On the evening of March 6, 1987, the Herald of Free Enterprise capsized just minutes after leaving the Belgian port of Zeebrugge, killing 193 passengers and crew. This maritime disaster, one of Britain’s worst peacetime shipping accidents, offers a powerful case study for understanding how modern human factors methodologies can be applied retroactively to reveal the complex web of failures that led to tragedy.
The COMAH regulations provide crucial guidance here, suggesting that “investigations follow a path similar to human failure analysis in reverse.” This insight points to an innovative approach where the same analytical frameworks used for proactive risk assessment can be applied retrospectively to incident investigation. Rather than treating these as separate processes, we can create an integrated methodology that strengthens both our ability to predict future failures and learn from past ones.
The Herald of Free Enterprise disaster demonstrates exactly why this “SCTA in reverse” approach is so valuable. Whilst the immediate cause – sailing with bow doors open – was quickly identified, the real learning lies in understanding the systematic human factors that created the conditions for this failure. How did multiple experienced crew members, operating under established procedures, collectively fail to prevent a catastrophic oversight?
The Power of SCTA in Reverse
Traditional incident investigation often stops at identifying what went wrong or the root cause. SCTA in reverse goes further, using the same analytical tools we employ for proactive risk assessment:
- Hierarchical Task Analysis (HTA) to map out exactly what actually occurred versus what should have happened
- Failure analysis to systematically identify the human error modes that contributed to the disaster
- Performance Influencing Factors (PIFs) analysis to understand why these failures occurred
- Accident Sequence and Precursor (ASAP) model to examine both the precursor events that created latent failures and the missed opportunities for recovery
This approach reveals not just the immediate causes, but the latent conditions and systemic vulnerabilities that made the disaster almost inevitable. More importantly, it generates insights that can be directly applied to prevent similar failures in the future.
The Herald of Free Enterprise case perfectly illustrates this concept. By working backwards from the capsizing through the departure procedures, maintenance activities, and organisational conditions, we can demonstrate how SCTA methods illuminate failure pathways that traditional investigation might miss – and how this analysis points towards more effective interventions.
Let’s examine how this tragic event unfolds when viewed through the lens of “SCTA in reverse,” and explore what this innovative approach reveals about both the disaster itself and the future of incident investigation methodologies.
What does SCTA in Reverse Mean?
To understand “SCTA in reverse,” we first need to consider what SCTA looks like when applied proactively. Safety Critical Task Analysis – sometimes referred to by the HSE as the “Seven Steps Approach” – typically follows a forward-looking process:
- Identify critical tasks
- Conduct hierarchical task analysis
- Identify potential failure modes
- Assess consequences
- Analyse Performance Influencing Factors (PIFs)
- Quantify human error probabilities (if required)
- Develop risk reduction measures
One might initially think “SCTA in reverse” means literally working backwards through these seven steps. However, this proves neither practical nor particularly insightful in practice.
Instead, SCTA in reverse represents a more conceptual reversal – a fundamental shift in starting point and direction of analysis. Rather than beginning with a task and working forward to predict what might go wrong, we start with what actually did go wrong and work backwards through the accident sequence to understand how and why it happened.
The Conceptual Reversal:
- Starting point: Begin with the final catastrophic event (the Herald capsizing) rather than with a routine task (ferry departure procedures)
- Direction of analysis: Work backwards through the accident sequence, identifying the chain of events, decisions, and conditions that led to disaster
- Analytical framework: Apply the same rigorous SCTA tools – HTA, failure analysis, PIF assessment – but retrospectively rather than prospectively
- Integration of timelines: Examine not just the immediate incident sequence, but also the precursor events (maintenance activities, organisational decisions) that created latent failure conditions
The Herald of Free Enterprise Disaster: Event Summary
On the evening of 6 March 1987, the Herald of Free Enterprise, an eight-deck roll-on/roll-off (RORO) ferry operated by Townsend Thoresen, was operating the Dover to Zeebrugge route. The ship was not on her normal Dover-Calais service, which created complications with the port infrastructure at Zeebrugge—the loading ramp couldn’t be raised high enough to reach the upper vehicle deck (E deck), requiring the ship to take on ballast water to lower her bow.
At approximately 18:05 GMT, the Herald departed Zeebrugge with 459 passengers, 80 crew members, 81 cars, 3 coaches, and 47 trucks aboard. The ship was slightly overloaded by weight, a common occurrence that the captain had even reported to shore-side management.
The departure sequence unfolded under time pressure – the Herald was running five minutes behind schedule due to the slower loading procedure at Zeebrugge. Company memos had previously emphasised sailing “15 minutes early” and putting “pressure on the first officer” to maintain tight turnaround times.
As the ship left port, a catastrophic oversight was already in motion. Assistant Boatswain Mark Stanley, responsible for closing the bow doors, had returned to his cabin for a short break after clearing the car deck and fell asleep, missing the “harbour stations” call. Chief Officer Leslie Sabel, under pressure to reach his bridge station for departure, left G deck assuming Stanley would soon return to close the doors. Boatswain Terence Ayling, the last person remaining on deck, knew it wasn’t his responsibility to close the doors and didn’t realise both other crew members had left the area.
Captain David Lewry assumed the doors were closed – he couldn’t see them from the bridge due to the ship’s design, and there were no indicator lights to show their status. With no one checking this critical safety function, the Herald of Free Enterprise sailed into the shallow waters of Zeebrugge harbour with her massive bow doors wide open.
