shift work shift work shift work is an employment practice designed to make use of, or provide service across, all 24 hours of the clock each day of the week (often abbreviated as 24/7). the practice typically sees the day divided into shifts, set periods of time during which different groups of workers perform their duties. the term "shift work" includes both long-term night shifts and work schedules in which employees change or rotate shifts. part of a series onorganized labour labour movement timeline new unionismproletariat social movement unionism social democracydemocratic socialismsocialismcommunismsyndicalism anarcho-syndicalismnational-syndicalism labour rights freedom of associationcollective bargaining child labourunfree labour equal payemployment discrimination legal working agefour-day weekeight-hour day annual leavepaid time offsick leaveminimum wage occupational safety and healthemployment protection trade unions trade unions by country trade union federations international comparisons ituciwawftu strike action chronological list of strikes general strikesecondary actionovertime banquiet quitting sitdown strikework-to-rulelockout labour parties australia barbados brazil fiji georgia hong kong ireland israel malta new caledonia new zealand netherlands norway portugal singapore south korea united kingdom sweden academic disciplines industrial relations labour economics labour history labour law in medicine and epidemiology, shift work is considered a risk factor for some health problems in some individuals, as disruption to circadian rhythms may increase the probability of developing cardiovascular disease, cognitive impairment, diabetes, altered body composition and obesity, among other conditions. history the shift work system in modern industrial manufacturing originated in the late 18th century. in 1867, karl marx wrote on the shift work system in capital, volume 1: capitalist production therefore drives, by its inherent nature, towards the appropriation of labour throughout the whole of the 24 hours in the day. but since it is physically impossible to exploit the same individual labour-power constantly, during the night as well as the day, capital has to overcome this physical obstacle. an alternation becomes necessary, between the labour-powers used up by day and those used up by night ... it is well known that this shift-system, this alternation of two sets of workers, predominated in the full-blooded springtime of the english cotton industry, and that at the present time it still flourishes, among other places, in the cotton-spinning factories of the moscow gubernia. this 24-hour process of production exists today as a system in many of the as yet 'free' branches of industry in great britain, in the blast-furnaces, forges, rolling mills and other metallurgical establishments of england, wales and scotland. the cromford mill, starting from 1772, ran day and night with two twelve-hour shifts. health effects main article: shift work sleep disorder shift work increases the risk for the development of many disorders. shift work sleep disorder is a circadian rhythm sleep disorder characterized by insomnia, excessive sleepiness, or both. shift work is considered essential for the diagnosis. the risk of diabetes mellitus type 2 is increased in shift workers, especially men. people working rotating shifts are more vulnerable than others. women whose work involves night shifts have a 48% increased risk of developing breast cancer. this may be due to alterations in circadian rhythm: melatonin, a known tumor suppressor, is generally produced at night and late shifts may disrupt its production. the who's international agency for research on cancer listed "shift work that involves circadian disruption" as probably carcinogenic. shift work may also increase the risk of other types of cancer. working rotating shift work regularly during a two-year interval has been associated with a 9% increased the risk of early menopause compared to women who work no rotating shift work. the increased risk among rotating night shift workers was 25% among women predisposed to earlier menopause. early menopause can lead to a host of other problems later in life. a recent study, found that women who worked rotating night shifts for more than six years, eleven percent experienced a shortened lifespan. women who worked rotating night shifts for more than 15 years also experienced a 25 percent higher risk of death due to lung cancer. shift work also increases the risk of developing cluster headaches, heart attacks, fatigue, stress, sexual dysfunction, depression, dementia, obesity, metabolic disorders, gastrointestinal disorders, musculoskeletal disorders, and reproductive disorders.children going to a 12-hour night shift in the united states, 1908 shift work also can worsen chronic diseases, including sleep disorders, digestive diseases, heart disease, hypertension, epilepsy, mental disorders, substance abuse, asthma, and any health conditions that are treated with medications affected by the circadian cycle. artificial lighting may additionally contribute to disturbed homeostasis. shift work may also increase a person's risk of smoking. the health consequences of shift work may depend on chronotype, that is, being a day person or a night person, and what shift a worker is assigned to. when individual chronotype is opposite of shift timing (day person working night shift), there is a greater risk of circadian rhythms disruption. nighttime workers sleep an average of 1–4 hours less than daytime workers. different shift schedules will have different impacts on the health of a shift worker. the way the shift pattern is designed affects how shift workers sleep, eat and take holidays. some shift patterns can exacerbate fatigue by limiting rest, increasing stress, overworking staff or disrupting their time off. muscle health is also compromised by shift work: altered sleep and eating times, changes to appetite-regulating hormones and total energy expenditure, increased snacking and binge drinking, and reduced protein intake can contribute to negative protein balance, increases in insulin resistance and increases in body fat, resulting in weight gain and more long-term health challenges. compared with the day shift, injuries and accidents have been estimated to increase by 15% on evening shifts and 28% on night shifts. longer shifts are also associated with more injuries and accidents: 10-hour shifts had 13% more and 12-hour shifts