& STRESS, OCTOBER \u0001 DECEMBER 2003, 17, NO. 4, 321 \u0001/336 WORK VOL. / 12-h workdays: current knowledge and future directions SALAHEDDINE BENDAKw Department of Industrial Engineering, King Saud University, PO Box 800, Riyadh 11421, Saudi Arabia Keywords: 12-h workday; Fatigue; Safety; Workers' health and well-being. Work schedules other than those based on the traditional 8-h workday duration have become much more common in recent years. Many such schedules compress the work week into three or four longer workdays and include an increased number of days off. In particular, rosters based on 12-h workdays have gained in popularity, and such rosters have been the focus of considerable research. The literature on 12-h workdays is, however, full of inconsistencies. Not surprisingly, there is considerable evidence from some of these studies that 12-h shifts tend to cause more fatigue than 8-h shifts. This extra fatigue may be associated with lower work efficiency, and with more errors and accidents. There is also strong evidence that workers prefer 12-h shifts due to some perceived advantages. The present paper reviews and examines these studies and their findings and discusses some possible reasons for the apparent contradictions in reported findings. Directions for decision makers and future research are suggested. 1. Background Workday duration is important from the points of view of workers and employers. This duration has the potential of affecting the lifestyle, leisure time, social activities, health, well-being and satisfaction of workers (Duchon & Smith, 1993; Johnson & Sharit, 2001; Macdonald & Bendak, 2000; Rosa, Colligan & Lewis, 1989). Employers are also concerned with workday duration due to its potential effects on work productivity and efficiency, workers' motivation and number of work-related accidents (Australian Council of Commerce and Industry, 1991; Nelson & Holland, 1999; Stones, 1987). In recent decades, there has developed an increased need to operate many workplaces continuously over 24 h daily due to the nature of many technological developments, increased economic pressures and increased demand for 24-h services. Related to such changes, there has been a move away from the traditional roster of 8-h workdays for 5 or 6 days per week to new patterns of working rosters (Duchon & Smith, 1993; Kogi, 1991; Wallace & Greenwood, 1995). Many rosters now compress the workweek into a smaller number of days by adding more work hours per day: typically, workday duration is extended from 8 h to 9, 10 or 12 h (Duchon, Keran, & Smith, 1994; Rosa, 1991; Stones, 1987; Williamson, Gower, & Clarke, 1994). In particular, rosters based on 12-h workdays w Author for correspondence: e-mail: bendak@ksu.edu.sa Work & Stress ISSN 0267-8373 print/ISSN 1464-5335 online # 2003 Taylor & Francis Ltd http://www.tandf.co.uk/journals/ DOI: 10.1080/02678370310001643478 322 S. Bendak with 3 or 4 workdays per 'week' have gained popularity in a wide range of industries, including manufacturing, health care, transportation, mining and a range of service industries. Such rosters have been the focus of considerable research (Hannan, 1997; Kogi, 1991; Smith et al. , 1998a; Stones, 1987). However, the methods and measures used in these studies vary widely, and not surprisingly, their results do not support unequivocal conclusions. The present paper reviews these studies and discusses some possible reasons for apparent contradictions in reported findings. It also gives some suggestions to managers regarding the implementation of 8- and 12-h shifts. Finally, directions for future research are suggested. There have been three attempts to review the literature of extended work durations, by Duchon and Smith (1993); Smith et al. , 1998a and Rosa, Bonnet, and Cole (1998). However, this current review is different in that it concentrates on 12-h shifts (unlike the one by Duchon and Smith which included all 9-,10- and 12-h shifts) and presents a critical analysis of the assessment measures and the results presented in the literature, especially in relation to the workload experienced by the participants. 2. Literature on 12-h workdays The literature on 12-h shift schedules includes many studies. Studies in which one of the aims was to assess 12-h workdays are listed in Table 1, identifying sample size, type of work performed, workday duration, measures used, and main findings. This list was gathered by doing a manual search and by searching several databases. Preference for inclusion in the list was given to studies published in peer-reviewed journals and to studies that were conducted in a diversity of work fields and countries. The aim was that the list would be as comprehensive as possible, but it is inevitable that it will be incomplete. 