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.   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. 
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.
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  and as a chronic or acute state of exhaustion.  More specifically, fatigue is a state in which a person’s physical and cognitive performance is substantially decreased.  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 
The most common causes of fatigue are insufficient (less than 7-8 hours) or poor-quality sleep.  Fatigue can be largely attributed to the timing of sleep within the circadian rhythm  and to lifestyle factors such as substance abuse, obesity, inactivity and also diseases that affect alertness (e.g., diabetes and sleep apnea).     Acute fatigue is most common between the hours of 02.00 - 06.00 am, when alertness and vigilance levels begin to decline. 
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.    
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.  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. 
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.   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.   
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.  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.  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.  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.
|Topic||The role of fatigue as a contributing factor|
Abnormal safety behaviour
Diseases and medications
|Sleep disorders (e.g. sleep apnea)
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
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
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
|Less than 10 hours recovery from the previous shift
Non-ergonomic shift changes
Irregular or intermittent breaks
Work stress factors
High cognitive load
High alertness requirement
Prolonged exposure to cold or heath
Repetitive or one-sided repetitive movements
: Stacey, N., Ellwood, P., Bradbrook, S., Reynolds, J., Williams, H. & Lye, D. 2018. Foresight on new and emerging occupational safety and health risks associated digitalization by 2025 — Final report. European Agency for Safety and Health at Work. ISBN: 978-92-9479-043-9. Available: https://doi.org/10.2802/515834
: Uehli, K., Mehta, AJ., Miedinger, D., Hug, K., Schindler, C., Holsboer-Trachsler, E., Leuppi, JD. & Künzli, N. 2014. Sleep problems and work injuries: a systematic review and meta-analysis. Sleep Med Rev. 18(1). S. 61-73. Available: https://doi.org/10.1016/j.smrv.2013.01.004
: Kalakoski V., Ratilainen H., Puro V., Perttula P., Salminen S., Lukander J., Mattila S., Leskinen T., Mäkelä T. & Plaketti P. 2015. Better work flow, less errors: Decreasing human errors at work, the SUJUVA project. Finnish Institute of Occupational Health. Available: Sujuvaa työtä vähemmän virheitä.pdf (julkari.fi)
: Partinen, M. & Sulander, P. 1999. Vireysongelmat ja havaintovirheet liikenneonnettomuuksien syinä. Duodecim, 115(6), S. 709-716
: Jan, T. von, Karnahl, T., Seifert, K., Hilgenstock, J., & Zobel, R. 2005. Don’t sleep and drive – VW’s fatigue detection technology. In National Highway Traffic Safety Administration (Chair), 19th International Technical Conference on the Enhanced Safety of Vehicles (ESV), Washington DC, United States.
: Löytty, M. 2014. Moottoriajoneuvon kuljettajien ajokunto ja ajoterveys tieliikenteen turvallisuustekijöinä. Trafin julkaisuja. Liikenteen turvallisuusvirasto Trafi. ISSN 1799-0157
 :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
: Matthews, G., Desmond, P. A. & Hancock, P. 2012. The Handbook of Operator Fatigue. First edition. Boca Raton, FL: CRC Press. 536 s.
: 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
: Tasdelen A. & Ozpinar A. 2020. Perception of Mental and Physical Fatigue Effect and Risk of Accident. Perception of Mental and Physical Fatigue Effect and Risk of Accident. European Journal of Science and Technology, (Special Issue), S. 195-205. Available: https://doi.org/10.31590/ejosat.820996
: 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
: Flanagan, R. P. 2014. Employee fatigue in the U.S. railroad industry: In-depth analyses. New York: Nova Science Publishers. 168 s.
: 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
: 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
: 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
: Folkard, S. & Tucker, P. 2003. Shift work, safety and productivity. Occupational medicine, 53, S. 95-101.
: Onnettomuustutkintakeskus. 2004. Tutkintaselostus. Väsymyksen syyt ja yleisyys komentosiltatyöskentelyssä. [Ref. 2.10.2022] Available: https://turvallisuustutkinta.fi/material/attachments/otkes/tutkintaselostukset/fi/vesiliikenneonnettomuuksientutkinta/
: Partonen, T. 2020. Epäsäännöllinen työaika ja vuorotyö. Lääkärikirja Duodecim. [Ref. 2.10.2022] Available: https://www.terveyskirjasto.fi/terveyskirjasto/tk.koti?p_artikkeli=dlk01013
: 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
: 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
: Reiman, T. & Oedewald, P. 2008. Turvallisuuskriittiset organisaatiot: Onnettomuudet, kulttuuri ja johtaminen. Helsinki: Edita. 243 s.
: 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
: Kaleva, 2022. Väsymyksenhallinta osana turvallisuusjohtamista ja riskienhallintaa (Diplomityö–Oulun yliopisto).