Success in global markets requires companies to be flexible and ready to make rapid changes. For workers, this can mean an increasing amount of shift work or extended working days. The aim of this review is to examine whether these factors (long working hours, shift work, and breaks) are related to occupational injuries.

For this literature review, the studies were collected on the following criteria:

1) Occupational injuries included in this review are only accident injuries and diseases are excluded.

2) The studies were published, most of them in peer-reviewed journals. All the studies reviewed were published in English.

3) The study included a comparison of injury rates of morning, afternoon and night shifts. Especially studies presented in the summary table fill the criteria.

4) In the part of extended working days all studies identified in the literature and related to occupational safety during extended working days were included in the text. However, only studies including exact injury rates of 8 working hours compared to 10 hours, 12 hours or longer working hours were presented at the Table 2.

The search of literature was done by picking articles from those that I have read. For example, titles did not told that the articles concerning long working hours and occupational injury.

The term “risk” in this review is meaning the risk of occupational accident. In the most cases the risk is determined by the multiplication of the probability of accidents and consequences of accidents.

According to the European Union Survey on Working Conditions in 2000, 18.8% of the workforce is engaged in shift work including night work. More men (24%) than women (12%) were involved in shift work. About 7% of shift workers worked permanently at night [1Costa G. Shift work and occupational medicine: an overview. Occup Med (Lond) 2003; 53(2): 83-8.
[http://dx.doi.org/10.1093/occmed/kqg045] [PMID: 12637591] ].

In a review of 19 studies done between 1910 and 1985 in England, USA, Germany, and Netherlands etc., eight showed a higher frequency of accidents during night shifts, one during day shifts, two during morning shifts and two during afternoon shifts. In six studies there were no statistical significant differences between shifts [2Costa G. The impact of shift and night work on health. Appl Ergon 1996; 27(1): 9-16.
[http://dx.doi.org/10.1016/0003-6870(95)00047-X] [PMID: 15676307] ].

The recent review showed that compared to morning shifts, the risk of occupational injury during afternoon shifts increased by 18.3% and in night shifts by 30.4%. This review is based on five studies published between years of 1972 and 1995 [3Folkard S, Tucker P. Shift work, safety and productivity. Occup Med (Lond) 2003; 53(2): 95-101.
[http://dx.doi.org/10.1093/occmed/kqg047] [PMID: 12637593] , 4Folkard S, Åkerstedt T. Trends in the risk of accidents and injuries and their implications for models of fatigue and performance. Aviat Space Environ Med 2004; 75(3)(Suppl.): A161-7.
[PMID: 15018280] ]. However, the authors [5Folkard S, Lombardi DA, Tucker PT. Shiftwork: safety, sleepiness and sleep. Ind Health 2005; 43(1): 20-3.
[http://dx.doi.org/10.2486/indhealth.43.20] [PMID: 15732299] -7Folkard S, Lombardi DA, Spencer MB. Estimating the circadian rhythm in the risk of occupational injuries and accidents. Chronobiol Int 2006; 23(6): 1181-92.
[http://dx.doi.org/10.1080/07420520601096443] [PMID: 17190704] ] later added two studies made in 2000 and 2001 to their review, and concluded that the risk of occupational injury was 15% higher during afternoon shifts and 28% higher during night shifts compared to morning shifts, which were 3.3% and 2.4% lower than the previous reviews. When they examined successive night shifts, the risk of occupational injury was 6% higher on the second night, 17% higher on the third night, and 36% higher on the fourth night. Compared to day shifts, the risk of injury increased by 2% for the second morning, 7% for the third morning, and 17% for the fourth morning. It was concluded that older workers had a greater risk of occupational injury in the shiftwork both in the review [8Folkard S. Shift work, safety, and aging. Chronobiol Int 2008; 25(2): 183-98.
[http://dx.doi.org/10.1080/07420520802106694] [PMID: 18484360] ] and empirically in New Zealand (n=2,685) [9Gander P, Signal L. Who is too old for shift work? Developing better criteria. Chronobiol Int 2008; 25(2): 199-213.
[http://dx.doi.org/10.1080/07420520802077556] [PMID: 18484361] ], although this claim requires more research.

Working on the off-shore platforms are a special case for shift work, because employees stay 2-3 weeks at the platform without leaving. A review studies published between 1996 and 2011 of shift schedules on North Sea oil-gas installations found 31 studies. Based on them, it was concluded that the risk of serious injuries requiring medical treatment was 22-32% higher in night shifts than of day shift injuries [10Parkes KR. Shift schedules on North Sea oil/gas installations: A systematic review of their impact on performance, safety and health. Saf Sci 2012; 50: 1636-51.
[http://dx.doi.org/10.1016/j.ssci.2012.01.010] ]. However, there was no possibility of comparing the injury rates for fixed-shift and swing-shift rotation schedules. Another review based on the four studies published between 1990 and 2001 in the offshore petroleum industry concluded that results are inconsistent and insufficient as a base for drawing general conclusion [11Fossum IN, Bjorvatn B, Waage S, Pallesen S. Effects of shift and night work in the offshore petroleum industry: a systematic review. Ind Health 2013; 51(5): 530-44.
[http://dx.doi.org/10.2486/indhealth.2013-0054] [PMID: 23803497] ]. In Norwegian drilling rigs, operators had more injuries during the day shift than during the night shift (number of injuries = 3229, 1980-1987) (p<0.05), due to higher activity level and more people working at day time. However, there was no difference between day and night shifts in the injury rate among drilling crews [12Lauridsen O, Tønnesen T. Injuries related to the aspects of shift working - a comparison of different offshore shift arrangements. J Occup Accid 1990; 12: 167-76.
[http://dx.doi.org/10.1016/0376-6349(90)90095-D] ]. At Campos Basin offshore drilling units in Brazil (n=172) working at dark period increased the risk of occupational injury by 51% compared to light period [13Rodrigues VF, Fischer FM, Brito MJ. Shift work at a modern offshore drilling rig. J Hum Ergol (Tokyo) 2001; 30(1-2): 167-72.
[PMID: 14564877] ]. In the North Sea oil and gas installations shift pattern was significantly associated with work-related injury (p<0.05). Construction workers had almost three times more injuries than the reference group (OR = 2.91, 95% CI 1.58-5.36, n=1,462 exposed workers) [14Parkes KR. Shiftwork, job type, and the work environment as joint predictors of health-related outcomes. J Occup Health Psychol 1999; 4(3): 256-68.
[http://dx.doi.org/10.1037/1076-8998.4.3.256] [PMID: 10431285] ].

