Human Error and Fatigue: Psychological Factors in Manufacturing

Why does human error happen and how do fatigue and stress raise it? Read about error types in manufacturing, just culture and steps employers can take.

In the "root cause" section of a workplace accident report, two of the most frequently written words are "carelessness" and "failure to follow rules". The report is closed, the employee receives a warning, perhaps some extra training is held. A few months later a similar incident happens on the same line. Because the real question was never asked: why was this employee careless at that moment? Human error is often not the starting point of an incident but the visible result of deeper factors such as fatigue, workload, design, training and organisational culture. In this article I look at the psychological dimensions of error in manufacturing, how fatigue and stress increase error, and what employers, factory managers and occupational health and safety (OHS) specialists can do to reduce errors.

What Is Human Error, and Why Is "Finding Someone to Blame" Not Enough?

An error is a person failing to achieve the outcome they intended. The human mind is an extremely powerful system but one with limits: attention is limited, memory can fail, and decision-making ability deteriorates under fatigue and stress. These limits apply to everyone; the most experienced foreman and the most careful engineer can make mistakes.

According to an approach widely accepted in safety science, seeing error only as the individual's fault overlooks two important questions:

• What were the conditions that made this error possible? Fatigue, time pressure, a complex equipment design, incomplete training or an unclear instruction.
• Why was the error not noticed and stopped in time? A missing check step, a warning system that did not work, a team reluctant to report errors.

The "culprit found, case closed" approach may seem reassuring in the short term, but as long as the same conditions do not change, the error is repeated by someone else. On top of that, employees begin to hide their errors and near misses. This removes the organisation's chance to learn.

Imagine that in a furniture factory an experienced operator slightly injured his hand on a circular saw. The first report was closed saying "the employee did not use the guard". When the incident was examined in more detail, a different picture emerged: the operator had worked overtime six days in a row that week; because the machine's guard slowed cutting on parts of a certain size, the team had been working with it removed for years; the foreman knew this but turned a blind eye because of pressure from orders. Seen with this information, the problem is not just one person's carelessness but a combination of workload, equipment design and an established habit. The solution differs accordingly.

Types of Human Error: Not All Errors Are the Same

To understand and prevent errors, it helps to separate them by type:

Attention slips and lapses

The person knows what to do, but their attention slips during execution: pressing the wrong button, skipping a step, mixing up two similar parts. These errors increase especially in monotonous, repetitive work and under fatigue.

Memory errors

Forgetting to do a step, not noticing that you skipped a check, remembering an instruction wrongly. They are common in interrupted work, for example when an operator is called to another task in the middle of a job.

Wrong decisions and errors of judgement

The person misjudges the situation or chooses an unsuitable method. These errors often arise from missing information, inadequate training or an unfamiliar situation.

Rule violations

The person knowingly bends the rule: removing a guard, skipping the lockout-tagout step, not wearing personal protective equipment. Violations most often come not from bad intent but from the pressure to "get the job done", from a rule that is unworkable in practice, or from the habit of "we always do it this way and nothing has happened". So asking about the reason behind violations is more effective than simply punishing them. Seeing that a rule is constantly bent by many people is an important sign that the problem may lie not in the individual but in the rule itself or in the organisation of the work. In such cases, revisiting the rule together with employees increases both compliance and trust.

An organisation that looks at an error asking "who did it?" finds a culprit; an organisation that asks "why did it happen?" prevents the next accident.

How Do Fatigue and Stress Increase Human Error?

Fatigue

Sleeplessness and long working hours shorten attention span, lengthen reaction time and weaken decision-making ability. A tired mind makes more attention slips and memory errors while doing the same job. According to Folkard and Tucker's 2003 review, productivity and safety can deteriorate during night hours; safety worsens over consecutive nights, with increasing working hours and as the time between breaks lengthens. According to data reported with reference to this review, accident risk is about 30% higher on the night shift than on the morning shift, and in the 12th hour of a shift it is more than double the average of the first 8 hours (Folkard and Tucker, 2003). In the OSH Pulse 2022 survey carried out in Europe, general fatigue was also at the top of the health problems caused or made worse by work, at 37% (EU-OSHA, 2022).

Time pressure and workload

In the same survey, 46% of employees reported severe time pressure or excessive workload (EU-OSHA, 2022). Under time pressure, people shorten check steps, bend rules and notice risks less. The perception that the production target comes before safety is one of the strongest causes of violations.

Chronic stress and burnout

An employee whose mind is occupied with financial worries, problems at home or tension in the workplace has to spend part of their attention away from the job. According to a report published by Gallup in 2026, 66% of employees in Turkey report having experienced stress during a large part of the previous day; the global average is 40% (Gallup, 2026; 2025 data). In a systematic review of 36 prospective studies, burnout was found to predict a range of later negative outcomes, including serious injuries (Salvagioni et al., 2017). This finding shows that mental health is directly an occupational safety issue in the factory environment.

Monotony

Repeating the same movement for hours causes the mind to go on "autopilot". This increases attention slips. Article 5 of Law No. 6331 (Occupational Health and Safety Law) also requires the employer to prevent, or if it cannot be prevented to minimise, the negative effects of monotonous work and production pace on health and safety.

The Importance of the Human Factor in Manufacturing: Data from Turkey

According to the SGK (Social Security Institution) Statistical Yearbook 2025, 766,039 workplace accidents and 1,931 deaths from workplace accidents were recorded in Turkey in 2025. About 41% of accidents and about 22% of deaths took place in the manufacturing sector. Workplace accidents caused a total of 4,639,930 days of temporary incapacity for work (SGK, 2025). In Çorum, 3,821 workplace accidents and 12 deaths were recorded in the same year.

