HMI Design for Operator Effectiveness

Understanding the Critical Role of HMI Design in Modern Industrial Operations

In today's increasingly automated industrial landscape, the Human-Machine Interface (HMI) serves as the critical bridge between complex control systems and the operators who manage them. For manufacturing facilities, processing plants, and utilities across Nova Scotia and Atlantic Canada, a well-designed HMI can mean the difference between optimal operational efficiency and costly downtime, between safe working conditions and potential incidents.

The Maritime provinces have seen significant growth in sectors requiring sophisticated automation solutions, from food processing facilities in the Annapolis Valley to aquaculture operations along our coastlines. As these industries modernise their control systems, the importance of operator-centred HMI design has never been more apparent. Studies consistently show that poorly designed interfaces contribute to approximately 70% of industrial incidents where human error is cited as a factor—a statistic that underscores the need for thoughtful, ergonomic design principles.

This comprehensive guide explores the essential principles of HMI design for operator effectiveness, providing practical insights for engineers, plant managers, and technical decision-makers looking to optimise their control room interfaces and mobile monitoring solutions.

Fundamental Principles of High-Performance HMI Design

The evolution of HMI design has progressed significantly from the early days of mimicking physical control panels with colourful, cluttered displays. Modern high-performance HMI design follows established standards, including those outlined in ISA-101 (Human Machine Interfaces for Process Automation Systems) and the ASM Consortium guidelines, which emphasise clarity, consistency, and operator-centred functionality.

The Hierarchy of Visual Information

Effective HMI screens present information in a logical hierarchy that supports rapid situation awareness. This hierarchy typically follows a four-level model:

• Level 1 - Overview displays: Plant-wide or area-wide status at a glance, showing key performance indicators and abnormal situations without excessive detail

• Level 2 - Process area displays: Functional groupings of equipment and processes with essential operating parameters

• Level 3 - Unit control displays: Detailed views of individual equipment or control loops with full parameter access

• Level 4 - Diagnostic and support displays: Trending, historical data, and maintenance information

Each level should be accessible within three clicks or fewer from any other display, ensuring operators can navigate quickly during both normal operations and upset conditions. For facilities operating in Atlantic Canada's challenging climate conditions, where equipment stress from temperature extremes and salt air can create sudden operational changes, this rapid navigation capability becomes particularly valuable.

Colour Theory and Visual Standards

One of the most significant shifts in modern HMI design involves the strategic use of colour. Traditional interfaces often featured vibrant, multicoloured displays that, while visually striking, actually impeded operator effectiveness. Contemporary best practices recommend:

• Grey-scale backgrounds: Using neutral grey tones (typically between 40-60% grey) for normal operating conditions

• Colour reservation: Reserving saturated colours exclusively for abnormal conditions and alarms

• Consistent colour coding: Red for emergency/critical states, amber/yellow for warnings, and limited use of green for confirmed safe states

• Contrast ratios: Maintaining minimum 3:1 contrast ratios for standard elements and 7:1 for critical information

This approach ensures that when a colour does appear on screen, it immediately captures operator attention, rather than competing with dozens of other coloured elements.

Alarm Management Integration and Rationalisation

Alarm management represents one of the most critical aspects of HMI design, directly impacting operator effectiveness and plant safety. The Engineering Equipment and Materials Users Association (EEMUA) Publication 191 provides benchmark guidelines suggesting that operators should receive no more than one alarm every ten minutes during normal operations and no more than ten alarms in the first ten minutes of a major upset.

Designing for Alarm Clarity

Effective HMI alarm presentation requires careful consideration of several factors:

• Alarm prioritisation: Clear visual and audible distinction between critical, high, medium, and low priority alarms

• Contextual information: Each alarm should provide sufficient information for the operator to understand the situation without navigating to additional screens

• State-based alarming: Implementing alarm suppression and shelving strategies that adapt to current operating modes

• First-out indication: Clear identification of the initiating alarm in cascade situations

For Nova Scotia industries such as pulp and paper operations, power generation facilities, and food processing plants, where equipment reliability directly impacts profitability, proper alarm management can reduce nuisance alarms by 80% or more, allowing operators to focus on genuinely significant events.

Alarm Summary and Historical Analysis

Well-designed HMI systems include comprehensive alarm summary displays that allow operators to quickly review active alarms, recently acknowledged alarms, and alarm history. These displays should support filtering by priority, area, equipment type, and time period, enabling both real-time management and post-incident analysis.

Situation Awareness and Abnormal Situation Management

Situation awareness—the operator's understanding of what is happening, why it is happening, and what is likely to happen next—forms the foundation of effective process control. HMI design directly influences all three levels of situation awareness and can either support or hinder an operator's ability to manage abnormal situations.

Trend Displays and Predictive Indicators

Real-time trending is essential for supporting operator situation awareness. Effective trend displays should:

• Show current values in context with historical data spanning at least 24 hours by default

• Include high and low operating limits as reference lines

• Allow easy adjustment of time scales from minutes to weeks

• Support comparison of multiple related parameters on a single trend

• Provide rate-of-change indicators for critical variables

In Atlantic Canadian facilities where seasonal variations significantly impact operations—from summer peak demand periods to winter heating requirements—trend displays that can show weekly or monthly patterns provide valuable context for operational decisions.