A study involving workers of a large English engineering company (n= 4,645) showed that during afternoon shifts the risk of occupational injury was 15% higher (RR= 1.15, 95% CI 1.07-1.23), and during night shifts 23% higher than during morning shifts (RR = 1.23, 95% CI 1.14-1.31, p<0.001). Moreover, injuries in the self-paced work were more serious on the night shift compared with the morning shift [15Smith L, Folkard S, Poole CJ. Increased injuries on night shift. Lancet 1994; 344(8930): 1137-9.
[http://dx.doi.org/10.1016/S0140-6736(94)90636-X] [PMID: 7934499] ].

Driving home after a night shift increased the risk of fatigue-related traffic accidents both in the review [16Monk TH, Folkard S, Wedderburn AI. Maintaining safety and high performance on shiftwork. Appl Ergon 1996; 27(1): 17-23.
[http://dx.doi.org/10.1016/0003-6870(95)00048-8] [PMID: 11542593] ] and among American medical students (n=3,429, OR = 2.3, 95% CI 1.6-3.3, p<0.001) [17Barger LK, Cade BE, Ayas NT, et al. Extended work shifts and the risk of motor vehicle crashes among interns. N Engl J Med 2005; 352(2): 125-34.
[http://dx.doi.org/10.1056/NEJMoa041401] [PMID: 15647575] ]: a systematic review concluded that the risk of crashing doubles after extended shifts [18Robb G, Sultana S, Ameratunga S, Jackson R. A systematic review of epidemiological studies investigating risk factors for work-related road traffic crashes and injuries. Inj Prev 2008; 14(1): 51-8.
[http://dx.doi.org/10.1136/ip.2007.016766] [PMID: 18245316] ].

Employees of evening and night shifts had a respectively higher risk of occupational injury of 43% (HR = 1.43, 95% CI 1.26-1.62) and 30% (HR = 1.30, 95% CI 1.12-1.52) compared to conventional day shifts according to the National Longitudinal Survey of Youth in U.S. (n=12 686). In addition, rotating shift work increased injury risk by 36% (HR = 1.36, 95% CI 1.17-1.58) and irregular shift work by 15% (HR = 1.15, 95% CI 1.03-1.30) [19Dembe AE, Erickson JB, Delbos RG, Banks SM. Nonstandard shift schedules and the risk of job-related injuries. Scand J Work Environ Health 2006; 32(3): 232-40.
[http://dx.doi.org/10.5271/sjweh.1004] [PMID: 16804627] ]. The greatest risk of occupational injury in evening shifts was found among construction workers (n = 264, HR = 2.86, 95% CI 1.38-5.98) [20Dembe AE, Delbos R, Erickson JB. The effect of occupation and industry on the injury risks from demanding work schedules. J Occup Environ Med 2008; 50(10): 1185-94.
[http://dx.doi.org/10.1097/JOM.0b013e31817e7bf2] [PMID: 18849764] ].

In a metallurgic plant in the former German Democratic Republic, occupational injuries (n=688 in 1968-1969) reached a maximum during night shifts (p<0.01) [21Quaas M, Tunsch R. Problems of disablement and accident frequency in shift- and night work. Proceedings of the Second International Symposium on Night and Shift Work Slanchev Bryag. International Archives of Occupational and Environmental Health 1971; 58(4): pp 301-20 ]. In an American paint company, workers (n=1,691) had a 25% greater injury rate during night shifts than during morning shifts, and the injury risk was highest in the last three hours of the night shift (p<0.05) [22Levin L, Oler J, Whiteside JR. Injury incidence rates in a paint company on rotating production shifts. Accid Anal Prev 1985; 17(1): 67-73.
[http://dx.doi.org/10.1016/0001-4575(85)90009-0] [PMID: 4091934] ]. Occupational injuries occurred most often in the fourth working hour during the morning shifts and the fifth and sixth hour during night shift in Indian textile industries (n=3,470 fatal and non-fatal injuries) [23Nag PK, Patel VG. Work accidents among shiftworkers in industry. Int J Ind Ergon 1998; 21(3-4): 275-81.
[http://dx.doi.org/10.1016/S0169-8141(97)00050-4] ]. In an Iranian mining industry in 2006-2007, shift workers (n=137) injured more often than non-shift workers (n=130, p = 0.03) and shift workers reported more often fatigue-related injuries (p<0.001) [24Halvani GH, Zare M, Mirmohammadi SJ. The relation between shift work, sleepiness, fatigue and accidents in Iranian Industrial Mining Group workers. Ind Health 2009; 47(2): 134-8.
[http://dx.doi.org/10.2486/indhealth.47.134] [PMID: 19367041] ]. In a synthetic fiber factory in Iran the occupational injury rate (n=836 injury events) was one and half time higher (OR = 1.50, 95% CI 1.10-2.00) during the first half of the shift than during the second half [25Sanati KA, Yadegarfar G, Naghavi H, Mansouri M, Sanati JG. Temporal trend of occupational injuries; first versus second half of a working shift. Int J Occup Saf Ergon 2010; 16(1): 49-54.
[http://dx.doi.org/10.1080/10803548.2010.11076828] [PMID: 20331918] ].

Fire fighters (n=447) from a Northeastern state were injured more often during the night shifts (p>0.05) [26Glazner LK. Factors related to injury of shiftworking fire fighters in the Northeastern United States. Saf Sci 1996; 21(3): 255-63.
[http://dx.doi.org/10.1016/0925-7535(95)00069-0] ]. Police officers (n=419) from a mid-sized urban police department in the U.S. were injured on the midnight shift 72% more often than in the day shift (Incident Rate Ratio = 1.72, 95% CI 1.26-2.36, p = 0.0007). High activity level combined with midnight shift doubled the risk of occupational injury for police officers (IRR = 2.31, 95% CI 1.46-3.65, p = 0.0003) [27Violanti JM, Fekedulegn D, Andrew ME, et al. Shift work and the incidence of injury among police officers. Am J Ind Med 2012; 55(3): 217-27.
[http://dx.doi.org/10.1002/ajim.22007] [PMID: 22228219] ]. A long-term injury (>89 days) for the same police officers occurred three times more often during night versus day shift (IRR = 3.12, 95% CI 1.35-7.21, p = 0.01) and two times more often in night shift versus afternoon shifts (IRR = 2.21, 95% CI 1.06-4.68, p = 0.04) [28Violanti JM, Fekedulegn D, Andrew ME, et al. Shift work and long-term injury among police officers. Scand J Work Environ Health 2013; 39(4): 361-8.
[http://dx.doi.org/10.5271/sjweh.3342] [PMID: 23503596] ].

