Monday: Alarm Floods and HMI Blindness
Why hundreds of low-priority alarms can drown out a critical trip warning, blinding operators during an emergency.
When hundreds of nuisance alarms trigger concurrently on an HMI screen, an operator isn’t just annoyed—they are functionally blinded. This is known as an alarm flood, and it is a leading human-factors cause of catastrophic industrial blowouts.
According to ANSI/ISA-18.2 standards, a human operator can effectively manage about one or two alarms per ten minutes. During a process upset, a poorly configured SCADA system might throw 150 alarms at the operator in the first 60 seconds. A critical high-pressure trip warning looks exactly the same in the event log as a low-cooling-water-flow warning from an unused subsystem.
In major incidents like the Texas City refinery disaster, operators were completely overwhelmed by meaningless, un-prioritized alarms. The critical warning was buried on page three of the alarm summary. If every alarm is treated as critical, then nothing is critical.
Effective alarm management requires strict rationalization. Nuisance alarms must be suppressed or downgraded to “logged events” rather than screaming banners, ensuring that when the HMI flashes red, the operator knows exactly what pipeline or vessel is about to fail and exactly what action to take.