Embedded Status Indicators

Modern HMI design incorporates embedded indicators that provide operators with at-a-glance status information without requiring navigation to detailed displays. These indicators might include:

• Equipment health status: Visual indication of equipment approaching maintenance thresholds

• Control loop performance: Quick identification of loops operating in manual mode or experiencing excessive deviation

• Throughput indicators: Real-time production rate compared to targets

• Energy consumption metrics: Particularly relevant for Nova Scotia facilities managing electricity costs and emissions targets

Mobile HMI and Remote Monitoring Considerations

The increasing adoption of mobile HMI solutions presents both opportunities and design challenges. For industries across the Maritime provinces, where facilities may be geographically dispersed and staffing efficiencies are essential, mobile access to control system information has become increasingly valuable.

Responsive Design Principles

Effective mobile HMI applications must adapt to smaller screen sizes while maintaining usability. Key considerations include:

• Touch-friendly targets: Minimum touch target sizes of 44 x 44 pixels for reliable interaction

• Simplified navigation: Streamlined menu structures appropriate for mobile contexts

• Bandwidth optimisation: Efficient data transmission for reliable performance on cellular networks, particularly important in rural Nova Scotia areas with limited connectivity

• Role-based access: Clear distinction between monitoring and control capabilities based on operator credentials and context

Security Considerations for Remote Access

Mobile HMI deployments must incorporate robust cybersecurity measures, including encrypted communications, multi-factor authentication, and appropriate network segmentation. Canadian facilities should ensure compliance with relevant standards including CSA C22.2 and applicable provincial regulations governing industrial control system access.

Ergonomic Considerations for Control Room Design

While HMI software design is crucial, the physical environment in which operators interact with these systems significantly impacts effectiveness. Control room ergonomics encompasses workstation design, lighting, and environmental factors.

Workstation Layout and Display Positioning

Optimal control room workstation design follows established ergonomic principles:

• Primary display positioning: Critical information displays should be positioned within 15 degrees of the operator's direct line of sight

• Secondary displays: Supporting information can be positioned up to 35 degrees from centre

• Viewing distance: Typically 50-70 centimetres for primary workstation monitors, with appropriate text sizing (minimum 3mm character height at viewing distance)

• Multi-monitor configurations: Consistent bezel alignment and seamless mouse movement between screens

Lighting and Environmental Factors

Control room lighting requires careful balance to support both screen visibility and document reading. Recommended illumination levels range from 300-500 lux at work surfaces, with provisions for task lighting where needed. Glare control through appropriate window treatments and indirect lighting fixtures helps reduce eye strain during extended shifts.

Implementation Best Practices and Continuous Improvement

Successful HMI design is not a one-time project but an ongoing process of refinement based on operator feedback and operational experience. A structured approach to implementation maximises the benefits of improved interface design.

Operator Involvement and Training

Engaging operators throughout the design process ensures that interfaces reflect actual operational needs rather than theoretical ideals. This involvement should include:

• Requirements gathering sessions: Structured interviews with experienced operators to understand current pain points and workflow requirements

• Prototype reviews: Iterative evaluation of proposed designs before final implementation

• Comprehensive training: Ensuring operators understand both the mechanics of new interfaces and the rationale behind design decisions

• Post-implementation support: Readily available assistance during the transition period

Performance Monitoring and Optimisation

Establishing baseline metrics before HMI improvements and tracking performance afterward provides objective evidence of effectiveness. Key metrics might include:

• Alarm rates and response times

• Operator navigation patterns and screen usage statistics

• Production efficiency and quality metrics

• Incident rates and near-miss reports

For facilities across Nova Scotia and Atlantic Canada, where operational efficiency directly impacts competitiveness in national and international markets, demonstrable improvements in these metrics can justify continued investment in HMI optimisation.

Partner with Sangster Engineering Ltd. for Expert HMI Design

Implementing effective HMI design requires a combination of technical expertise, understanding of human factors principles, and practical experience with industrial control systems. Sangster Engineering Ltd., based in Amherst, Nova Scotia, brings decades of automation engineering experience to clients throughout the Maritime provinces and beyond.

Our team understands the unique challenges facing Atlantic Canadian industries, from the demanding environmental conditions to the need for efficient operations with lean staffing. We work closely with our clients to develop HMI solutions that enhance operator effectiveness, improve safety, and optimise production performance.

Whether you are planning a new automation system, upgrading existing HMI displays, or seeking to improve alarm management performance, Sangster Engineering Ltd. offers the professional engineering services you need. Contact us today to discuss how we can help your facility achieve operator-centred HMI design that delivers measurable results.

Partner with Sangster Engineering

At Sangster Engineering Ltd. in Amherst, Nova Scotia, we bring decades of engineering experience to every project. Serving clients across Atlantic Canada and beyond.

Contact us today to discuss your engineering needs.