3. An evaluation of 12-h workday duration literature As can be seen in Table 1, results of studies on the effects of 12-h shifts were not consistent. For example, of the 49 studies that compared 12-h with 8-h workdays, some found negative effects attributable to 12-h shifts when compared with 8-h shifts (Baker, Olson, & Morisseau, 1994; Daniel, 1989; Iskra-Golec, Folkard, Marek, & Noworel, 1996; Rosa & Bonnet, 1993), others found positive effects (Daniel, 1985; Heaslip, 1988; Jaffe, Wun, & Smolensky, 1994; Vik & MacKay, 1982), some found mixed results (Daniel & Potasova, 1989; Duchon et al. , 1994; Mills, Arnold, & Wood, 1983; Williamson et al. , 1994) and some others found no differences between the two work durations (Frese & Semmer, 1986; Jennings & Rademaker, 1987). These inconsistencies appeared irrespective of the type of work being studied, i.e. no one type of work (e.g. manual work) showed greater effects than others. There appear to be three reasons for these inconsistencies in the results: differences between studies in assessment measures, shift design factors (e.g. shift rotating pattern, number of consecutive shifts worked) and (uncontrolled) differences in levels of work demands and associated workload. 3.1. Differences in assessment measures In evaluations of the effects of work duration, a wide range of constructs have been assessed by means of a great variety of measures (both objective and subjective) as can be seen in Table 1. This has led to a set of results from which it is difficult to draw conclusions Study Type of work Some research studies related to 12-h workday duration. Sample size (shift duration) Measures used Results Radio monitoring work 29 (rest days vs 12 h) SSS Increased sleepiness at work of long sleepers as compared with short sleepers Axelsson et al. , 1998 Power plant operators 31 (8 vs 12 h) Sleep length and quality, sleepiness at work, RT, physical effort, vigilance No major differences between 8-h and 12-h shifts Baker et al. , 1994 Nuclear power plant 102 (8 vs 12 h) Number of work-related errors of different types (e.g. operator-related, safety system failures) Number of operator-related errors increased in 12-h shifts, other types of error were stable Colquhoun et al. , 1969 Simulated sign detection & addition 22 (8 vs 12 h) Body temperature, participants' performance on simulated tasks Performance was worse on 12-h shifts; participants' adaptation to night shifts was worse in 12-h shifts Daniel, 1985 Chemical production 236 (8 vs 12 h) Questionnaire about socio-psychological parameters and JS Improved JS and better social aspects associated with 12-h shifts Daniel, 1989 Chemical production 29 (8 vs 12 h) OT, CFF, absenteeism due to health reasons, fatigue and health complaints questionnaire Increased absenteeism and fatigue, more health complaints related to 12-h shifts Daniel and Potasova, 1989 Chemical factory 32 (8 vs 12 h) OT, RT, tapping, GR, memory & search Better tapping but worse GR, memory & search, and OT in 12-h than in 8-h shifts Duchon et al. , 1994 Underground metal mining 41 (8 vs 12 h) Pursuit tracking, GR, RT, tapping, ergometry (cycling performance on an ergometer) HR, work-food-sleep diary, JS Worse sleepiness, tiredness and tapping performance on 12-h night shifts; better sleep quality and higher JS with 12-h shifts Eaton and Gottsleig, 1980 Nursing Not clear (8 vs 12 h) Questionnaire about JS, health, fatigue and AR Positive changes in health, fatigue and alertness after introducing 12-h shifts Frese and Semmer, 1986 Several chemical industries 3446 (8 vs 12 h) Questionnaire about stress/strain, health state No difference in responses due to shift duration Gardner and Dagnall, 1977 Oil refining plant 356 (8 vs 12 h) Sickness-related absenteeism No change in sickness-attributed absence upon changing to 12-h shifts Heaslip, 1988 Nursing Not clear (8 vs 12 h) Questionnaire about general satisfaction with 8- and 12-h shifts Higher general satisfaction with 12-h than with 8-h shifts Hibberd, 1973 Nursing Not clear (8 vs 12 h) Subjective patient care, staffing cost, JS Lower JS after implementing12-h shifts Iskra-Golec et al. , 1996 Nursing 126 (8 vs 12 h) Questionnaire on fatigue, sleep, stress, satisfaction and physical symptoms Greater fatigue and stress but higher satisfaction related to 12-h shifts Jaffe et al. , 1994 Petrochemical company 361 (8 vs 12 h) SSI (illness complaints, sleep quality/duration, social activities) More health and social complaints and worse sleep quality on 8-h shifts than on 12-h shifts 323 Anderson and Bremer, 1987 12-h workdays: current knowledge and future directions Table 1. 