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.

Description

Fatigue Fatigue is a major human factor that has contributed to many maintenance errors resulting in accidents. [Figure 14-21] 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. 14-18 9 12 15 18 21 24 3 6 9 20 15 10 5 0 Alertness Level Multiple Sleep Latency Test (MSLT) Peak alertness Dangerously drowsy Time of Day 1-3 AM Reduced alertness Slightly impaired Figure 14-22. 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. [Figure 14-22] 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. AMTs 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 14-19 THE DIRTY DOZEN Twelve human factors for aircraft maintenance proficiency Lack of Teamwork Fatigue Lack of Resources Pressure Lack of Assertiveness Stress Lack of Awareness Norms Complacency Lack of Knowledge Distraction Lack of Communication MITIGATING THE RISK Maintain a sufficient supply of parts and order any anticipated parts before they are required. Preserve all equipment through proper maintenance. Never replace a part with one that is not compatible for the sake of getting the job done. When there is a lack of resources available to properly fix something, a decision should be made to cease maintenance until the proper parts are available. Figure 14-23. Lack of resources. 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.