Behind each of these figures lies a story in which technical, organisational and human factors come together. In the ESENER 2024 survey of 41,458 workplaces in Europe, the workplaces that reported none of the psychosocial risk factors were most numerous in the manufacturing and agriculture sectors; this was presented as a finding that may point to a lack of awareness (EU-OSHA, 2025). In other words, although psychological factors are an important part of risk on the production floor, they may remain among the least discussed subjects.

Psychological Safety and Just Culture

One of the strongest tools in reducing errors is employees being able to report their errors, near misses and the risks they notice without fear. In research carried out by Amy Edmondson in 1999 in 51 work teams at a manufacturing company, psychological safety, defined as "a shared belief held by members of a team that the team is safe for interpersonal risk taking", was found to be linked to the team's learning behaviour (Edmondson, 1999).

The "just culture" approach strikes an important balance at this point. In this approach:

• Unintentional errors are not punished; the focus is on how to improve the system.
• Risky behaviours (bending a rule) are dealt with through coaching and removing the causes.
• Deliberate and reckless violations are assessed within a framework of accountability.

This distinction gives employees a message of both safety and fairness: errors reported honestly are an opportunity to learn, but knowingly putting others at risk is not acceptable. I cover the team dimension of this subject in detail in the article on psychological safety, and reporting systems in the article on near-miss reporting.

Legislation also supports an approach based on learning. According to Article 12 of the Occupational Health and Safety Risk Assessment Regulation, a risk assessment must be renewed when a workplace accident, occupational disease or near miss occurs. Article 17 of Law No. 6331 provides for additional training to be given to an employee who has had a workplace accident before they start work again.

What Can Employers and Managers Do?

1. Deepen accident and incident investigations. Do not end the investigation with "carelessness" or "failure to follow the rule". Ask about the level of fatigue at the time of the incident, the shift time, workload, equipment design, training and the clarity of instructions.
2. Manage fatigue risk. Limit the number of consecutive nights and the length of shifts, protect breaks, and keep the riskiest tasks away from the hours when fatigue is highest. I cover this subject in detail in the article on night shifts and the sleep-wake pattern.
3. Use designs that make error harder. Colour coding, physical barriers, checklists and automatic stop systems reduce dependence on memory and attention.
4. Reduce interruptions. Prevent the operator being called to other tasks during critical operations; set "uninterrupted work" rules for critical steps.
5. Make rules workable. A rule that is constantly bent is often a rule that cannot be applied in practice. Review it together with employees and redesign it if needed.
6. Be clear about the conflict between production and safety. Managers need to show clearly and consistently that they support an employee who stops the work for safety.
7. Reward near-miss reports. Meet reports with thanks and feedback, not blame. Share the improvements made with employees.
8. Train managers. Noticing the signs of fatigue and stress, talking to an employee who is struggling and holding a constructive conversation after an error are learnable skills. In the World Health Organization's guidelines on mental health at work, the recommendation with the strongest evidence is to train managers in mental health (WHO, 2022).
9. Support the employee after an error too. An employee involved in a serious error or accident may experience intense guilt, anxiety and sleep problems. Providing psychological first aid and, when needed, professional support for these people makes both recovery and a safe return to work easier.

How to Start in Your Organisation

1. Needs analysis: Review the workplace accident, near-miss and quality error records of the last one to two years together with information on shift, time of day, consecutive working days and overtime. Look at how many of the cases closed as "human-caused" in incident reports had the underlying conditions examined. Measure fatigue, workload, time pressure and trust in reporting errors in an anonymous survey.
2. Programme: Based on the findings, prepare a plan made up of shift and workload adjustments, human factors and just culture training for managers and foremen, fatigue and stress management workshops for employees, and a post-accident psychological support process.
3. Measurement: After six to twelve months, compare the number of near-miss reports, accident and error indicators and the survey results. An initial increase in near-miss reports is often a sign that an atmosphere of trust is getting stronger.

You can look at the corporate services page to see how this process can be planned with the support of a psychologist.

Frequently Asked Questions

Can human error be prevented completely?

No; making errors is a natural part of being human. The aim is not to reduce errors to zero but to reduce the likelihood of making errors and to ensure that errors are noticed and stopped before they turn into harm. For this, job design, fatigue management and a safe reporting culture should be addressed together.

Is it right to punish an employee who makes an error?

For unintentional errors, punishment generally leads to errors being hidden and prevents the organisation from learning. Deliberate and reckless violations, on the other hand, should be assessed within a framework of accountability. The just culture approach protects both trust and responsibility by separating the two.

How do we tell whether fatigue played a part in an error?

The first step is to look at what time of the shift the incident occurred, after how many consecutive working days and with how much overtime. Asking the employee, in a non-judgemental conversation, about their sleep pattern and their condition that day also gives important information. Similar incidents clustering at particular times is a strong sign of fatigue.

How can a psychologist contribute to reducing errors in manufacturing?

A psychologist can work with the OHS team on assessing human factors such as fatigue, stress, attention and decision-making, on developing managers' and foremen's communication and feedback skills, and on supporting employees after accidents. This contribution does not replace technical measures; it complements them.

• #human error
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• #safety culture
• #near miss

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Eda Erkan Alapala

Klinik Psikolog. İstanbul Kent Üniversitesi Klinik Psikoloji Tezli Yüksek Lisans mezunu; bilişsel davranışçı terapi, çocuk merkezli oyun terapisi ve çocuk-ergen psikoterapisi alanlarında eğitimlerini tamamlamıştır.

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