324 Table 1 (Continued ) Study Type of work Sample size (shift duration) Measures used Results 146 (8 vs 12 h) Questionnaire about fatigue, sickness, JS, sleep patterns No major differences between 8-h and 12-h shifts Johnson and Sharit, 2001 Production workers Not clear (8 vs 12 h) Number of injuries, questionnaire on health problems, JS, psychosocial issues and sleep difficulties 12-h shifts preferred, no difference in number of injuries, better psychosocial ratings and less sleep difficulties and health problems on 12-h shifts Kaliterna and Prizmic, 1998 Nurses, air-traffic controllers & police officers 208 (8 vs 12 h) SOS Less disruption in social, domestic and non-domestic life on 12-h shifts than on 8-h shifts Kelly and Schneider, 1982 Nuclear power plant operators 45 (8 vs 12 h) Error rates on work elements (e.g. verbal communication, taking corrective actions) Human error rates almost doubled on all work elements upon changing from 8-h to 12-h shifts Keran et al. , 1994 Underground metal mining 30 (8 vs 12 h) Pursuit tracking, GR, RT, tapping, SSS, AR, work hardness, exercise testing on an ergometer No reported differences due to varying work duration Kundi et al. , 1994 Nursing 880 (8 vs 12 h) Questionnaire on health state, working times and conditions 8-h shifts preferred. Some social and health problems related to 12-h shifts Latack and Foster, 1985 Computer operations 84 (8 vs 12.5 h) Number of errors, sick and personal leave, JS Lower number of errors and leave and higher JS recorded on 12.5-h than on 8-h shifts Lees and Laundry, 1991 Synthetic yarn production plant 775 (8 vs 12 h) NOA, morbidity rates, stress-related illnesses NOA and stress-related illnesses dropped after introducing 12-h shifts Lemerle, 1991 Wool production 63 (8 vs 12 h) Blood pressure, glucose level, drug and alcohol abuse, cholesterol, weight, physical symptoms, income management, emotions Worse alcohol problems; more family stress; lower caffeine intake; better exercise associated with 12-h shifts Lewis and Swaim, 1986 Control room workers at a process plant 107 (8 vs 12 h) GR, TE, DT, DA, HS, AR, RT, daily sleep, 2-point tapping, AD Subjective alertness improved more on 12-h shifts than on 8-h shifts Lowden et al. , 1998 Control room operators at a chemical plant 32 (8 vs 12 h) Activity, RT, PAR, sleep quality & duration, AR, satisfaction, subjective health, mental fatigue Satisfaction, AR and sleep quality improved after changing from 8- to 12-h shifts Macdonald and Bendak, 2000 34 (7.2 vs 12 h) Production operators and lab and maintenance technicians Bodily discomfort assessment chart, PAR, HS, CFF, GR, DT, code substitution, AR, pattern comparison, tapping Worse bodily discomfort, AR, HS and GR errors on 12-h workdays than on 8-h workdays when workload levels are high Milia, 1998 Electricians 12 (8 vs 12 h) Sleep diary and satisfaction Sleep duration after night shift dropped and satisfaction improved after changing to 12-h shifts Mills et al. , 1983 Nursing 29 (8 vs 12 h) Questionnaire about subjective symptoms of fatigue, JS and quality of patient care, GR, vital signs forms test More fatigue symptoms, more errors but faster responses on GR, improvement in JS after changing to 12-h shifts S. Bendak Jennings and Rademaker, 1987 Nursing Table 1 (Continued ) Type of work Sample size (shift duration) Measures used SSI, sleeping periods, quality and patterns, RT, GR, vigilance task, critical tracking task, sick leave, NOA Results Power station workers 27 (8 vs 12 h) Longer and better sleeping behaviour, better mood status, less physical health symptoms, greater satisfaction on 8-h as compared with 12-h shifts Nelson and Holland, 1999 Mining, manufacturing, service and other industries N/A \u0001/ 10 plants \u0001/ (8 vs 12 h) Interviews with managers about workers' health, efficiency and JS Increased JS, greater stress and fatigue after changing from 8-h to 12-h shifts Northrup et al. , 1979 Petroleum and chemical industries N/A \u0001/ 50 plants \u0001/ (8 vs 12 h) Interviews with managers about workers' health, JS, wages, safety, NOA Improved JS and an increase in wages related to 12-h shifts Palmer, 1991 Nursing Not given (8 vs 12 h) JS, absenteeism, work performance Higher JS with 12-h shifts than 8-h shifts Peacock et al. , 1983 Police 75 (8 vs 12 h) CFF, alertness, OT, urinary catecholamine, GR, JS Alertness decreased and JS improved after changing from 8-h to 12-h shifts Pierce and Dunham, 1992 Police 50 (8 vs 12 h) Questionnaire about work-schedule, stress & fatigue, satisfaction, organizational effectiveness Improvements associated with 12-h shifts in