Working different shifts at odd hours is a notorious disrupter of sleep. In the United States, over 13 million people—roughly 20 percent of the work force—work either full-time or part-time shifts in the evening or at night. A surprising variety of people work hours other than the standard nine to five: actors, disk jockeys, journalists, and broadcasters; waiters, cooks, and bakers; truckers, taxi drivers, and train engineers; police, fire fighters, and security guards; air-traffic controllers, pilots, and cabin crews; computer programmers, communications workers, and telephone operators; doctors, residents, nurses, and medical students; construction crews and road repair teams; soldiers and sailors; athletes, salesclerks, students, maintenance personnel, and turnpike toll takers.

The statistical profile of shift workers is revealing. In one study, shift workers were twice as likely as day workers to report trouble sleeping; one plant's personnel registered a rate of sleep difficulty of 76 percent. Another study reported that half of all shift workers fell asleep on the job at least once a week. Of course, on-the-job napping can pose a threat not only to workers and colleagues but to the public as a whole, as in the case of security guards, transportation workers, and plant operators.

The nuclear accidents at Chernobyl and Three Mile Island were in part the consequence of decisions made by sleepy shift workers. One study also found that 15 percent of the shift workers reported falling asleep while behind the wheel of a car at least once every three months. These drowsy drivers are a hazard to themselves and everyone else on the road.

The problem is compounded on weekends when, naturally, these workers try to adopt a schedule that permits them to interact socially with family and friends, most of whom enjoy a nine-to-five work day.

*39\225\8*