At 18:24 GMT, the ship passed the outer harbour mole. Captain Lewry, eager to make up lost time, accelerated to 18 knots – the maximum permitted speed. In the shallow water, this created a dramatically larger bow wave due to the “squat effect.” The bow wave, nearly four metres high, began cascading through the open bow doors onto G deck.
Within 30 seconds, approximately 2,000 tonnes of seawater had flooded the main vehicle deck. Unlike traditional ships with watertight compartments, the Herald’s open vehicle deck allowed the water to surge freely from side to side as the ship rocked – the “free surface effect.” This moving water mass destroyed the ferry’s stability.
At 18:28 GMT, just four minutes after leaving the outer harbour, the Herald began listing 30 degrees to port. The ship briefly attempted to right herself, but the physics were inexorable. Within 90 seconds of the initial flooding, the Herald of Free Enterprise had capsized onto her port side on a sandbar, half-submerged in shallow water approximately one kilometre from shore.
The speed of the disaster was devastating. There was no time for a mayday call, no opportunity to deploy lifeboats, no chance for passengers to don life jackets. The ship’s electrical systems failed immediately, plunging the vessel into darkness. Many passengers and crew were trapped inside as freezing seawater flooded the tilted corridors and cabins.
Rescue efforts began immediately as nearby vessels, including the Belgian dredger Sanderus, responded to the emergency. Despite heroic efforts by rescue services, the Belgian Navy, and surviving crew members, 193 people lost their lives – most from drowning or hypothermia in the near-freezing March waters.
The Herald was eventually refloated in April 1987, but with no buyers found for repair, she was sold for scrap. The Townsend Thoresen brand, fatally damaged by the disaster, was quickly rebranded by new owners P&O as P&O European Ferries.
Coming Next: Deep Dive Analysis and Future Directions
This tragic sequence – from routine departure to catastrophe in under five minutes – provides a compelling case for examining how multiple human factors combined with systemic pressures to create the conditions for disaster. Each element, from time pressures to communication failures to design limitations, offers insight into how SCTA methods can illuminate the complex causation behind major accidents.
But identifying the contributing factors is only the beginning. The real power of SCTA in reverse lies in the systematic analysis that follows – mapping the exact task breakdowns, categorising the specific failure modes, and understanding the Performance Influencing Factors that drove each critical decision.
In Part 2 of this series, we’ll conduct a detailed SCTA analysis of the Herald disaster, including:
- Hierarchical Task Analysis mapping what should have happened versus what actually occurred during the critical departure sequence
- Systematic failure mode analysis identifying the specific human error types at each stage
- Performance Influencing Factors assessment examining why these failures occurred—from organisational pressures to design limitations
- ASAP model application tracing both the precursor events that created latent failures and the missed opportunities for recovery
In Part 3, we’ll explore how this approach is evolving beyond traditional incident investigation methods. We’ll examine cutting-edge developments in incident analysis, including how to represent the complex relationships between immediate events and long-term latent conditions, and how to systematically identify the “non-events” – the things that should have happened but didn’t.
The Herald of Free Enterprise disaster reminds us that behind every “human error” lies a complex system of influences, pressures, and design decisions. SCTA in reverse gives us the tools to understand these systems—and more importantly, to design better ones.
Acknowledgements
This blog post was written with the assistance of Claude (Anthropic), which provided valuable support in structuring the analysis, synthesising information from multiple sources, and drafting content. The author remains responsible for the final content and any errors or omissions.
References
Primary Sources:
Sheen, Mr Justice (1987). mv Herald of Free Enterprise: Report of Court No. 8074 Formal Investigation. Crown Department of Transport. Available at: https://assets.publishing.service.gov.uk/media/54c1704ce5274a15b6000025/FormalInvestigation_HeraldofFreeEnterprise-MSA1894.pdf
Video Sources:
“193 Dead After Bow Doors Left Open!” YouTube video. Available at: https://www.youtube.com/watch?v=-YDpmdT9hzU(Accessed 2025)
“The Zeebrugge Ferry Disaster | A Short Documentary | Fascinating Horror.” YouTube video. Available at: https://www.youtube.com/watch?v=whvdjg6i2Hc&t=1s (Accessed 2025)
“Seconds from Disaster: Zeebrugge Ferry Disaster.” YouTube video. Available at: https://www.youtube.com/watch?v=1mHPGOvLX0k (Accessed 2025)
Additional Sources:
MS Herald of Free Enterprise. Wikipedia. Available at: https://en.wikipedia.org/wiki/MS_Herald_of_Free_Enterprise(Accessed 2025)
Embrey, D. (2025). TABIE: A Task Analysis Based Incident Evaluation technique. HRA Technical Paper. Human Reliability Associates Ltd.
Regulatory Guidance:
Health and Safety Executive. Human Factors Delivery Guide for COMAH Sites. HSE, December 2023.
Health and Safety Executive. COMAH SRAM 2015 – Human factors criteria. Available at: https://www.hse.gov.uk/comah/assets/docs/s12d.pdf
Note: This is Part 1 of a three-part series examining how Safety Critical Task Analysis methods can be applied retrospectively to major incidents. Future parts will include additional technical references and case study materials.