stress, fatigue, work-schedule attitudes, personal activities Pollock et al. , 1994 Petrochemical & fertilizer manufacturing 300 (8 vs 12 h) Attitudes, JS, NOA, injury type and severity More severe injuries but less minor injuries and higher JS in 12-h shifts than in 8-h shifts Rosa et al. , 1985 Simulated data entry 6 (8 vs 12 h) GR, DA, simple and choice RT, DT, tapping, AR, HS, SSS, HS, TE, AD, word memory, subjective fatigue, activationdeactivation adjective checklist More errors on data entry task, slower responses on GR, less correct additions on DA, and fatigue and drowsiness were worse in 12-h shifts as compared with 8-h shifts Rosa and Colligan, 1988 Simulated Data entry 11 (rest days vs 12 h) GR, DA, simple and choice RT, DT, tapping, AR, SSS, HS, AD, TE, word memory, subjective fatigue, activation-deactivation adjective checklist Performance on GR was faster but less accurate, slower responses on DA, simple RT, choice RT and DT-choice RT, worse HS on 12-h shifts than on rest days Rosa et al. , 1989 Control room work at a process plant 107 (8 vs 12 h) DA, simple auditory RT, AR, HS, DT, daily sleep and personal factors questionnaire More errors on GR and DA, slower responses on GR and DT-choice RT, more misses on DT-choice RT, lower quality and shorter duration of sleep related to 12-h shifts Rosa, 1991 Control room operations at a process plant 34 (8 vs 12 h) DA, DT, simple auditory RT, HS, AR, daily sleep and personal factors questionnaire More errors on GR, slower responses on GR and on DT-choice RT, lower quality and shorter duration of sleep, more gastrointestinal problems attributed to 12-h shifts 325 Mitchell and Williamson, 2000 12-h workdays: current knowledge and future directions Study 326 Table 1 (Continued ) Study Type of work Sample size (shift duration) Measures used Results Rosa and Bonnet, 1993 Gas control station 27 (8 vs 12 h) DA, simple auditory RT, DT, HS, AR, positive mood, daily sleep and personal factors questionnaire More RT misses, worse sleepiness, decline in sleep time and alertness related to 12-h shifts Rosa et al. , 1998 Simulated manual assembly 16 (8 vs 12 h) Fatigue symptoms, bodily discomfort Fatigue symptoms increased more during 12-h than during 8-h shifts Smith et al. , 1995 Nuclear power 48 (8 vs 12, 10 vs 12 h) AR, sleepiness, RT, search and memory Lower alertness on 12-h shifts than on 8-h shifts Smith et al. , 1998a Police officers 48 (8 vs 12, 10 vs 12 h) Questionnaire on social domestic interference, alertness, satisfaction, chronic fatigue, general & physical health No major differences reported Smith et al. , 1998b Sewage treatment plants workers 72 (8 vs 12 h) Questionnaire on satisfaction, attitudes towards shiftwork, health, fatigue, sleep quality, impact on life Greater satisfaction, fewer psychological health complaints and better home and social lives reported with 12-h shifts Todd et al. , 1989 Nursing Nurses of ten wards (8 vs 12 h) MONITOR (quality of nursing care) Planning, non-physical care and evaluation of care scales decreased with 12-h shifts Tucker et al. , 1996 Chemical workers 162 (8 vs 12 h) SSI Lower satisfaction, less social disruptions and more cardiovascular and disease symptoms on 12-h shifts Tucker et al. , 1998 Manufacturing & engineering companies 356 (8 vs 12 h) SOS No major differences between 8- and 12-h shifts Vernon, 1921 Fuse factory Not given (10 vs 12 h) NOA NOA dropped after changing from 12-h to 10-h shifts Vik and Mackay, 1982 Nursing 50 patients (8 vs 12 h) Quality patient care scale Better patient care was given by nurses on 8-h shifts Wallace and Levens, 1994 Aluminium smelter 20 (8 vs 12 h) RT, short term memory, AR, perception of time Performance on RT and short term memory improved with 12-h shifts Williamson et al. , 1994 Computer operations 75 (8 vs 12 h) Questionnaire about physical symptoms, JS, sick leave, # of errors, food and sleep patterns Drop in stress, irritability, gastrointestinal and sleep problems but more sick leave due to 12-h shifts Yamada and Kameda, 2001 Cleanroom workers 205 (8 vs 12 h) Body weight, blood pressure, height, subjective health symptoms Increased body weight and psychological fatigue after change from 8-h to 12-h shifts S. Bendak AD\u001e/Auditory Discrimination, DA\u001e/Digit Addition, DT\u001e/Dual Task, HR\u001e/Heart Rate, RT \u001e/Reaction Time, GR \u001e/Grammatical Reasoning, HS\u001e/Hand Steadiness, CFF \u001e/ Critical Flicker Fusion, JS\u001e/Job Satisfaction; AR\u001e/Alertness Rating, SSS\u001e/Stanford Sleepiness Scale, PAR \u001e/Perceived Accident Risk, SSI\u001e/Standard Shiftwork Index, SOS\u001e/Survey of Shiftworkers, NOA\u001e/Number of Accidents, TE\u001e/Time Estimation, OT \u001e/Oral Temperature. 