Shift work is an employment practice designed to make use of the 24 hours of the clock, rather than a standard working day. The term shift work includes both long-term night shifts and work schedules in which employees change or rotate shifts.
A related yet different concept, the work shift, is the time period during which a person is at work.
Twelve-hour work shifts are also in use. In a modern steelworks, four sets of personnel are used, working consecutive days in one twelve hour shift (06:00–18:00 and vice-versa). Shift A will work days, and shift B nights, over a 48-hour period, before handing over to shifts C and D and taking 48 hours off. In the offshore petroleum industry, employees may work 14 consecutive days or nights, 06:00–18:00 or 18:00–06:00, followed by three or four weeks free. The svingskift (literally: swing shift) in the offshore petroleum industry in Norway refers to a two-week tour during which employees work 12-hour days the first seven days and 12-hour nights the second (or vice versa).
Shift work was once characteristic primarily of manufacturing industry, where it has a clear effect of increasing the use that can be made of capital equipment and allows for up to three times the production compared to just a day shift. It contrasts with the use of overtime to increase production at the margin. Both approaches incur higher wage costs. In general, requiring workers to live on a time-shifted schedule for extended periods, is unpopular, and this typically must be paid for at a premium. It is common in heavy industry, particularly automobile and textile manufacturing and is becoming more common in locations where a shut-down of equipment would incur an extensive restart process. Food manufacturing plants, in particular, have extensive cleaning programs that are required before any restart. The use of shift work in manufacturing varies greatly from country to country. Shift work has been traditional in law enforcement and the armed forces: 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.
Service industries now increasingly operate on some shift system; for example a restaurant or convenience store will normally each day be open for much longer than a working day. Shift work is also the norm in governmental and private employment in fields related to public safety and healthcare, such as police, fire prevention, security, emergency medical transportation and hospitals. Companies working in the field of meteorology, such as the National Weather Service and private forecasting companies, also utilize shift work, as constant monitoring of the weather is necessary.
The "three-shift system" is the most common pattern, comprised of "first" from 6:00 a.m. to 2:00 p.m., "second" from 2:00 p.m. to 10:00 p.m., and a "third" (or "night") shift from 10:00 p.m. to 6:00 a.m. This is generally worked over a five-day week; to provide coverage 24/7, employees have their days off ("weekends") on different days.
All of the shifts have desirable and less desirable qualities. First shift has very early starts, so time in the evening is heavily cut short. The second shift (or "swing shift") occupies the times during which many people finish work and socialize. The third shift creates a situation in which the employee must sleep during the day.
Generally, employees stay with the same shift for a period of time, as opposed to cycling through them; this is seen as healthier.
|06:00 to 14:00||Shift 1||Shift 1||Shift 1||Shift 1||Shift 1||Off||Off|
|14:00 to 22:00||Shift 2||Shift 2||Shift 2||Shift 2||Shift 2||Off||Off|
|22:00 to 06:00||Shift 3||Shift 3||Shift 3||Shift 3||Shift 3||Off||Off|
"Four on, four off" is a shift pattern that is being heavily adopted in the United Kingdom and in some parts of the United States. An employee works for four days, usually in 12-hour shifts (7:00 to 7:00) then has four days off. While this creates a "48-hour week" with long shifts, it may be preferred because it shrinks the workweek down to four days, and then gives the employee four days rest – double the time of a usual weekend. Due to the pattern, employees effectively work an eight-day week, and the days they work vary by "week". As with three-shift system, most employees stay with the same shift rather than cycling through them.
Four on, four off example:
|07:00 to 19:00||Day 1||Day 2||Day 3||Day 4||Off||Off||Off||Off|
In "Four on, two off" the employee only gets two days off. In a seven-day period, this adds up to 56 hours worked (on average, based on 12 hour shifts). Four on, two off is mainly adopted by industries in which employees do not engage in much physical activity, such as security guards, who for the most part sit at a desk or watch monitors.
Four on, two off example:
|07:00 to 19:00||Day 1||Day 2||Day 3||Day 4||Day 5||Off||Off|
A variation is the "two days, two nights, four off" pattern of working. In this shift schedule, employees work 12-hour shifts from 7:00 a.m. to 7:00 p.m. on day shifts and from 7:00 p.m. to 7:00 a.m. on nights. This pattern is currently in use by HM Coastguard in the UK, and employs four separate teams to maintain 24/7 coverage.
Two days, two nights, four off example:
|07:00 to 19:00||Day 1||Day 2||Off||Off||Off||Off||Off||Off|
|19:00 to 07:00||Off||Off||Day 3||Day 4||Off||Off||Off||Off|
"12/24/12/48" (or "12/24") is another variation. Employees work in shifts of 12 hours; first a daily shift (e.g., 7:00 a.m. to 7:00 p.m.), followed by 12 hours rest, then a nightly shift (7:00 p.m. to 7:00 a.m.), finishing with 24 hours rest. This pattern needs four teams for full coverage, and makes an average 42-hour workweek.
