In the UK, organisations handling highly hazardous materials are required by the Control of Major Accident Hazards (COMAH) Regulations to demonstrate that they understand and manage Human Factors risks, which includes Safety Critical Task Analysis (SCTA) reviews.
Historically, SCTA has been associated with strengthening reliability by finding potential errors and strengthening defences to prevent them. But that’s only half of the story.
In the real world, variability is constant. Equipment behaves unexpectedly, conditions change, and goals conflict. Because of this, people need to adapt to keep the system safe. This is where resilience comes in. Resilience is about those adaptations: how people recover, improvise and maintain control when the conditions shifts. It is about understanding why and how things usually go right, and not just why they could go wrong.
Reliability Example A boiler system is fitted with automated alarms and shut-off controls that activate when pressure rises above safe operating limits. These systems ensure the boiler shuts down safely even if an operator is distracted. Resilience Example Before any alarm sounds, an operator walking past hears a faint hissing noise and recognises it as an early sign of a steam leak. They isolate the feedwater system and call maintenance before pressure starts to climb. Their detection and early action prevent the situation from reaching the point where the automatic safety controls would have triggered. |
SCTA can bridge both reliability and resilience. It helps organisations prevent failures and understand how people adapt, cope, and succeed in real operational environments.
We break down how each stage of the SCTA process helps organisations understand system behaviour and strengthen both reliability and resilience.
Hierarchical Task Analysis (HTA): Understanding How Work Actually Holds Together
Once a task has been selected for analysis, the first step for any SCTAs is to do a task analysis or a Hierarchical Task Analysis (HTA). This involves breaking the task into step-by-step components to understand how the work is done.
Even at this early stage, SCTAs can start to reveal resilience. Through HTAs, you can spot where the task sequence naturally supports safe performance and where the task might feel clunky, overloaded, or overly dependent on judgement. The task flow can indicate how easily operators can maintain control when things change and how well they can recover when things drift.
HTAs also highlight where operators might rely on cues to continue their tasks. People often use sounds, sights, timings, or “feel” to guide their actions, even when these are not written down. Such cues play a major role in helping operators detect possible shifts within the system early, and prevent predictable problems from escalating.
Insights from the HTA also help guide later conversations during workshops and walkthroughs, building early awareness of where resilience already exists within the task.
Workshops: Exploring Variability, Vulnerabilities, and Strengths
During the SCTA workshops, we sit down with the operators and other relevant personnel to discuss the possible failure modes, the Performance Influencing Factors (PIFs), and potential controls to prevent and mitigate unwanted scenarios.
Beyond identifying reliability risks, these discussions also uncover resilience. Operators often reveal informal steps or safeguards they use to navigate the task such as a quick visual check, listening for a familiar sound, or pausing at a natural break point. These informal practices enrich the analysis and turn the SCTA into a conversation about how work is actually done, not just how it is documented.
Workshops also help us understand the contextual factors that support smooth performance. It’s easy to focus on negative PIFs, but identifying positive PIFs is equally valuable. These positive influences help us understand what makes a task successful and can be reinforced or replicated across other tasks.
These workshops are not only about analysing risk. They are about capturing the tacit knowledge operators use to manage variability.
Walkthroughs & Talk-throughs: Seeing Real-World Adaptation
Walkthroughs are another valuable aspect of the SCTA process that bridges reliability and resilience. During walkthroughs, we observe how the task is performed and the environment it is performed in, and highlight possible areas to optimise the context in which the task happens, supporting reliability.
Walkthroughs also reveal adaptation and workarounds that may emerge due to design limitations or contextual pressures. This is resilience in action, finding out how people detect discrepancies early, diagnose changing conditions, and help the system recover when things drift.
Walkthroughs turn the SCTA from a desktop exercise into a learning dialogue. They show how the system actually behaves, and how people help maintain stability and safety day to day.
Improvements and Recommendations: Designing for Safer, More Resilient Performance
The final part of the SCTA review, identifying interventions and improvements, is where organisations strengthen both reliability and resilience. Training and procedures still have a role, but they are rarely enough on their own. Systems-level changes, aligned with Hierarchy of Control, create more sustainable, long-term improvements.
When we reduce reliance on the human element by fixing design issues, simplifying interfaces, and strengthening barriers, we build reliability.
When we create systems that help people notice changes, adapt safely, and recover quickly, we build resilience. This could be through better feedback loops, clearer informational cues, and environments that support human performance more effectively.
A resilient system is not one that expects operators to cope better, it is one that is designed to help people succeed even when conditions shift.
Feeding Insights Back Into the Organisation: Learning and Quality Improvement
Once the SCTA is complete, the findings go beyond just words in a report. They feed into procedure design, training materials, competence development, and safety management reviews, all of which contribute into a more resilient system.
SCTA captures both vulnerabilities and strengths, including the positive PIFs and good practices that make tasks successful. When these strengths are formalised and reinforced, good practice becomes standard practice within the organisation.
This turns SCTA into a continuous feedback loop that supports not only safety but quality improvement as well, shaping decisions across human, technical, and organisational layers.
Reliability and Resilience Go Hand In Hand
Reliability helps us prevent failure while resilience helps us recover and learn from it.
Both of these are essential for a sustainable system. Focusing only on reliability risks brittleness, expecting consistency, unchangeable actions despite different circumstances. Focusing solely on resilience risks normalising workarounds.
There can also be trade-offs between the two. Increasing reliability through standardisation or automation can sometimes reduce opportunities for operators to maintain or develop adaptive skills. For example, automating a routine task may reduce human error, but over time it can erode situational awareness or hands-on competence, making operators less able to intervene effectively when automation fails.
Similarly, leaning too heavily on resilience, such as allowing people to adapt, improvise, or work around design weaknesses, can mask underlying system problems and normalise drift.
A good SCTA brings both together: tightening engineering controls where needed while preserving human judgement where it matters. This balance underpins safer operations and sustained quality improvement. Learning from how systems succeed, not just how they could fail, creates a stronger foundation for safe and effective work.
There is also an interesting relationship between the two: sometimes resilient behaviours can be formalised and become part of reliability. For example, operators may consistently perform an informal check because it catches early signs of trouble. Once this behaviour is recognised and incorporated into procedures or design improvements, it becomes a dependable barrier rather than an ad-hoc adaptation. In this way, resilience often reveals opportunities to strengthen reliability.
Each SCTA becomes an opportunity for organisational learning, revealing how systems succeed, how people protect them, and how those insights can drive lasting improvement.
Does you SCTA reflect how work is really done, and does it capture how people succeed?
If you would like to benchmark your current approach, try our SCTA Health Check, a simple one-page tool to reflect on your practice and identify where reliability and resilience can grow together: HRA’s SCTA Top 10 Quickfire Self-Assessment Sheet | Human Reliability
We are planning to launch a course exploring how the SCTA process applies in high-hazard industries beyond COMAH, such as pharmaceutical manufacturing, civil services, and other safety-critical sectors. If you are interested in the course, express your interest here: SYSTEMS Critical Task Analysis (SCTA) Course