In a Canadian glass factory and steel plant, injuries (n=3 309) peaked at noon, just before lunch time and between 2 and 4 a.m. during the night shift [29Wojtczak-Jaroszowa J, Jarosz D. Time-related distribution of occupational accidents. J Safety Res 1987; 18: 33-41.
[http://dx.doi.org/10.1016/0022-4375(87)90062-4] ]. During afternoon and night shifts, injuries were less severe than in the morning shift in six automotive plants in Ontario, Canada (n=over 8 000 workers) [30Barsky I, Dutta SP. Age, shiftwork and industrial accidents - a longitudinal study. In: Kumar S, Ed. Advances in Industrial Ergonomics and Safety IV. London: Taylor & Francis 1992; pp. 113-20.]. Based on two population-based data sources in Ontario over 5 years 2004-2008 (n=457 141 injuries), in evening and night schedules women had 12.5% and men 5.8% more injuries than in the morning shift [31Mustard CA, Chambers A, McLeod C, Bielecky A, Smith PM. Work injury risk by time of day in two population-based data sources. Occup Environ Med 2013; 70(1): 49-56.
[http://dx.doi.org/10.1136/oemed-2012-100920] [PMID: 23014592] ]. On the other hand, based on the Survey of Labor and Income Dynamics 1996-2006 (n=approximately 30 000), shift work increased risk of occupational injury 14.4% for Canadian women and 8.2% for men. Night shift work doubled the injury risk among women (OR = 2.04, 95% CI 1.13-3.69) and almost doubled among men (OR = 1.91, 95% CI 1.21-3.03), while rotating shift work increased the injury risk for women over two times (OR = 2.29, 95% CI 1.37-3.82) [32Wong IS, McLeod CB, Demers PA. Shift work trends and risk of work injury among Canadian workers. Scand J Work Environ Health 2011; 37(1): 54-61.
[http://dx.doi.org/10.5271/sjweh.3124] [PMID: 20890587] ]. However, injuries were more serious during night shifts, although the injury rate was lower during night shifts than during the morning and afternoon shifts (p<0.001) in an iron and steel plant in Singapore (n=664 production workers) [33Ong CN, Phoon WO, Iskandar N, Chia KS. Shiftwork and work injuries in an iron and steel mill. Appl Ergon 1987; 18(1): 51-6.
[http://dx.doi.org/10.1016/0003-6870(87)90070-6] [PMID: 15676606] ].

Dutch bus drivers (n=1 564 man-years 1973-1980) suffered injury more often during the morning shift than the afternoon shift (p<0.001). Starting early particularly increased the risk (p<0.001), so that the peak was during the fourth hour of the shift [34Pokorny ML, Blom DH, van Leeuwen P. Shifts, duration of work and accident risk of bus drivers. Ergonomics 1987; 30(1): 61-88.
[http://dx.doi.org/10.1080/00140138708969678] [PMID: 3830128] ]. In the Belgian metal factory (n=730 male shift-workers), the higher accident rate was found in the morning shift compared to the late shift or to the night shift (p<0.01) [35Kantermann T, Haubruge D, Skene DJ. The shift-work accident rate is more related to the shift type than to shift rotation. Hum Ecol Risk Assess 2013; 19: 1586-94.
[http://dx.doi.org/10.1080/10807039.2012.708263] ].

In Australia, the risk of fatal occupational injury (n=1020, from 1982 to 1984) was double during the night shift compared to other shifts [36Williamson AM, Feyer A-M. Causes of accidents and the time of day. Work Stress 1995; 9(2-3): 158-64.
[http://dx.doi.org/10.1080/02678379508256550] ]. Female adolescents working on night shift in Queensland, Australia, were involved in occupational injuries almost five times more often than their adult counterparts, whereas male adolescents injured three times more often than adult males (n=3201 injured adolescents) [37Loudoun R, Allan C. The effect of time of day on injury patterns amongst adolescents in Australia. Appl Ergon 2008; 39(5): 663-70.
[http://dx.doi.org/10.1016/j.apergo.2007.12.005] [PMID: 18308291] ]. Based on Multipurpose Household Survey (n= 14,267 in 2009-2010), it was shown that the risk of work injury in shift work was higher for women than for men (OR = 2.43, 95% CI 1.95-3.03 vs. OR = 1.56, 95% CI 1.26-1.94, p = 0.005). Women working in shiftwork and having children had the highest risk of occupational injury (OR = 3.67, 95% CI 2.41-5.59, p = 0.02) [38Smith PM, Ibrahim-Dost J, Keegel T, MacFarlane E. Gender differences in the relationship between shiftwork and work injury: examining the influence of dependent children. J Occup Environ Med 2013; 55(8): 932-6.
[http://dx.doi.org/10.1097/JOM.0b013e31829178e1] [PMID: 23887698] ]. Nurses in the Philippines (n=655) had an increased risk of occupational injury at non-day shift (OR = 1.54, 95% CI 1.07-2.24) and when working mandatory overtime (OR = 1.22, 95% CI 1.06-1.41) [39de Castro AB, Fujishiro K, Rue T, Tagalog EA, Samaco-Paquiz LP, Gee GC. Associations between work schedule characteristics and occupational injury and illness. Int Nurs Rev 2010; 57(2): 188-94.
[http://dx.doi.org/10.1111/j.1466-7657.2009.00793.x] [PMID: 20579153] ].The risk of occupational injury doubled among American nurses (n=502 injured workers) after three and more 12-hour night shifts (OR = 2.09, 95% CI 1.10-4.98) [40Hopcia K, Dennerlein JT, Hashimoto D, Orechia T, Sorensen G. Occupational injuries for consecutive and cumulative shifts among hospital registered nurses and patient care associates: a case-control study. Workplace Health Saf 2012; 60(10): 437-44.
[http://dx.doi.org/10.3928/21650799-20120917-39] [PMID: 22998692] ].

