Ergonomics

Warding Off Sleepiness

By Bruce Oliver, Jim Dillingham · March 2008

Is your shift schedule depriving employees of their sleep?

Facilities that operate across multiple shifts face a significant challenge when it comes to maintaining the alertness of their employees. According to the National Sleep Foundation, “Sleep deprivation is greatest among shiftworkers, who average only 6.5 hours of sleep compared to 6.8 hours for people on regular ‘9 to 5’ work schedules and 6.9 hours for all respondents. . . . Shift workers are more likely to suffer from insomnia as well as excessive daytime sleepiness. They are also more likely to drive while fatigued and almost twice as likely to fall asleep at the wheel.” This is a serious issue for management because the lack of sleep or poorquality sleep can lead to accidents, injuries, absenteeism, and lower productivity.

Although most managers are aware that shiftworkers don’t sleep as well as other employees, few understand how their organizations’ shift schedules contribute to the problem. In this article, we examine three major shift schedule attributes that affect employee sleep: (1) shift length, (2) fixed vs. rotating shifts, and (3) shift start times. The data comes primarily from our proprietary database of employee surveys conducted with more than 20,000 shiftworkers.

Shift Length
When we compare the survey results of people working eight-hour shifts with those working 12-hour shifts, we can see how shift length affects the amount of sleep that shiftworkers get. The average daily hours of sleep for people working eight-hour shifts are shown in Figure 1. The average daily hours of sleep for people working 12-hour shifts are shown in Figure 2.

At first glance, it appears the people working 12-hour shifts get less sleep than those on eight-hour shifts. But this is not the case over a span of several days or weeks because 12-hour shifts provide twice as many days off, and employees sleep longer on their days off. Figure 3 shows the average hours of sleep during a fourweek period. Regardless whether you compare people working day shifts only, night shifts only, or a rotating shift schedule, the average hours of sleep during the four-week period is greater on 12s.


A number of articles have been written about safety risks with eight-hour shifts vs. 12-hour shifts. The results are mixed. Although our shiftworker surveys rely on self-reported safety problems rather than documented incidents, the survey results suggest longer shifts are just as safe as eight-hour shifts, as shown in Figure 4.

Fixed vs. Rotating Shifts
When we compare the survey results of people working rotating shifts with those working fixed or “steady” shifts, we can see how this schedule attribute affects sleep. As seen in Figure 5, people working a rotating shift schedule average roughly the same amount of sleep during a fourweek period as people working a fixed night shift schedule. They get less sleep than people working a fixed day shift or fixed afternoon shift.

In addition to improved predictability, fixed shifts allow shiftworkers to sleep at approximately the same time each day.

This avoids the physical stress (and poorquality sleep) most people experience when they adjust their circadian rhythm to a new sleep period with each rotation. This benefit is realized by those working fixed day, evening, and voluntary night shifts. Unfortunately, many people assigned to work on a fixed night shift try to rotate back to a day routine on their days off, mitigating some of this benefit.

With regard to safety or performance problems due to sleepiness, Figure 6 shows that workers on rotating shifts report problems more frequently than workers on fixed shifts.

Impact at an Auto Manufacturing Plant
A large auto manufacturing plant we worked with had two different schedules that were an hour apart. Three-quarters of the workers on day shift started work at 6:30 a.m. The rest started an hour later. When surveyed, employees with the later starting time said they got an average of 34 minutes more sleep on the days they worked than did the employees with the early start time. Employees with the earlier start time did not go to sleep earlier, probably because of personal, family, or social activities. On their days off, both groups got about the same amount of sleep.

The later start times had mixed results with the afternoon and night shifts at the plant. As seen in Figure 6, the afternoon shift with late start times got a little more sleep and the night shift with late start times got less sleep. The day shift experienced the most significant change.

Asked how often they had problems with safety or performance due to sleepiness, the group with the later starting time reported they had frequent problems 31 percent less often than the employees on the earlier day shift. In addition, the “later starters” accounted for only 14 percent of the reported accidents during a one-year period despite representing 24 percent of the total workers.

This is not an isolated case. The National Institute for Occupational Safety and Health (NIOSH) and the Finnish Institute of Occupational Health found that a one-hour delay in morning shift start times at a steel mill increased worker sleep and improved waking alertness during the shift. They concluded sleep was truncated when workers have early start times because of family and social activities in the evenings. They found the evening and night shifts were affected negatively by starting work later; however, the results were less consistent across all measures.

Summary
This article focused on the sleep effects of three schedule attributes. Ideally, business requirements and employee preferences also will be taken into account when selecting the “best” shift schedule for your site.

About the author

Bruce Oliver
Bruce Oliver is the office manager at Shiftwork Solutions LLC in San Rafael, Calif. Shiftwork Solutions specializes in helping organizations with multi-shift operations. Its Web site contains a wealth of information related to shift schedules; the company can be reached at 415-472-3688.

You can visit the company Web site at www.shift-work.com .


About the author

Jim Dillingham
Jim Dillingham is a partner at Shiftwork Solutions LLC in San Rafael, Calif. Shiftwork Solutions specializes in helping organizations with multi-shift operations.



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