12-h workdays: current knowledge and future directions 327 concerning the overall desirability of 12-h workdays in a given situation. For example Iskra-Golec et al. (1996) found from a questionnaire study that nurses on 12-h shifts had worse health, lower well-being and higher burnout levels than those working 8-h shifts, while Latack and Foster (1985) found that the number of computer operator errors increased significantly more during 8-h than during 12.5-h shifts. In other studies, the same measure produced conflicting results. For example, Daniel and Potasova (1989) found that chemical industry operators working 12-h shifts had slower responses on a grammatical reasoning task than those working 8-h shifts, whereas Mills et al. (1983) found the opposite in nurses. In Table 2, a number of studies that reported results in favour of 8-h or 12-h shifts and those that reported no significant differences together with authors' own interpretation of the results are given. As can be seen in Table 2, most, or 18 out of 23, studies that asked for the workers' opinion on shift duration found that workers were in favour of 12-h shifts. Only workers in 3 out of these 23 studies were in favour of 8-h shifts (with the remaining 2 studies yielding neutral results). On the other hand, only three of the 20 studies that utilized objective performance measures of workers found positive results attributed to 12-h shifts as compared with 8-h shifts. Nine of these 20 studies found negative effects attributable to this long shift duration while the remaining eight reported no differences in objective performance measures. At the same time, slightly more studies found positive effects attributed to 8-h as compared to 12-h shifts based on employee's subjective ratings (14 vs 12 out of 32 studies) and documented workplace information (3 vs 2 out of 10 studies). Studies assessing documented workplace information and employer reported information were balanced in their findings between 8-h and 12-h shifts. Although the different types of work involved in these studies and the different ways of assessing shift durations would be expected to contribute to differences between their results, there is an indication in these studies that objective assessment measures tend to reveal results in favour of 8-h shift schedules while studies that asked about employees' attitudes and opinions tend to reveal results in favour of 12-h shifts. Although operators' Table 2. Number of studies that compared 12-h with 8-h shifts grouped according to their results and methodology. Upon comparing 8-h with 12-h shifts, number of studies that: Type of study Based on employee-reported information (e.g. amount of sleep) Based on employee subjective ratings (e.g. alertness) Based on employee opinion of shift duration (e.g. satisfaction) Based on objective measures of employee performance (e.g. no. of errors, battery task performance) Based on documented workplace information (e.g. accident records) Based on employer reported information (e.g. productivity) Authors' own interpretation of the results Favoured 12-h shifts Favoured 8-h shifts Reported no differences or were neutral Total 8 8 4 20 12 14 6 32 18 3 2 23 3 9 8 20 2 3 5 10 1 1 1 3 20 18 12 50 328 S. Bendak satisfaction is important in any successful workplace, results of objective assessment measures and operators' subjective ratings should also be taken into consideration in order to maintain high personal and work performance and the long-term health and well-being of workers. This issue will be further discussed in the following sections. Finally, Table 2 revealed that the number of authors who favoured 12-h shift rosters based on their own interpretation of the results is very close to the number of authors who favoured 8-h shift rosters (20 out of 50 in the former category and 18 in the latter). Some of the authors (12 out of 47) were neutral in their opinion and did not favour any shift duration based on their results. 