In a Korean steel company shift workers (n=8,311) were 30% more often involved in occupational accidents than day workers (n.s) [41Seo Y-J, Kazuya M, Moon S-K, Jung M-S, Kim M-I. Relationships between shift work and occupational accidents in a steel company. J KOSOS 2005; 20(3): 188-96.]. In 26 Korean companies (n=4,127 workers), the accident rate in 2-shifting system was 1.7 times higher than 3-shifting system (p<0.01) and 4 times higher than non-shift system (p<0.01) [42Kim J-Y. A study on the safety accidents by shift systems. Korean J Occup Med 1996; 8(2): 330-9.]. Based on the Korean Working Condition Survey of 2006 (n=7,075), it was shown that shift workers had two times more often occupational injuries than non-shift workers (OR = 2.40) [43Park T-J, Paek D-M, Joh K-O, Park J-S, Cho S-I. The relationship between shift work and work-related injuries among Korean workers. Korean J Occup Environ Med 2012; 24(1): 52-60.] or in the later analysis (OR = 1.89, p= 0.026) [44Lu M-L, Nakata A, Park JB, Swanson NG. Workplace psychosocial factors associated with work-related injury absence: a study from a nationally representative sample of Korean workers. Int J Behav Med 2014; 21(1): 42-52.
[http://dx.doi.org/10.1007/s12529-013-9325-y] [PMID: 23794229] ].

The effect of rotating shift work on occupational injuries was examined in three studies. Working in rotating shifts with nights also doubled the risk of occupational injury among New Zealand Blood Donors (n=15 687, RR = 1.9, 95% CI 1.5-2.4) [45Fransen M, Wilsmore B, Winstanley J, et al. Shift work and work injury in the New Zealand blood donors health study. Occup Environ Med 2006; 63(5): 352-8.
[http://dx.doi.org/10.1136/oem.2005.024398] [PMID: 16621855] ] and Massachusetts nurses (n=635, OR = 1.97, 95% CI 1.07-3.63, p<0.05) [46Gold DR, Rogacz S, Bock N, et al. Rotating shift work, sleep, and accidents related to sleepiness in hospital nurses. Am J Public Health 1992; 82(7): 1011-4.
[http://dx.doi.org/10.2105/AJPH.82.7.1011] [PMID: 1609900] ]. In a large German electronic factory, employees in rotating shifts (n=14 128) had 34% more injuries than employees in day shifts (n=17 218, HR = 1.34, 95% CI 1.30-1.39, p<0.0001) [47Ott MG, Oberlinner C, Lang S, et al. Health and safety protection for chemical industry employees in a rotating shift system: program design and acute injury and illness experience at work. J Occup Environ Med 2009; 51(2): 221-31.
[http://dx.doi.org/10.1097/JOM.0b013e318192bd0f] [PMID: 19209044] ]. However, a fixed-term shift system was superior in performance to the rotating shift system in a resistor manufacturing company in Taiwan (n=180, p<0.05) [48Liou T-S, Wang M-J. Rotating-shift system vs. fixed-shift system. Int J Ind Ergon 1991; 7: 63-70.
[http://dx.doi.org/10.1016/0169-8141(91)90059-U] ].

Extreme morning-types suffered more from shift work than their evening-type counterparts [49Monk TH. Shiftwork and safety. Prof Saf 1989; 34(4): 26-30.]. In the U.S.A. Lake Superior iron ore mining region, 65% of occupational injuries (n=465) occurred in Sunday night and Monday morning shift after the weekend break (p<0.01) [50Monk TH, Wagner JA. Social factors can outweigh biological ones in determining night shift safety. Hum Factors 1989; 31: 721-4.]. Workers in the day-to-evening shift had an elevated risk of occupational injury based on the Taiwan Social Development Trend Survey in 2005 (n=18,794, OR = 1.14, 95% CI 1.01-1.29, p<0.05) [51Chiu H-Y, Tsai P-S. The impact of various work schedules on sleep complaints and minor accidents during work or leisure time: evidence from a national survey. J Occup Environ Med 2013; 55(3): 325-30.
[http://dx.doi.org/10.1097/JOM.0b013e31827cba69] [PMID: 23439272] ]. In a Turkish margarine production factory (n=25), accidents declined after the change from two-day rotation to weekly rotation [52Bell CR, Telman N. Errors, accidents and injuries on rotating shift-work: a field study. Int Rev Appl Psychol 1980; 29: 271-91.
[http://dx.doi.org/10.1111/j.1464-0597.1980.tb00962.x] ]. Based on the review of five studies with 441 shift workers, it is concluded that night work should be reduced as much as possible, and perhaps replaced by quickly rotating shift systems [53Knauth P. Designing better shift systems. Appl Ergon 1996; 27(1): 39-44.
[http://dx.doi.org/10.1016/0003-6870(95)00044-5] [PMID: 15676310] ].

The review of Folkard and Åkerstedt [4Folkard S, Åkerstedt T. Trends in the risk of accidents and injuries and their implications for models of fatigue and performance. Aviat Space Environ Med 2004; 75(3)(Suppl.): A161-7.
[PMID: 15018280] ] is based on studies published from 1962 to 1995, and the oldest studies in the review did not report exact results. That is why I have carried out the same review on more recent studies.

Table 1 summarizes the main details of the studies relating to the trend across the three shifts. The risk of occupational injury during morning shifts was set at 1.0 and the relative risk during afternoon shifts was calculated by dividing the injury frequency of the afternoon shift by the frequency of the morning shift. The same calculation was also carried out for night shifts.

Table 1
Summary of studies reporting incident rates across three shifts.

The new review showed that the risk of occupational injury was 6% lower during afternoon shifts than morning shifts (Table 1). However, it is important to note the difference between the USA and developing countries. In the USA, workers of afternoon shifts had a 31% higher risk of occupational injury, whereas in the developing countries the risk during afternoon shifts was almost half (57%) that of morning shifts.

The analysis showed that the risk of occupational injury during night shifts was 15% lower than during morning shifts (Table 1). Once again, the risk was 30% higher during the night shifts in American companies, but in developing countries, the risk of occupational injury during night shifts was 60% lower than during morning shifts.

The results of the actual revision are in line with the review of Folkard and Åkerstedt [4Folkard S, Åkerstedt T. Trends in the risk of accidents and injuries and their implications for models of fatigue and performance. Aviat Space Environ Med 2004; 75(3)(Suppl.): A161-7.
[PMID: 15018280] ], if we focus on results from the USA. For both the afternoon and night shifts I found a slightly higher risk of occupational injury than Folkard and Åkerstedt. However, the new results from developing countries changed the overall situation, when both afternoon and night shifts had a lower accident frequency than morning shifts. One reason for this could be that there are fewer supervisors during afternoon and nights shifts and accidents are not registered as often as during morning shifts.

