Effects of fatigue on safety

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Fatigue is a major safety concern in many fields, but especially in transportation, because fatigue can result in disastrous accidents. Fatigue is considered an internal precondition for unsafe acts because it negatively affects the human operator's internal state. Research has generally focused on pilots, truck drivers, and shift workers.

Why the hours of service are important: a graph outlining the relationship between number of hours driven and the percent of crashes related to driver fatigue.
Source: Federal Motor Carrier Safety Administration[1]

Fatigue can be a symptom of a medical problem, but more commonly it is a normal physiological reaction to exertion, lack of sleep, boredom, changes to sleep-wake schedules (including jet lag), or stress.

In some cases, driving after 18–24 hours without sleep is equivalent to a blood alcohol content of 0.05%–0.10%.[2]


Fatigue can be both physical and mental. Physical fatigue is the inability to continue functioning at the level of one's normal abilities; a person with physical fatigue cannot lift as heavy a box or walk as far as he could if not fatigued.[3][4][5]

Mental fatigue, on the other hand, rather manifests in sleepiness or slowness. A person with mental fatigue may fall asleep, may react very slowly, or may be inattentive. With microsleeps, the person may be unaware that he was asleep. Without proper amount of sleep, it will feel like certain tasks seem complicated, concentration will drop and ultimately result in fatal mistakes[6]


The Federal Motor Carrier Safety Administration identifies three main factors in driver fatigue: Circadian rhythm effects, sleep deprivation and cumulative fatigue effects, and industrial or "time-on-task" fatigue.

  • Circadian rhythm effects describe the tendency for humans to experience a normal cycle in attentiveness and sleepiness through the 24-hour day. Those with a conventional sleep pattern (sleeping for seven or eight hours at night) experience periods of maximum fatigue in the early hours of the morning and a lesser period in the early afternoon. During the low points of this cycle, one experiences reduced attentiveness. During the high points, it is difficult to sleep soundly. The cycle is anchored in part by ambient lighting (darkness causes a person's body to release the hormone melatonin, which induces sleep),[7] and by a person's imposed pattern of regular sleeping and waking times. The influence of the day-night cycle is never fully displaced (artificial lighting inhibits melatonin release more weakly than sunlight),[8] and the performance of night shift workers usually suffers. Circadian rhythms are persistent, and can only be shifted by one to two hours forward or backward per day. Changing the starting time of a work shift by more than these amounts will reduce attentiveness, which is common after the first night shift following a "weekend" break during which conventional sleep times were followed.[1] This effect can also be seen in non-shift-workers who revert to a later schedule on the weekend and experience fatigue and sleepiness when returning to work early on Monday morning. The effects of sleep deprivation vary substantially from person to person.[9][10]
  • Sleep deprivation and cumulative fatigue effects describe how individuals who fail to have an adequate period of sleep (7–8 hours in 24 hours) or who have been awake longer than the conventional 16–17 hours will suffer sleep deprivation. A sleep deficit accumulates with successive sleep-deprived days, and additional fatigue may be caused by breaking daily sleep into two shorter periods in place of a single unbroken period of sleep. A sleep deficit is not instantly reduced by one night's sleep; it may take two or three conventional sleep cycles for an individual to return to unimpaired performance.[1]
  • Industrial or "time-on-task" fatigue describes fatigue that is accumulated during the working period, and affects performance at different times during the shift. Performance declines the longer a person is engaged in a task, gradually during the first few hours and more steeply toward the end of a long period at work. Reduced performance has also been observed in the first hour of work as an individual adjusts to the working environment.[1]

In addition to the primary factors identified by the FAA, other potential contributors to fatigue during transportation have been identified. These include endogenous factors such as mental stress and age of the vehicle operator, as well as exogenous or environmental stressors, such as the presence of non sea-level cabin pressure in-flight, vehicle noise, and vehicle vibration/acceleration (which contributes to the sopite syndrome). Many of the exogenous contributors merit further study because they are present during transportation operations but not in most lab studies of fatigue.

In aviationEdit

The International Civil Aviation Organization (ICAO) that codifies standards and regulations for international air-navigation defines fatigue as: "A physiological state of reduced mental or physical performance capability resulting from sleep loss or extended wakefulness, circadian phase, or workload (mental and/or physical activity) that can impair a crew member's alertness and ability to safely operate an aircraft or perform safety related duties." [11]

Human factors are the primary causal factor aviation accidents.[12] In 1999, the National Aeronautics and Space Administration, NASA, testified before the U.S. House of Representatives that pilot fatigue impacts aviation safety with "unknown magnitude". The report cited evidence of fatigue issues in areas including aviation operations, laboratory studies, high-fidelity simulations, and surveys. The report indicates that studies consistently show that fatigue is an ongoing problem in aviation safety.[13] In 2009, Aerospace Medical Association listed long duty work hours, insufficient sleep, and circadian disruptions as few of the largest contributing factors to pilot fatigue.[14] Fatigue can result in pilot error, slowed responses, missed opportunities, and incorrect responses to emergency situations.

