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 term shift work includes both long-term night shifts and work schedules in which employees change or rotate shifts. [cite web |url=,%20Definition(s)%20of |title=Shift work, Definition(s) of |accessdate=2007-12-01 |author=Sloan Work and Family Research, Boston College |publisher= |quote= ] [cite web |url= |title=Fact Sheet, Shiftwork |accessdate=2007-12-01 |author=Institute for Work & Health, Ontario, Canada |date= |format=PDF |work= |publisher= |quote=...outside regular daytime hours (i.e. between approximately 7 a.m. and 6 p.m., Monday through Friday). ]

A related yet different concept, the work shift, is the time period during which a person is at work.


A day may be divided into three shifts, each of eight hours, and each 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. Generally, "first shift" refers to the day shift, with "second shift" running from late afternoon to midnight or so, and "third shift" being the night shift. On occasion, more complex schedules are used, sometimes involving employees changing shifts, in order to operate during weekends as well, in which case there will be four or more sets of employees.

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.

hift patterns

Three-shift system

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.Fact|date=September 2008

Three-shift example:

Two days, two nights, four 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:

plit shift

"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:


Industries requiring 24/7 cover are those that employ workers on a shift basis, for example:

* Agriculture (during harvest months)
* Customer service (including call centres, help-desks and receptions)
* Health care
* Manufacturing
* Petroleum and natural gas processing
* Logistics
* Military, police, and security
* Rescue services
* Retail
* Television and radio broadcasting
* Transportation
* Food
* Bars, fast food restaurants, and hotels
* Engineers/repair persons

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 rhythms has been investigated also. A study by Knutsson "et al" 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.

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. [Cohen M, Lippman M, Chabner B. Role of pineal gland in aetiology and treatment of breast cancer. Lancet 1978;2:14–16.] 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. [Schernhammer E, Schulmeister K. Melatonin and cancer risk: does light at night compromise physiologic cancer protection by lowering serum melatonin levels? Br J Cancer 2004;90:941–943.] [Hansen J. Increased breast cancer risk among women who work predominantly at night. Epidemiology 2001; 12:74–77.] [Hansen J. Light at night, shiftwork, and breast cancer risk.J Natl Cancer Inst 2001; 93:1513–1515.] [Schernhammer E, Laden F, Speizer FE et al. Rotating night shifts and risk of breast cancer in women participating in the nurses' health study. J Natl Cancer Inst 2001; 93:1563–1568.]

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). [ [ IARC Press release No. 180] ] [cite web |url= |title=The health of night shift workers |accessdate=2007-11-30 |author=WNPR, Connecticut Public Radio |publisher=Connecticut Public Radio, WNPR |quote= ]

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. [Navara KJ, Nelson RJ (2007) [ The dark side of light at night: physiological, epidemiological, and ecological consequences] . J. Pineal Res. 2007; 43:215–224]

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. [cite journal
last = Santhi | first = N. | coauthors = Aeschbach D, Horowitz TS, Czeisler CA
year = 2008 | month = | title = The impact of sleep timing and bright light exposure on attentional impairment during night work | journal = J Biol Rhythms | volume = 23 | issue = 4 | pages = 341-52 | publisher = | issn = | pmid = | doi = | bibcode = | oclc = | id = | url = | format = abstract online | accessdate = 2008-08-05 | quote =

hift work management practices

The practices and policies put in place by managers of round-the-clock or 24/7 operations can significantly influence shift worker alertness (and hence safety) and performance.Fact|date=July 2008

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.Fact|date=June 2008

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.

ee also

* Circadian rhythm sleep disorders
* Sleep
* Split shift
* Timebar scheduling
* Eight-hour day
* 28-hour day


Further reading

* Knutsson, A., Åkerstedt, T., Jonsson, B.G. & Orth-Gomer, K. (1986) 'Increased risk of ischaemic heart disease in shift workers'. "Lancet", 2("8498"), 89–92.

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