One critical question regarding the effect of shift work on occupational injuries is whether the employees permanently worked evening or night shifts or worked by rotating shifts. In two studies [22Levin L, Oler J, Whiteside JR. Injury incidence rates in a paint company on rotating production shifts. Accid Anal Prev 1985; 17(1): 67-73.
[http://dx.doi.org/10.1016/0001-4575(85)90009-0] [PMID: 4091934] , 33Ong CN, Phoon WO, Iskandar N, Chia KS. Shiftwork and work injuries in an iron and steel mill. Appl Ergon 1987; 18(1): 51-6.
[http://dx.doi.org/10.1016/0003-6870(87)90070-6] [PMID: 15676606] ] they worked in rotating shifts, whereas in the other two studies [19Dembe AE, Erickson JB, Delbos RG, Banks SM. Nonstandard shift schedules and the risk of job-related injuries. Scand J Work Environ Health 2006; 32(3): 232-40.
[http://dx.doi.org/10.5271/sjweh.1004] [PMID: 16804627] , 23Nag PK, Patel VG. Work accidents among shiftworkers in industry. Int J Ind Ergon 1998; 21(3-4): 275-81.
[http://dx.doi.org/10.1016/S0169-8141(97)00050-4] ] employees worked only evening or night shifts. However, permanently working evening and night shifts or in rotating shifts did not seem to influence injury rates.

Extended working days are generally referring to working more than 48 hours per week [54Harrington JM. Health effects of shift work and extended hours of work. Occup Environ Med 2001; 58: 68-72.
[http://dx.doi.org/10.1136/oem.58.1.68] ]. Per a study in Australia, the primary reasons for employers to introduce 12-hour shifts are financial and productivity considerations (54% of employers in Australian Workplace Industrial Relations Survey 1995, n = 37 200 workplaces) [55Loudoun R, Harley B. Industrial relations: Decentralisation and the growth of 12-hour shifts in Australia. J Ind Relat 2001; 43(4): 402-21.
[http://dx.doi.org/10.1111/1472-9296.t01-1-00026] ]. Based on the 2002 General Social Survey made in the U.S. (n=1,744), overtime workers were more likely male (p<0.01), white (p<0.05), and middle-aged (p<0.01) with higher level of education (p<0.01) and income (p<0.01) [56Grosch JW, Caruso CC, Rosa RR, Sauter SL. Long hours of work in the U.S.: associations with demographic and organizational characteristics, psychosocial working conditions, and health. Am J Ind Med 2006; 49(11): 943-52.
[http://dx.doi.org/10.1002/ajim.20388] [PMID: 17036350] ].

In their review from 1985 to 1992, Duchon and Smith [57Duchon JC, Smith TJ. Extended workdays and safety. Int J Ind Ergon 1993; 11(1): 37-49.
[http://dx.doi.org/10.1016/0169-8141(93)90053-G] ] found that in six out of seven studies, long working hours increased the number of occupational accidents, while in one study accidents decreased after the change to 12-hour shifts. In the later review of 49 studies from 1969 to 2001, Bendak [58Bendak S. 12-h workdays: current knowledge and future directions. Work Stress 2003; 17(4): 321-36.
[http://dx.doi.org/10.1080/02678370310001643478] ] concluded that most workers preferred 12-hour shifts than 8-hour shifts although most of the objective performance measures showed negative effects. The extra 4 hours increased fatigue, which may in turn lead to an increased accident risk. Folkard and Lombardi [6Folkard S, Lombardi DA. Modeling the impact of the components of long work hours on injuries and accidents. Am J Ind Med 2006; 49(11): 953-63.
[http://dx.doi.org/10.1002/ajim.20307] [PMID: 16570251] ] concluded that, based on four studies, 10-hour shifts increased the injury risk by 13% and 12-hour shifts by 28% compared to the risks of an 8-hour working day. Knauth [59Knauth P. Extended work periods. Ind Health 2007; 45(1): 125-36.
[http://dx.doi.org/10.2486/indhealth.45.125] [PMID: 17284884] ] showed in his review of 18 studies from 1970 to 2005 that half of them showed increased risk of occupational injury with long work hours, whereas 5 were not significant associations, and 4 reported that the long work hours were associated with fewer injuries. Both in review of three studies published in the 1990’s [60Costa G. Shift work and health: current problems and preventive actions. Saf Health Work 2010; 1(2): 112-23.
[http://dx.doi.org/10.5491/SHAW.2010.1.2.112] [PMID: 22953171] ] and 14 studies (up to June 2008) [61Wagstaff AS, Sigstad Lie J-A. Shift and night work and long working hours: a systematic review of safety implications. Scand J Work Environ Health 2011; 37(3): 173-85.
[http://dx.doi.org/10.5271/sjweh.3146] [PMID: 21290083] ] it was concluded that working in a 12-h shift double the risk of occupational accident compared to a 8-h shift. According to these reviews, extended working days increased the risk of occupational injury.

A change from a three 8-hour shift system to a two 12-hour shift system in a Canadian synthetic yarn manufacturing company (n=247) decreased the occupational injury rate (p<0.05), but did not influence off-the-job injuries [62Laundry BR, Lees RE. Industrial accident experience of one company on 8 and 12-hour shift systems. J Occup Med 1991; 33(8): 903-6.
[http://dx.doi.org/10.1097/00043764-199108000-00018] [PMID: 1941288] ]. The workers of a large American manufacturing site (n=350) preferred the change from 8-hour/7-day rotating shifts to 12-hour rotating shifts, because of subjective feelings regarding health and family life. However, the change had no effect on the occupational injury rate [63Johnson MD, Sharit J. Impact of a change from an 8-h to a 12-h shift schedule on workers and occupational injury rates. Int J Ind Ergon 2001; 27: 303-19.
[http://dx.doi.org/10.1016/S0169-8141(00)00058-5] ]. In an Australian coal mine, a change from an 8-hour/7-day roster to a 12-hour/7-day schedule decreased accident frequency in a coal preparation plant (n=40, p<0.05), but increased absenteeism in the maintenance department (n=65, p<0.05) [64Baker A, Heiler K, Ferguson SA. The impact of roster changes on absenteeism and incident frequency in an Australian coal mine. Occup Environ Med 2003; 60(1): 43-9.
[http://dx.doi.org/10.1136/oem.60.1.43] [PMID: 12499456] ]. When workers of an Australian power station (n=27, p<0.02) [65Mitchell RJ, Williamson AM. Evaluation of an 8 hour versus a 12 hour shift roster on employees at a power station. Appl Ergon 2000; 31(1): 83-93.
[http://dx.doi.org/10.1016/S0003-6870(99)00025-3] [PMID: 10709754] ] and an American nuclear power station (n=104 stations, p<0.05) [66Baker K, Olson J, Morisseau D. Work practices, fatigue, and nuclear power plant safety performance. Hum Factors 1994; 36(2): 244-57.
[PMID: 8070790] ] moved from an 8-hour roster to a 12-hour roster, operator errors increased. In an American police station (n=74), on the other hand, the change from 8-hour shifts to 12-hour shifts improved organizational effectiveness (p<0.01) and decreased the stress and fatigue of police officers (p<0.01) [67Pierce JL, Dunham RB. The 12-hour work day: a 48-hour, eight-day week. Acad Manage J 1992; 35(5): 1086-98.
[http://dx.doi.org/10.2307/256542] ]. To conclude, two studies showed that the change to longer working days decreased the occupational injury rate, one showed no changes, and operator errors increased in two studies.

