Fatigue

Fatigue is a term that has significantly evolved over its history from routine labor to extreme tiredness. In the military, fatigue is low-skill non-combat physical work like cleaning, kitchen chores, or fence painting. Fatigue or fatigues may also be used to indicate clothes of the military personnel performing those routine physical duties. In psychology, fatigue is a subjective sudden or gradual feeling of tiredness. In human factors, fatigue is a factor that can cause a human error. In mechanical engineering, fatigue is one of causes of material's failure. In systems engineering, fatigue is device's loss of capacity to function.

Types

Physical fatigue

Physical fatigue is inability to work or work properly. For materials, fatigue is the tendency to break under constant or repeated stress. For devices, fatigue is the loss of capacity to perform properly usually after extended periods of functioning. For human beings, physical fatigue is weariness or exhaustion from exertion, which is caused by deficit of sleep, stress, fatty foods, circadian rhythms, unclean air, and hard labor.

Mental fatigue

Mental fatigue is a feeling of extreme tiredness usually after extended or repeated performance especially if one is doing non-physical tasks. Usually, mental fatigue includes a feeling of monotony and boredom. Mental fatigue can also indicate a state or attitude of indifference or apathy brought on by overexposure, for instance, to a repeated series of similar events or appeals.

People may suffer from mental fatigue when they have been doing something for a long time and feel they can no longer continue to do it. Mental fatigue can be also caused by the same factors like physical fatigue, so simply stretching or other physical exercises, or stepping into the fresh air once in a while can break the monotony.

As a human factor

The fatigue factor (or, simply, fatigue) is the human factor that is characterized by weariness from labor or exertion, nervous exhaustion, as well as a temporary loss of power to respond. This factor is one of the Dirty Dozen of Human Factors.

In aviation maintenance

According to the FAA AMT Handbook,

Fatigue is a major human factor that has contributed to many maintenance errors resulting in accidents. Fatigue can be mental or physical in nature. Emotional fatigue also exists and effects mental and physical performance. A person is said to be fatigued when a reduction or impairment in any of the following occurs: cognitive ability, decision-making, reaction time, coordination, speed, strength, and balance. Fatigue reduces alertness and often reduces a person’s ability to focus and hold attention on the task being performed.

Many human variables rise and fall daily due to one's natural circadian rhythm.

Symptoms of fatigue may also include short-term memory problems, channeled concentration on unimportant issues while neglecting other factors that may be more important, and failure to maintain a situational overview. A fatigued person may be easily distracted or may be nearly impossible to distract. He or she may experience abnormal mood swings. Fatigue results in an increase in mistakes, poor judgment, and poor decisions or perhaps no decisions at all. A fatigued person may also lower his or her standards.

Tiredness is a symptom of fatigue. However, sometimes a fatigued person may feel wide awake and engaged in a task. The primary cause of fatigue is a lack of sleep. Good restful sleep, free from drugs or alcohol is a human necessity to prevent fatigue. Fatigue can also be caused by stress and overworking. A person’s mental and physical state also naturally cycles through various levels of performance each day. Variables such as body temperature, blood pressure, heart rate, blood chemistry, alertness, and attention rise and fall in a pattern daily. This is known as one’s circadian rhythm. A person’s ability to work (and rest) rises and falls during this cycle. Performance counter to circadian rhythm can be difficult. Until it becomes extreme, a person may be unaware that he or she is fatigued. It is easier recognized by another person or in the results of tasks being performed. This is particularly dangerous in aviation maintenance since the lives of people depend on maintenance procedures performed at a high level of proficiency. Working alone when fatigued is particularly dangerous.

The best remedy for fatigue is to get enough sleep on a regular basis. The technician must be aware of the amount and quality of sleep obtained. Caution or time off is justified when too little sleep has occurred and errors are probable during maintenance.

Countermeasures to fatigue are often used. Effectiveness can be short lived and many countermeasures may make fatigue worse. Caffeine is a common fatigue countermeasure.

Pseudoephedrine found in sinus medicine and amphetamines are also used. While effective for short periods, a fatigued person remains fatigued and may have trouble getting the rest needed once off the job due to this drug use.