3.2. Shift design factors Shift design factors may affect fatigue experienced by workers and, consequently, alter their view of and performance during any specific shift duration. These design factors include shift rotation pattern, number of consecutive shifts worked, rest break regimes and shift starting and finishing times. These factors might have contributed to some of the contradictory results seen in Table 1, especially where the same measure produced conflicting results in different studies. Considering the shift rotation pattern, for example, a system of backward slowly rotating shifts (8-h shifts: night \u0001/afternoon \u0001/morning \u0001/break; 12-h shifts: night \u0001/day\u0001/ break) has the greater potential to create sleep debt and reduce sleep quality than forward rapidly rotating shifts (Jaffe et al. , 1994; Lowden, Kecklund, Axelsson, & Akerstedt, 1998), with probable consequent effects on some types of evaluation measure. In fact, Jaffe et al. (1994) reported that impairment in sleep quality in backward rotating 8-h shifts as compared with forward rotating 12-h shifts might have been the result of the shift rotation pattern rather than shift duration. In more than half of the tabulated papers there was little or no information about the shift roster worked. The remaining studies, for which shift details were reported, varied to such an extent that few could be meaningfully categorized for comparison purposes. Moreover, most studies mentioned in Table 1 did not, apparently, control for the particular shift design factors. Nevertheless, from the information available it could be seen that many levels of shift design factors have been experienced in both shift rosters. All of these factors (shift start and finish times, rest break regimes, number of consecutive shifts worked and direction of rotation) differ significantly among and between the two shift durations. This makes it even harder to make proper comparisons and draw conclusions. 3.3. Work demands and workload Workload differences might have contributed to the contradictory results seen in Table 1. Workload, as a property of the task, the worker and the interaction between them (Huey & Wickens, 1993), is thought to play an important role in modifying workers' responses to different work durations (Rosa & Bonnet, 1993; Wallace & Greenwood, 1995). Variations in workload also have the potential to change workers' responses during the same work duration. A potentially important issue associated with 12-h shift systems is that they appear to increase workers' perceived workload, fatigue and stress despite unchanged weekly work duration and work demands (Colquhoun, Blake, & Edwards, 1969; Daniel & Potasova, 1989; International Labour Office (ILO), 1977; Nelson & Holland, 1999; Rosa & Bonnet, 12-h workdays: current knowledge and future directions 329 1993; Wallace & Greenwood, 1995). Given that 12-h workdays result in greater fatigue and, subsequently, in a decrease in workers' performance capacities towards the end of the day, an increase in perceived workload would be expected at that time (Rosa & Bonnet, 1993). Such a drop in performance capacity is likely to be associated with lower work efficiency and more errors and accidents (Rosa & Colligan, 1989). The possibility of higher levels of fatigue, impaired performance capacities and lower levels on some subjective indices related to long workday durations, has gained greater attention and recognition in the last two decades (Kundi et al. , 1994; Wallace & Greenwood, 1995). In addition, the effects of workload on levels of fatigue, performance capacities and subjective indices within 12-h shifts have gained some attention (Duchon & Smith, 1993) since high workloads are seen to have the potential to produce extremely high levels of fatigue when combined with long work durations of 12-h shifts (Bi & Salvendy, 1994; Macdonald & Bendak, 2000; Rosa & Bonnet, 1993; Tepas & Popkin, 1994). Only six studies out of the 53 mentioned in Table 1 addressed the issue of workload level: Axelsson, Kecklund, Akerstedt, and Lowden, 1998; Macdonald and Bendak, 2000, Rosa and Bonnet, 1993, Rosa et al. , 1998, Smith, Totterdell, and Folkard, 1995; and Wallace and Levens, 1994. All of these six studies except Macdonald and Bendak (2000) and Rosa et al. (1998) either did not aim at assessing these interacting effects or reported only minor changes in workload levels and, therefore, could not properly assess possible workload effects. In the laboratory-based study by Rosa et al. (1998), subjective fatigue increased more with increasing time on shifts. However, work duration effects were most apparent at low workload levels. Minimal effects were observed at high workload levels. In this study, the authors controlled the workload while the subjects self-adjusted their work cycle duration to maintain fatigue at moderate levels. This made it difficult to generalize the findings of this study to most real-life workplaces where the workload usually varies over time and the work cycle is usually not controlled by the workers. The study by Macdonald and Bendak (2000) presented some evidence that the interacting effects of workday duration and workload level on workers' performance capacities and subjective indices were greater than the effects of either factor alone. In