HMI screen design is the discipline of creating operator displays that support fast, accurate situational awareness and reduce errors under pressure.
ANSI/ISA-101.01-2015 defines the industry standard for HMI screen design in process automation — specifying screen hierarchy, colour rules, navigation, and performance requirements.
This guide covers the 7 essential ISA 101 principles that every SCADA and DCS HMI screen design must follow.
The most common HMI screen design mistake is treating the interface as a digital P&ID copy.
Engineers think in equipment layout. Operators think in tasks: is this running correctly, and what do I need to do next?
ISA 101 exists to close this gap to build displays that work with the operator's brain rather than against it.
Why ISA 101 HMI Screen Design Matters
Poorly designed HMI screens are a documented contributor to process incidents. The US Chemical Safety Board has identified operator interface inadequacy as a contributing factor in multiple major incidents.
ISA 101 defines HMI screen design around one core idea: the display should support situational awareness.
The operator should be able to read the current state, predict where it is heading, and take the right action — all within the time available to respond.
The ASM Consortium was a joint industry and academic research programme funded by major process companies including Honeywell, ExxonMobil, and Chevron. Their research on operator interface design under abnormal conditions formed the evidence base for ISA 101's colour philosophy and screen hierarchy requirements.
The standard was revised in 2024 to address touchscreen HMIs, mobile operator interfaces, and integration of data analytics displays alongside traditional process graphics.
7 Essential HMI Screen Design Principles from ISA 101
The most visible change from legacy HMI to ISA 101 compliant design is the colour philosophy. Legacy screens used bright colours everywhere: green pipes, blue vessels, red motors.
The result was visual noise — operators could not identify real alarms because the whole screen was already colourful.
ISA 101 mandates a predominantly grey background. Equipment in normal operation is shown in grey tones. Colour appears only when the state is abnormal or requires operator attention.
The ISA 101 colour hierarchy: grey for normal running; yellow for advisory; red for active alarm; blue for operator action required; cyan for suppressed alarm.
Never use green for all running equipment — when everything is green, green means nothing.
Start by removing all animated fills (pumps that spin, valves that flash). Change normal-state equipment from coloured fills to medium grey. Change pipe colours from blue or brown to dark grey.
Run the updated screen with the operator shift for one week before changing colour alarm states. Operators need time to adapt to grey-based displays before the alarm colour system becomes meaningful to them.
ISA 101 defines four levels of display, each serving a different operator need. Navigation between levels must be consistent and require no more than two clicks from any point.
Level 1 — Plant Overview: One screen showing the entire plant. Only KPIs and abnormal conditions are visible — no individual instrument values. Used to scan for anything needing attention.
Level 2 — Unit Overview: One screen per process unit. Shows main process flows, key controlled variables, and active alarms. Mimics the P&ID layout but simplified — major equipment only.
Level 3 — Unit Detail: Individual control loops, faceplate pop-ups, valve positions, and flow totals. Used to investigate an abnormal condition identified at Level 2 or to take a specific control action.
Level 4 — Equipment Detail: Motor control faceplates, valve positioner status, interlock permissive lists, alarm set points. Used for maintenance and detailed diagnosis, not normal operation.
Progressive disclosure means showing only the information relevant to the current task, and revealing more detail only when the operator requests it. It is the same principle used in smartphone interfaces: the home screen shows only key status; you drill in to access detail.
Research from the ASM Consortium showed that legacy SCADA HMI screens typically placed Level 3 and Level 4 detail on the same screen as Level 1 and Level 2 information. Operators spent cognitive effort filtering out irrelevant detail rather than responding to the abnormal condition that mattered. The four-level hierarchy separates these concerns.
A numeric display shows the current value. A trend shows where the value is heading and how fast.
ISA 101 requires process trends to be accessible within one click from any Level 2 or Level 3 display.
Beyond trends, ISA 101 recommends deviation indicators showing how far a value is from its setpoint. A bar filling towards a limit is faster to read under stress than a four-digit display.
A temperature of 78°C means nothing without context. A temperature 3°C below its setpoint, trending upward at 2°C per minute, means a great deal.
Design deviation indicators that change colour relative to the normal operating range, not just against a fixed alarm limit. Yellow at 90% of the high alarm limit gives the operator time to act before the alarm fires. The alarm is the last line of defence — the display design should help the operator intervene before it is reached. See the ISA-18.2 alarm management guide for the companion standard on alarm rationalization.
ISA 101 requires the navigation header and footer to follow the same layout on every screen. The alarm summary, screen title, and navigation buttons must occupy the same position every time.
