n
Ensure that the loss of the alarm during this period will not cause excessive process
risk, and
n
Deploy alternative precautions if deemed necessary.
ACM provides a formal way to enforce such a work process.
Another option is to use Experion alarm shelving to:
n
Shelve the alarm
n
Set the shelving reason to “Maintenance”
n
Define the scope of responsibility to ensure that appropriate supervision takes place.
Dealing with alarms related to changes in equipment mode
Even if an alarm system is well rationalized, excessive alarms may arise because a given piece
of equipment may operate differently in different situations. This happens sometimes in
continuous processes, and very often in batch processes. To deal with this, alarm
rationalization must put the alarm trip points at their most conservative settings, possibly
resulting in large numbers of standing alarms in situations where those alarm settings are too
aggressive.
A good solution is to have a controlled way to change alarm settings by equipment mode.
This can be done by what is sometimes called static alarm suppression or mode-based
alarming. Options here include:
n
Controller logic, where, for example, sequences can be used to manipulate alarm
attributes to change trip points, priorities, the journal-only state and the disable/journal-
only status appropriately as batch phases progress.
n
ACM operating modes which provide a good, well-documented means for configuring
and changing alarm settings (alarm enable state, the disable/journal-only status, trip
points, and priorities) for each operating mode on an asset or piece of equipment. This
allows the alarm settings to be better tailored to the specific operating situations,
resulting in far fewer standing alarms.
Note that while DAS can be useful for suppressing alarms on a device that is out of
service, it cannot adjust alarm properties like trip points.
Caution:
Any solution that affects safety-related or otherwise critical alarms should be
carefully considered as well as carefully designed and implemented.
Alarms and events
Honeywell 2017 87
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