Prevention of accidents by transportation shiftworkers.

For commercial transportation operations, around-the-clock operations are not a recent development. Despite the tenure of these practices, many accidents related to hours worked continue to be a problem. Although efforts by shiftwork experts to solve these problems are often mode specific, the transportation field does suggest several alternative approaches, which may be relevant to general shiftwork problems outside the transportation area. Four contemporary approaches to transportation shiftwork are discussed: environmental design, equipment design, organizational design, and information access systems. Examples are presented within each of these approaches.

Do maritime crew members have sleep disturbances?

Data obtained from surveys of two samples of maritime crew members were studied for differences in self-reported sleep lengths and sleep problems. The data addressed both on- and off-duty variables. Statistical analysis of the data found that on-duty sleep length was shorter than off-duty sleep length for both groups. The two groups' responses to various sleep-problem items were significantly different. Most responses were below the scale mid-point. The differences between on- and off-duty sleep-problem items were not significant. Following a factor analysis, selected sleep-problem items were combined to form a composite Sleep Disturbance Scale. Using this composite measure, the correlation between the composite and sleep length was not significant. Overall, the results indicate that caution should be exercised before labeling shift workers as having "disturbed sleep" or suffering from "sleep disorders." The results do confirm the previous findings that shiftwork reduces sleep length on workdays.

Fatigue and the shiftworker: firefighters working on a rotating shift schedule.

Fatigue has often been viewed as a simple variable that is positively correlated with time on task in the workplace and is produced mainly by physical activity. However, shiftwork researchers have demonstrated time-of-day differences for variables including sleepiness and mood, thereby challenging this notion of fatigue. Using a within-subjects design, the present study advances this research by searching for differences in time-of-day interactions in firefighters' sleep length, sleepiness, and mood ratings as a function of shift. We examined reductions in sleep length associated with shiftwork and used sleepiness and mood scales to assess the effects of these reductions. Participants completed surveys throughout a complete cycle of their shift schedule. The study showed that firefighters working on a rotating 8-h shift schedule will sleep less and will report lower positive mood scores, higher negative mood scores, and greater sleepiness ratings on the night shift. Additionally, it was shown that over the course of a shift (two weeks), firefighters were unable to adapt to changes in their sleep schedule. Finally, the significant interactions that were observed challenge the historical, singular notion of fatigue.

Shiftwork and the older worker.

The number of workers employed on shiftwork is large, and it appears to be increasing. The impact of shiftwork on the occupational safety and health of workers is complex and involves both biological and behavioral variables. Current conceptual models propose that the impact of shiftwork, where night work is involved, increases with exposure. At some point the worker is said to reach a tolerance limit beyond which shiftwork is no longer safe. Sleep variables have proven to be sensitive markers for the effects of night shiftwork. Data from U.S. workers show a statistically significant interaction among age, gender, and shift for the workday sleep length of workers on permanent day, afternoon/evening, and night shifts. Sleep length declines with age for both male and female night workers, as well as for male workers on afternoon/evening shifts. In addition, female night workers in the 18-49 age range sleep significantly less than same-age male night workers. Nap behavior also varies with shift, but age and gender effects do not appear to account for the variance. The results support the assumption that most night shiftworkers are at risk even though they often give the appearance of being able to tolerate nocturnal work hours. However, it is not yet clear how age and gender are related to the social, circadian, and environmental factors that influence the sleep length of shiftworkers.

Locomotive engineers and their spouses: coffee consumption, mood, and sleep reports.

Locomotive engineers (train drivers) on irregular work schedules reported a general coffee consumption rate higher than that reported by a comparison sample of permanent shift factory workers. The present study examines the impact of this consumption on workday and non-workday sleep behaviour and mood ratings. Twenty-seven engineers and their spouses each completed daily logs for 30 consecutive days. Daily logs were then sorted into workday and non-workday categories. Workday sleep length was significantly shorter than non-workday sleep length for both engineers and spouses. For the engineers only, coffee consumption on workdays was higher than on non-workdays. This increased coffee consumption was correlated with longer sleep latency, increased negative mood, and decreased positive mood on both work and non-workdays. This was not true for spouses. These results may be related to a days-off carry-over effect of caffeine or a general consumption behaviour characteristic.

Sleep patterns of shiftworkers.

Work hours affect sleep because the sleep behavior of people on nonworkdays differs from that on workdays. For most workers, workday sleep is shorter than nonworkday sleep. On nonworkdays most workers sleep at night. Work schedule interacts with the effects of work hours on workday sleep. On workdays, people on the nightshift sleep the least, people on the afternoon/evening shift sleep the most, and people on the dayshift sleep less than those on the afternoon/evening shift but more than those on the nightshift. Thus, the infradian sleep strategy elected by a shiftworker is ordinarily related to the schedule worked. Despite historical preconceptions that nightshift work disturbs sleep, the primary problem appears to be a workday reduction in sleep length, which most workers do not usually compensate for by getting more sleep on their nonworkdays. Polysomnographic studies of workers on the nightshift show ultradian sleep-stage sequencing similar to that of people who have chronically reduced their usual sleep duration. This chronic reduction in sleep length is evident in data from experienced night shiftworkers, including those who most prefer to work nights. Experienced night shiftworkers also manifest decrements in performance of the sort expected of people suffering from chronic sleep deprivation. It seems reasonable to suggest that chronic sleep deprivation of night shiftworkers may often be a productivity, safety, or health hazard. Sleep disorders may be a secondary problem also facing night shiftworkers. In general, shiftworkers who do night shiftwork report difficulty falling asleep or staying asleep at rates higher than workers who do not work nights. Data suggest that this may be due to the regular practice of inappropriate infradian sleep strategies or to chronic napping habits. At this point in our study of shiftworker sleep behavior, there is as yet no clear evidence that night shiftworkers suffer from clinical sleep disorders at a higher rate than other workers. It is reasonable to suggest that occupational health professionals can make initial assessments of the sleep complaints made by night shiftworkers. Subjective measurements can be used for these assessments if care is taken to use appropriate methods. It is recommended that this data be collected by asking workers quite literal and concrete questions about the time of day they usually elect to go to sleep and get up. A sleep survey of this sort should gather main sleep period and napping times for both workdays and nonworkdays, so that the infradian sleep strategy of the worker can be identified.(ABSTRACT TRUNCATED AT 400 WORDS)

Intervention factors for promoting adjustment to nightwork and shiftwork.

This chapter reviews a broad range of factors that, if controlled, might promote adaptation to nightwork, shiftwork, and extended workshifts. Systematic study has begun in four of the areas reported here: work schedule design, napping, bright light stimulation, and drugs. Physical activity, ambient temperature, diet, and individual behaviors have been studied only superficially.