Good HMI design follows a lifecycle (an HMI philosophy, a style guide, templates, testing and ongoing review), uses restrained colour so that abnormal conditions stand out, and manages alarms so operators are not overwhelmed. ISA-101 is the international standard for human machine interfaces in process automation, and the HSE-endorsed EEMUA alarm guidance sets a target of no more than one alarm every ten minutes on average in normal operation. This guide covers the principles and then the practical steps in TIA Portal and WinCC.
What does ISA-101 actually say?
ISA-101 provides a lifecycle framework for designing, implementing, operating and maintaining HMIs. ISA's own page describes ISA-101.01-2015, Human Machine Interfaces for Process Automation Systems, as covering design, implementation, operation and continuous improvement, with key focus areas of human-centred design, effective display structures, intuitive user interaction and operator training. It applies across continuous, batch and discrete industries.
ISA also publishes supporting technical reports: ISA-TR101.01-2022 on HMI philosophy, and ISA-TR101.02-2019 on HMI usability and performance. The standard is paid for, although ISA says its members can view most ISA standards for free.
One caution before you copy a colour chart from any blog, including ours. ISA's public pages describe a philosophy and style-guide lifecycle rather than a fixed palette, so treat colour tables as a starting point for your own site style guide, agreed with operators, rather than as something the standard dictates.
Why does HMI design matter?
Poor HMIs and poor alarm systems contribute to real incidents. In the 1994 Texaco refinery explosion at Milford Haven, which injured 26 people and caused around £48 million of damage, HSE's investigation found too many poorly prioritised alarms and control room displays that did not help operators understand what was happening; in the last 11 minutes before the explosion the two operators had to recognise, acknowledge and act on 275 alarms (HSE, Better alarm handling). On a wider scale, a 1996 paper from the Abnormal Situation Management (ASM) Consortium estimated that preventable losses from abnormal situations cost the US economy at least $20 billion a year, about half in direct losses to petrochemical companies. That figure is old and American, but it shows why the discipline exists.
What is a high-performance HMI?
A high-performance HMI is a display designed for situational awareness: it shows the operator at a glance whether everything is normal, what has changed and where to focus. The idea, popularised by the ASM Consortium and reflected in ISA-101 practice, is a move away from busy, colourful, photo-realistic screens towards simple, information-rich ones.
The screen above is a typical conventional display: saturated colours everywhere, so nothing stands out when something is wrong. A high-performance version would use a muted background and equipment in neutral tones, and reserve bright colour for abnormal conditions. This video explains the approach clearly.
Practical principles that follow from this:
- Neutral background, colour for meaning. Use a light-to-mid grey background, grey equipment outlines and dark text. If everything is coloured, nothing is an alarm.
- Show values in context. A number alone is weak; show the range, setpoint, alarm limits and a small trend so the operator can judge at a glance.
- Limit animation and effects. Animated 3D tanks and decorative graphics hide information and add noise.
- Keep layouts consistent. Put navigation, alarm summary and status in the same place on every screen.
How should screens be organised?
Use a hierarchy of screens with consistent navigation, so operators always know where they are and how to reach the detail they need.
| Level | Purpose | Typical content |
|---|---|---|
| 1. Site or area overview | See the whole plant at a glance | Simplified units, aggregate health, alarm summary, key KPIs |
| 2. Unit overview | Operate one unit or line | Equipment, operating mode, key values and trends |
| 3. Equipment detail | Diagnose and tune | Tags, setpoints, trends, local alarms, interlock status |
| 4. Diagnostic and maintenance | Troubleshoot | I/O status, device parameters, alarm history |
Good navigation practice: a home button in the same position on every screen, breadcrumbs showing the current location, consistent button layout (do not move Start and Stop between screens) and a style-guide target for how many steps it takes to reach any detail screen. Three clicks is a common target, but it is a design choice rather than a rule from the standard.
What are the best colour and layout rules?