A November 2007 report by the National Transportation Safety Board indicates that air crew fatigue is a much larger, and more widespread, problem than previously reported.[15] The report indicates that since 1993 there have been 10 major airline crashes caused by aircrew fatigue,[16][17] resulting in 260 fatalities. Additionally, a voluntary anonymous reporting system known as ASAP, Aviation Safety Action Program,[18] reveals widespread concern among aviation professionals about the safety implications of fatigue. The NTSB published that FAA's response to fatigue is unacceptable and listed the issue among its "Most Wanted" safety issues.[19]

Safety experts estimate that pilot fatigue contributes to 15-20% of fatal aviation accidents caused by human error. They also establish that probability of a human factor accident increases with the time pilots are on duty, especially for duty periods of 13 hours and above (see following statements):

"It is estimated (e.g. by the NTSB) that fatigue contributes to 20-30% of transport accidents (i.e. air, sea, road, rail). Since, in commercial aviation operations, about 70% of fatal accidents are related to human error, it can be assumed that the risk of the fatigue of the operating crew contributes about 15-20% to the overall accident rate. The same view of fatigue as a major risk factor is shared by leading scientists in the area, as documented in several consensus statements."[20]

"For 10-12 hours of duty time the proportion of accident pilots with this length of duty period is 1.7 times as large as for all pilots. For pilots with 13 or more hours of duty, the proportion of accident pilot duty periods is over five and a half times as high. [...] 20% of human factor accidents occurred to pilots who had been on duty for 10 or more hours, but only 10% of pilot duty hours occurred during that time. Similarly, 5% of human factor accidents occurred to pilots who had been on duty for 13 or more hours, where only 1% of pilot duty hours occur during that time. There is a discernible pattern of increased probability of an accident the greater the hours of duty time for pilots.".[21]

Among driversEdit

Many countries regulate working hours for truck drivers to reduce accidents caused by driver fatigue. The number of hours spent driving has a strong correlation to the number of fatigue-related accidents. According to numerous studies, the risk of fatigue is greatest between the hours of midnight and six in the morning, and increases with the total length of the driver's trip.[22]

Among healthcare providersEdit

Fatigue among doctors is a recognized problem. It can impair performance, causing harm to patients. A study using anonymous surveys completed by junior doctors in New Zealand found that 30% of respondents scored as "excessively sleepy" on the Epworth Sleepiness Scale and 42% could recall a fatigue related clinical error in the past 6 months[23]

In the US, shift length is limited for nurses by federal regulation and some state laws.[24]

On shipsEdit

Fatigue on board is still a major factor of accidents which lead to casualties, damage and pollution. Studies show that most accidents happen during the night[25] especially around 4 am due to the Circadian rhythm of humans.[10] Studies like Project Horizon[26] have recently been done to analyse which factors cause this fatigue. The lack of sleep and quality of the sleep are two of the main issues. The lack of sleep is due to the long hours that the workers (especially the Officers) have to do (work weeks of 70 hours +).[27] After that there is the quality of their sleep which is affected by lots of different factors.[26] There will be the quality of the food on board, the vibrations due to the engine and waves, the noise of repair or works or engine, only naps (not sleeping 8 hours in a single run but 2 or 3 naps a day) because of the watch system and secondary jobs. Stress on board especially when arriving in port when all hands have to be on deck whatever the time.

With companies trying to reduce the costs there is less crew. Turn around in port have to be as fast as possible because the time spent in ports is very expensive. All of this adds work and stress to the crew on board which drains them of their energy which will lead to errors due to fatigue. The ILO have conventions for trying to restrict the maximum working hours on board and to determine the minimum rest period of seafarers.[27] Unfortunately, the maritime industry is so competitive and there are fewer and fewer crew members on board that it makes it difficult to not work overtime; otherwise the workers will fall behind on their work load.[28]

