Impact of a change from an 8-h to a 12-h shift schedule on workers and occupational injury rates

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Abstract

Many industries find it necessary to operate 24 h per day, 7 d per week. Traditionally, industries have relied on 8-h work schedules that rotate on a weekly basis. In recent years, industries have begun implementing rotating 12-h schedules. The purpose of this study was to evaluate the impact on a group of production workers of changing from an 8-h to a 12-h rotating schedule. Factors evaluated in the study included the frequency of occupational injuries, the impact on workers’ health, social and family life, and their overall schedule preference. Results of the study indicated a strong preference of the workers for the 12-h schedule with positive influences on the workers’ subjective feeling toward health and social family life. The study also indicated that there was no significant change in the occupational injury rate.

Relevance to industry

Many industries are concerned about adopting an appropriate shift schedule for their workers. This study provides valuable data that these industries could use to support job design strategies with regard to shiftwork.

Introduction

The 12-h shift schedule is not a recent phenomenon. Iron industries and steel mills in the late 19th century employed a 12-h rotating shift schedule, allowing them to operate 24 h a day, 7 d a week. This resulted in employees receiving only 1 d a month off, requiring their shift partner to work the entire 24 h of that day off. It was not until the 1920s, with pressure from unions as well as from religious and political leaders, that industry began to adopt plans to eliminate the 84-h work week. Shift hours were reduced to 56 h per week (8 h/day, 7 d/week). The Walsh-Healy Act further reduced the work week to 40 h. To allow for continuous operations, a main reason for shifts and which required a 42-h work week, an overtime premium was established to monetarily compensate for the extra hours worked (Coleman, 1986). The 28-d cycle, 42-h work week is still used today, and examples of some of these shift schedules are presented in Tables 1a–d.

The Office of Technology Assessment has estimated that 1 in 5 working Americans, approximately 20 million people in the United States are shift workers. This figure includes an estimated 2 million night workers and 3.1 million rotating shift workers, (U.S. Congress, Office of Technology Assessment, 1991). For the purpose of this paper, shift work will be considered to be: “Any system of fixed working hours, about 8 hours in length, most of which falls outside the standard day work period (between 0800 and 1700)” (Tepas, 1985, p. 148). Examples include night shiftwork, evening shiftwork, and rotating shiftwork.

There are a number of reasons why shiftwork has been implemented. In capital-intensive industries where equipment is very expensive, shifts are implemented to make more efficient use of the costly equipment in an effort to remain competitive. Some operations involve processes that require more than 8 h to complete or that cannot be started up and shut down at the beginning and end of the normal workday in a cost-effective manner. In addition, demands have significantly increased for around the clock availability of many services such as food, travel accommodations, communication, entertainment access, and health and emergency services. While many of these areas still employ an 8-h rotating shift schedule to meet these needs, since about 1955 the 12-h shift schedule has been slowly becoming reestablished in the US (Coleman, 1986). Although much research has been done on the health and safety issues surrounding the 8-h schedule, comparable research on 12-h schedules is relatively lacking.

Section snippets

Shiftwork and safety

The effects of shiftwork on worker safety have been inconclusive. In his critical review of shiftwork and health, Harrington (1978) concluded that the variability in the results of studies on performance and accidents in both field studies and laboratory studies were due to the authors’ failure to recognize that the situations were not comparable. Some of the factors he identified that the studies failed to control for or even recognize included: “the individual worker, differences in work load

Subjects

The study group consisted of production workers from one division of a large manufacturing site. This division consisted of approximately 350 personnel from two major departments, each in its own building, in different areas of the site. Although physically separated, the production departments reported to the same general management and utilized the same site safety, health, and medical support staffs. In January 1988, this division, at the request of the workers, changed from an 8-h, 7-d

Injury data

The crude and adjusted data corresponding to the recordable incident rates, lost workday rates, and lost time case rates are presented in Table 2, Table 3, Table 4, respectively, according to age and gender. Table 5 indicates that the injury rates for both the control and study groups increased from 1986–87 to 1988–95; however, only the rate change for the control group was statistically significant ( p<0.05). Moreover, the control group's injury rate from 1988–95 increased to a level that was

Discussion

Overall, based on the occupational injury data and the opinions expressed by the employees in the study group working the schedules, the transition from 8- to 12-h rotating work schedules was found to be a positive experience. The 12-h schedule exhibited no detrimental effects in any of the measures evaluated in this study.

One of the reasons for establishing a control group in this study was to handle possible changes by OSHA in scrutinizing companies’ OSHA injury/illness records. Based on

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