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. mandating a minimum of 10 hours between shifts is an effective strategy to encourage adequate sleep for workers. allowing frequent breaks and scheduling 8- or 10-hour shifts instead of 12-hour shifts can also minimize fatigue and help to mitigate the negative health effects of shift work. miners waiting to go to work on the 4 p.m. to midnight shift at the virginia-pocahontas coal co., 1974 multiple factors need to be considered when developing optimal shift work schedules, including shift timing, length, frequency and length of breaks during shifts, shift succession, worker commute time, as well as the mental and physical stress of the job. even though studies support 12-hour shifts are associated with increased occupational injuries and accident (higher rates with subsequent, successive shifts), a synthesis of evidence cites the importance of all factors when considering the safety of a shift. shift work was once characteristic primarily of the 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. although 2nd-shift worker efficiency levels are typically 3–5% below 1st shift, and 3rd shift 4–6% below 2nd shift, the productivity level, i.e. cost per employee, is often 25% to 40% lower on 2nd and 3rd shifts due to fixed costs which are "paid" by the first shift. shift system the 42-hour work-week allows for the most even distribution of work time. a 3:1 ratio of work days to days off is most effective for eight-hour shifts, and a 2:2 ratio of work days to days off is most effective for twelve-hour shifts. eight-hour shifts and twelve-hour shifts are common in manufacturing and health care. twelve-hour shifts are also used with a very slow rotation in the petroleum industry. twenty-four-hour shifts are common in health care and emergency services. shift schedule and shift plan main article: shift plan the shift plan or rota is the central component of a shift schedule. the schedule includes considerations of shift overlap, shift change times and alignment with the clock, vacation, training, shift differentials, holidays, etc., whereas the shift plan determines the sequence of work and free days within a shift system. rotation of shifts can be fast, in which a worker changes shifts more than once a week, or slow, in which a worker changes shifts less than once a week. rotation can also be forward, when a subsequent shift starts later, or backward, when a subsequent shift starts earlier. evidence supports forward rotating shifts are more adaptable for shift workers' circadian physiology. one main concern of shift workers is knowing their schedule more than two weeks at a time. shift work is stressful. when on a rotating or ever changing shift, workers have to worry about daycare, personal appointments, and running their households. many already work more than an eight-hour shift. some evidence suggests giving employees schedules more than a month in advance would give proper notice and allow planning, their stress level would be reduced. management though shift work itself remains necessary in many occupations, employers can alleviate some of the negative health consequences of shift work. the united states national institute for occupational safety and health recommends employers avoid quick shift changes and any rotating shift schedules should rotate forward. employers should also attempt to minimize the number of consecutive night shifts, long work shifts and overtime work. a poor work environment can exacerbate the strain of shift work. adequate lighting, clean air, proper heat and air conditioning, and reduced noise can all make shift work more bearable for workers. good sleep hygiene is recommended. this includes blocking out noise and light during sleep, maintaining a regular, predictable sleep routine, avoiding heavy foods and alcohol before sleep, and sleeping in a comfortable, cool environment. alcohol consumption, caffeine consumption and heavy meals in the few hours before sleep can worsen shift work sleep disorders. exercise in the three hours before sleep can make it difficult to fall asleep. free online training programs are available to educate workers and managers about the risks associated with shift work and strategies they can use to prevent these. scheduling a clock-based device for recording workers' working hours, from the beginning of 20 century. exhibit of the national polytechnical museum in sofia, bulgaria algorithmic scheduling of shift work can lead to what has been colloquially termed as "clopening" where the shift-worker has to work the closing shift of one day and the opening shift of the next day back-to-back resulting in short rest periods between shifts and fatigue. co-opting employees to fill the shift roster helps to ensure that the human costs are taken into account in a way which is hard for an algorithm to do as it would involve knowing the constraints and considerations of each individual shift worker and assigning a cost metric to each of those factors. shift based hiring which is a recruitment concept that hires people for individual shifts, rather than hiring employees before scheduling them into shifts enables shift workers to indicate their preferences and availability for unfilled shifts through a shift-bidding