Fatigue (safety) - AbsoluteAstronomy.com

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

Jet lag

Jet lag, medically referred to as desynchronosis, is a physiological condition which results from alterations to the body's circadian rhythms; it is classified as one of the circadian rhythm sleep disorders...

), or stress.

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.

Mental fatigue, on the other hand, rather manifests in sleepiness

Somnolence

Somnolence is a state of near-sleep, a strong desire for sleep, or sleeping for unusually long periods . It has two distinct meanings, referring both to the usual state preceding falling asleep, and the chronic condition referring to being in that state independent of a circadian rhythm...

or slowness. A person with mental fatigue may fall asleep, may react very slowly, or may be inattentive. With microsleep

Microsleep

A microsleep is an episode of sleep which may last for a fraction of a second or up to thirty seconds. Often, it is the result of sleep deprivation, mental fatigue, depression, sleep apnea, hypoxia, narcolepsy, or hypersomnia...

s, the person may be unaware that he was asleep.

Factors

The Federal Motor Carrier Safety Administration

Federal Motor Carrier Safety Administration

The Federal Motor Carrier Safety Administration , established January 1, 2000, regulates the trucking industry in the United States. FMCSA is headquartered in Washington, DC and employs more than 1,000 people in all 50 States and the District of Columbia...

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
Circadian rhythm
A circadian rhythm, popularly referred to as body clock, is an endogenously driven , roughly 24-hour cycle in biochemical, physiological, or behavioural processes. Circadian rhythms have been widely observed in plants, animals, fungi and cyanobacteria...

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
Melatonin
Melatonin , also known chemically as N-acetyl-5-methoxytryptamine, is a naturally occurring compound found in animals, plants, and microbes...

, which induces sleep), 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), 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. The effects of sleep deprivation vary substantially from person to person.
Sleep deprivation
Sleep deprivation
Sleep deprivation is the condition of not having enough sleep; it can be either chronic or acute. A chronic sleep-restricted state can cause fatigue, daytime sleepiness, clumsiness and weight loss or weight gain. It adversely affects the brain and cognitive function. Few studies have compared the...

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.
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.

In aviation

Human factors

Human factors science or human factors technologies is a multidisciplinary field incorporating contributions from psychology, engineering, industrial design, statistics, operations research and anthropometry...

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. Fatigue can result in pilot error

Pilot error

Pilot error is a term used to describe the cause of an accident involving an airworthy aircraft where the pilot is considered to be principally or partially responsible...

, slowed responses, missed opportunities, and incorrect responses to emergency situations.

A November 2007 report by the National Transportation Safety Board

National Transportation Safety Board

The National Transportation Safety Board is an independent U.S. government investigative agency responsible for civil transportation accident investigation. In this role, the NTSB investigates and reports on aviation accidents and incidents, certain types of highway crashes, ship and marine...

indicates that air crew fatigue is a much larger, and more widespread, problem than previously reported. The report indicates that since 1993 there have been 10 major airline crashes caused by aircrew fatigue, resulting in 260 fatalities. Additionally, a voluntary anonymous reporting system known as ASAP, Aviation Safety Action Program, 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.

In military aviation

In early 2007, the 201 Airlift Squadron of the District of Columbia Air National Guard

Air National Guard

The Air National Guard , often referred to as the Air Guard, is the air force militia organized by each of the fifty U.S. states, the commonwealth of Puerto Rico, the territories of Guam and the U.S. Virgin Islands, and the District of Columbia of the United States. Established under Title 10 and...

(ANG), successfully integrated the Fatigue Avoidance Scheduling Tool FAST

Fatigue Avoidance Scheduling Tool

Fatigue is a major human factors issue in aviation safety. The Fatigue Avoidance Scheduling Tool was developed by the United States Air Force in 2000–2001 to address the problem of aircrew fatigue in aircrew flight scheduling. FAST is a Windows program that allows scientists, planners and...

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

Sustained wakefulness within military combat operations has long been an issue directly related to safety and its impact on those who enter battle. Fatigue remains a formidable enemy in theater operations due to its pervasive impact on cognitive effectiveness during flight...

(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.

Among drivers

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.

Types

Factors

In aviation

In military aviation

Among drivers

See also