Posted on May 15th, 2025

Dr. Chizaram Nwankwo

In high-hazard industries, where human error can lead to catastrophic outcomes, understanding the interactions between people, processes, and systems is vital. At Nancheez Ltd, we specialize in applying Safety Critical Task Analysis (SCTA) to ensure that safety-critical human actions are both understood and safeguarded. This blog post explores the purpose, methodology, benefits, and practical applications of SCTA—making the case for why it should be an essential part of your risk reduction strategy.

What is Safety Critical Task Analysis?

Safety Critical Task Analysis (SCTA) is a structured, systematic approach used to identify, analyse, and mitigate the potential for human error in safety-critical tasks. These are tasks where failure or deviation could directly lead to a major accident hazard (MAH) such as explosions, toxic releases, or fatalities.

It goes beyond traditional job analysis by specifically targeting tasks that, if performed incorrectly, could undermine the integrity of safety barriers, lead to process upsets, or compromise emergency response. SCTA is grounded in human factors and systems thinking, integrating technical, operational, and psychological considerations into one cohesive framework.

Why is SCTA Important?

Human reliability is a fundamental pillar of safety performance. In many major incidents—such as Piper Alpha, Texas City, or Buncefield—human error played a pivotal role. Often, these errors were not due to incompetence or negligence but because of unrealistic procedures, poor interface design, insufficient training, or fatigue.

SCTA helps organisations:

• Understand how tasks are performed in real-world conditions (not just how they are described on paper)
• Identify gaps between designed procedures and actual practice
• Reduce the likelihood of error through redesign, simplification, training, and controls
• Demonstrate compliance with COMAH, CDM, ISO 45001, and HSE guidance (HSG48, HSG65, HSE RR1189)
• Protect the workforce and public from serious harm

Who Needs SCTA?

SCTA is especially relevant for safety-critical industries where human error can contribute to:

• Loss of containment
• Fire and explosion
• Environmental pollution
• Equipment failure
• Delayed or failed emergency response

Sectors we support at Nancheez Ltd include:

• Oil and Gas (Upstream and Downstream)
• Offshore Installations
• Chemical and Petrochemical Plants
• Power Generation (Nuclear and Conventional)
• Pharmaceuticals and Biotech Labs
• Utilities and Infrastructure
• Maritime and Transportation

Regulatory and Industry Expectations

Regulators such as the UK Health and Safety Executive (HSE) and frameworks such as the OGUK Human Factors Guidelines, IOGP Report 454, and Energy Institute Guidance all emphasise the importance of integrating human factors and SCTA in safety case submissions.

The HSE’s Human Factors Roadmap highlights SCTA as a key enabler to reduce MAH risks. Moreover, the Control of Major Accident Hazards (COMAH) regulations specifically call for analysis and control of human contributions to safety barriers.

By proactively conducting SCTA, organisations are better positioned to meet legal requirements and provide assurance to regulators, shareholders, and the public.

The SCTA Process: Step-by-Step Approach

At Nancheez Ltd, we follow a best-practice, five-phase approach to SCTA, adapted from HSE RR1189 and other industry guidance. This ensures consistent, repeatable, and defensible analysis.

Phase 1: Identify Safety Critical Tasks

We begin by identifying tasks that are linked to safety barriers or risk controls. These may include:

• Equipment start-up and shutdown
• Isolation and re-instatement of plant
• Permit to Work operations
• Emergency response actions
• Manual overrides or resets
• Sampling, draining, or depressurising
• Control room operator interventions

We engage with engineers, operators, process safety leads, and SMEs to map these tasks to MAH scenarios.

Phase 2: Prioritise Tasks Using Screening Tools

Given the volume of operational tasks, not all require detailed analysis. We apply preliminary screening matrices that assess:

• Consequence of human error
• Frequency of task performance
• Level of discretion or judgement involved
• Complexity of task steps
• Existing safeguards

Only tasks scoring medium or high proceed to the full SCTA phase.

Phase 3: Task Analysis

This involves breaking the selected task into step-by-step actions, identifying:

• What must be done
• By whom
• Using what tools, systems, or interfaces
• Under what conditions or time constraints

We use methods such as Hierarchical Task Analysis (HTA) and conduct walkthroughs and interviews with frontline workers to capture operational realities. These are often cross-referenced with procedures, training documents, and permit systems.

Phase 4: Human Error Identification and Risk Assessment

At this stage, we identify potential human failure modes, such as:

• Action errors (e.g. omission, repetition)
• Checking errors
• Selection errors
• Retrieval errors (e.g. from memory)
• Communication errors

We then evaluate the likelihood and consequence of each failure using a risk matrix and assign safeguards or recovery measures, such as:

• Alarms and indicators
• Procedural checks
• Peer verification
• System interlocks
• Training and competence checks

Each risk is documented with supporting rationale and evidence.

