The ISA-101 Standard: Start Here
ISA-101 is the international standard for HMI design. Its core principle: use grey as the dominant background colour, reserve colour ONLY for alarming states, and design for rapid abnormal situation detection — not aesthetics. Most factory HMIs we see violate all three principles.
Colour Hierarchy That Works
Grey = normal running. Yellow = warning, needs attention soon. Red = alarm, immediate action required. Green should be used sparingly and NEVER for "everything is OK" — it blends with normal grey and trains operators to ignore it. Use green only for confirmed safety states.
Information Density
Operators in an abnormal situation cannot process more than 7±2 items simultaneously. Each HMI screen should have one clear primary KPI and fewer than 5 secondary data points. If you need more, use drill-down navigation — not more data on the same screen.
Alarm Management
A well-designed HMI alarm system has fewer than 1 alarm per 10 minutes per operator during normal operations. If operators are acknowledging 30+ alarms per shift, your alarm system is trained them to ignore everything. Audit, rationalise, and suppress nuisance alarms before adding new ones.
The best HMIs are boring to look at and instantly obvious in an emergency. Design for the 2AM crisis situation, not for the demo to management.
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