had 28% more than 8-hour shifts. other studies have shown a link between fatigue and workplace injuries and accidents. workers with sleep deprivation are far more likely to be injured or involved in an accident. breaks reduce accident risks. one study suggests that, for those working a night shift (such as 23:00 to 07:00), it may be advantageous to sleep in the evening (14:00 to 22:00) rather than the morning (08:00 to 16:00). the study's evening sleep subjects had 37% fewer episodes of attentional impairment than the morning sleepers. there are four major determinants of cognitive performance and alertness in healthy shift-workers: circadian phase, sleep inertia, acute sleep deprivation and chronic sleep deficit. the circadian phase is relatively fixed in humans; attempting to shift it so that an individual is alert during the circadian bathyphase is difficult. sleep during the day is shorter and less consolidated than night-time sleep. before a night shift, workers generally sleep less than before a day shift. the effects of sleep inertia wear off after 2–4 hours of wakefulness, such that most workers who wake up in the morning and go to work suffer some degree of sleep inertia at the beginning of their shift. the relative effects of sleep inertia vs. the other factors are hard to quantify; however, the benefits of napping appear to outweigh the cost associated with sleep inertia. acute sleep deprivation occurs during long shifts with no breaks, as well as during night shifts when the worker sleeps in the morning and is awake during the afternoon, prior to the work shift. a night shift worker with poor daytime sleep may be awake for more than 18 hours by the end of his shift. the effects of acute sleep deprivation can be compared to impairment due to alcohol intoxication, with 19 hours of wakefulness corresponding to a bac of 0.05%, and 24 hours of wakefulness corresponding to a bac of 0.10%. much of the effect of acute sleep deprivation can be countered by napping, with longer naps giving more benefit than shorter naps. some industries, specifically the fire service, have traditionally allowed workers to sleep while on duty, between calls for service. in one study of ems providers, 24-hour shifts were not associated with a higher frequency of negative safety outcomes when compared to shorter shifts. chronic sleep deficit occurs when a worker sleeps for fewer hours than is necessary over multiple days or weeks. the loss of two hours of nightly sleep for a week causes an impairment similar to those seen after 24 hours of wakefulness. after two weeks of such deficit, the lapses in performance are similar to those seen after 48 hours of continual wakefulness. the number of shifts worked in a month by ems providers was positively correlated with the frequency of reported errors and adverse events. sleep assessment during shift work a cross-sectional study investigated the relationship between several sleep assessment criteria and different shift work schedules (3-day, 6-day, 9-day and 21-day shift) and a control group of day shift work in korean firefighters. the results found that all shift work groups exhibited significant decreased total sleep time (tst) and decreased sleep efficiency in the night shift but efficiency increased in the rest day. between-group analysis of the different shift work groups revealed that day shift sleep efficiency was significantly higher in the 6-day shift while night shift sleep efficiency was significantly lower in the 21-day shift in comparison to other shift groups (p < 0.05). overall, night shift sleep quality was worse in shift workers than those who just worked the day shift, whereas 6-day shift provided better sleep quality compared to the 21-day shift. safety and regulation shift work has been shown to negatively affect workers, and has been classified as a specific disorder (shift work sleep disorder). circadian disruption by working at night causes symptoms like excessive sleepiness at work and sleep disturbances. shift work sleep disorder also creates a greater risk for human error at work. shift work disrupts cognitive ability and flexibility and impairs attention, motivation, decision making, speech, vigilance, and overall performance. in order to mitigate the negative effects of shift work on safety and health, many countries have enacted regulations on shift work. the european union, in its directive 2003/88/ec, has established a 48-hour limit on working time (including overtime) per week; a minimum rest period of 11 consecutive hours per 24-hour period; and a minimum uninterrupted rest period of 24 hours of mandated rest per week (which is in addition to the 11 hours of daily rest). the eu directive also limits night work involving "special hazards or heavy physical or mental strain" to an average of eight hours in any 24-hour period. the eu directive allows for limited derogations from the regulation, and special provisions allow longer working hours for transportation and offshore workers, fishing vessel workers, and doctors in training (see also medical resident work hours). aircraft traffic flight controllers and pilots for fewer operational errors, the faa goal calls for flight controllers to be on duty for 5 to 6 hours per shift, with the remaining shift time devoted to meals and breaks. for aircraft pilots, the actual time at the controls (flight time) is limited to 8 or 9 hours, depending on the time of day. industrial disasters fatigue due to shift work has contributed to several industrial disasters, including the three mile island accident, the space shuttle challenger disaster and the chernobyl disaster. the alaska oil spill commission's final report on the exxon valdez oil spill disaster found that it was "conceivable" that excessive work hours contributed to crew fatigue, which in turn contributed to the vessel's running aground. prevention management practices 4 o'clock shift at the ford motor company assembly plant in detroit, michigan, 1910s 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. 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-minute intervals (with 30 minutes between intervals). these practices and policies can include selecting an appropriate shift schedule or rota and using an employee scheduling software to maintain it, setting the length of shifts, managing overtime, increasing lighting levels, providing shift worker lifestyle training, retirement compensation based on salary in the last few years of employment (which can