High Performance HMI (ISA-101): Principles and Design
High performance HMI explained — the ISA-101 philosophy, gray backgrounds and muted color, situational awareness, hierarchy of displays, and analog indicators.
High performance HMI is a display design methodology that prioritizes operator situational awareness over visual decoration. It uses subdued gray backgrounds, muted process colors, and analog-style indicators so that genuine abnormal conditions — alarms, deviations, and emergencies — stand out immediately against an otherwise quiet screen. The approach is codified in ANSI/ISA-101.01-2015, the industry standard for human machine interfaces in process automation, and has become the required design philosophy across oil and gas, chemical, power generation, water treatment, and advanced manufacturing.
The core promise is straightforward: an operator glancing at a well-designed high performance display should be able to identify any abnormal condition within seconds, without scanning every value or interpreting a rainbow of competing colors. When every pixel is fighting for attention, none of them wins.
What Is High Performance HMI?
A high performance HMI is an operator interface engineered around human perceptual psychology rather than software default palettes. It flips the traditional design assumption — instead of making screens look busy and "rich," it makes them look calm until something genuinely needs attention.
The key characteristics that define a high performance HMI:
- Subdued gray base background (typically 60–70% gray) that creates a neutral visual field
- Muted, desaturated process colors — pipelines, vessels, and equipment rendered in grays and light blues rather than full-saturation primaries
- Color reserved exclusively for alarm and deviation states — red, amber, and magenta appear only when action is required
- Analog indicators and trend plots rather than digital number readouts
- Consistent layout and navigation across all displays so operators do not have to reorient between screens
- Minimal decoration — no gradients, shading, 3D effects, shadows, or logo graphics that consume attention without adding information
The phrase "high performance" refers to the interface's performance in supporting operator decision-making, not to graphics rendering speed. A high performance display helps an operator perform at a higher level during abnormal situations.
For a broader look at how these principles sit within the full discipline of operator interface development, see our guide to HMI design best practices.
The Problem With Traditional, Colorful HMIs
Most legacy HMI screens were designed by control engineers who had deep process knowledge and little formal training in human factors. The result is predictable: screens that reflect how the engineer thinks about the plant, not how an operator perceives and responds to it under stress.
The five failure modes of traditional HMI design:
-
Alarm overload masked by visual noise. When 40 process values are displayed in green, blue, yellow, and red by default, a new alarm in red does not stand out — it blends into the existing color noise.
-
Digital readouts with no context. A field reading "217.4 °F" tells an operator nothing unless they already know the normal operating range is 195–210 °F. A static number provides no trend, no deviation cue, and no comparison.
-
No situational awareness at a glance. An operator should be able to look at a process overview screen and know immediately whether anything is abnormal. Colorful, detail-dense screens require active reading rather than rapid perception.
-
Inconsistent layouts across displays. When each screen is designed differently, operators spend cognitive effort reorienting rather than monitoring the process.
-
Decoration that consumes attention. Gradients on pipe segments, 3D equipment models, animated logos, and corporate color schemes all draw the eye toward elements that carry no process information.
The consequence of these failures is measurable. Research by the ASM (Abnormal Situation Management) Consortium found that operator response delays in abnormal situations are a leading contributing factor in industrial incidents — and that most of those delays originate in interface design, not operator skill.
High performance HMI solves this by making the normal state visually quiet and the abnormal state visually loud — without any additional effort from the operator.
For the alarm side of this problem, read our deep dive on alarm management best practices, which covers rationalization, deadbands, and flood reduction that complement the display layer.
ISA-101 Principles
ANSI/ISA-101.01-2015 (commonly shortened to ISA-101) is the primary standard governing HMI design for process automation systems. It covers the full HMI lifecycle — from design philosophy through display creation, implementation, operation, and continuous improvement — but its most operationally impactful sections cover graphics philosophy and display hierarchy.
The standard's core principles, summarized:
Principle 1 — Detect abnormal situations quickly. The primary purpose of an operator display is to enable fast detection of conditions that require action. Every design decision should be evaluated against this criterion.
Principle 2 — Minimize cognitive load. Operators carry significant mental workload during normal operations. Interfaces that require active reading, color interpretation, or layout relearning consume mental capacity that should be available for process decisions.
