A control-room screen crammed with blinking colors doesn't help an operator catch a problem faster — it just adds noise. What ISA-101 actually standardizes about HMI screen design, and why situational awareness beats visual complexity.
“Gray is normal, everything else is an alarm” sounds like an
obvious HMI design principle until you’ve watched an operator’s screen
light up in red, yellow, and flashing orange the moment a process
drifts even slightly — at which point nothing on the screen actually
communicates what matters most.
ISA-101, published by the International Society of Automation, is
the industry style guide for Human Machine Interfaces in process
automation — addressing how control-room and plant-floor screens
should present information so operators can actually maintain
situational awareness, not just technically display every available
data point. Poorly designed HMIs are a documented contributing factor
in serious industrial incident investigations, which is exactly why
screen design gets treated as a safety-relevant discipline, not just an
aesthetic choice.
| Screen state | Design approach |
|---|---|
| Normal operation | Muted, low-contrast colors (typically gray) that don’t compete for attention |
| Abnormal condition | Reserved bright colors used sparingly, so they actually stand out when they appear |
The problem with older, “bright and busy” HMI designs is that
vivid colors used everywhere — for navigation buttons, labels,
decorative elements, and actual alarms alike — train an operator’s eye
to tune out color entirely, since color no longer reliably signals
anything unusual. A screen where 90% of the display is calm gray makes
the 10% that turns red genuinely noticeable.
Alarm rationalization is the broader process of reviewing every
configured alarm and asking whether it’s actually necessary, correctly
prioritized, and set at a threshold that reflects genuine operator
action rather than noise. An HMI redesigned with good color discipline
still fails if it’s layered on top of hundreds of poorly-tuned alarms
firing during every minor process fluctuation — the screen design and
the underlying alarm configuration have to be addressed together.
The HMI is the human-facing layer of a SCADA system — see our
related guide on SCADA
systems for how the HMI connects to the PLCs and supervisory
systems generating the data it displays. Good HMI design doesn’t
change what data exists; it changes whether an operator can actually
interpret that data quickly enough to act on it during an abnormal
situation.
HMI design itself isn’t a standalone course in SCMEP’s current
catalog — it builds on the automation and controls fundamentals
covered in our Automation and Robotics
training. As a NIST Manufacturing Extension
Partnership affiliate serving South Carolina manufacturers since
1989, our focus is helping teams connect good screen design
principles to the operator situational-awareness problems they’re
actually meant to solve.
If your plant is redesigning HMI screens or working through alarm
rationalization, you can browse the
Automation and Robotics training catalog or email
the training
team.
ISA-101 is an International Society of Automation style guide for Human Machine Interfaces in process automation, addressing how screens should present information so operators maintain situational awareness rather than being overwhelmed by data.
It means normal operating screens use muted, low-contrast colors like gray, reserving bright colors for abnormal conditions. This makes genuine alarms stand out instead of blending into a screen that’s already visually busy.
The process of reviewing every configured alarm to confirm it’s necessary, correctly prioritized, and set at a threshold reflecting genuine operator action, rather than firing constantly during minor process fluctuations.
The HMI is the human-facing display layer of a SCADA system. Good HMI design doesn’t change the underlying data — it changes whether an operator can interpret that data quickly enough to act during an abnormal situation.
