Stop Alarm Floods: Interlock the Real Hazards

Last month we had a 2 a.m. compressor cascade because the lube oil skid dipped pressure during cold starts. The HMI vomited 40 alarms in 60 seconds. Nobody knew which one mattered, so they stared at a wall of red until the machine saved itself. Well, there's your problem.

We fixed it by moving the low-pressure switch to pump discharge, adding a dP across the duplex filters with a proof test, and wiring a first-out capture. Start permissive now requires oil > 275 kPa for 5 s. A hard trip hits on confirmed low oil for 1 s. The warning band is just an alarm. Debounce killed the chatter, and we rationalized priorities so 'loss of cooling water' shouts while 'level trend bad' whispers.

Since then: zero nuisance trips, one clean first-out on a sticky bypass valve, and my phone sleeps. My rule: if operator action must be faster than a human can reliably deliver, it's an interlock; if not, it's an alarm; if it's informational, log it.

Where do you draw the line between warnings, permissives, and hard trips in your plants?