Phase 5: Recommendations and Risk Reduction

The final phase involves formulating practical, tailored actions, such as:

• Simplifying or clarifying procedures
• Improving interface design (e.g. better HMI layouts)
• Introducing prompts, aids, or checklists
• Adjusting roles or responsibilities
• Enhancing training or supervision
• Applying automation or engineering controls where feasible

We prioritise recommendations using the hierarchy of risk controls and ensure alignment with the organisation’s ALARP (As Low As Reasonably Practicable) principle.

SCTA Outputs and Deliverables

At Nancheez Ltd, our SCTA deliverables are designed to support decision-making and regulatory assurance. These include:

• SCTA Register and Screening Matrix
• Task Breakdown and HTA Diagrams
• Human Error Analysis Table
• Barrier Mapping (linking tasks to safety functions)
• Risk Assessment Summary
• Recommendations Tracker
• Executive Summary for Senior Stakeholders

Our outputs are tailored to your project stage—whether pre-FEED, commissioning, or operational—and formatted to suit your safety case or COMAH report.

Real-World Applications: Case Examples

Here are a few anonymised case studies illustrating how SCTA added value to our clients:

Offshore FPSO: Turret Turnaround and Cargo Offload

We worked with a North Sea operator to assess complex marine and production tasks involving turret locking, offloading, and ESD testing. SCTA revealed excessive reliance on manual interventions and identified conflicting instructions between control room and deck operations. Our recommendations led to procedural revisions and additional HMI safeguards, significantly reducing risk.

Laboratory Operations: Biological Agent Sampling

In a multi-site health agency, SCTA was used to assess operator interactions during pathogen sampling, transfer, and inactivation. Our analysis highlighted a potential for mislabelling and containment breach. The client introduced a double-check protocol and improved vial colour-coding systems to enhance error recovery.

Refinery: Firewater Pump Activation

We analysed the emergency startup of firewater pumps during system failure scenarios. Task walkthroughs revealed that operators had to physically navigate to two distant control cabinets with no clear status indicators. We recommended control panel redesign and remote monitoring integration, which streamlined response times.

Common Pitfalls to Avoid in SCTA

Despite its benefits, SCTA can become a tick-box exercise if poorly executed. Watch out for:

• Over-reliance on desktop reviews without engaging operators
• Copy-pasting from procedures without observing task performance
• Ignoring latent conditions such as fatigue, distractions, or unclear roles
• Treating SCTA as a one-off exercise instead of integrating with Management of Change (MoC) and continuous improvement

At Nancheez Ltd, we ensure SCTA is a collaborative, evidence-based, and dynamic process.

How SCTA Links with Other Safety Management Systems

SCTA should not exist in isolation. It integrates naturally with:

• Bowtie Analysis – linking human actions to prevention and mitigation barriers
• Permit to Work Systems – validating critical tasks and control measures
• Competence Assurance – defining the skills needed to perform critical tasks reliably
• Incident Investigations – identifying task and system failures in past events
• Design Reviews (HAZOP/LOPA) – informing or validating critical control points

By embedding SCTA within broader safety processes, organisations can create a resilient operating environment.

Why Choose Nancheez Ltd?

At Nancheez Ltd, we are not just analysts—we are human factors practitioners, engineers, and safety leaders. Our SCTA services stand out because we:

• Bring deep industry expertise in oil & gas, chemicals, healthcare, and critical infrastructure
• Use proven frameworks based on HSE RR1189, IOGP 454, and EI guidance
• Collaborate across disciplines—engaging engineers, SMEs, and operators alike
• Translate findings into actionable, risk-reducing improvements
• Provide regulator-ready reports and support through audits and inspections

Whether you're preparing a new project, conducting a review after an incident, or updating your COMAH submission, we tailor our SCTA services to your needs.

Final Thoughts: A Human-Centred Approach to Safety

Technology continues to evolve, but humans remain a critical part of any high-risk system. When safety depends on timely, accurate, and reliable human actions, SCTA offers a powerful tool to protect people, assets, and reputation.

By investing in Safety Critical Task Analysis today, you are strengthening your operational resilience for tomorrow.

Ready to start your SCTA journey?

Contact Nancheez Ltd today for a no-obligation consultation on how we can help reduce human error and improve task reliability in your operation.

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🌐 www.nancheez.co.uk
📍 UK-based | Supporting clients globally