Inconsistent navigation is one of the most common violations in existing HMI screen designs. Engineers add shortcuts based on what they think operators need for each screen.
The result: a different navigation model on every screen, and operators cannot develop the automatic spatial memory needed for fast navigation under stress.
All process screens must inherit from this template. New screens built by different engineers or integrators automatically have consistent navigation — it cannot be accidentally moved or deleted.
In Ignition, use the Perspective template feature. In FactoryTalk View, use the global object. In Wonderware, use the application object. Every major SCADA platform has a mechanism for locked inherited screen elements — use it from day one of a project, not as a retrofit.
3D pipe renders, gradient fills, animated equipment, company logos on process screens, and decorative shadows all consume screen space and cognitive bandwidth without adding process information.
ISA 101 prohibits decoration that adds no process information. Equipment should be flat shapes; pipes should be single-pixel lines. See the HMI systems guide for platform implementation.
An alarm on an ISA 101 screen changes the element colour (red) and adds an alarm footer entry.
An alert also appears on the Level 1 overview so the operator sees it at every hierarchy level.
The alarm presentation must include the tag, description, current value, and alarm limit — all visible on the Level 3 screen. See the SCADA alarm management guide for the ISA-18.2 rationalisation approach.
EEMUA Publication 191 and ISA-18.2 set the target at fewer than 150 alarms per operator per hour as an acceptable rate. Above 300 per hour is described as "likely unmanageable."
HMI screen design contributes to alarm flood prevention by ensuring that nuisance alarms (alarms that fire repeatedly without requiring operator action) are visually de-emphasised or shelved rather than displayed with the same priority as critical process alarms.
ISA 101 specifies measurable performance targets: any process screen must refresh within 1.0 second under normal load. Alarm-relevant data must refresh within 0.5 seconds. Faceplates must open within 0.5 seconds.
These are operator performance requirements, not cosmetic targets. An operator who waits 3 seconds for a screen to refresh during an abnormal event loses the mental thread and may make an error.
Screen performance must be tested at maximum tag load and maximum concurrent operator session count before commissioning.
HMI Screen Design ISA 101 Compliance Checker
Legacy HMI vs ISA 101 HMI Screen Design: Key Differences
| Design Element | Legacy HMI Screen Design | ISA 101 Compliant HMI Screen Design |
|---|---|---|
| Colour philosophy | Bright colours for all equipment states: green = running, red = stopped, blue = pipes, grey = off | Neutral grey base for all normal states. Colour reserved exclusively for abnormal conditions and required operator actions. |
| Screen hierarchy | One or two levels. Detailed instrument data and overview data on the same screen. | Four defined levels: Plant Overview, Unit Overview, Unit Detail, Equipment Detail. Progressive disclosure. |
| Navigation | Navigation varies per screen. Engineers add shortcuts based on individual screen content. | Consistent global template on all screens. Same header, footer, and navigation bar position on every display. |
| Process graphics | 3D pipe renders, gradient fills, animated equipment, shadow effects, company logos on process screens. | Flat, simple shapes. Single-line pipes. No decoration that does not carry process information. |
| Alarm presentation | Alarm list in a separate window. Alarm colour overrides only on the alarm list, not on the process graphic. | Alarm colour change on the affected process graphic, entry in the alarm footer, and alert on the Level 1 overview simultaneously. |
| Trend access | Trends in a separate trend application, not linked from the process screen. | Trend accessible within one click from any Level 2 or Level 3 screen for any controlled variable. |
| Deviation indication | Raw numeric values only. Operator must know the normal range from memory. | Deviation indicators showing position within the normal operating range. Colour change as value approaches a limit. |
Watch: HMI Design Using ISA 101
HMI Screen Design Questions
External References
- ISA-101 Human Machine Interfaces for Process Automation Systems | ISA (2024)
- SCADA HMI Design Standards: ISA-101 Complete Reference | Industrial Monitor Direct (2026)
What We Learn Today
- ISA 101 defines 7 core HMI screen design principles: grey colour base with colour for abnormal states only, four-level screen hierarchy, consistent navigation template, trend access within one click, elimination of visual clutter, alarm presentation at every hierarchy level, and 1-second refresh performance targets.
- The most impactful single change in any HMI screen design upgrade is removing the bright-colour normal-state scheme and replacing it with a grey base. This alone makes real alarms visible and reduces operator visual fatigue on long shifts.
- HMI screen design and alarm management (ISA-18.2) are companion disciplines. A well-designed screen reduces the alarm rate by making operators aware of developing conditions before the alarm limit is reached. Both standards must be applied together for a high-performance operator interface.