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Fatigue is defined as a biological drive for recuperative rest. It affects a large majority of workers. The major cause of fatigue is insufficient or disrupted sleep. Fatigue occurs as a function of the length of time awake, the time of day, workload, general health, and lifestyle outside of work. It is a function of the homeostatic drive for sleep and the circadian rhythm of sleep/wakefulness. Fatigue and excessive daytime sleepiness (EDS) are also consequences of disorders of the central or peripheral nervous systems and/or other disease states, including common illnesses such as infections, asthma, gastrointestinal disorders, and metabolic abnormalities. Attention to fatigue in workers is important, not only because it affects work and safety but because of the negative impacts of fatigue on overall health.

Fatigue and workplace sleepiness are found in all work settings. Excessive sleepiness in the workplace and on highways is a serious safety hazard. Insufficient or disrupted sleep may result in accidents and injuries and may have adverse effects on mental and physical health. Workers are at a higher risk of fatigue when their work causes sleep deprivation and sleep deficit. Physical workload affects fatigue-related performance and safety outcomes. Intense mental workload can also contribute significantly to fatigue development. Most workers in service economies are assigned to alternative work schedules, many of which result in fatigue. For safety critical tasks, the consequences of a mistake or error in judgment may result in serious injury or death. Identifying and preventing fatigue is particularly important in the transportation sector, health care sector, and among first responders.

Work is organized into a variety of different work schedules which can be fixed or flexible. Shiftwork is a working time arrangement in which workers succeed one another at the workplace so that the establishment can operate longer than the hours of a normal workday. The basic categories of shift systems are fixed shift systems in which workers always work the same shift, and rotating shift systems, in which workers are assigned to work shifts that vary regularly over time, typically often through the night shift. Night work has additional implications for fatigue because it requires work in opposition to the biological clock.

Table 37–1.Signs and symptoms of fatigue-related performance impairment.

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