In a Canadian underground metal mine, workers (n=165) changed from seven by two 8-hours schedule to a four by four 12-hour shift schedule. An overwhelming majority of workers supported the change, because it improved sleep quality (p<0.001). No changes were found in fatigue-sensitive behavioral and physiological performance measures [68Duchon JC, Keran CM, Smith TJ. Extended workdays in an underground mine: a work performance analysis. Hum Factors 1994; 36(2): 258-68.
[PMID: 8070791] ], and older workers in the same mine (n=25) had no more difficulties with a 12-hour shift than with an 8-hour schedule [69Keran CM, Duchon JC, Smith TJ. Older workers and longer work days: are they compatible? Int J Ind Ergon 1994; 13(2): 113-23.
[http://dx.doi.org/10.1016/0169-8141(94)90078-7] ]. This study, in line with other studies, supported the claim that the majority of workers prefer 12-hour shifts due to improved sleep and family life.

In South Korea, people working over 60 hours per week had almost four times (OR = 3.94, 95% CI 3.04-5.09) more often occupational injuries than those working under 46 hours per week (n=1,576 injured workers) [70Im H-J, Oh D-G, Ju Y-S, Kwon Y-J, Jang T-W, Yim J. The association between nonstandard work and occupational injury in Korea. Am J Ind Med 2012; 55(10): 876-83.
[http://dx.doi.org/10.1002/ajim.22055] [PMID: 22544429] ]. Based on the Occupational Safety and Health Survey in 2004 (n=65,921), it was found that people working 44-54 hours per week were one and half times (OR = 1.6, 95% CI 1.5-1.8) more often involved in occupational injuries and those working more than 54 hours had three times (OR = 3.0, 95% CI 2.7-3.4) more injuries than those working less than 44 hours per week [71Lee KS, Kim H, Chang SH, et al. Relationship between injury occurrence and workplace organization in small-sized manufacturing factories. Korean J Occup Environ Med 2006; 18(2): 73-86.]. The Korean experience showed that long work days increased the risk of occupational injury many times.

Based on the National Longitudinal Survey of Youth (n=12,686), Dong [72Dong X. Long workhours, work scheduling and work-related injuries among construction workers in the United States. Scand J Work Environ Health 2005; 31(5): 329-35.
[http://dx.doi.org/10.5271/sjweh.915] [PMID: 16273958] ] found that among construction workers, working over 50 hours per week increased the risk of occupational injury (OR = 1.18, 95% CI 1.17-1.19). The risk was double for those working over 60 hours compared to those working 40 hours (OR = 1.98, 95% CI 1.88-2.05). Based on the same data set, Dembe and his co-workers [73Dembe AE, Erickson JB, Delbos RG, Banks SM. The impact of overtime and long work hours on occupational injuries and illnesses: new evidence from the United States. Occup Environ Med 2005; 62(9): 588-97.
[http://dx.doi.org/10.1136/oem.2004.016667] [PMID: 16109814] ] showed that working at least 12 hours per day increased the risk of occupational injury by 37% (HR = 1.37, 95% CI 1.16-1.59). Working over 60 hours per week raised the injury risk by 23% (HR = 1.23, 95% CI 1.05-1.45), working in a job with overtime (for overtime pay) increased it by 61% (HR = 1.61, 95% CI 1.43-1.79). Working overtime increased the risk of occupational injury among professional, technical and managerial personnel in particular [74Dembe AE, Delbos R, Erickson JB. Estimates of injury risks for healthcare personnel working night shifts and long hours. Qual Saf Health Care 2009; 18(5): 336-40.
[http://dx.doi.org/10.1136/qshc.2008.029512] [PMID: 19812094] ]. These results showed that working overtime, especially over 60 hours per week, dramatically increased the risk of occupational injury.

Based on the US National Health Interview Study in 2004-2008 (n=69,248), it was shown that the longer work hours, the higher injury frequency (77% higher for over 60 hours/week). This effect is related to decreased sleeping time, for example working over 60 hours/week and sleeping less than five hours per night increased the risk of occupational three times (OR = 3.12, 95% CI not presented) [75Lombardi DA, Folkard S, Willetts JL, Smith GS. Daily sleep, weekly working hours, and risk of work-related injury: US National Health Interview Survey (2004-2008). Chronobiol Int 2010; 27(5): 1013-30.
[http://dx.doi.org/10.3109/07420528.2010.489466] [PMID: 20636213] ]. Later based on the same interview study in 2004-2010 (n=96,915), it was found that women working 41-50 hours per week had 51% (OR = 1.51, 95% CI 1.03-2.21) higher risk of suffering an occupational injury and those working over 50 hours had 69% (OR = 1.69, 95% CI 1.06-2.70) higher risk of injury compared to women working 31-40 hours per week. For men, there was no significant difference [76Wirtz A, Lombardi DA, Willetts JL, Folkard S, Christiani DC. Gender differences in the effect of weekly working hours on occupational injury risk in the United States working population. Scand J Work Environ Health 2012; 38(4): 349-57.
[http://dx.doi.org/10.5271/sjweh.3295] [PMID: 22466526] ]. Based on the Canadian Community Health Survey in 2003 (n=75,184) men working over 80 hours per week had twice more injuries than those working less than 35 hours per week (OR = 2.1, 95% CI 1.5-3.1, p<0.05), whereas among women the difference was not significant [77Wilkins K, Mackenzie SG. Work injuries. Health Rep 2007; 18(3): 25-42.
[PMID: 17892250] ]. A questionnaire study to American and Canadian companies (n=326) showed that accident frequency in the companies using 12-hour shift was 25% lower and accident severity rate 50% lower than in the companies with 8-hour shift [78Campbell LH. Can new shift schedules motivate? Hydrocarbon Process. 1980; pp. 249-56.].