Principle 3 — Support abnormal situation management. When an upset occurs, the interface must present relevant information in a form that supports diagnosis and response — not one that adds to the confusion.
Principle 4 — Use color as a deviation signal, not a process identifier. Color should communicate state change, not process identity. Equipment should not be colored green because it is running — that wastes the meaning of green as a "good" signal.
Principle 5 — Standardize. Consistent navigation, consistent alarm colors, consistent widget behavior, and consistent layout structure allow operators to transfer knowledge between areas and onboard faster.
ISA-101 does not specify exact hex values or grid dimensions — it defines the philosophy and requirements, leaving implementation specifics to each facility. The ASM Consortium's "Effective Console Operator HMI" style guide and the EEMUA Publication 201 supplement ISA-101 with more prescriptive recommendations.
Muted Gray Backgrounds and Color Used Only for Alarms
The gray background is the most visually distinctive feature of a high performance HMI and the one most often misunderstood. Engineers and managers seeing a gray display for the first time sometimes react negatively — it looks "unfinished" compared to colorful legacy screens. That reaction is itself evidence of the problem: they have become conditioned to equate visual complexity with information richness.
The gray background serves a specific perceptual function: it creates a neutral visual field against which deviations immediately register as figure against ground. When a value goes out of range and turns amber or red, that color change is visible in peripheral vision without the operator looking directly at the element.
Recommended background and element color approach:
| Element | Color approach | Rationale |
|---|---|---|
| Display background | Medium gray (approx. 60–70% gray, e.g., RGB 128/128/128 or 96/96/96) | Creates neutral visual field |
| Process equipment (vessels, exchangers) | Light gray, slightly lighter than background | Visible without competing |
| Pipelines | Gray, color-coded by service using muted tones (light blue for water, medium gray for gas) | Minimal, functional differentiation |
| Normal running values | Dark gray or black text | High legibility without color meaning |
| Deviation — low/high warning | Amber / yellow | Pre-alarm, action may be needed soon |
| Alarm — active, unacknowledged | Flashing red | Requires immediate attention |
| Alarm — active, acknowledged | Solid red | Acknowledged, still requires response |
| Abnormal but safe state | Magenta or cyan (platform-dependent) | Reserved for specific process states |
| Equipment stopped (non-alarmed) | Dark gray or black fill | Off-state, not alarmed |
| Equipment running normally | No color change from background | Running is normal; no color needed |
The last row is the critical insight: a running pump should not be green. Green says "good, I approve." Running is the expected state — it requires no annotation. Reserving color for deviation makes the transition from normal to abnormal immediately perceptible.
Analog and Trend Indicators Over Digital Readouts
A digital readout — "217.4 °F" — requires the operator to know the expected range, recall it from memory, and mentally calculate whether the value is normal. An analog indicator presents the same information with context built in: the needle is in the middle of the green zone, or it is creeping toward the upper limit.
Why analog indicators improve situational awareness:
- Pattern recognition is faster than number reading. The human visual system recognizes shapes and positions much faster than it reads and interprets text strings.
- Trend is implicit. A falling needle communicates direction without requiring the operator to compare the current value to a previous reading.
- Normal range is visible. Setpoints, safe operating limits, and alarm thresholds can be marked on the scale, giving the number meaning without requiring memory.
- Deviation is pre-attentive. A needle at the edge of the scale registers as "off normal" before the operator consciously reads it.
Recommended indicator types for high performance displays:
| Indicator type | Best use case |
|---|---|
| Horizontal or vertical bar with marked limits | Flow, level, pressure — variables with clear normal ranges |
| Arc gauge (circular analog) | Temperature, speed — values with wide operating ranges |
| Trend plot (sparkline or mini-trend) | Any variable where direction and rate of change matter |
| Faceplates with analog bar | Loop controllers — shows PV, SP, and output on one element |
Digital readouts should be present but secondary — displayed as a precise number adjacent to the analog indicator for operators who need the exact value. The analog indicator drives perception; the digital number confirms it.
Embedded trend plots are particularly powerful. Even a small 80×30 pixel sparkline showing the last 15 minutes of a value communicates whether the process is stable, drifting, or cycling — information that a single digital readout cannot provide.
