The process industry hinges on a close relationship between machines and people. This has always been the case, but the moments when human judgment must take over have become especially noteworthy given how precisely today’s advanced control systems, predictive analytics and safety instrumented systems can now handle routine tasks. One of the most defining challenges of the modern process industry is negotiating the line between what automation can do and what a trained human must judge. Automated systems count on human decision-making in the loop during critical moments, so taking steps to reduce operator error also means strengthening reliability and plant safety as a whole.

The gap between automation and human judgment

Automation performs repeatable, well-defined tasks with a high degree of reliability. Novel situations (ones that no engineer explicitly anticipated) require a different kind of response. When conditions fall outside programmed logic, the system hands control back to a person. That handoff often happens during an abnormal situation, with alarms active and time pressure mounting. The quality of that handoff and subsequent results depends entirely on how well the interface, procedures and training prepared the operator for the moment.

We often see operators left interpreting inconsistent interfaces that pull data from multiple, poorly integrated sources, with limited contextual information available to quickly address abnormal conditions. This is a well-documented pattern across high-hazard operations such as those involving reactive chemicals or dangerous physical conditions. When an incident occurs, the technical layers surrounding the operator, including the design of displays, procedures and system feedback, determine whether that person is equipped to react optimally under pressure. Automation professionals must be empowered in the moment with the right knowledge they need to make decisions and act on them quickly.

Practical steps to reduce operator error

1. Design interfaces around the operator's task and situational awareness needs. Sometimes, displays organized to mirror piping diagrams fail to match the way operators actually think through a problem. Establishing a clear navigational hierarchy helps, as operators can then easily see an overview of their full realm of control, drill-downs to unit operations, task-detail screens and diagnostic layers. The structure enables operators to move quickly from the big picture to a specific fault.

This thinking is foundational to ISA-101, the widely used human-machine interface (HMI) series of standards for industrial operations. The series describes a lifecycle approach spanning HMI philosophy, style guide, design, implementation and continuous improvement.

2. Build in barriers and buffers. Operators need to be able to catch a problem before it propagates. Physical guards and interlocks, failsafe defaults, redundant confirmation steps for high-consequence actions and time delays all help give that chance. These concepts align with best practices in human factors engineering, which call for barriers to prevent errors with unacceptable consequences and buffers, such as redundant structures and reversible or staged actions, to catch issues before they escalate.

3. Treat alarm management as a core safety system. Alarm floods during abnormal situations are common precursors to operator error. Prioritizing and rationalizing alarms so the critical ones stand out clearly supports an operator's ability to detect, diagnose and respond to abnormal situations, a core objective of well-structured HMI and alarm philosophy work. Another standard, ISA-18.2, provides a lifecycle framework for alarm management in process control and is broadly implemented across manufacturing and critical infrastructure applications.

4. Invest in realistic, scenario-based training. Simulator-based training on abnormal situations, near-miss reviews and tabletop walkthroughs of past incidents build the pattern recognition operators need when the unexpected occurs. This kind of preparation gives operators a mental library of scenarios to draw from during real events. Some owner operators have even invested in digital twins and virtual or augmented reality applications to help train and acclimate operators before a real incident takes place.

5. Invest in change management as a living discipline. Even a small alteration to a control scheme, a setpoint or a display can impact what the operator needs to know. A rigorous change management process, with mandatory human factors review, keeps operator understanding of the system aligned with the plant as it evolves.

6. Close the loop with audits and validation. Periodic audits against the site's HMI philosophy and style guide, when combined with operator feedback, help to keep interfaces and procedures aligned with plant modifications, new hazards and lessons learned across the industry. Treating this as ongoing work keeps the system and operators up to date.

7. New methods for human-dependent safety functions. Many safety layers rely on a person to correctly detect, decide and act under time pressure. The International Society of Automation (ISA) has been developing a dedicated framework for these barrier types. The framework defines a human-dependent active barrier (HDAB) as an active protection layer in which one or more barrier functions depend on human detection, decision and/or action, potentially supported by technical, procedural or organizational elements.

To correctly allocate a safety function to an HDAB, the framework under development will ask organizations to demonstrate “meaningful human control” across five dimensions: authority to intervene, reject, override or stop the function; situational awareness supported by the barrier's design; context and conditions, including interface design, workspace, communications and staffing; sufficient time for detecting, deciding and acting; and workload that remains manageable even under credible worst-case conditions.

Where a protection layer blends human-dependent and instrumented elements, the allocation basis must state whether the function is treated as an HDAB, a low-integrity protection layer, a safety instrumented function or a safeguard. Protection layers must be independent enough that shared operators, shared interfaces, alarm floods, workload peaks or common organizational conditions don't undermine the risk reduction a plant is counting on. When a safety function depends on human action, that role needs to be specified explicitly rather than just implied in training or procedure documents. ISA recommends a multi-disciplinary approach to these determinations, drawing on process engineers, hazard and risk specialists, instrument, automation, process safety and human factors engineering and human reliability specialists.

This emerging framework builds on long-standing concepts from the ISA-84 series of standards, including the requirement in ANSI/ISA-84.00.01 that when human action forms part of a safety instrumented system, the availability and reliability of that action must be specified in the safety requirements specification and factored into performance calculations. The framework also complements ISA-TR84.00.04, which addresses basic process control system (BPCS)-based protection layers, operator supervision and administrative controls, and the newer ISA-84.91.03 standard on low-integrity protection layers, which references ANSI/ISA-101.01 for human-machine interface requirements.

Improving plant safety through human-machine partnership

Plants making strong progress on reliability and safety focus on redesigning the partnership between people and systems. This means giving operators real-time, contextual information to act decisively, building interlocks and buffers that account for natural lapses in attention and treating operator training, interface design and change management as interconnected disciplines.

At ISA, we believe that “automation depends on people.” The facilities that are best positioned to prevent the next incident ask how they can make sure operators have everything they need to make the right call when they are needed the most. Designing systems that actively support human judgment, backed by standards like ISA-101 and ISA's emerging framework for human-dependent active barriers, is where the real gains in reliability and safety are being made.