Suggestions to help mitigate the problems caused by fatigue include looking for symptoms of fatigue in one's self and in others. Have others check your work, even if an inspector sign off is not required. Avoid complex tasks during the bottom of your circadian rhythm. Sleep and exercise daily. Eight to nine hours of daily sleep are recommended to avoid fatigue. Aircraft maintenance technicians in airline operations are part of a system in which most maintenance is performed at night. Fleet aircraft are operated primarily during the daytime hours to generate company revenue. Therefore, shift work is required to maintain the fleet. It is already known that turning work over to other technicians during shift change is a problem that can lead to errors due to lack of communication. But shift work alone is a cause of fatigue that can degrade performance and also lead to errors. Shift work requires technicians to work during low cycles of their natural circadian rhythm. It also makes sleep more difficult when not on the job.

Furthermore, regular night shift work makes one’s body more sensitive to environmental disturbances. It can degrade performance, morale, and safety. It can also affect one’s physical health. All of these can be reflected in degraded maintenance performance—a dangerous situation.

The technician must be aware that shift work is the norm in aviation. Avoidance of fatigue is part of the job. Title 14 of the Code of Federal Regulations (14 CFR) part 121, section 377, only requires 24 hours time off during a week of work. Since this is obviously not enough, it is up to companies and technicians to regulate shift work and time off to reduce the potential for errors. Most importantly, each technician must monitor and control his or her sleep habits to avoid fatigue.

In maintenance training

According to the FAA AC 120-72,

1. Fatigue degrades a person's ability to work effectively. One cause of fatigue is sleep deprivation. Some of the effects of sleep deprivation are reduced reaction time, impaired short-term memory, decreased vigilance, reduced motivation, increased irritability, and an increase in the number of errors made, among others. Failure to act on stimuli, even dangerous ones, is also a common result of fatigue.
2. Sleep deprivation is not the only cause of fatigue. Time on duty and time since awake are common criteria researchers use to determine if fatigue may be a factor on the job. Environmental factors, such as extreme temperatures, noise, vibration, and task difficulty can also induce fatigue.
3. A great deal of anecdotal evidence points to fatigue in maintenance personnel as a factor leading to human error. MRM attempts to increase awareness of fatigue and its causes. MRM also teaches individuals about the consequences of fatigue, especially in terms of human error in maintenance. Though presently no significant quantitative research has been conducted on fatigue in aviation maintenance, studies are currently underway evaluating the factors associated with fatigue and its effect on maintenance personnel.

For aviation crew

According to the CAA Flight-crew human factors handbook CAP737,

Fatigue can be defined as the likelihood of falling asleep. Therefore, in practical terms, there is little difference between chronic fatigue and acute tiredness. However, the state of fatigue is more complex than simple sleepiness. When experiencing fatigue, the individual’s sleep is affected, taking longer to fall asleep, sleeping for a shorter period and having a reduced sleep quality. Increasing fatigue is associated with deterioration in mood ratings. Fatigue can be caused by sleep loss and circadian desynchronosis, but it can also result from low motivation and low levels of external stimulation. In aviation, fatigue becomes important when it reduces efficiency and impairs performance.

In commercial aviation, fatigue is controlled by the imposition of flight time limitations, which are complex and take account of work rest schedules and previous flight duty periods. These do not apply in non-commercial flying but it is important to recognise the effect that fatigue or sleepiness can have on an individual’s performance and limit flying time accordingly.

Factors leading to the development of fatigue include early starts, night flying, a high number of sectors and long duty days for short-haul flight crew. For long-haul flight crew there is the additional problem of long flight duration and regular crossing of time zones.

There are two principal components of sleepiness or fatigue:

1. Physiological sleepiness - this is a requirement like hunger or thirst and can only be reversed by sleep;
2. Subjective sleepiness - this is an individual’s perception of his or her sleepiness but it may be affected by other factors. It may be difficult for an individual to subjectively assess his or her own alertness. In general, individuals over-estimate the time taken to fall asleep and under-estimate the total sleep time. Individuals tend to report a greater level of alertness than is actually the case.

Management of fatigue

According to the CAA Flight-crew human factors handbook CAP737,

Fatigue can be either short-term acute physiological or long-term chronic fatigue.

