Fatigue (safety)

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 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.

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.^{[citation needed]}

Types

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.^[2][3][4]

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.

Factors

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),^[5] 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 is not strong enough to inhibit the release of melatonin),^[6] 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] The effects of sleep deprivation vary substantially from person to person.^[7][8]
• 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 aviation

Human factors are currently the most common factor of aviation crashes. 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 on-going problem in aviation safety.^[9] 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.^[10] The report indicates that since 1993 there have been 10 major airline crashes caused by aircrew fatigue^[11][12], resulting in 260 fatalities. Additionally, a voluntary anonymous reporting system known as ASAP, Aviation Safety Action Program,^[13] 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.^[14]

In military aviation

In early 2007, the 201 Airlift Squadron of the District of Columbia Air National Guard (ANG), successfully integrated the Fatigue Avoidance Scheduling Tool FAST into its daily scheduling operations. This integration required the full-time attention of two pilot schedulers, but yielded valuable risk mitigation data that could be used by planners and leaders to predict and adjust critical times of fatigue in the flight schedule. In August 2007, the Air National Guard Aviation Safety Division, under the direction of Lt Col Edward Vaughan, funded a project to improve the user interface of FAST, permitting daily use by pilot schedulers and integration with automated flight scheduling software. This improved, user-responsive interface, known as Flyawake (FlyAwake.org), was conceived and managed by Captain Lynn Lee and developed by Macrosystems. The project cited empirical data collected in combat and non-combat aviation operations, and challenged the U.S. government's established policies regarding fatigue as a factor in degrading human performance.^[15]

Among drivers

Further information: Hours of service and Drivers working hours

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 also greatest between the hours of midnight and six in the morning, and increases with the total length of the driver's trip.^[16]

On ships

See also

• Human reliability
• Fatigue Avoidance Scheduling Tool
• Sleep deprived driving

References

1. ^ ^{a b c d} "Regulatory Impact and Small Business Analysis for Hours of Service Options". Federal Motor Carrier Safety Administration. http://www.fmcsa.dot.gov/rules-regulations/topics/hos/regulatory-impact-analysis.htm. Retrieved 2008-02-22. 
2. ^ Gandevia SC (1992). "Some central and peripheral factors affecting human motoneuronal output in neuromuscular fatigue". Sports medicine (Auckland, N.Z.) 13 (2): 93–8. doi:10.2165/00007256-199213020-00004. PMID 1561512. 
3. ^ Hagberg M (1981). "Muscular endurance and surface electromyogram in isometric and dynamic exercise". Journal of Applied Physiology 51 (1): 1–7. PMID 7263402. 
4. ^ Hawley JA, Reilly T (1997). "Fatigue revisited". Journal of sports sciences 15 (3): 245–6. doi:10.1080/026404197367245. PMID 9232549. 
5. ^ "Melatonin". University of Maryland Medical Center. http://www.umm.edu/altmed/articles/melatonin-000315.htm. Retrieved 2008-04-24. 
6. ^ Czeisler, Charles A. "Pathophysiology and Treatment of Circadian Rhythm Sleep Disorders". Insomnia and Beyond: The Neurochemical Basis for Targeted Sleep Therapeutics. Medscape. http://www.medscape.com/viewarticle/465494_25. Retrieved 2008-04-24. 
7. ^ 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. PMID 16956110. 
8. ^ 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. http://www.informaworld.com/openurl?genre=article&doi=10.1080/07420520601100971&magic=pubmed. 
9. ^ NASA report to Congress on fatigue, http://comair-5191.com/NASA%20Statement%20on%20Pilot%20Fatigue.pdf
10. ^ USA Today coverage of NTSB report, http://www.usatoday.com/news/washington/2007-04-10-fatigue-air-safety_N.htm
11. ^ Fatigue and Aviation Safety
12. ^ Events which include fatigue as a contributory factor on SKYbrary
13. ^ FAA's ASAP Program, http://www.faa.gov/safety/programs_initiatives/aircraft_aviation/asap/
14. ^ NTSB Most Wanted List, fatigue, http://www.ntsb.gov/Recs/mostwanted/aviation_reduce_acc_inc_humanfatig.htm
15. ^ www.SeeAndAvoid.org
16. ^ "Hours of Service of Drivers; Driver Rest and Sleep for Safe Operations; Proposed Rule". Federal Motor Carrier Safety Administration. http://www.fmcsa.dot.gov/espa%F1ol/english/pdfs/050200p.htm. Retrieved 2008-02-16.