system is often only appropriate for normal running — for example, many standing alarms derive from plant equipment that’s not in service. Operators have to recognize as such the many inappropriate alarms activated during other modes of operation. This devalues the integrity and value of the alarm system.
A better approach is to identify the various modes and define alarm parameter settings that suit each mode of operation. So, for instance, a standby or shutdown mode can be used to eliminate alarms from out-of-service equipment.
If a MAD is being used, various sets of alarm parameters can be stored in the MAD and written to the DCS when a plant mode change occurs. The enforcement functionality can handle this activity — effectively overwriting old alarm parameters with the ones required for the new mode of operation. This type of enforcement is much more efficient than requiring operators to make large numbers of manual configuration parameters changes.
Most sites currently don’t use mode-based alarming. So this means for improvement has considerable potential, although this clearly depends on the character of operations of the particular plant unit.
5. Alarm testing. All alarms should have a real meaning and value to operators. It makes no sense if some alarms are out of service (due to one or more failures) and aren’t clearly recognized as being out of service.