See alsoEdit


  1. ^ a b c d "Regulatory Impact and Small Business Analysis for Hours of Service Options". Federal Motor Carrier Safety Administration. Archived from the original on 26 January 2008. Retrieved 22 February 2008.
  2. ^ "CDC Features - Drowsy Driving: Asleep at the Wheel". www.cdc.gov. Retrieved 13 October 2015.
  3. ^ Gandevia SC (1992). "Some central and peripheral factors affecting human motoneuronal output in neuromuscular fatigue". Sports Medicine. 13 (2): 93–8. doi:10.2165/00007256-199213020-00004. PMID 1561512.
  4. ^ Hagberg M (1981). "Muscular endurance and surface electromyogram in isometric and dynamic exercise". Journal of Applied Physiology. 51 (1): 1–7. doi:10.1152/jappl.1981.51.1.1. PMID 7263402.
  5. ^ Hawley JA, Reilly T (1997). "Fatigue revisited". Journal of Sports Sciences. 15 (3): 245–6. doi:10.1080/026404197367245. PMID 9232549.
  6. ^ http://www.betterhealthusa.com/public/235.cfm
  7. ^ "Melatonin". University of Maryland Medical Center. Retrieved 24 April 2008.
  8. ^ Czeisler, Charles A. "Pathophysiology and Treatment of Circadian Rhythm Sleep Disorders". [Insomnia and Beyond: The Neurochemical Basis for Targeted Sleep Therapeutics]. Medscape. Retrieved 24 April 2008.
  9. ^ Van Dongen HP, Caldwell JA, Caldwell JL (May 2006). "Investigating systematic individual differences in sleep-deprived performance on a high-fidelity flight simulator". Behav Res Methods. 38 (2): 333–43. doi:10.3758/BF03192785. PMID 16956110.
  10. ^ a b Van Dongen HP (2006). "Shift work and inter-individual differences in sleep and sleepiness". Chronobiol. Int. 23 (6): 1139–47. doi:10.1080/07420520601100971. PMID 17190701.
  11. ^ Millar, Michelle (2012). "Measuring Fatigue" (PDF). ICAO.int. ICAO/IATA/IFALPA. p. 8.
  12. ^ Wickens, C. D.; Lee, J. D.; Gordon, S. E.; Liu, Y. (2003). An introduction to human factors engineering. New York: Longman.
  13. ^ NASA report to Congress on fatigue, http://comair-5191.com/NASA%20Statement%20on%20Pilot%20Fatigue.pdf Archived 2 October 2008 at the Wayback Machine
  14. ^ Caldwell, J.A., Mallis, M.M., Caldwell, J.L., Paul, M.A., Miller, J.C., & Neri,mD.F. Fatigue Countermeasures in Aviation Archived 7 October 2015 at the Wayback Machine. Aviation, Space, and Environmental Medicine, 80(1), 29-59.
  15. ^ Levin, ALan (10 April 2007). "NTSB: Fatigue threatens air safety". USA Today. Retrieved 22 December 2018.
  16. ^ Fatigue and Aviation Safety
  17. ^ Events which include fatigue as a contributory factor on SKYbrary
  18. ^ FAA's ASAP Program, https://www.faa.gov/about/initiatives/asap/
  19. ^ NTSB Most Wanted List, fatigue, https://www.ntsb.gov/Recs/mostwanted/aviation_reduce_acc_inc_humanfatig.htm
  20. ^ Akerstedt, T.; Mollard, R.; Samel, A; Simons, M.; Spencer, M. (2003). Paper prepared for the ETSC “Meeting to discuss the role of EU FTL legislation in reducing cumulative fatigue in civil aviation” in Brussels on Wednesday 19th February 2003 (PDF) (Report). European Transport Safety Council.
  21. ^ Goode, Jeffrey H. (August 2003). "Are pilots at risk of accidents due to fatigue?" (PDF). Journal of Safety Research. 34 (3): 309–313. doi:10.1016/S0022-4375(03)00033-1. PMID 12963077.
  22. ^ "Hours of Service of Drivers; Driver Rest and Sleep for Safe Operations; Proposed Rule". Federal Motor Carrier Safety Administration. Archived from the original on 1 October 2006. Retrieved 16 February 2008.
  23. ^ Gander, P.; Purnell, H.; Garden, A.; Woodward, A. (2007). "Work patterns and fatigue-related risk among junior doctors". Occupational and Environmental Medicine. 64 (11): 733–738. doi:10.1136/oem.2006.030916. PMC 2078416. PMID 17387138.
  24. ^ "Safety and Health Topics | Long Work Hours, Extended or Irregular Shifts, and Worker Fatigue - Limitations on Work Hours | Occupational Safety and Health Administration". osha.gov. Retrieved 12 August 2018.
  25. ^ "Safety Digest" (PDF). Marine Accident Investigation Branch (MAIB). February 2004.
  26. ^ a b Leeuwen, Wessel M.A. Van (2012). "(PDF) Final report project HORIZON". ResearchGate. doi:10.13140/rg.2.1.4844.7127. Retrieved 18 November 2018.
  27. ^ a b "Convention C109 - Wages, Hours of Work and Manning (Sea) Convention (Revised), 1958 (No. 109)". www.ilo.org. Retrieved 29 November 2018.
  28. ^ "Guidelines for the Development of Tables of Seafarers' Shipboard Working Arrangements and Formats of Records of Seafarers' Hours of Work or Hours of Rest" (PDF). IMO. 29 November 2018.