The risk of occupational injury increased exponentially beyond the 9th work hour among German workers (n=more than 1.2 million accidents in 1994). After 12 hours the risk was double compared to the first eight working hours (p<0.0001) [79Hänecke K, Tiedemann S, Nachreiner F, Grzech-Sukalo H. Accident risk as a function of hour at work and time of day as determined from accident data and exposure models for the German working population. Scand J Work Environ Health 1998; 24(Suppl. 3): 43-8.
[PMID: 9916816] ]. American metal workers (n=6,895) who worked over 64 hours per week had an 88% higher risk of occupational injury than those working 40 hours per week (HR = 1.88, 95% CI 1.16-3.05, p<0.05) [80Vegso S, Cantley L, Slade M, et al. Extended work hours and risk of acute occupational injury: A case-crossover study of workers in manufacturing. Am J Ind Med 2007; 50(8): 597-603.
[http://dx.doi.org/10.1002/ajim.20486] [PMID: 17594716] ]. A survey of American workers in 2001 (n=2,746) showed that those working over 60 hours per week were more likely to report occupational injuries (p<0.01) [81Allen HM Jr, Slavin T, Bunn WB III. Do long workhours impact health, safety, and productivity at a heavy manufacturer? J Occup Environ Med 2007; 49(2): 148-71.
[http://dx.doi.org/10.1097/JOM.0b013e31802f09ee] [PMID: 17293756] ]. Based on the National Health Interview Survey in 2004-2009 (n=89,366), 10-hour increase in weekly working hours increased the injury risk by 14% (OR = 1.14, 95% CI 1.06-1.22) and 1-hour decrease in sleep increased the injury risk by 10% (OR = 1.10, 95% CI 1.02-1.19, p<0.01). In addition, long working hours increased the risk of short sleep duration (p<0.05), which in turn increased occupational injury risk [82Arlinghaus A, Lombardi DA, Willetts JL, Folkard S, Christiani DC. A structural equation modeling approach to fatigue-related risk factors for occupational injury. Am J Epidemiol 2012; 176(7): 597-607.
[http://dx.doi.org/10.1093/aje/kws219] [PMID: 22956514] ] In the Thai Cohort Study in 2009 (n=51,751), women working over 49 hours per week had 1.4 times (OR = 1.4, 95% CI 1.1-1.9) more occupational injuries and men working as much as women had 1.3 times (OR = 1.3, 95% CI 1.0-1.6) more injuries than those working 40 hours per week [83Berecki-Gisolf J, Tawatsupa B, McClure R, Seubsman S-A, Sleigh A. Determinants of workplace injury among Thai Cohort Study participants. BMJ Open 2013; 7: p. e003079.
[http://dx.doi.org/10.1136/bmjopen-2013-003079] ]. These studies show that the risk of occupational injury is almost double when working hours exceed 60 per week compared to 40 hours per week.

Table 2 shows the main details of the 12 studies relating to extended work days. The risk of occupational injury in an 8-hour working day was set at 1.0 and the relative risk of a 10-hour working day was calculated by dividing the injury frequency of the 10-hour working day by the frequency of the 8-hour working day. The same calculation was made for working days of 12 hours and over. Only studies with exact injury rates were included in the Table 2.

Table 2
Summary of the studies across hours on duty (accident rate).

Based on seven studies, the review showed that the risk of occupational injury was 15% higher for 10-hour working days compared to 8-hour working days (Table 2). Twelve comparisons were found between 8-hour and 12-hour working days, showing that working 12 hours increased the risk of occupational injury by 38%. Four studies showed a 147% increase in occupational injuries when working more than 12 hours per day.

Compared to the review of Folkard and Lombardi [6Folkard S, Lombardi DA. Modeling the impact of the components of long work hours on injuries and accidents. Am J Ind Med 2006; 49(11): 953-63.
[http://dx.doi.org/10.1002/ajim.20307] [PMID: 16570251] ], this review showed a slightly lower increased risk of occupational injury during a 10-hour working day than during an 8-hour shift. The newest study [81Allen HM Jr, Slavin T, Bunn WB III. Do long workhours impact health, safety, and productivity at a heavy manufacturer? J Occup Environ Med 2007; 49(2): 148-71.
[http://dx.doi.org/10.1097/JOM.0b013e31802f09ee] [PMID: 17293756] ] in particular showed a high increase in the risk of injury during 10-hour shifts. On the other hand, I found a slighter higher elevated risk of occupational injury during 12-hour shifts than Folkard and Lombardi [6Folkard S, Lombardi DA. Modeling the impact of the components of long work hours on injuries and accidents. Am J Ind Med 2006; 49(11): 953-63.
[http://dx.doi.org/10.1002/ajim.20307] [PMID: 16570251] ]. I used 12 studies compared to the four studies in their review, three of which [62Laundry BR, Lees RE. Industrial accident experience of one company on 8 and 12-hour shift systems. J Occup Med 1991; 33(8): 903-6.
[http://dx.doi.org/10.1097/00043764-199108000-00018] [PMID: 1941288] , 64Baker A, Heiler K, Ferguson SA. The impact of roster changes on absenteeism and incident frequency in an Australian coal mine. Occup Environ Med 2003; 60(1): 43-9.
[http://dx.doi.org/10.1136/oem.60.1.43] [PMID: 12499456] , 81Allen HM Jr, Slavin T, Bunn WB III. Do long workhours impact health, safety, and productivity at a heavy manufacturer? J Occup Environ Med 2007; 49(2): 148-71.
[http://dx.doi.org/10.1097/JOM.0b013e31802f09ee] [PMID: 17293756] ] showed a lower risk of injury during a 12-hour working day than during an 8-hour working day.

One critical point for occupational safety is to note that the risk of occupational injury is highest during the last working hour on an extended working day [6Folkard S, Lombardi DA. Modeling the impact of the components of long work hours on injuries and accidents. Am J Ind Med 2006; 49(11): 953-63.
[http://dx.doi.org/10.1002/ajim.20307] [PMID: 16570251] , 73Dembe AE, Erickson JB, Delbos RG, Banks SM. The impact of overtime and long work hours on occupational injuries and illnesses: new evidence from the United States. Occup Environ Med 2005; 62(9): 588-97.
[http://dx.doi.org/10.1136/oem.2004.016667] [PMID: 16109814] , 74Dembe AE, Delbos R, Erickson JB. Estimates of injury risks for healthcare personnel working night shifts and long hours. Qual Saf Health Care 2009; 18(5): 336-40.
[http://dx.doi.org/10.1136/qshc.2008.029512] [PMID: 19812094] , 77Wilkins K, Mackenzie SG. Work injuries. Health Rep 2007; 18(3): 25-42.
[PMID: 17892250] ]. As this is an exception to the hourly distribution of occupational injuries during the 8-hour work shift, it shows the hazardousness of extended working hours more clearly. It is recommended that employees work 8-hours per day for a longer period if necessary, rather than extended working days for a shorter time period.

