The International Civil Aviation Organization (ICAO), which regulates international air navigation, defines fatigue as: "A physiological state of reduced mental or physical performance capacity resulting from loss of sleep or prolonged wakefulness, circadian phase, or workload (mental or physical activity) that may affect a crew member's alertness and ability to safely operate an aircraft or perform safety-related tasks."[11]​.

The human factor is the predominant factor in air accidents.[12] In 1999, the National Aeronautics and Space Administration (NASA) testified before the United States House of Representatives that pilot fatigue affects aviation safety to an "unknown magnitude." The report cited evidence of fatigue problems in areas including aviation operations, laboratory studies, high-fidelity simulations and surveys. The report stated that studies consistently show that fatigue is an ongoing problem in aviation safety. In 2009, the Aerospace Medical Association listed long work hours, lack of sleep, and circadian disruptions as some of the major factors contributing to pilot fatigue. Fatigue can lead to pilot errors, slower responses, missed opportunities, and incorrect responses to emergency situations.

A November 2007 report from the National Transportation Safety Board (NTSB) indicates that aircrew fatigue is a much larger and more widespread problem than previously reported.[13] The report indicates that since 1993 there have been 10 major airline accidents caused by aircrew fatigue resulting in 260 deaths. 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 the Federal Aviation Administration's (FAA) response to fatigue is unacceptable and classified the problem among its safety priorities.

Safety experts estimate that pilot fatigue contributes to 15 to 20 percent of fatal aviation accidents caused by human error. They also state that the probability of a human factor accident increases with the time pilots are on duty, especially for duty periods of 13 hours or more (see the following statements):

“It is estimated (e.g., NTSB) that fatigue contributes to 20 to 30 percent of transportation accidents (air, sea, land, and rail). Given that in commercial aviation operations approximately 70% of fatal accidents are related to human error, the risk of crew fatigue can be considered to account for approximately 15-20% of accidents. "Leading scientists in the area share the same view of fatigue as an important risk factor, as documented in several consensus statements."

«For pilots with between 10 and 12 hours of service, the proportion of accidents is 1.7 times higher than for the total number of pilots. For pilots with 13 or more hours of service, the accident rate is 5.5 times higher. [...] 20% of human factor accidents occurred in pilots with 10 or more hours of service, but only 10% of the hours of service occurred during that time. Similarly, 5% of human factor accidents occurred in pilots with 13 or more hours of service, while only 1% of service hours occurred during that time. There is a perceptible pattern of greater probability of accident the longer the pilots' service time is” [14]​.

Many countries regulate the working hours of truck drivers to reduce accidents caused by driver fatigue. The number of hours spent driving has a strong correlation with the number of fatigue-related accidents. According to numerous studies, the risk of fatigue is greatest between midnight and six in the morning, and increases with the total duration of the driver's trip.[15]​.

Physician fatigue is a recognized problem. It can impair performance and cause harm to patients. A study using anonymous surveys completed by junior doctors in New Zealand found that 30% of respondents scored "excessively sleepy" on the Epworth Sleepiness Scale and 42% could recall a fatigue-related clinical error in the past six months.[16]​.

In the US, the length of nurses' work shifts is limited by federal regulation and some state laws.[17]​.

Fatigue on board remains a major factor in accidents resulting in casualties, damage and pollution. Studies show that most accidents occur at night [18]​ with a peak around 4 a.m. m., due to the circadian rhythm of humans.[10]​ Recently, studies such as the Horizon Project[19]​ have been carried out to analyze what factors cause this fatigue. Lack of sleep and poor quality of sleep are two of the main problems. Lack of sleep is due to the long hours that workers (especially officers) have to work (work weeks of 70 hours or more).[20]​ The quality of sleep can be affected by various factors:[19]​ the quality of the food on board, vibrations due to the engine and waves, noise from repairs or the engine, sleeping only 2 or 3 naps a day instead of 8 eight hours in a row due to the system of guards and secondary jobs; and the stress on board, especially when arriving at port, when all crew members have to be on deck whatever the time.

As companies try to reduce costs, there are fewer crews. The time in ports should be as minimal as possible, because it is very expensive. All of this adds work and stress to the crew on board, which saps their energy and can lead to errors due to fatigue. The International Labor Organization (ILO) has put in place conventions to restrict the maximum hours of work on board and determine the minimum rest period for seafarers.[20]​ As the maritime industry is highly competitive and there are fewer and fewer crew members on board, it is difficult to avoid overtime.[21]​.