The Display Hierarchy: Level 1 Through Level 4
ISA-101 defines a four-level display hierarchy that structures how information is organized across an operator interface. This hierarchy is not just an organizational convenience — it directly supports situational awareness by ensuring operators can always find the right level of detail without hunting.
Level 1 — Site or Unit Overview
The highest-level display. It shows the entire plant, production unit, or major process area in a single view. Level 1 displays do not show individual valve states or analog values — they show aggregate status indicators for each major area so an operator can determine at a glance whether any area requires attention.
Level 1 displays typically show:
- Color-coded area status tiles (normal, advisory, alarm)
- Key performance indicators for each major unit (production rate, efficiency)
- Active alarm counts per area
An operator arriving at a console should look at the Level 1 display first. If all tiles are normal, they can proceed with their routine. If one area is amber or red, they navigate to the relevant Level 2 display.
Level 2 — Area or Unit Display
The working display for normal operations. Level 2 shows a complete process area — a distillation column, a compressor train, a water treatment loop — with all major equipment, primary instrumentation, and control loops visible on a single screen.
Level 2 is where most operator monitoring happens. It should be designed so that an operator can identify any abnormal condition within the area within 5 seconds of looking at the screen — this is the central performance criterion for high performance HMI design.
Level 2 displays use:
- Full process flow representation (P&ID-style, simplified)
- Analog indicators for all key variables
- Embedded trend plots for critical loops
- Alarm state coloring on equipment and value displays
- Direct navigation links to Level 3 details
Level 3 — Unit or Equipment Detail
Detailed displays for specific equipment or control loops. A Level 3 display might show a single heat exchanger with its full instrumentation, or a motor control center with all individual starters. Operators navigate to Level 3 to diagnose a problem identified at Level 2 or to perform detailed adjustments.
Level 3 displays include:
- Full instrumentation detail (all transmitters, valves, switches)
- Trend plots for key variables
- Control faceplates
- Calculated values and derived indicators
Level 4 — Diagnostic and Support Displays
The lowest level: maintenance, calibration, tuning, and diagnostic displays. Level 4 is not used during normal operations. It is accessed by engineers, technicians, and advanced operators for troubleshooting, loop tuning, device configuration, and alarm history review.
Navigation between levels must be consistent and fast. An operator in an abnormal situation who cannot quickly navigate from a Level 1 alarm indicator to the relevant Level 2 or Level 3 display has lost critical response time. ISA-101 requires clear, predictable navigation pathways — typically via consistent button locations, breadcrumb indicators, and direct hyperlinks from alarm banners.
For a full look at how HMI screens are structured and programmed, see our HMI programming tutorial, which covers faceplates, navigation design, and data binding in detail.
Layout and Consistency
Consistency is the enabler of speed. When every display in a facility uses the same layout structure, the same widget styles, the same color meanings, and the same navigation elements, operators develop muscle memory for finding information. That memory is available under stress, when deliberate search is difficult.
Core layout requirements for high performance HMI:
Fixed navigation zones. Place navigation controls — back, home, level links, alarm banner — in the same location on every display. Top bar or left rail navigation is most common. Operators should never have to search for the alarm banner.
Consistent alarm summary. A persistent alarm banner showing the most critical active alarm, alarm count by priority, and a link to the full alarm list should appear on every display.
Standard widget library. Define and enforce a library of approved widgets: a standard flow indicator, a standard tank level, a standard motor symbol, a standard controller faceplate. Deviation from the library should require formal approval. Inconsistent widgets are a patient safety hazard in pharmaceutical applications and a production risk everywhere else.
Process flow left to right. Material flows from left to right on the display, matching the operator's natural reading direction. Exceptions for specific equipment configurations are acceptable, but the general rule should be enforced.
Equipment in fixed positions. Key equipment should appear in the same screen location across related displays. If a charge pump appears in the upper-left of a Level 2 display, its detail faceplate should open in a consistent location.
No decorative elements. Gradients, drop shadows, corporate logos, animated graphics, and 3D renderings are excluded. Every pixel that does not carry process information is a pixel that can compete with an alarm color.
