A Matter of Fatigue: How it can affect performance

May 1, 2004

Human Factors

Why and how it can affect your performance

By Barb Zuehlke

You’re working second shift, trying to complete some do-it-yourself projects around the house, and attempting to spend quality time with your spouse and children. There aren’t enough hours in the day to get everything done and you’re tired. How is this affecting you physically and your job performance? And what can you do about it?

Fatigue, while often covered in human factors training and one of the Dirty Dozen, is often overlooked but can have serious safety and health-related implications.

Fatigue is a loss of alertness and a feeling of tiredness that can be caused by a lack of sleep, a change in your work schedule due to working overtime or working second shift, or trying to fit too many things in a 24-hour period.

The National Transportation Safety Board (NTSB) has found fatigue to be a causal or contributory factor in accidents in every mode of transportation and has issued almost 80 fatigue-related safety recommendations since 1972. The National Aeronautics and Space Administration (NASA) Ames Fatigue Countermeasures program has addressed fatigue in aviation through research and other activities since 1980.

The Dirty Dozen 1. Lack of communication 5. Lack of teamwork9. Lack of assertiveness2. Complacency6. Fatigue 10. Stress 3. Lack of knowledge 7. Lack of resources 11. Lack of awareness 4. Distraction 8. Pressure 12. Norms

A look at the causes
Our internal clock or circadian clock controls immune function, digestion, performance, alertness, and mood. The lowest point occurs around 3 to 5 a.m. each day making this time period one of the lowest levels of performance activity, although sometimes it can be anywhere from midnight to 6 a.m. A second period of sleepiness occurs around 3 to 5 p.m. These low circadian levels are associated with decreased performance and alertness. And these time periods can become more relevant if there is an accident and a followup investigation.

Fatigue is most often associated with being extra tired and the usual cause and effect scenario leads one to consider sleep (or sleeplessness). Eight hours of sleep is considered the norm for the average person, although it can vary by the individual and range from six to 10 hours. Sleep loss can be acute, the amount of sleep loss in a 24-hour period, and cumulative, sleep loss over several days. Recovery from cumulative sleep loss requires more deep sleep and not an hour-for-hour exchange.

How long an individual remains awake is a factor that can affect performance and alertness. Studies have examined the lengths of shifts and the results on performance. NTSB data has shown an increased risk beyond 12 hours. And at 16 hours of work, a national occupation-injury database revealed an accident/injury rate three times greater than a nine-hour shift. Seventeen hours or longer of prolonged wakefulness can be similar to changes experienced with alcohol consumption.

Research has shown that the effects of fatigue are similar to moderate alcohol consumption. On-the-job performance loss for every hour of wakefulness between 10 and 26 hours is equivalent to a .004 percent rise in blood alcohol concentration. Eighteen hours of wakefulness are usually considered to be equivalent to a blood alcohol concentration of .05 percent. A person who has been awake for this length of time will act and perform as if he or she has consumed one glass of beer. The result is significantly delayed response and reaction times, impaired reasoning, reduced vigilance, and impaired hand-eye coordination.

Tied in with the study of circadian rhythms is the effect of light. The National Lighting Bureau (NLB) reveals that research shows that lighting supports more than visual needs, it affects health. The amount of light needed to influence health tends to be about 10 times greater than for vision, according to John Bachner of the NLB. Studies have shown that a lack of light can cause certain forms of cancer. And having greater amounts of light can reduce the risk of colon and prostate cancer; prevent myopia; counteract airborne disease transmission; and cure psoriasis, seasonal affective disorder, and sleep disorders.

Other factors that influence fatigue include stress, drugs, medications, illness, large temperature variations, noise, boredom, vibration, and dehydration (See sidebar on page 85).

Sources of fatigue can be very easy to underestimate. Who reads the packages of cold and sinus medication? Caution: This drug may cause drowsiness and impair the ability to drive or operate machinery. So even a runny nose could affect your job performance.

Effect on performance
Some of the most common effects due to fatigue are feeling lethargic, becoming withdrawn, having difficulty concentrating, and a reduced attention span. Other effects include short-term memory loss (what was I working on?); complacency (it doesn’t matter); lack of awareness affected by hearing and eyesight; loss of coordination; lack of good judgment and decision making; and lengthened reaction time. All of these conditions increase the possibility of reduced safety and increased risk.

So what can you do? The best solution is to be aware of your performance level. If you think there is a problem take a break; a short walk, a glass of water, or a snack might give you the burst of energy you need. Talk to your co-workers; it will increase your awareness of things around you. Research has shown that a short nap can also improve alertness and performance. Other solutions concern your lifestyle. Try and get adequate sleep, exercise regularly, eat a balanced diet, and drink at least eight glasses of water a day.

The typical cup of coffee can improve alertness but only for a limited time. Coffee is a stimulant and causes a temporarily increased level of alertness, but fatigue is a symptom of its withdrawal. And it’s a diuretic, which causes the body to discharge more fluid than it is taking in, resulting in dehydration, which can also cause fatigue.

If your schedule is too hectic to eat a balanced diet, you can always take vitamins and supplements to fight fatigue. To make up for deficiencies in your diet consider vitamins A, B complex, C, E, zinc, iron, potassium, and calcium. Use carefully and check with a physician about use and possible side effects.

Work conditions and practices also need to be considered. A culture that supports safety and conducts human factors training so you are more aware of factors that influence performance is one that will help prevent fatigue or injuries from occurring.

Management should have adequate staff to handle tasks, this includes having the right experience levels as well as the manpower. And when designing and planning work schedules, circadian rhythms should be taken into consideration.

Other management practices should include additional inspections, rotating shifts, and longer rest periods following night shifts. If possible more critical tasks should be allocated for day shifts. Procedures should be documented so that there is a record of what has been done. This will ensure tasks are completed or indicate where someone left off in case someone else has to follow up to complete maintenance procedures.


Dehydration is one factor that can lead to fatigue. A 2 percent water loss causes loss of alertness and fatigue. Symptoms of dehydration include dry lips and mouth, increased heart rate and breathing, drop in blood pressure, nagging headache, decreased urine output, becoming mentally irritated and depressed, eyes becoming sunken and eyesight becoming blurry, stomach ache, dizziness, and becoming mentally confused. If dehydration is allowed to continue you enter a coma, and die.

To prevent these symptoms drink lots of water. Know how much you should drink and drink more than that. And avoid diuretics such as tea, coffee, or alcohol.

— From Fatigue and Maintenance, presented by Johnny Rush and Gordon Dupont at 2003 PAMA Symposium, Las Vegas, Nevada

Know your own limits and adjust your behavior in areas that you can, such as hours of sleep, proper diet, and exercise. And if work affects your energy level, see what steps you can take or recommend to make work procedures safe and productive.

Additional ReSources
System Safety Services

National Lighting Bureau

About the Author

Barb Zuehlke | Past Senior Editor | AMT