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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.[1][2]

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.

Much of the internet services industry rely on shift work to maintain worldwide operations and uptime.


Graveyard shift

Graveyard shift or night shift or third shift (3rd shift) means a shift of work running through the early hours of the morning, especially one from midnight until 8 am. There is no certainty as to the origin of this phrase; according to Michael Quinion it is little more than "an evocative term for the night shift ... when ... your skin is clammy, there's sand behind your eyeballs, and the world is creepily silent, like the graveyard.".[3]

In 2007, the World Health Organization announced that working the graveyard shift would be listed as a 'probable' cause of cancer.[4][5]

Shift patterns

Three-shift system

The "three-shift system" is the most common pattern, with "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.[citation needed]

Three-shift example:

Time Sat Sun Mon Tues Wed Thur Fri
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

"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:

Time Sat Sun Mon Tues Wed Thur Fri Sat
07:00 to 19:00 Day 1 Day 2 Day 3 Day 4 Off Off Off Off

Four on, two 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.

Four on, two off example:

Time Sat Sun Mon Tues Wed Thur Fri
07:00 to 19:00 Day 1 Day 2 Day 3 Day 4 Off Off Day 1

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:

Time Sat Sun Mon Tues Wed Thur Fri Sat
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


"5/4/9's" (or "Five/Four Nine's") is another variation. Employees work in 2 week cycles. Week 1 the employee works 4 days of 9 hours followed by 1 day of 8 hours with 2 days off (week 1: 44 hours). Week 2 the employee works 4 days of 9 hours with 3 days off (week 2: 36 hours). This pattern works to 80-hours in a 2 week pay-period (comparable to working 8 hours a day for 5 days a week). The benefit to working a extra hour a day gives you a 'normal' 2 day weekend followed by a long 3 day weekend the next. Typical working hours for this type of shift would be 6:00 a.m. to 3:30 p.m. (9hrs with 30 minutes lunch) and 6:00 a.m. to 2:30 p.m. (8hrs with 30 minutes lunch) on the 8 hour work day. Often the employer will alter the starting times (e.g., start at 7:00 a.m. or 8:00 a.m.).

5/4/9's shift example:

Week Mon Tues Wed Thur Fri Sat Sun
Week 1 9 hrs 9 hrs 9 hrs 9 hrs 8 hrs Off Off
Week 2 9 hrs 9 hrs 9 hrs 9 hrs 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 24 hours rest, then a nightly shift (7:00 p.m. to 7:00 a.m.), finishing with 48 hours rest. This pattern needs four teams for full coverage, and makes an average 42-hour workweek.

12/24/12/48 shift example:

Time Sat Sun Mon Tues Wed Thur Fri
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

"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:

Time Sat Sun Mon Tues Wed Thur Fri
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

"Split shift" is used primarily in the catering, transport, 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.

Split shift example:

Time Sat Sun Mon Tues Wed Thur Fri
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

"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:

Time Sat Sun Mon Tues Wed Thur Fri
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

7-day fortnight shift

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, as well as many law enforcement agencies in the United States.

7-day fortnight shift example:

Time Sat Sun Mon Tues Wed Thur Fri Sat Sun Mon Tues Wed Thur Fri
08:00 to 20:00 Shift 'A'
Day 1
Shift 'A'
Day 2
Off Off Off Shift 'A'
Day 3
Shift 'A'
Day 4
Off Off Shift 'A'
Day 5
Shift 'A'
Day 6
Shift 'A'
Day 7
Off Off
20:00 to 08:00 Shift 'B'
Night 1
Shift 'B'
Night 2
Off Off Off Shift 'B'
Night 3
Shift 'B'
Night 4
Off Off Shift 'B'
Night 5
Shift 'B'
Night 6
Shift 'B'
Night 7
Off Off

DuPont 12 Hour Rotating Shift

The "DuPont 12 Hour Rotating Shift" provides 24/7 coverage using 4 crews and 12 hour shifts while providing a week off. Average hours is 42 per week but contains a 72 hour week which can be challenging. It is used in several manufacturing industries in the United States.

DuPont 12 Hour Rotating Shift example:

Week Fri Sat Sun Mon Tues Weds Thurs
1 Nights Nights Nights Nights Off Off Off
2 Days Days Days Off Nights Nights Nights
3 Off Off Off Days Days Days Days
4 Off Off Off Off Off Off Off

Seven Day Eight Hour Rotating Shift

The "Seven Day Eight Hour Rotating Shift" provides 24/7 coverage using 8 hour shifts with 4 crews. Consisted of a day shift from 7:00 am to 3:00 pm, a swing shift from 3:00 pm to 11:00 pm and a graveyard shift from 11:00 pm to 7:00 am. Each shift was worked for seven days straight. The eight hour shifts allowed vacations and absences to be covered by splitting shifts or working double shifts. The run of day shifts was 56 hours but the eight hour shift provided time for some socializing after work. Was once common in the pulp and paper industry in the Western United States but has been largely replaced by a 4 days, 4 off, 4 nights, 4 off, 12 hour rotation.

