Fatigue in work-related accidents

Fatigue is a growing concern in working life today and an issue that requires attention in occupational safety and health management. 

This article discusses the significance of fatigue as a cause of accidents and its identification during the investigation of safety deviations.

With the increasing role of cognitive work, fatigue is recognised as a major contributor to human errors. [1] [2] Human factors-related accidents and injuries will not disappear despite advances in technology and automation. As many as 80-90% of Finnish workplace accidents are caused by human factors. [3]

However, fatigue, as a human factor that is a familiar and daily reality to everyone, can easily be overlooked in the investigation of the root causes of incidents. The link between fatigue and errors in alertness, perceptual motor skills and attentiveness is well known, particularly in the transport sector, but its consideration in corporate occupational safety and risk management is not necessarily a given. 

Fatigue-increasing factors

There is no single clear definition for fatigue because it also involves significant individual variations. Fatigue can be defined as a reduced mental or physical state of alertness [7] and as a chronic or acute state of exhaustion. [8] More specifically, fatigue is a state in which a person’s physical and cognitive performance is substantially decreased. [9] From an occupational safety perspective, the main symptoms of fatigue include:

  • slow reaction time
  • reduced eye movements
  • blurred vision
  • reduced coordination and motor skills
  • memory problems
  • concentration problems
  • increased risk-taking
  • loss of situational awareness and judgement
  • reduced motivation [10]

 The most common causes of fatigue are insufficient (less than 7-8 hours) or poor-quality sleep. [11] Fatigue can be largely attributed to the timing of sleep within the circadian rhythm [12] and to lifestyle factors such as substance abuse, obesity, inactivity and also diseases that affect alertness (e.g., diabetes and sleep apnea). [8] [13] [14] [15] Acute fatigue is most common between the hours of 02.00 - 06.00 am, when alertness and vigilance levels begin to decline. [9][16][17]

Work stress factors contributing to fatigue are shift work (3-shift work and especially night shift work), irregular working hours, long working hours (more than 12 hours per day or 48 hours per week), monotony, time pressure and alertness demands. [8] [11] [13] [18]

Psychosocial overload (e.g., constant interruptions and processing large amounts of information) is known to break concentration and impair information processing ability, while underload (e.g., monotony and boredom) impairs alertness and attentiveness. [19] Sleep deprivation is a major risk factor for injury in itself, but when combined with other workload factors, the risk of human errors becomes significant. [20]  

Fatigue and accidents

A fatigued worker has an approximately 62% higher risk of accidents, which is explained by the increase in human errors as a result of a fatigued individual’s performance decline. [2] [15] A review of various road accident statistics shows that fatigue is a contributing factor in approximately 5-25% of accidents. Accidents due to fatigue are described as exceptionally severe compared to other causes. [4] [5] [6]

A fatigued person is more negligent of perceived risks, which can lead to abnormal safety behaviour. Consequently, in situations where some uncommon disturbance situation needs to be fixed, for example, it is easy to shortcut safe behaviour without intuitive risk assessment. [12] In the light of the figures, fatigue can be considered as a significant contributor to the risk of accident and injury.

Categories of work that require special consideration for risk management are shift work, on-call work, travelling work and seasonal work. [15] Fatigue is a major risk factor, particularly in safety-critical industries (e.g., maritime transport, air traffic control and heavy transport) where complex tasks might be performed around the clock and the potential for serious injury or damage to property exists. [21] For safety-critical tasks, fatigue is definitely a risk factor requiring management measures. The risk posed by fatigue in a task can be modelled as shown in Figure 1.

The model of the risk posed by fatigue in a task .
Figure 1. Factors contributing to fatigue-related risks.

Identifying fatigue

Around 93% of employers in the construction, industrial and transport sectors identify fatigue as a safety risk, but only 72% of employees feel the same way. [21] Raising awareness of the risks of fatigue is the first step to ensuring that fatigue is treated as a risk factor and reported as a factor in safety incidents, rather than being completely ignored in root cause investigations.

The background of safety incidents must be analysed to identify both individual and job-related factors that contribute to fatigue and its associated risk. Table 1 shows some of the factors that may reveal a contributing role of fatigue in an incident.  

The more of the factors in Table 1 that can be found in the background of the accident, the more likely it is that fatigue played a contributing role in the incident. On this basis, we can consider how to control the factors that cause fatigue, for example by making changes to shift patterns or workload factors.

Determining fatigue in the background of an accident [23]

Topic The role of fatigue as a contributing factor
Human error
Errors in
In reacting
Abnormal safety behaviour
Diseases and medications
Sleep disorders (e.g. sleep apnea)
Acute Illnesses
Arousal-related illnesses (e.g. diabetes)
Medicines that increase fatigue (e.g. tricyclies)
Assessment and others' assessments of the state of alertness of the person(s) involved
Plenty of yawning
Heavy eating before the incident
Reporting fatigue
Amount of sleep
Less than 7 hours of sleep the night before
Sleep deprivation early in the week
Time of day
Incident occurred 02.00-06.00 am
Occurred at the end of the shift
Occurred at the beginning of the morning shift
Hours worked
Working day over 12 hours
More than 48 hours per week
3-shift slow or back-to-to-back rotation
Consecutive or long night shifts
Recovery time
Less than 10 hours recovery from the previous shift
Long commutes
Non-ergonomic shift changes
Irregular or intermittent breaks
Work stress factors
High cognitive load
High alertness requirement
Poor lightning
Prolonged exposure to cold or heath
Repetitive or one-sided repetitive movements
Table 1.