the preliminary laboratory experiment conducted in this study, it was found that 12-h as compared with 7.2-h workdays were associated with a significantly greater increase in perceived workload among participants performing the same set of physical work tasks. Those working for the longer duration perceived the tasks to be harder, suggesting that a fatigue-related decrease in performance capacity among those working longer hours caused the tasks to be perceived as more difficult. In their field study, the same authors reported that some of the measured performance capacities as well as subjective alertness and bodily discomfort were more adversely affected by high workload levels on 12-h workdays than on 8-h workdays. These findings support the hypothesis that high workload levels might lead to excessive fatigue and associated decrements in performance capacities and alertness when combined with 12-h shifts (as indicated by the International Labour Office (ILO), 1977; Rosa, 1995; Wallace & Greenwood, 1995). 4. Advantages and problems associated with 12-h workdays According to the studies listed in Table 1, 12-h shifts seem to have many documented advantages. First, they provide greater opportunity for time off work because workers on 12-h shifts have more non-working days per week (Baker et al. , 1994; ILO, 1977; Rosa et al., 1989). In practice, this provides more uninterrupted time for recovery, family, leisure 330 S. Bendak and other social activities. This, in turn, increases workers' job satisfaction (Colligan & Tepas, 1986; Daniel, 1985; Duchon et al., 1994; Johnson & Sharit, 2001; Palmer, 1991; Rosa & Colligan, 1989; Williamson et al. , 1994). As a result, some studies (Colligan & Tepas, 1986; Latack & Foster, 1985) reported a drop in absenteeism after the introduction of 12-h shifts. At the same time, the smaller number of shifts worked per week leads to fewer trips to and from work and to some travel time saved. This makes 12-h shifts more popular with many workers and employees than 8-h shifts (Duchon et al. , 1994; Palmer, 1991; Peacock, Glube, Miller, & Clune, 1983; Williamson et al. , 1994). Besides this, 12-h shifts appear to result in some energy conservation and reduced traffic congestion due to the abovementioned fewer trips to and from work, particularly since some of these journeys are outside peak times (Kogi, 1991). 12-h shift schedules also offer fewer shift handovers than 8-h shifts in industries that work around the clock (Wallace & Greenwood, 1995). This may lead to substantial financial savings in some workplaces due to the drop in set-up costs and possible associated costly errors (Pierce & Dunham, 1992). There have also been problems attributed to the 12-h rostering systems. The extra 4 h worked by workers on 12-h shifts may lead to increased fatigue. This may lead to a general deterioration in workers' health and, consequently, to more health problems in the long term (Colligan & Tepas, 1986; Kogi, 1991; MacDonald & Bendak, 2000; Rosa, 1995; Yamada & Kameda, 2001). It is true that there is an extra recovery time, i.e. greater number of days off, in the 12-h shift roster, but it is not clear if this extra recovery time is enough to recover from the extra fatigue induced during the consecutive 12-h shifts due to the extra 4 h worked. The possible increase in fatigue levels due to extending work duration by 4 h may also lead to more errors at work (Baker et al. , 1994; Kelly & Schneider, 1982), which in turn may have negative effects on productivity and work quality (Colligan & Tepas, 1986; Williamson et al. , 1994). This made some organizations hesitant to adopt longer work durations of 12-h shifts (Kogi, 1991; Rosa, 1995; Rosa & Colligan, 1988). In general, this possible increase in fatigue due to the extra 4 h worked, may lead to increased accident risk, higher risk of severe sleepiness, safety problems, weight gain, low morale, lower productivity and economic loss (Harma, Salinnen, Ranta, Mutanen, & Muller, 2002; Kogi, 1991; Rosa et al. , 1989; Wallace & Greenwood, 1995; Yamada & Kameda, 2001) especially when 12-h shifts are combined with high workload levels (Macdonald & Bendak, 2000). The longer workday durations of 12 h provide less time for other activities during the workweek, thus this type of work roster may cause difficulty to some people (such as single mothers) in managing home duties, childcare activities, family and/or social life. This issue is more noticeable in remote areas where family support and other social facilities (such as childcare centres) are rare (Anderson & Bremer, 1987; Colligan & Tepas, 1986; Rosa, 1995). The higher number of days off work provided by 12-h shift rosters may lead to increased moonlighting where workers are sometimes encouraged to contemplate taking a second job (Nelson & Holland, 1999; Stones, 1987). This in turn may lead to less recreation time for workers and to possible negative effects on their health and well-being. Finally, the extra 4 h worked may lead to extended exposure to physical (such as noise) and chemical (such as solvents) hazards in certain industries, which in turn might put workers' health and well-being at risk and/or lead to a drop in performance (Kogi, 1991; Rosa, 1995; Wallace & Greenwood, 1995). 