Occupational Safety and Health Administration OSHA

Long Work Hours, Extended or Irregular Shifts, and Worker Fatigue

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Long Work Hours, Extended or Irregular Shifts, and Worker Fatigue Menu


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What Causes Worker Fatigue?

Several factors including too little, poor quality or interrupted sleep over a period of time can cause fatigue. Fatigue is the body's signal that a rest period is needed.  Long work hours and extended and irregular shifts may be stressful physically, mentally and emotionally. The body operates on a circadian rhythm sleep/wake cycle. It is naturally programmed for sleeping during night hours. Demanding work schedules may disrupt the body's natural cycle, leading to increased fatigue, stress and lack of concentration.

What are the Effects of Demanding Work Schedules?

Long work hours and extended and irregular shifts may lead to fatigue and to physical and mental stress. Working extended shifts may also involve prolonged exposure to potential health hazards such as noise, chemicals, and others. These exposures could exceed established permissible exposure limits (PELs) or violate other health standards. Employers must implement measures to monitor and limit worker exposures to health and physical hazards in the workplace as required by the Occupational Safety and Health Act.

What Worker Population Does This Affect?

Irregular and extended shifts are common among healthcare providers, transportation workers, first responders, firefighters, police officers, military personnel, construction workers, oil field workers, service and hospitality workers and many others.

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What Are the Effects of Worker Fatigue?
  • Worker fatigue increases the risk for illnesses and injuries. Accident and injury rates1 are 18% greater during evening shifts and 30% greater during night shifts when compared to day shifts. Reseach indicates that working 12 hours per day is associated with a 37% increased risk of injury2. In a 2005 study reporting on a survey of 2737 medical residents, every extended shift scheduled in a month increased by 16.2 % monthly risk of a motor vehicle crash during their commute home from work.
  • Decreased alertness from worker fatigue has been a contributing factor in:

Additional Information

How Can Fatigue Affect Worker Safety and Health?
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Fatigue can cause weariness, sleepiness, irritability, reduced alertness, impaired decision making, and lack of motivation, concentration and memory. Studies have shown that fatigue is linked to health problems such as:

  • Heart disease
  • Stomach and digestive problems
  • Musculoskeletal disorders
  • Reproductive problems
  • Depression
  • Some cancers (breast and prostate)
  • Sleep disorders
  • Poor eating habits/obesity
  • Worsening of existing chronic diseases such as diabetes and epilepsy

Additional Information




1 Smith CS, Folkard D, Tucker P, Evans MS [2011]. Work schedules, health, and safety. In Quick JC, Tetrick LE, eds. Handbook of occupational health psychology, 2nd ed.. Washington, DC: American Psychological Association, pp. 185 – 204.

2 Dembe A, Ericson JB, Delbos RG, Banks SM [2005]. The impact of overtime and long work hours on occupational injuries and illnesses: New evidence from the United States. Occup Environ Med 62:588_597.

3 Vegso S, Cantley L, Slade M, et al. [2007]. Extended work hours and risk of acute occupational injury: A case-crossover study of workers in manufacturing. Am J Ind Med 50(8):597-603.

4 Ricci JA, Chee E, Lorandeau AL, Berger J [2007]. Fatigue in the U.S. workforce: Prevalence and implications for lost productive work time. Occup Environ Med 49(1): 1-10.

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