Journal Detail back to listing
Why “User Error” Is Rarely the Root Cause of Workplace Injury
- Jun 16, 2026
- Latest Journal
Why “User Error” Is Rarely the Root Cause of Workplace Injury
by Adam King, EUR ING, MSc, CEng, TechIOSH, MIAAI, Associate Director, Forensic Investigation and Personal Injury at RIMKUS.
In workplace personal injury claims involving work equipment, an employer frequently cites “user error” as the cause of an incident. While user actions often feature in the final moments of an incident, forensic engineering investigations consistently demonstrate that user error is rarely the root cause. This article looks at why courts, regulators, and insurers increasingly expect an engineering‑led analysis of causation, and why reliance on “user error” alone presents both litigation and indemnity risk.
Introduction: The persistence of “user error”
From initial notification through to early expert instruction, claims documentation frequently characterises workplace incidents using phrases such as:
- The operator misused the equipment
- The injured party failed to follow the training
- The employee failed to follow the employer’s instructions.
Although such descriptions may appear straightforward, they are increasingly vulnerable to challenge under forensic and legal scrutiny. In litigation, courts now move beyond these surface explanations and ask a more fundamental question: why was the system capable of producing harm at all?
Forensic investigations across machinery operation, maintenance activities, and industrial environments have demonstrated that user action is typically the final link in a longer causal chain, rather than the initiating failure. These statements may describe what occurred, but they do not explain why injury was possible.
Courts increasingly require an analysis of whether:
- The equipment was inherently safe by design
- The incident was foreseeable
- Were engineering controls sufficient and correctly implemented
- Did the system rely excessively on procedural compliance rather than physical safeguards and supervision?
From a forensic perspective, reliance on user error alone risks oversimplification and can weaken a claim’s defensibility.
The distinction: Immediate cause, underlying cause and root cause
A recurring issue in personal injury claims is the confusion among three distinct concepts: immediate, underlying and root cause. These terms are often used interchangeably in claims narratives, despite having materially different meanings within an engineering-led causation analysis.
- Immediate Cause: The immediate action preceding the injury
- Underlying Cause: The means by which the work equipment was able to cause harm
- Root cause: The reason the hazardous condition existed.
For example:
- Immediate Cause: The operator’s hand entered the danger zone
- Underlying Cause: Exposure to unguarded moving parts
- Root cause: Inadequate guarding, ineffective interlocking, or unsafe by design
In practice, claims frequently focus on the immediate as though it were the cause. Whilst this initially looks convincing, this approach is increasingly vulnerable to forensic and legal scrutiny.
Consider the above scenario of a user reaching into a machine and sustaining injury. Labelling the cause as “user error may describe the final action, but it does not explain why the hazardous underlying cause remained accessible. The critical forensic question is not what the individual did, but why the system of use permitted injury to occur, the root cause.
Equipment does not fail randomly
From an engineering standpoint, for the use of equipment, workplace safe systems of work are designed on the premise that:
- People make mistakes
- People take shortcuts
- People deviate from training from time to time.
These assumptions are fundamental to established safety‑engineering principles, including:
- Hierarchies of guarding and protection
- Fail‑safe design philosophies
- Interlocks and system redundancy
- Ergonomic control layout and people–machine interface design
When an injury occurs, it is often because the system has tolerated foreseeable human behaviour without adequate engineering mitigation. In such cases, the presence of user action does not negate system failure, rather, it highlights a design or control deficiency that allowed predictable behaviour to result in harm.
Case study – electric saw injury during operations
Incident Summary
Unsafe use of saw machinery, specifically a failure to keep hands clear of the blade. The activity being undertaken formed part of normal, routine production operations. The physical guarding system in place was intended to provide primary protection against contact with the blade. However, damage and degradation of the guard reduced its effectiveness as a protective measure. As a result, the system relied on operator vigilance to compensate for diminished safeguarding performance.
Conclusion
The injured party’s interaction with the saw was the immediate cause of the incident, rather than its root cause. The underlying cause was that the safeguarding system was not delivering its intended level of protection. The root cause of the injury was systematic failures to implement statutory equipment maintenance and inspection requirements. The failure to identify the defect allowed foreseeable user interaction to result in harm.
Case study– entanglement during ship birthing
Incident Summary
The injured party was attaching lines to a newly installed capstan alone when a tangle began to develop. While the capstan remained in operation, an attempt was made to adjust the lines. During this interaction, the fingers became caught in the line, resulting in a crushing injury.
Conclusion
The injury occurred because the system permitted foreseeable user interaction with moving lines. The actions of the injured party constituted the immediate cause. The underlying causes were the absence of supervision and the lack of engineered measures to prevent access during operation. The failure to recognise the training needs of newly installed equipment and implement an engineered safe system of work was the root cause.