Why is it important to take fatigue into account?

Fatigue is a very individual and complex condition that can rarely be attributed to a single factor. The same can be said of accidents, where there are many different components in play before the accident occurs. Fatigue can be an indirect or direct risk factor leading to or enabling the accident. The question is, why is the importance of fatigue not more strongly emphasised in current safety management?

Perhaps fatigue is not seen as a risk worthy of action because it is such a commonplace issue and normal part of everyone’s life. This is peculiar given that the effect of severe fatigue on our performance is claimed to be equivalent to 1 per mil of intoxication. [11] [17] It may also be the case that there is a lack of knowledge about the impact of fatigue on occupational safety, which means that it does not come up in occupational safety discussions.

Although fatigue is rarely the only or most significant component of injury, it should be better taken into account in risk management and occupational safety management, given the knowledge of its effects, contributing factors and management responses.

By limiting the factors that contribute to fatigue, we can already prevent some of the damage caused by human error, because every incident prevented is important. Managing fatigue not only improves safety but also the quality and efficiency of the work performed, creating a competitive advantage for the company. 


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[7] :Williamson, A., Lombardi, D.A., Folkard, S., Stutts, J., Courtney, T.K. & Connor, J.L. 2011. The link between fatigue and safety. Accident Analysis and Prevention, 43, S. 498–515. Available: https://doi.org/10.1016/j.aap.2009.11.011

[8]: Matthews, G., Desmond, P. A. & Hancock, P. 2012. The Handbook of Operator Fatigue. First edition. Boca Raton, FL: CRC Press. 536 s.

[9]: U.S. Department of Transportation. 2013. Fatigue Risk Management Systems for Aviation Safety. Federal Aviation Administration. AC No: 120-103A. [Ref. 2.10.2022] Available: https://www.faa.gov/documentlibrary/media/advisory_circular/ac_120-103a.pdf

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[11]: WorkSafe Victoria. 2020. A guide for employers. Work-related fatigue, 3rd edition. 40 s. Available: https://content.api.worksafe.vic.gov.au/sites/default/files/2020-10/ISBN-Work-related-fatigue-guide-for-employers-2020-08.pdf

[12]: Flanagan, R. P. 2014. Employee fatigue in the U.S. railroad industry: In-depth analyses. New York: Nova Science Publishers. 168 s.

[13]: Murray, S. L. & Thimgan, M. S. 2016. Human fatigue risk management: Improving safety in the chemical processing industry. 1st edition. Amsterdam: Academic Press. 269 s. ISBN 978-0128024127

[14]: Laivuori, T. & Tuovinen, M., 2021. Väsymys ja uupumus-Mistä ne voivat johtua? Puhti. [Ref.  2.10.2022] Available: https://www.puhti.fi/tietopaketit/vasymys/#henkinen-vasymys 

[15]: Safe Work Australia, 2013. Guide for managing the risk of fatigue at work. [Viitattu 2.10.2022] Available: https://www.safeworkaustralia.gov.au/system/files/documents/1702/managing-the-risk-of-fatigue.pdf

[16]: Folkard, S. & Tucker, P. 2003. Shift work, safety and productivity. Occupational medicine, 53, S. 95-101.

[17]: Onnettomuustutkintakeskus. 2004. Tutkintaselostus. Väsymyksen syyt ja yleisyys komentosiltatyöskentelyssä. [Ref. 2.10.2022] Available: https://turvallisuustutkinta.fi/material/attachments/otkes/tutkintaselostukset/fi/vesiliikenneonnettomuuksientutkinta/

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[19]: Ojel-Jaramillo Romero, J.M., Reiman, A., Cañas Delgado, J.J., Väyrynen, S., Pekkala, J. & Forsman, M. 2018. Delivery truck drivers’ work outside the cab: psychosocial discomforts and risks based on participatory video analyses. Eur. Transp. Res. Rev. 10, 27. S. 1–10. Available: https://doi.org/10.1186/s12544-018-0299-3

[20]: Rosa, R., 1995. Extended work shifts and excessive fatigue. Journal of Sleep Research, 4 (2), S. 51–56. Available: https://doi.org/10.1111/j.1365-2869.1995.tb00227.x

[21]: Reiman, T. & Oedewald, P. 2008.Turvallisuuskriittiset organisaatiot: Onnettomuudet, kulttuuri ja johtaminen. Helsinki: Edita. 243 s. 

[22]: NSC. 2017. Fatigue in Safety-Critical Industries: Impact, Risks & Recommendations. NSC Fatigue Survey Reports. [Ref. 4.4.2022] Available: https://www.nsc.org/getmedia/4b5503b3-5e0b-474d-af19-c419cedb4c17/fatigue-in-safety-critical-industries.pdf.aspx

[23]: Kaleva, 2022. Väsymyksenhallinta osana turvallisuusjohtamista ja riskienhallintaa (Diplomityö–Oulun yliopisto).

Written by

Tuomas Kaleva, University of Oulu