The concern about the adverse health effects of night shift work has existed for over 100 years. In 1860, for example, some scientists were worried that bakers might be at increased risk of physical and emotional illness because they always worked at night and, subsequently, some effort was made to try to regulate their work hours and their working conditions. Since then, it has been shown that some persons who have been very productive while working standard 8‐hr/day, 40‐hr/week daytime schedules can become especially fatigued, unhappy, less productive, and perhaps even more susceptible to the effects of chemical agents and physical agents after they are placed on shift work. Even though many studies have been conducted, the degree to which shift work effects a worker's capabilities, longevity, mortality, and overall wellbeing is still not fully understood.
So‐called unusual work shifts and work schedules have been implemented in a number of industries in an attempt to eliminate or at least reduce, some of the problems caused by normal shift work that require three work shifts per day. These unusual or “other‐than‐normal” shifts have been termed odd, novel, extended, extraordinary, compressed, nonnormal, nonroutine, prolonged, exceptional, nonstandard, unusual, peculiar, weird, and nontraditional. In 1981 the AIHA established a committee to address the potential occupational health aspects of shift work and the need to adjust exposure limits for persons who work schedules that were markedly different than the “normal” workweek, which consists of five consecutive 8‐hr daylight workdays followed by two days off. At the committee's first meeting, it was agreed that the term
unusual work shift
should be used, for sake of consistency, to describe these other‐than‐normal shifts. The committee completed its work by 1990 and it was retired.
In general, most unusual work schedules will involve workdays markedly longer than 8 hr in duration, however, because many persons are regularly exposed to high concentrations of xenobiotics for very short periods during shifts and, because TWA occupational exposure limits were not necessarily intended for use during short exposures, these exposure periods were also classified as “unusual” by the committee. The assessment of the health aspects of unusual shifts is complex since some of these schedules require the worker to alternate between night and day work every few days (rapid rotation). These schedules have been called rapidly rotating, fast, or simply rapid‐roto shifts.
In order for the health professional to ensure protection of workers who are exposed to airborne chemicals during unusually long or unusually short work periods, he or she should be familiar with the toxicology and pharmacokinetics of the chemical of interest as well as understand the rationale for its occupational exposure limit, since most limits were established to prevent injury following exposure during a normal 8‐hr/day, 5‐day/workweek schedule.
