Cutting Nuisance Alarms with ISA 18.2 in Honeywell Experion and Emerson Ovation
Too many nuisance alarms make it harder for an operator to see the warning that matters. ISA-18.2 provides a lifecycle framework for deciding which alarms belong on the console, how they should behave, and how their performance should be reviewed.
Why do alarm counts grow out of control?
When every analog tag receives several default limits, normal process variation can create repeated notifications. An alarm should identify an abnormal condition requiring a defined operator response, not merely report that a value changed. Start with an alarm philosophy, rationalize alarms against it, manage changes, and review performance from real event history.
How should priority, deadband, and delay be set?
Assign priority from the consequence of inaction and the available response time using the site's approved matrix. Set deadband or hysteresis to prevent chattering around a threshold, and use an on-delay only when the process hazard allows it. There is no universal percentage or number of seconds for flow, level, or pressure loops. Verify that a delay cannot conceal a fast-developing hazardous condition.
In Honeywell Experion and Emerson Ovation, check the installed version and configured alarm object before changing attributes. Related products such as the Honeywell Experion Series 8 IOTA module and Emerson Ovation analog input module sit in systems whose alarm behavior must be verified in the actual configuration. Do not assume both platforms use identical settings or blocks.
What belongs in a master alarm database?
Record each alarm's tag, purpose, abnormal condition, consequence, required operator action, response time, priority, setpoint, deadband, delay, shelving or suppression rules, and review history. Reject or redesign alerts that have no useful operator action. Choose performance targets from the site's alarm philosophy and operating history rather than copying a fixed target for active alarms or floods from another facility.
When is shelving appropriate?
Shelving temporarily removes an alarm from the operator's active view under a controlled procedure. Define who may shelf it, why, the permitted duration, visibility, and automatic return. Avoid treating a fixed startup shelving timer as a substitute for proper state-based alarming. Safety-critical alarms require special scrutiny under the site policy.
How should alarms be routed through OPC UA?
If the server supports OPC UA Alarms & Conditions, subscribe to the relevant events and verify event type, source, timestamp, active state, acknowledgement, and return-to-normal transitions. Event subscriptions may preserve transitions better than periodic polling, but delivery and buffering still depend on the server and client configuration. Do not restrict downstream events to High and Emergency unless the receiving use case and retention policy explicitly allow lower-priority events to be excluded. Set publishing and queue parameters from tested throughput rather than fixed generic values.
How can an operator manage an alarm flood?
Analyze alarm sequences to find the initiating cause, then rationalize dependent alarms and apply approved suppression by design when the process state makes them irrelevant. Preserve visibility of actionable hazards. Test changes during realistic upset scenarios and track frequent alarms, chattering alarms, floods, and operator response by shift. Any forced test must follow an approved procedure that protects the plant and personnel.
What is the first practical step?
Take a representative alarm history from the installed Honeywell Experion or Emerson Ovation system. Identify the worst repeat offenders, confirm their required operator action, and rationalize priority, limits, deadband, and delay before changing many tags at once. Keep the master alarm database and the live configuration in sync through change control.
Author: Zhao Mingyuan is an industrial automation engineer with over 10 years of experience in PLC, DCS, and control systems.
