Shift Work - Human Factors and Ergonomics - page 296

TABLE 16.3 Typical Problems Associated with Working the Night Shift
Fatigue. On average a night-shift worker sleeps 1.5 h less.
Health disorders. Stomach problems, digestive disorders, and possibly an increased rate of
cardiovascular disease.
Disruption of social life. With family, friends, labor unions, meetings, and other gatherings.
Decreased productivity. More for knowledge-based tasks than skill- and rule-based tasks.
Safety. Accident rates may increase.
work, and perhaps those who remain in shift work are physically stronger and have better
health. Therefore the population of study may be biased to start with, and it is difficult to
arrive at a fair scientific comparison.
Some studies suggest that there is a greater possibility of an increased rate of
cardiovascular disease among shift workers (Rick et al., 2002). A longitudinal study of 50
workers in a Swedish paper mill showed that after 10-15 years of exposure to shift work,
the risk of heart disease was doubled compared with a population of workers on day shift
(Knutsson et al., 1986). But there were many uncontrolled factors. In addition to shift
work there might have been differences related to lifestyle, diet, and so forth, although
some of these factors were taken into account in the study. A later study by Olsen and
Kristensen (1992) indicated that shift workers are four times more likely to develop
cardiovascular disease as compared to non-shift workers. Bøggild and Knutsson (2000)
also indicated the increasing risk of cardiovascular disorders among shift workers.
The disruption of social life is another important consequence of shift work. Night
work can make it impossible to participate in gatherings of family and friends and other
social functions. This is one of the major reasons why several countries in Europe
propose a fast rotating shift-work schedule, with 2 or 3 days at most on each type of shift
(Table 16.4).
16.4 EFFECTS ON PERFORMANCE AND PRODUCTIVITY
It has been difficult to establish in research whether productivity is reduced during the
night shift. One of the problems is that the type of work tasks is often different, so there
cannot be fair comparisons with daytime work. For example, some plants schedule
maintenance work during the night shift, whereas in other plants maintenance work is
performed during the day shift. There is also a lack of supervisors and managers during
the night shift, which means that group morale can suffer.
The consensus from the research is that simple skill-based and rule-based tasks do not
suffer as much during shift work as cognitive knowledge-based tasks which require deep
thinking. Two interesting studies, however, show a detriment in skill-based task
performance. A classic study by Bjerner and Swensson (1953) evaluated records of error
frequency in reading meters at a gas company. The error frequency was greatest at 3:00
am. Browne (1949) evaluated the speed of switchboard operators. The slowest responses
were obtained between 3:00 am and 7:00 am.