The International Civil Aviation Organization (ICAO), which regulates international air navigation, defines fatigue as: "A physiological state of reduced mental or physical performance capacity resulting from loss of sleep or prolonged wakefulness, circadian phase, or workload (mental or physical activity) that may affect a crew member's alertness and ability to safely operate an aircraft or perform safety-related tasks."[11]​.

The human factor is the predominant factor in air accidents.[12] In 1999, the National Aeronautics and Space Administration (NASA) testified before the United States House of Representatives that pilot fatigue affects aviation safety to an "unknown magnitude." The report cited evidence of fatigue problems in areas including aviation operations, laboratory studies, high-fidelity simulations and surveys. The report stated that studies consistently show that fatigue is an ongoing problem in aviation safety. In 2009, the Aerospace Medical Association listed long work hours, lack of sleep, and circadian disruptions as some of the major factors contributing to pilot fatigue. Fatigue can lead to pilot errors, slower responses, missed opportunities, and incorrect responses to emergency situations.

A November 2007 report from the National Transportation Safety Board (NTSB) indicates that aircrew fatigue is a much larger and more widespread problem than previously reported.[13] The report indicates that since 1993 there have been 10 major airline accidents caused by aircrew fatigue resulting in 260 deaths. 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 the Federal Aviation Administration's (FAA) response to fatigue is unacceptable and classified the problem among its safety priorities.

Safety experts estimate that pilot fatigue contributes to 15 to 20 percent of fatal aviation accidents caused by human error. They also state that the probability of a human factor accident increases with the time pilots are on duty, especially for duty periods of 13 hours or more (see the following statements):

“It is estimated (e.g., NTSB) that fatigue contributes to 20 to 30 percent of transportation accidents (air, sea, land, and rail). Given that in commercial aviation operations approximately 70% of fatal accidents are related to human error, the risk of crew fatigue can be considered to account for approximately 15-20% of accidents. "Leading scientists in the area share the same view of fatigue as an important risk factor, as documented in several consensus statements."

«For pilots with between 10 and 12 hours of service, the proportion of accidents is 1.7 times higher than for the total number of pilots. For pilots with 13 or more hours of service, the accident rate is 5.5 times higher. [...] 20% of human factor accidents occurred in pilots with 10 or more hours of service, but only 10% of the hours of service occurred during that time. Similarly, 5% of human factor accidents occurred in pilots with 13 or more hours of service, while only 1% of service hours occurred during that time. There is a perceptible pattern of greater probability of accident the longer the pilots' service time is” [14]​.

Many countries regulate the working hours of truck drivers to reduce accidents caused by driver fatigue. The number of hours spent driving has a strong correlation with the number of fatigue-related accidents. According to numerous studies, the risk of fatigue is greatest between midnight and six in the morning, and increases with the total duration of the driver's trip.[15]​.

Physician fatigue is a recognized problem. It can impair performance and cause harm to patients. A study using anonymous surveys completed by junior doctors in New Zealand found that 30% of respondents scored "excessively sleepy" on the Epworth Sleepiness Scale and 42% could recall a fatigue-related clinical error in the past six months.[16]​.

In the US, the length of nurses' work shifts is limited by federal regulation and some state laws.[17]​.

Fatigue on board remains a major factor in accidents resulting in casualties, damage and pollution. Studies show that most accidents occur at night [18]​ with a peak around 4 a.m. m., due to the circadian rhythm of humans.[10]​ Recently, studies such as the Horizon Project[19]​ have been carried out to analyze what factors cause this fatigue. Lack of sleep and poor quality of sleep are two of the main problems. Lack of sleep is due to the long hours that workers (especially officers) have to work (work weeks of 70 hours or more).[20]​ The quality of sleep can be affected by various factors:[19]​ the quality of the food on board, vibrations due to the engine and waves, noise from repairs or the engine, sleeping only 2 or 3 naps a day instead of 8 eight hours in a row due to the system of guards and secondary jobs; and the stress on board, especially when arriving at port, when all crew members have to be on deck whatever the time.

As companies try to reduce costs, there are fewer crews. The time in ports should be as minimal as possible, because it is very expensive. All of this adds work and stress to the crew on board, which saps their energy and can lead to errors due to fatigue. The International Labor Organization (ILO) has put in place conventions to restrict the maximum hours of work on board and determine the minimum rest period for seafarers.[20]​ As the maritime industry is highly competitive and there are fewer and fewer crew members on board, it is difficult to avoid overtime.[21]​.