Be Alert for Key Factors that Promote Fatigue!28
- Time of day (circadian effect). The strongest dip in circadian rhythms of wakefulness occurs during the early morning hours - about 2 to 6 a.m. The second most-vulnerable times are in the afternoon about 2 to 5 p.m. (when people have a strong desire to take a nap) and about midnight to 2 a.m.
- Time awake and amount of sleep. The longer you have been awake, the greater your risk is for fatigue. Likewise, the poorer the quality and the shorter duration of sleep you have had recently (buildup of sleep debt), the greater your risk is for fatigue. Avoid building sleep debt.
- Time on task. The longer the time you spend on a task, particularly one that is monotonous, the more likely you will feel fatigue. Taking rest breaks and changing the task or conditions are strategies for reducing fatigue due to time-on-task effects.
A tragic example is a 5:30 a.m. bus crash that occurred in 2011 on a New York highway. The crash killed 15 people and injured 17.29 The bus hit the guard rail at 65 miles an hour, overturned, and struck a signpost which severed the entire roof of the bus. The National Transportation Safety Board determined the probable cause of the accident was the driver’s fatigue due to sleep debt and the circadian effect. The driver had slept less than 4 hours a day for three days prior to the accident. The crash occurred during the early morning hours, the time with the strongest pressure for sleep.
Another example is a case in which an experienced nurse made a medication error that immediately caused the death of a young mother.30 The previous day, the nurse had worked a long shift from 7 a.m. to 12:30 a.m. She stayed at the hospital to sleep and returned at 7 a.m. to work the day shift. As a result, she had not gotten enough sleep. At about noon of that day shift, she gave the wrong medication. The root cause analysis of the case determined a build-up of sleep debt was one of the factors that probably caused this tragedy.