Use colour sparingly, never rely on colour alone, and agree the meanings with your operators in the style guide. A sensible starting scheme looks like this.
| Meaning | Suggested treatment | Notes |
|---|---|---|
| Normal, running, stopped | Greys and muted tones | Normal should be visually quiet |
| Warning | Yellow or amber | Attention needed soon |
| Alarm | Red, with a shape or text cue | Reserve for conditions needing action |
| Out of service or bypassed | Blue or light blue | Distinguish from live equipment |
Dual coding matters because colour vision deficiency is common. According to Colour Blind Awareness, it affects approximately 1 in 12 men (8%) and 1 in 200 women, so add text, shape or position to every colour meaning. For text, the Web Content Accessibility Guidelines (WCAG 2.2) set a contrast ratio of at least 4.5:1 for normal text; WCAG is written for the web, but it is a useful, testable benchmark for HMI text too. Avoid pure black backgrounds that cause glare in bright control rooms, and size text and touch targets for the real operating environment, including gloved hands on tablets.
How should you manage alarms?
Alarm management is where HMI design most directly affects safety, so design it to a recognised standard from day one. The main references are EEMUA 191 (Alarm systems: a guide to design, management and procurement), ISA-18.2 (Management of Alarm Systems for the Process Industries) and the IEC 62682 lifecycle that EEMUA 191 aligns with. EEMUA's contents listing shows a fourth edition published in 2024.
HSE's information sheet, which quotes the EEMUA guide, gives the practical targets:
| Measure | Target | Source |
|---|---|---|
| Long-term average alarm rate in normal operation | No more than one every ten minutes | HSE information sheet, quoting EEMUA 191 |
| Alarms displayed in the first ten minutes after a major upset | No more than ten | HSE information sheet, quoting EEMUA 191 |
| Number of priorities | About three, based on consequence if the operator fails to respond | HSE information sheet |
| Priority split | About 5% high, 15% medium, 80% low | HSE information sheet, quoting EEMUA 191 |
HSE's approach is to measure first (how many alarms, how many are useful, how many during an upset, how many standing), ask operators about alarm floods and nuisance alarms, then plan and fix. Common remedies are alarm rationalisation to remove alarms that need no operator action, consistent priorities, suppression of chattering alarms, shelving of known conditions during maintenance with a log, and grouping related alarms so one cause does not produce fifty messages. Show an alarm summary on every screen.
What does this look like in TIA Portal and WinCC?
In Siemens projects, build the style guide first, then implement it centrally so every screen inherits it. Siemens offers a free HMI Template Suite library with templates, images and objects for WinCC Unified panels and PC runtime, and says you can change colours centrally in the TIA Portal Style Editor, for example to make the design grey rather than blue. That is a convenient way to apply a grey, low-saturation scheme once.
Practical tips:
- Define alarm priorities and acknowledgement rules once in your HMI philosophy, then map them to alarm classes in WinCC so behaviour is identical across the project.
- Build reusable faceplates for pumps, valves and motors so each shows state, mode, value in context and alarm status in the same way.
- Use consistent tag naming between the PLC and the HMI so alarm text and tags match what operators call the equipment.
- Test with operators on a simulated process before commissioning, because a screen that looks tidy to an engineer may fail an operator's workflow.
For the wider SCADA picture, see our SCADA tutorial and SCADA systems explained.
What are the most common HMI design mistakes?
- Too much colour, so red, yellow and green lose their meaning.
- Decorative 3D animation that hides information.
- Sound for every event, so operators mute everything and miss the critical alarm.
- No trend history, so operators cannot see what led to an event.
- Unfiltered alarm lists with hundreds of entries.
- Too many sub-screens for a single unit, which usually signals a weak hierarchy.
How EDWartens can help
The EDWartens UK Professional Module is a five-day live online class in Siemens TIA Portal. Day three covers HMI projects, screens, navigation and PLC-HMI integration, and days four and five cover WinCC SCADA including alarms and events and trending. It is online and Siemens-focused, using simulation rather than a physical rig. For free learning, try the TIA Portal HMI and WinCC course and the WinCC SCADA course. See the Professional Module page or sign up.