Migrating an Existing HMI to High Performance Standards
Most facilities have legacy HMIs that predate ISA-101 — colorful, detail-dense screens built on whatever defaults the software offered in 2005. Migrating these to high performance standards is a significant project, but it is manageable with the right approach.
Phase 1 — Assess and benchmark the current state
Before changing anything, document what you have:
- Screenshot every existing display and categorize by level
- Audit color usage — count distinct colors in use and identify what each one "means" (often nothing consistent)
- Interview operators: what do they find confusing, what do they have to memorize, where do they lose time during alarms?
- Measure alarm KPIs: average alarms per hour per operator, standing alarm count, most frequent alarms
The EEMUA 191 benchmark of fewer than 1 alarm per 10 operator-minutes during normal operations is a useful starting target. If your current rate is 5 or 10 per minute, display redesign alone will not solve it — you need alarm rationalization in parallel. See our guide on alarm management best practices for the rationalization process.
Phase 2 — Establish a style guide and widget library
Do not start redesigning screens until you have a written style guide. The style guide defines:
- Approved background colors and values
- Equipment symbol library with normal and alarm states
- Color meanings (what amber means, what red means, what magenta means — and that green is never used for "running")
- Typography standards (font family, sizes, weights)
- Layout grid and fixed navigation zones
- Navigation structure (how Level 1 links to Level 2, how Level 2 links to Level 3)
Getting operator and engineering sign-off on the style guide before screen work begins prevents rework and resolves debates that would otherwise recur on every display.
Phase 3 — Redesign top-down, starting with Level 1 and Level 2
Level 1 and Level 2 displays have the highest impact on situational awareness. Redesign them first so operators experience the perceptual benefit early in the project and can provide informed feedback on the approach.
Do not try to convert all screens simultaneously. A phased area-by-area rollout allows learning from early areas to improve later ones.
Phase 4 — Operator training and validation
High performance displays look different from what experienced operators are used to. Training is not optional — operators need to understand why the display looks gray, why running equipment has no color, and how to use analog indicators. Without this understanding, operators sometimes resist the change because "the old screens showed more information."
Validation should include timed abnormal situation detection tests: present operators with a Level 2 display containing a seeded abnormal condition and measure how quickly they identify it. Pre- and post-migration comparisons quantify the improvement.
Phase 5 — Continuous improvement
ISA-101 explicitly requires ongoing maintenance of the HMI as a living system. After migration, track:
- Alarm KPIs monthly
- Operator-reported display issues
- Near-miss incidents where display design contributed to delayed response
- Changes to process configuration that require display updates
High performance HMI is not a project that ends at go-live. It is a design discipline that requires sustained attention. For context on how HMI design fits within broader SCADA system architecture, the comparison of HMI vs SCADA clarifies where the display layer sits relative to data acquisition and control. For foundational screen-level design decisions, HMI screen design principles covers the element-level choices that support the ISA-101 framework.
Frequently Asked Questions
What is a high performance HMI?
A high performance HMI is an operator display system designed to maximize situational awareness using subdued gray backgrounds, muted process colors, and color reserved exclusively for alarm and deviation states. The methodology is defined by ISA-101 and is designed so operators can detect abnormal conditions at a glance rather than by actively reading every value on a screen.
What is ISA-101?
ISA-101 refers to ANSI/ISA-101.01-2015, the standard published by the International Society of Automation that governs human machine interfaces for process automation systems. It defines the display hierarchy (Levels 1–4), graphics philosophy including the high performance HMI methodology, alarm integration requirements, and the full HMI lifecycle from design through ongoing improvement.
Why are high performance HMIs gray?
The gray background creates a neutral visual field. When a process value deviates or an alarm activates, the color change — amber or red — stands out immediately against the gray background, even in peripheral vision. On a colorful traditional HMI, the same alarm color competes with dozens of other colors already on screen and is harder to detect quickly. Gray is not aesthetic preference; it is a perceptual engineering decision.
What are the four levels of HMI displays?
ISA-101 defines four display levels. Level 1 is a site or unit overview showing aggregate status for all major areas. Level 2 is the primary working display for a specific process area, showing all major equipment and instrumentation. Level 3 provides detailed information about specific equipment or control loops. Level 4 covers diagnostic, maintenance, and engineering displays used for troubleshooting and configuration rather than routine operations.
