Fatigue (safety)

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.

In some cases, driving after 18–24 hours without sleep is equivalent to a BAC of between 0.05% to 0.10%.

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 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

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.

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.

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."

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