Seven Day Eight Hour Rotating Shift example:

Week Sat Sun Mon Tues Weds Thurs Fri
1 Days Days Days Days Days Days Days
2 Off Off Off Off Grave Grave Grave
3 Grave Grave Grave Grave Off Off Swing
4 Swing Swing Swing Swing Swing Swing Off


Submarine sailors in the American navy engage in a pattern known as sixes while underway. Instead of a 24-hour day, the ship operates on an 18-hour schedule. Any given individual is scheduled to stand watch for six hours, perform any other duties and engage in leisure time for six hours, then sleep for six hours. If enough personnel are available, a given watchstation may benefit from a fourth man referred to as the "midnight cowboy". He will stand the same six-hour watch in a given 24-hour period, usually from midnight to 0600 (hence the "midnight" portion of the name, which is most often shortened to just "cowboy") and the person who would normally stand that watch is free. This gives rise to a schedule of six on, twelve off, six on, thirty off, six on, twelve off.


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

Health consequences

The February 15, 2005 issue of American Family Physician noted that shift work has been associated with cluster headaches. Health problems in the short term can also include fatigue, stress and loss of concentration, a higher rate of absence from the job and poor sexual performance, as shown in the majority of 200 variable-shift workers in a recent study in Kuwait.[6]

Long term consequences of disturbing natural circadian rhythms have 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, citing "environmental lighting" as a possible causal factor.[7] Working the night shift first became associated with higher rates of cancer in 1987. 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.[8][9][10][11]

The World Health Organization's International Agency for Research on Cancer listed "shiftwork that involves circadian disruption" as a probable carcinogen in 2007 (IARC Press release No. 180).[12][13]

UCSF neurologist Louis Ptacek, who studies circadian rhythms, genes and sleep behaviors, has been quoted: "It’s not surprising, we have evolved on a planet that is rotating every 24 hours. Our internal clock is more than just when we sleep and wake. It’s related to cell division and it regulates our immune systems. When we battle our internal clock, that has complications."[14]

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.[15]

One 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.[16]

The health consequences of shift work may depend on whether one is a day person or a night person and what shift one is assigned to.

Shift 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.[citation needed]

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).

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.

See also


  1. ^ Sloan Work and Family Research, Boston College. "Shift work, Definition(s) of".,%20Definition(s)%20of. Retrieved 2007-12-01. 
  2. ^ Institute for Work & Health, Ontario, Canada. "Fact Sheet, Shiftwork" (PDF). Retrieved 2007-12-01. "...outside regular daytime hours (i.e. between approximately 7 a.m. and 6 p.m., Monday through Friday)." 
  3. ^ "Saved by the Bell",, March 27, 2000
  4. ^ [1] An estimated twenty percent of the American labour force works the night shift
  5. ^ Overnight shift to be classified as 'probable' cancer cause", CNN, November 29, 2007
  6. ^ Fido A, Ghali A. "Detrimental effects of variable work shifts on quality of sleep, general health and work performance" (Abstract). Med Princ Pract 2008;17(6):453-7. 
  7. ^ Cohen M, Lippman M, Chabner B. Role of pineal gland in aetiology and treatment of breast cancer. Lancet 1978;2:14–16.
  8. ^ 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.
  9. ^ Hansen J. Increased breast cancer risk among women who work predominantly at night. Epidemiology 2001; 12:74–77.
  10. ^ Hansen J. Light at night, shiftwork, and breast cancer risk.J Natl Cancer Inst 2001; 93:1513–1515.
  11. ^ 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.
  12. ^ IARC Press release No. 180
  13. ^ WNPR, Connecticut Public Radio. "The health of night shift workers". Connecticut Public Radio, WNPR. Retrieved 2007-11-30. 
  14. ^ Erin Allday, Chronicle Staff Writer (24 March 2008). "Keeping the ‘grave’ out of ‘graveyard shift’". San Francisco Chronicle. Retrieved 2009-11-19. 
  15. ^ Navara KJ, Nelson RJ (2007) The dark side of light at night: physiological, epidemiological, and ecological consequences. J. Pineal Res. 2007; 43:215–224
  16. ^ Santhi, N.; Aeschbach D, Horowitz TS, Czeisler CA (2008). "The impact of sleep timing and bright light exposure on attentional impairment during night work" (abstract online). J Biol Rhythms 23 (4): 341–52. doi:10.1177/0748730408319863. Retrieved 2008-08-05. 

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.
  • Burr, Douglas Scott (2009) 'The Schedule Book', 'ISBN 978-1-4392-2674-2'.

Simple English

Shift work is a working practice which is designed to use all 24 hours of a day, and not only the standard working day hours.

A day for example can be divided into three eight-hour shifts. An employee only works one of the shifts in each day. The "first shift" is in the morning, the "second shift" is in the afternoon and evening and the "third shift" is overnight.

The "second shift", also known as the swing shift in some places, is the work shift which takes place in the afternoon and evening. It usually extends from 4 PM (16:00) to midnight, or from 3 PM (15:00) to 10 PM (22:00).

The "third shift", the night shift, is usually from 12-midnight (00:00) to 07 or 08 in the morning.

Health effects

The World Health Organization (WHO) decided in December 2007 that shift work, especially work at night, probably causes cancer.[1]

A study by Knutsson et al in 1986 showed that people who work shift work for more than 15 years, are 3 times more likely to develop ischaemic heart diseases.[2]


  1. «Shiftwork that involves circadian disruption is “probably carcinogenic to humans”.»
  2. 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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