(Caldwell 2002) .
That is the equivalent of a 180-pound man having three beers in one hour, prior to flying. Some people reach this point by their 2nd drink and all reach it by their 3rd or 4th. Functioning and judgment are very seriously affected. Responses are greatly slowed. Behavior is greatly affected. There is a very high risk of an accident. In 35 U.S. States, with a BAC of .08% or higher, you will be arrested if driving a car. (NIAA 1996).
The consequences of being tired are often underestimated. One of the reasons is that there are no biological markers or "Breathalyzers [TM]" for fatigue. Fatigue is a subjective state of tiredness associated with prolonged work and/or prolonged wakefulness (or sleep loss). Fatigue affects people differently. It is a huge risk factor in aviation. It is impossible to determine how many accidents and other problems are caused by fatigue. Fatigue-related performance is under reported because tired pilots are reluctant to admit they fell asleep (or were tired) on the job, especially if an accident results. (J. Caldwell 2002).
Despite the fact that fatigue is difficult to measure, there are signs that fatigue-related problems have reached serious proportions. Truck drivers fall asleep behind the wheel more frequently at night (after midnight) than during the day. They are more likely to be involved in a drowsy driving accident between midnight and 0800 than at other times. Studies have shown that time of day is more likely to impact driving performance than the amount of time on duty or the number of consecutive trips. (Miller1999).
Errors and accidents have been shown to increase at night. Time of day is as important a determinant of fatigue as is the time since the last sleep period. These factors together influence alertness levels. Both must be addressed when attempting to minimize fatigue on the job.
Sleep deprivation affects almost every aspect of daily functioning, but attention, complex thinking, judgment, decision-making and motivation are the most vulnerable.