Regulatory and legal context
The Health and Safety Executive has consistently emphasised that employers must anticipate foreseeable user interaction and misuse, and that training alone cannot compensate for unsafe design or systems of work. The risk should be eliminated through adequate engineering measures included in the safe system of work.
These principles are embedded within the statutory framework, including the Provision and Use of Work Equipment Regulations (PUWER) and the Health and Safety at Work etc. Act (HSWA). Under these duties, employers are expected to:
- Anticipate foreseeable misuse of equipment
- Design out risk wherever reasonably practicable
- Avoid excessive reliance on procedural controls alone.
In civil litigation, arguments founded solely on “user error” are increasingly vulnerable. Such positions are open to challenge based on contributory negligence analysis, strict statutory duties, and expert evidence demonstrating that the risk was foreseeable and should have been controlled through engineering measures.
Conversely, expert opinions that attribute causation solely to operator behaviour, without examination of the adequacy of engineering controls, are often exposed under cross‑examination and carry reduced evidential weight.
When user error is the root cause
A safe system of work does not exclude findings of genuine user error. Where engineering controls are appropriate, effective, and properly maintained, forensic investigation can demonstrate that the injured party’s actions were the proximate cause of injury. Crucially, this conclusion must be physically evidence‑led rather than procedural or documentation-focused.
From a forensic engineering perspective, user error is defensible where the system is shown to be fundamentally safe, and the behaviour leading to injury was exceptional or unforeseeable.
Key considerations include:
- Engineering integrity: Confirmation that guarding, interlocks, and safety systems were present, compliant, and functioning as intended, with no defects or degradation.
- Foreseeability: Assessment of whether the action was a clear deviation from normal operation
- Training and instructions: Evidence that clear, reasonable, and task‑appropriate training and instructions were in place and aligned with system design.
- Deviation from safe systems: Identification of unjustified change from established systems of work, such as bypassing isolation or removing safeguards.
Why this matters to stakeholders
Claims Strategy
Early acceptance of “user error” as the cause of an incident can have adverse consequences. It may:
- Obscure potential third‑party liability, including that of equipment manufacturers, installers, or maintenance contractors
- Undermine subrogation prospects by prematurely narrowing the causation narrative
- Reduce leverage in liability apportionment and settlement discussions by conceding primary fault too early.
An engineering analysis at an early stage helps identify all contributing factors and preserves recovery and liability options.
Policy Response
Forensic engineering causation analysis frequently informs policy response by providing clarity on:
- Compliance with policy conditions relating to maintenance, inspection, and safe use
- The appropriate application of policy exclusions
- Allocation of liability between insured and uninsured parties, including third‑party contributors.
- Early technical scrutiny therefore supports both defensible coverage decisions and effective claims management.
Conclusion
User behaviour is almost always present in workplace accidents. However, it is rarely the root cause. Across machinery, industrial, and marine environments, forensic engineering analysis repeatedly demonstrates that injuries occur when systems fail to adequately manage predictable user interaction.
For insurers, brokers, and legal advisers, moving beyond default reliance on “user error” is essential to achieving defensible liability positions, accurate apportionment, and informed commercial outcomes. User actions provide the immediate context for many incidents, but they are seldom the originating cause of injury. It is the ‘system’s tolerance of foreseeable behaviour, through design, safeguarding, or control deficiencies, that typically enables harm.
Where forensic investigation establishes that equipment was appropriately designed, safeguarded, and maintained, and that risks were controlled through effective engineering measures, injury may properly be attributed to user error. In such cases, the decisive factor is not the mere presence of user action, but evidence that the behaviour was exceptional, unforeseeable, or involved deliberate circumvention of safety systems.
References:
1. Health and Safety Executive (HSE). Safe use of work equipment (PUWER Approved Code of Practice L22).
2. ISO 12100:2010 – Safety of machinery – General principles for design – Risk assessment and risk reduction.
3. HSE. Reducing risk, protecting people – HSG65.
About the Author
Adam King, EUR ING, MSc, CEng, TechIOSH, MIAAI
Associate Director, Forensic Investigation and Personal Injury
adam.king@rimkus.com
Adam is a Chartered Mechanical Engineer with over 20 years of multi-sector experience in engineering, mechanical maintenance, technical operations, and forensic investigation. He specialises in CPR 35 expert reporting, technical causation analysis, and evidence gathering for insurers, solicitors, and corporate clients.
He has led complex investigations across the UK and internationally, covering industrial facilities, biomass and CHP systems, marine fires, and large commercial and residential incidents. Adam also brings extensive expertise in PSSR and LOLER compliance, including developing and managing statutory inspection schemes to support operational safety, regulatory compliance, and equipment integrity.
He is recognised as a Chartered Engineer by the Engineering Council and as a European Engineer by Engineers Europe.