mechanism. through this process, the shift hours are evened out by human-driven market mechanism rather than an algorithmic process. this openness can lead to work hours that are tailored to an individual's lifestyle and schedule while ensuring that shifts are optimally filled, in contrast to the generally poor human outcomes of fatigue, stress, estrangement with friends and family and health problems that have been reported with algorithm-based scheduling of work-shifts. mental (cognitive) fatigue due to inadequate sleep an/or disturbances of circadian rhythms is a common contributor to accidents and untoward incidents. while the this risk cannot be eliminated, it can be managed through personal and administrative controls. this type of management is conducted through a fatigue risk management system (frms). one method used within an frms is objective fatigue modeling to predict periods of high risk within a 24-hour shift plan. modeling is accomplished with tools such as the fatigue avoidance scheduling tool (fast) and the faid quantum software missing income is also a large part of shift worker. several companies run twenty-four hour shifts. most of the work is done during the day. when the work dries up, it usually is the second and third shift workers who pay the price. they are told to punch out early or use paid time off if they have any to make up the difference in their paychecks. that practice costs the average worker $92.00 a month. medications melatonin may increase sleep length during both daytime and nighttime sleep in people who work night shifts. zopiclone has also been investigated as a potential treatment, but it is unclear if it is effective in increasing daytime sleep time in shift workers. there are, however, no reports of adverse effects. modafinil and r-modafinil are useful to improve alertness and reduce sleepiness in shift workers. modafinil has a low risk of abuse compared to other similar agents. however, 10% more participants reported adverse effects (nausea and headache) while taking modafinil. in post-marketing surveillance, modafinil was associated with stevens–johnson syndrome. the european medicines agency withdrew the license for modafinil for shift workers for the european market because it judged that the benefits did not outweigh the adverse effects. using caffeine and naps before night shifts can decrease sleepiness. caffeine has also been shown to reduce errors made by shift workers. epidemiology worker health charts provides a distribution of shift work by industry from 2015 nhis data. according to data from the national health interview survey and the occupational health supplement, 27% of all u.s. workers in 2015 worked an alternative shift (not a regular day shift) and 7% frequently worked a night shift. prevalence rates were higher for workers aged 18–29 compared to other ages. those with an education level beyond high school had a lower prevalence rate of alternative shifts compared to workers with less education. among all occupations, protective service occupations had the highest prevalence of working an alternative shift (54%). one of the ways in which working alternative shifts can impair health is through decreasing sleep opportunities. among all workers, those who usually worked the night shift had a much higher prevalence of short sleep duration (44.0%, representing approximately 2.2 million night shift workers) than those who worked the day shift (28.8%, representing approximately 28.3 million day shift workers). an especially high prevalence of short sleep duration was reported by night shift workers in the transportation and warehousing (69.7%) and health-care and social assistance (52.3%) industries. industries it is estimated that 15-20% of workers in industrialized countries are employed in shift work. shift work is common in the transportation sector as well. some of the earliest instances appeared with the railroads, where freight trains have clear tracks to run on at night. shift work is also the norm in fields related to public protection and healthcare, such as law enforcement, emergency medical services, firefighting, security and hospitals. shift work is a contributing factor in many cases of medical errors. shift work has often been common in the armed forces. military personnel, pilots, and others that regularly change time zones while performing shift work experience jet lag and consequently suffer sleep disorders. those in the field of meteorology, such as the national weather service and private forecasting companies, also use shift work, as constant monitoring of the weather is necessary. much of the internet services and telecommunication industry relies on shift work to maintain worldwide operations and uptime. service industries now increasingly operate on some shift system; for example a restaurant or convenience store will normally be open on most days for much longer than a working day. there are many industries requiring 24/7 coverage that employ workers on a shift basis, including: caregiver direct support professional customer service including call centers data center and it operations death care (medical examiner or coroner) emergency services police firefighting emergency medical services 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