12/24/12/48 shift example:
|07:00 to 19:00||Day 1||Off||Off||Off||Day 3||Off||Off|
|19:00 to 07:00||Off||Day 2||Off||Off||Off||Day 4||Off|
"Continental shift", adopted primarily in central Europe, is a rapidly changing three-shift system that is usually worked for seven days straight, after which employees are given time off. For example, three mornings, two afternoons, and then two nights.
Continental shift example:
|06:00 to 14:00||Shift 1||Shift 1||Shift 1||Off||Off||Off||Off|
|14:00 to 22:00||Off||Off||Off||Shift 1||Shift 1||Off||Off|
|22:00 to 06:00||Off||Off||Off||Off||Off||Shift 1||Shift 1|
"Split shift" is used primarily in the catering, hotel, and hospitality industry. Waiters and chefs work for four hours in the morning (to serve lunch), then four hours in the evening (to serve an evening meal). The average working day of a chef on split shifts could be 10:00 a.m. to 2:00 p.m. and then 5:00 p.m. to 9:00 p.m. The downside is more travel to the workplace every day.
Split shift example:
|10:00 to 14:00||On||On||On||On||On||Off||Off|
|14:00 to 17:00||Off||Off||Off||Off||Off||Off||Off|
|17:00 to 21:00||On||On||On||On||On||Off||Off|
"Earlies and lates" is used primarily in industries such as customer service (help desk/phone-support), convenience stores, child care (day nurseries), and other businesses that require coverage greater than the average 9:00 to 5:00 working day in the United Kingdom. Employees work in two shifts that largely overlap, such as "early shift" from 8:00 a.m. to 4:00 p.m. and "late shift" from 10:00 a.m. to 6:00 p.m.
Earlies and lates shift example:
|08:00 to 16:00||Shift 1||Shift 1||Shift 1||Shift 1||Shift 1||Off||Off|
|15:00 to 23:00||Shift 2||Shift 2||Shift 2||Shift 2||Shift 2||Off||Off|
In the "7-day fortnight shift" pattern, employees work their allotted hours within 7 days rather than 10. Therefore, 41 hours per week equate to 82 hours per fortnight (fourteen days and nights), which is worked in seven days, at 11–12 hours per shift. This shift structure is used in the broadcast television industry.
7-day fortnight shift example:
|Day 1||Day 2||Off||Off||Off||Day 3||Day 4||Off||Off||Day 5||Day 6||Day 7||Off||Off|
|Day 1||Day 2||Off||Off||Day 3||Day 4||Off||Off||Off||Day 5||Day 6||Off||Off||Day 7|
In 1978 Cohen et al proposed that reduced production of the hormone melatonin might increase the risk of breast cancer and citing "environmental lighting" as a possible causal factor. In 1987, working the night shift first became associated with higher rates of cancer. This may be due to alterations in circadian rhythm: melatonin, a known tumor suppressant, is generally produced at night and late shifts may disrupt its production. Multiple studies have documented a link between night shift work and the increased incidence of breast cancer.
In 2007, "shiftwork that involves circadian disruption" was listed as a probable carcinogen by the World Health Organization's International Agency for Research on Cancer. (IARC Press release No. 180).
A good review of current knowledge of the health consequences of exposure to artificial light at night and an explanation of the causal mechanisms was published in the Journal of Pineal Research in 2007.
A study suggests that, for those working a night shift (such as 11:00 p.m. to 7:00 a.m.), it may be advantageous to sleep in the evening (2:00 p.m. to 10:00 p.m.) rather than the morning (8:00 a.m. to 4:00 p.m.). The study's evening sleep subjects had 37% fewer episodes of attentional impairment than the morning sleepers.
Air traffic controllers typically work an 8-hour day, 5 days per week. Research has shown that when controllers remain "in position" for more than two hours, even at low traffic levels, performance can deteriorate rapidly, so they are typically placed "in position" for 30 minutes intervals (with 30 minutes between intervals).
After 18 hours of work, the typical person's reaction times are similar to people with 0.05 ppm of alcohol.
These practices and policies can be fairly obvious: selecting an appropriate shift schedule or rota, setting the length of shifts, managing overtime, increasing lighting levels, or providing shift worker lifestyle training to help shift workers better handle issues such as understanding basic circadian physiology, sleep and napping, caffeine usage, social life issues, diet and nutrition, etc. They may also be more indirect: retirement compensation based on salary in the last few years of employment (which can encourage excessive overtime among older workers who may be less able to obtain adequate sleep), or screening and hiring of new shift workers that assesses adaptability to a shift work schedule.