Three health researchers have found a way to help workers adapt more sucessfully to rotating shifts. Last year, Charles A. Czeisler and Martin C. Moore-Ede, faculty members at Harvard University, and Richard M. Coleman of Stanford University visited Great Salt Lake Minerals & Chemicals Corp.'s potash harvesting and processing operation in Ogden, Utah. Each week, part of the work force there would switch shifts. A crew would work for seven days on the graveyard, or late night, shift, switch the following week to the swing, or evening, shift, then change the following week to the day shift.

"That's one of the most common kinds of schedule in companies that operate around the clock," Czeisler says. The weekly rotation, though, may be one of the tonghest schedules to live with

"Most people think that as long as you set aside eight hours a day for sleep, then you're okay -- that any eight hours will do," Czeisler says. But the body has two different "pacemaking" systems, he explains. The simple ability to fall asleep adjusts to a schedule change fairly rapidly. Other important physiological functions, though, such as dreaming and alertness/sleepiness cycles, typically take almost a week to readjust after an eight-hour change in the sleeping pattern.

Thus, although a worker may quickly adapt to new sleeping hours, he may spend several more days of a new shift weary and inattentive and have difficulty sleeping on his time off. Abont 26% of the potash workers said they couldn't adjust fully before being rotated again.

The scientists made two changes at the potash operation. They put the workers on a "phase delay" rather than a "phase advance" rotation: Instead of switching to an earlier shift each time, they changed to the later one. That way -- like a traveler flying west -- they gained, rather than lost, eight hours of rest at each change. Also, the number of days on each shift was lengthened to 21. The workers overwhelmingly preferred the new pattern. The company saw a significant increase in productivity and has put all the shift workers on the new schedule.

"A qnarter of the U.S male work force is exposed to major changes in day-night schedules," says Czeisler, who heads the nonprofit Center for Design of Industrial Schedules in Boston to help educate companies about effective rotation schedules. "Modern industry and workers unnecessarily accept sleep loss and lack of alertness on the job," he says.