performance and alertness the next day (Dinges et al., 1996). After 5 to 10 days of shortened sleep periods, the sleep debt (sleep loss) is significant enough to impair decision making, initiative, information integration, planning, and plan execution (Krueger, 1994). The effects of sleep loss are insidious and usually not recognized by the sleep-deprived individual until they have become severe (Dinges et al., 1996; Rosenkind et al., 1999). Schedules that require workers to return to work after an 8-hour rest period or to transition from night to day or evening shifts without at least 24 hours off are considered particularly dangerous (Olson and Ambrogetti, 1998; Rosa and Colligan, 1988).

Recovery from extended work periods requires more than 1 day. Off-duty intervals ranging from 10 to 16 hours are either suggested or already mandated for many transportation workers (Dinges et al., 1996; Gander et al., 1991; Mitler et al., 1997). Two consecutive nights of recovery sleep can return performance and alertness to normal levels, even following two or three 12-hour shifts (Dinges et al., 1996; Tucker et al., 1996); longer intervals between works days are even more beneficial. Workers obtain more sleep and start their next shift with less fatigue. The first or second night on a new series of night shifts, however, may be the most fatiguing because of circadian desynchrony (Rosa, 2001).

The combination of sustained wakefulness and working at night is particularly hazardous (Gold et al., 1992; Smith et al., 1994). When the Exxon Valdez ran aground around midnight on March 23, 1989, the third mate had been awake 18 hours and anticipated working several more hours (Alaska Oil Spill Commission, 1990). Although the explosion of the Challenger space shuttle occurred during the daytime, the decisions made the night before the launch by mission control staff have been cited as a major factor contributing to the explosion (Mitler et al., 1988). In a small study of the use of extended (16-hour) night shifts in seven wards of a Japanese university hospital, several compensatory measures were employed to protect against the dual effects of sustained operations and night shift work. These measures included increases in the numbers of night staff to allow all nursing staff to take a 2-hour nap in a dedicated resting room. Staff was also allowed to take at least one recovery day off after a 16-hour shift. The increase in staff, 2-hour nap, and day off were believed to contribute to the extended shift nurses’ less frequent complaints of fatigue and general decreased physical activity as compared with nurses working 8-hour shifts (Fukuda et al., 1999). The study also found that sleep inertia (characterized by sleepiness, fatigue, and dullness) increased immediately after the nap, but then decreased to the same levels as existed before the nap. The researchers concluded that nap length would need to be carefully regulated to avoid persistent sleep inertia and its attendant risks (Takahashi et al., 1999).



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