HMI Design Best Practices for Industrial Operators
Key Takeaway
Effective HMI (Human-Machine Interface) design follows the ISA-101 high-performance principles: gray backgrounds instead of colorful graphics, information hierarchy from overview to detail, limited use of color (reserved for abnormal states), analog indicators showing context (range, limits, normal), and consistent navigation. Well-designed HMIs reduce operator errors by 40-60% and improve abnormal situation response time.
Why HMI Design Matters
The HMI (Human-Machine Interface) is the operator's window into the process. A poorly designed HMI causes operator confusion, delayed response to abnormal situations, and errors that can result in safety incidents, environmental releases, or production losses. Research by the ASM (Abnormal Situation Management) Consortium found that poor HMI design contributes to 42% of abnormal situations in industrial operations.
High-Performance HMI Principles
The high-performance HMI methodology, formalized in the ISA-101 standard and Bill Hollifield's influential book, represents a paradigm shift from traditional "realistic" P&ID-style displays to information-rich, operator-focused displays.
1. Gray Background, Not Black
Use a medium gray (RGB: 192, 192, 192 or similar) background instead of the traditional black:
- Reduces eye fatigue during 12-hour shifts
- Makes color coding more effective (colors stand out against gray)
- Reduces glare in control rooms with varied lighting
- Matches ISA-101 recommendations
2. Reserve Color for Meaning
The most common HMI design mistake is using too many colors. In a high-performance HMI:
- Gray: Normal operating state (equipment, piping, vessels)
- Green: Use sparingly — open valve, running pump (some standards avoid green entirely)
- Red: Alarm state or safety-critical condition only
- Yellow/Amber: Warning or approaching limit
- Blue: Information or non-process data
- Avoid: Bright gradients, 3D effects, photographic backgrounds, decorative colors
3. Information Hierarchy (4 Levels)
- Level 1 — Overview: Entire plant or field on one screen. Key KPIs, overall status. Operator sees everything at a glance.
- Level 2 — Area: Major process area (e.g., one tank battery, one pump station). Shows all equipment and key values.
- Level 3 — Detail: Individual equipment (e.g., one pump, one separator). Shows all parameters, trends, and controls.
- Level 4 — Diagnostic: Detailed diagnostics, configuration, and maintenance data. Accessed on demand.
4. Analog Indicators with Context
Replace raw numeric values with analog indicators that show:
- Current value (needle or bar position)
- Operating range (full scale of the instrument)
- Normal operating range (highlighted zone)
- Alarm limits (color-coded thresholds)
- Trend direction (is the value rising or falling?)
An operator should be able to assess the health of a process variable at a glance without reading the number.
5. Consistent Navigation
- Consistent button placement across all screens
- Breadcrumb navigation showing current location in the hierarchy
- One-click access to related screens (e.g., clicking a pump opens its detail screen)
- Alarm summary always visible or one click away
- Consistent left-to-right process flow matching physical layout
Common HMI Design Mistakes
- Too many colors: "Christmas tree" displays where everything is brightly colored make it impossible to spot abnormal conditions
- 3D graphics: Photorealistic tank and pipe graphics waste screen space and add no operational value
- Crowded screens: Trying to show everything on one screen. Use hierarchy instead.
- No trending: Operators need to see how values are changing, not just current snapshots
- Hidden alarms: Alarm information buried in pop-ups instead of visible on the operating display
- Inconsistent layout: Different navigation patterns and color meanings on different screens
Platform-Specific Tips
- Ignition (Perspective): Use Ignition's built-in responsive design for mobile-friendly HMIs. Leverage the component library for consistent look and feel.
- FactoryTalk View: Use global objects for reusable components. Implement navigation via display macros.
- Geo SCADA ViewX: Take advantage of the web-based client for remote access. Use mimic templates for consistency.
- AVEVA InTouch: Use ArchestrA graphics for scalable, reusable display elements.
Frequently Asked Questions
ISA-101 (Human Machine Interfaces for Process Automation Systems) is an international standard published by the International Society of Automation (ISA) that defines best practices for HMI design in industrial automation. It covers display hierarchy, color usage, alarm integration, user interaction, and lifecycle management. ISA-101 formalizes the 'high-performance HMI' principles developed by the ASM Consortium.
ISA-101 and high-performance HMI guidelines recommend a medium gray background (not black, not white). Dark/black backgrounds cause eye fatigue during long shifts and reduce color discrimination. White backgrounds create glare. Medium gray (roughly RGB 192,192,192) provides the best balance: colors stand out clearly, eye fatigue is minimized, and the display is comfortable in varied lighting conditions.
Redesign in phases: (1) Audit current displays and identify the highest-impact screens (Level 1 overviews and most-used area displays). (2) Design new screens following high-performance principles while keeping existing screens operational. (3) Deploy new screens alongside old ones, allowing operators to switch between them during a transition period. (4) Gather operator feedback and refine. (5) Retire old screens once operators are comfortable. Never remove existing screens without a tested replacement.