• Short-term fatigue is akin to tiredness and is usually a result of lack of sleep, hard physical or mental exertion, long duty period or jet lag.
• Chronic fatigue is much more difficult to recognise and quantify. It may be a result of lack of physical or mental fitness, domestic or work stress, financial problems and/or a high workload. It is subjective, with one individual being able to tolerate a greater level of stress than another before the onset of fatigue.

Fatigue gives rise to impaired performance and reduced levels of awareness.

Symptoms of fatigue

According to the CAA Flight-crew human factors handbook CAP737, symptoms of fatigue include:

1. tiredness
2. slow reactions
3. diminished motor skills
4. diminished visual acuity
5. reduced short term memory capacity
6. channelled or tunnelled concentration

Effects of fatigue

According to the CAA Flight-crew human factors handbook CAP737, effects of fatigue include:

1. reduced awareness
2. easy distraction
3. poor instrument flying
4. increased slips and mistakes
5. abnormal mood swings

Individuals have different needs and react differently to sleep loss. Therefore each individual must apply recommendations to suit his or her own particular circumstances.

Mitigating the risk

According to the FAA AMT Handbook, measures that mitigate the risk include:

1. Be aware of the symptoms and look for them in yourself and coworkers,
2. Eating healthy, exercising and regular sleep patterns can prevent fatigue,
3. Forfeit complex tasks if you know you are exhausted.

Occupations that require an individual to work long hours or stay up overnight can lead to fatigue. Fatigue can cause a decrease of attention and a decreased level of consciousness, which can be very dangerous.

Preventative measures

Sleep

Main wikipage: Sleep

Alertness

Main wikipage: Alertness

Other measures

According to the CAA Flight-crew human factors handbook CAP737,

Decreased wakefulness leads to a state of hypovigilance, which helps to control energy consumption by reducing activity of the central nervous system. Its total prevention in flight is not possible.

Strategies for delaying the onset of hypovigilance during flight include:

• Maintain sleep credit - always plan sleep patterns whenever possible
• Be aware of the symptoms - drowsiness, slower sensory perception, preoccupation with an out of context problem, moodiness, reluctance to communicate
• Alternate periods of activity and relaxation
• Engage in social conversation
• Engage in physical activity such as arm and leg stretching
• In a multi-crew operation, it is possible for crew-members to take planned naps during the flight - these should not exceed 30-45 minutes, and recovery from a nap takes a period of five minutes.

Strategies for delaying or preventing the onset of fatigue include:

• Keep fit
• Eat regular balanced meals
• Avoid regular use of alcohol
• Ensure control of emotional and psychological aspects of life
• Ensure adequate preparation for flight, including flight planning and flight deck comfort.

During flight it is helpful to alternate periods of activity and relaxation. Engaging in social conversation and physical activity such as arm and leg stretching may also assist in maintaining wakefulness.

Caffeine consumption may be used to increase alertness. A cup of coffee usually takes about 15 and 30 minutes to become effective, and the effect lasts for between three and four hours, although this is less effective for those who consume regular large quantities of coffee. A balanced diet including drinking plenty of fluids can also help to prevent the onset of fatigue.

Bright light (more than 2,500 lux), used at the appropriate time in the circadian cycle, can help to reset the circadian clock.

Temazepam is a short acting benzodiazepine which is rapidly cleared from the body. Many people find this drug helpful in promoting sleep and used for two or three days after travel, it can assist in resetting the sleep cycle. However, it should only be used under medical supervision and should never be taken within 8 hours of flying as a member of crew.

Melatonin is a substance secreted by the pineal gland with a rhythm that is linked to the light/short cycle through the suprachiasmatic nucleus. It is available in tablet form and has been used by many people to assist sleep. However, despite being a natural substance, the long-term side effects are not fully understood, particularly those affecting reproductive function and heart activity. It therefore does not have a pharmaceutical licence for general use.

Although alcohol is used by some aircrews as an aid to sleep, it is a non-selective nervous system depressant and is effectively a drug. Although it may induce sleep, REM sleep is considerably reduced and early waking is likely. It is important to remember the decrement in cognitive performance and the after effects on the vestibular system of even small amounts of alcohol. It is therefore not appropriate to use alcohol in this manner.

Finally, it should be remembered that there is no simple or single solution for combating the effects of sleep loss and jet lag. The individual has to discover what helps him or her to cope.