ABSTRACT
This chapter attempts to understand the basic nature of fatigue. It considers the impact of three primary factors that affect alertness/sleepiness. The first factor, time since last sleep, is responsible for what has become known as the homeostatic drive. Second factor, time of day according to the body clock, is referred to as the circadian drive. The third factor, sleep inertia, or the short-term grogginess that occurs immediately upon awakening from any sleep period, is not a concern in most workplaces. Insufficient sleep logically produces increased sleepiness to signal an elevation in the drive for restorative slumber. The degree of loss associated with extended sleep deprivation would be bad enough if it were simply straightforward, linear, and predictable. However, an examination of fatigue-related decrements reveals that they are modulated by temporary cyclical peaks and troughs that can make it impossible to predict moment-to-moment changes in operator status.
