Shift work

Shift work is an employment practice designed to make use of the 24 hours of the clock, rather than a standard working day. The work shift is the time period during which a person is at work.

A day may for example be divided into three shifts each of eight hours, and an employee works just one of those shifts; they might for example be 00:00 to 08:00, 08:00 to 16:00, 16:00 to 24:00 (times given in the 24-hour clock). Generally, first shift refers to the day shift, with second shift running from late afternoon to nightfall, and third shift being the night shift. On occasion, more complex schedules are used, perhaps involving employees changing shifts, in order to operate during weekends as well, in which case there will be four or more sets of employees.

Shift work was once characteristic of manufacturing industry, where it has a clear effect of increasing the use that can be made of capital equipment, and allowing for up to three times the production compared to an eight-hour day. It contrasts with the use of overtime to increase production at the margin. Both approaches incur higher wage costs, in general; shift work, requiring workers to live on a time-shifted schedule for extended periods, is unpopular, and typically pay must be at a premium. It has at times been common in heavy industry, particularly automobile and textile manufacturing. The use of shift work in manufacturing varies greatly from country to country.

Service industries now increasingly operate on some shift system; for example a convenience store will normally each day be open for much longer than a working day. Shift work has been traditional in the armed forces, and for clear reasons: for example sailors must be available to handle a vessel around the clock, and a system of naval watches organised to ensure enough hands are on duty at any time. This is shift work by another name. Shift work is also the norm in governmental and private employment in fields related to public safety and health, such as police, fire prevention, emergency medical transportation, and hospitals.

The swing shift, also known as second shift, is an employment schedule during the evening, for example 4 p.m. to midnight.

The graveyard shift is a popular name for the aforementioned third shift covering the small hours, in particular for radio presenters or in the retail trade. Current popular explanations for the origin of the phrase "graveyard shift" reference the 19th century problem of accidentally burying people who were still alive. To prevent this from happening caskets were equipped with a bell-ringing device enabling a waking "corpse" to notify the world that they were no longer dead (this is also the origin of the terms "dead ringer" and "saved by the bell"). The graveyard attendants who remained vigilant throughout the day and night worked the graveyard shift.

Health consequences
The February 15, 2005 issue of American Family Physician noted that shift work has been associated with cluster headaches.

The consequences of disturbing natural circadian sleep rhythms has been investigated also.

A study by Knutsson in 1986 found that shift workers who had worked in that method for 15 years or more were 300% more likely to develop ischaemic heart disease.