Shift work

# Overview
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.

# Practice
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.
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.

# Shift Patterns
- In some areas, the swing shift, also known as "second shift", is scheduled during the afternoon and evening, such as 16:00 to 24:00 or 15:00 to 22:00.  Some shift work expertsTemplate:Who consider this swing shift to be the least desirable of the three possibilities in an 8-hour shift schedule. The swing shift (svingskift) in the offshore petroleum industry in Norway refers to a two week tour where one works 12-hour days the first seven days and 12-hour  nights the second, or vice versa.
- The graveyard shift, also known as "third shift", means a shift of work running through the early hours of the morning, especially one from midnight until 08:00. 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."
- In the 7 day fortnight shift pattern, employees do 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 will be done in seven days by working 11-12 hours per shift.  This shift structure is used in the broadcast television industry.
7 day fortnight shift example

# 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.
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 has been published in the Journal of Pineal Research in 2007.

# Fatigue countermeasures and shift worker lifestyle training
The behaviors and decisions made by people who work shift work affect their alertness, safety, and performance (and possibly their short-term and long-term health, although that has not been adequately studied at this time).  There are a number of areas in which shift workers can implement certain fatigue countermeasures and other ways in which they can modify their lifestyles to better adapt to the realities of their work schedules.  These include managing what and how much they eat, managing their use of caffeine and other substances to increase alertness or induce sleep, creating a sleep-friendly environment for sleeping during the day time, avoiding drowsy driving, how to nap effectively, and tips for maintaining family and social life.

# Shift work management practices
The practices and policies put in place by managers of round-the-clock or 24/7 operations can significantly influence shiftworker alertness (and hence safety) and performance.
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 shiftworker lifestyle training to help shiftworkers 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 shiftworkers that assesses adaptability to a shift work schedule.