In his review, Tucker [84Tucker P. The impact of rest breaks upon accident risk, fatigue and performance: a review. Work Stress 2003; 17(2): 123-37.
[http://dx.doi.org/10.1080/0267837031000155949] ] concluded, based on six studies from 1977 to 2003, that rest breaks are an effective means of controlling the accumulation of accidents during industrial shift work. He considered that there is only limited direct epidemiological evidence on the effects of rest breaks on accident occurrence. The risk of occupational injury increased during the second and third half-hours after the break in a large engineering company in the US (n=4,250 shift workers, p<0.01) and among patients of traumatic occupational hand injuries (n=1,179, p<0.001) [85Tucker P, Lombardi D, Smith L, Folkard S. The impact of rest breaks on temporal trends in injury risk. Chronobiol Int 2006; 23(6): 1423-34.
[http://dx.doi.org/10.1080/07420520601070315] [PMID: 17190724] ]. On the other hand, at a car assembly plant in the United Kingdom (n=2,224), the accident risk rose significantly during the fourth half-hour after the break (RR = 2.08, 95% CI 1.73-2.43, p<0.0001), and fell immediately after the break [86Tucker P, Folkard S, Macdonald I. Rest breaks and accident risk. Lancet 2003; 361(9358): 680.
[http://dx.doi.org/10.1016/S0140-6736(03)12566-4] [PMID: 12606184] ]. Based on the work-related ladder-fall picked up from National Electronic Injury Surveillance System (NEISS, n=306) used in the United States, longer accumulated break time was associated with a longer time to injury. Workers without rest breaks worked a median 3.0 hours before the injury, workers with 1-15 minute break time worked 3.8 hours (HR = 0.60, 95% CI 0.44-0.83), with 16-30 minutes break they worked 6.0 hours (HR = 0.50, 95% CI 0.33-0.75) and over 30 minutes break moved the injury a median of 5.0 hours (HR = 0.34, 95% CI 0.23-0.51, p<0.05) [87Arlinghaus A, Lombardi DA, Courtney TK, Christiani DC, Folkard S, Perry MJ. The effect of rest breaks on time to injury - a study on work-related ladder-fall injuries in the United States. Scand J Work Environ Health 2012; 38(6): 560-7.
[http://dx.doi.org/10.5271/sjweh.3292] [PMID: 22430076] ]. The results of these studies supported the present system in which workers take a break after two hours of work.

Increasing flexibility in work life also means working longer hours in order to increase productivity [55Loudoun R, Harley B. Industrial relations: Decentralisation and the growth of 12-hour shifts in Australia. J Ind Relat 2001; 43(4): 402-21.
[http://dx.doi.org/10.1111/1472-9296.t01-1-00026] , 58Bendak S. 12-h workdays: current knowledge and future directions. Work Stress 2003; 17(4): 321-36.
[http://dx.doi.org/10.1080/02678370310001643478] ]. On the other hand, workers are no longer tied to their work all the time, or to one particular place. This flexibility also requires workers to maintain their work capacity and health by themselves, which MacEachen, Polzer and Clarke [88MacEachen E, Polzer J, Clarke J. You are free to set your own hours: governing worker productivity and health through flexibility and resilience. Soc Sci Med 2008; 66(5): 1019-33.
[http://dx.doi.org/10.1016/j.socscimed.2007.11.013] [PMID: 18180090] ] called “strategies of resilience”. It also supports workers with personal and home-related stress to sustain productivity levels. Especially women worked more often overtime without compensation than men in Finland as part of flexible work life [89Lehto A-M. Pitkittyvät työajat ja tasa-arvo (Longer work hours and equality). In: Sutela H, Lehto A-M Tasa-arvo työn takana. Helsinki: Statistics Finland 2007; pp. 76-91.].

In conclusion, this review showed that extended work hours increased the risk of occupational injury. Especially working over 12 hours per day doubled the risk of injury. Extended working days may be suitable, if the nature of the work and the workload allow it [53Knauth P. Designing better shift systems. Appl Ergon 1996; 27(1): 39-44.
[http://dx.doi.org/10.1016/0003-6870(95)00044-5] [PMID: 15676310] ].

On the other hand, afternoon and night increased the risk of occupational injury compared to morning shift in industrialized countries. A new finding was that in the developing countries the situation is vice versa; the injury frequency was higher in morning shifts than in afternoon and night shifts. One possible explanation is the lack of supervisors during afternoon and nights shifts, and that is why more injuries were not reported during afternoon and night shifts. Both stimulus and transactional models of stress explained the link between shift work and health [90Taylor E, Briner RB, Folkard S. Models of shiftwork and health: an examination of the influence of stress on shiftwork theory. Hum Factors 1997; 39(1): 67-82.
[http://dx.doi.org/10.1518/001872097778940713] [PMID: 9302880] ]. Napping before working a night shift is an effective countermeasure to fatigue with night shift among Italian police drivers (p<0.05) [91Garbarino S, Mascialino B, Penco MA, et al. Professional shift-work drivers who adopt prophylactic naps can reduce the risk of car accidents during night work. Sleep 2004; 27(7): 1295-302.
[PMID: 15586782] ].

The aim of this review is to examine whether long working hours, shift work, and breaks are related to occupational injuries.

An exact analysis of five studies showed that employees had 6% lower risk of occupational injury during afternoon shift and 15% lower in night shift compared to morning shift. The new finding of this review was that there is a total difference between USA and developing countries. In the U.S. working in afternoon increased the risk of injury by 13% and in night shift by 30%, whereas in developing countries employees in afternoon shift had 43% lower and in night shift 60% lower risk of injury compared to morning shift.

A review of 12 studies showed that employees working over 12 hours per day had 38% higher risk of occupational injury than those working 8 hours. Working 10 hours per day increased the risk of injury by 15% compared to working 8 hours per day. It is recommended that employees work 8 hours per day in the long run because of increased injury risk.

Four studies showed that accidents increased linearly after the break, escpecially two hours after the break. The results supported the present system: employees have a break when they had worked two hours.

The results of this review supported the present system of 8 hours work day. Night work, long work hours and long work periods without breaks increased considerable the risk of occupational injury.