12-h workdays: current knowledge and future directions 331 5. Conclusions and recommendations for decision makers Failure to take account of the nature and demands of jobs while determining work duration may result in a high degree of fatigue being experienced by workers. Night 12-h shifts are of particular concern here because of the excessive fatigue induced from a long workshift and high workload levels when combined with low alertness levels due to lower endogenous arousal at night. The European Union (1993) in its Working Time Directive, restricted the length of night shift to 8 h on average in any 24-h period and entitled workers to a free health checkup before commencing employment on the night shift and regular check-ups thereafter. The European Union through this legislation has put restrictions on night shifts longer than 8 h in order to minimize any possible negative effects of these shifts on workers' health and well-being. At the same time, various researchers have concluded that 12-h workdays are not appropriate, especially at night, for work that includes high physical or mental loads; however, jobs that impose low work demands or that include long natural rest breaks may be appropriate for such a system (ILO, 1977; Kogi, 1991; Mattila, 1985). Unfortunately no one has yet provided any clear criteria for decision makers as to levels of workload that are acceptable for 12-h shifts. Similarly, Baker et al. (1994) and Harma et al. (2002) stated that longer work durations might not necessarily cause decrements in human performance through induced fatigue if managed properly. Proper management might occur through moderating workload levels and thus minimizing possible negative consequences of prolonged fatigue. Proper management might occur also by sensibly allocating and distributing rest breaks to allow appropriate temporary recovery from work-induced fatigue and by sensibly scheduling the shift system to allow a complete recovery. The consequences of possible human errors should also be taken into consideration when deciding on workday duration. It might not be advisable to introduce long workday durations of 12 h where some errors would have dire consequences, as is the case, for example, in nuclear power plants (Kelly & Schneider, 1982; Rosa, 1995). It is true that the 12-h shift roster does not necessarily lead to extended overall exposure to occupational hazards, knowing that the weekly work time is usually the same in all rosters. However, single exposure to hazards is extended in this roster because of the extra 4 h worked. At the same time, there is a lack of substantial research, codes of practice and regulatory standards regarding extended (i.e. longer than 8-h) single exposure to occupational hazards. Nevertheless, it can probably be advised that 12-h shifts should be avoided in workplaces where there is substantial exposure to physical or chemical hazards or where tasks are considered to be 'dangerous' in nature (Kogi, 1991; Rosa, 1995; Wallace & Greenwood, 1995). Finally, it is advisable that decision makers take into consideration the day-to-day home activities as well as family commitments and social life of their workforce when deciding on shift duration. This will help in improving work performance and workers' satisfaction as well. 6. Recommendations for future research An issue that future research needs to consider is what type of measures they use in their evaluation of shift duration. From Table 2, there are clear indications that most workers prefer 12-h shifts than 8-h shifts. However, only three out of 20 studies that used objective measures of employees' performance, were in favour of 12-h shifts. It was observed that the 332 S. Bendak majority of authors who were in favour of 12-h workdays based their opinion on results obtained mainly from 'subjective' attitude-related measures while most authors who were in favour of 8-h workdays based their opinion on results derived mainly from 'objective' measures. This phenomenon has also been emphasized by Colligan and Tepas (1986) and by Jennings and Rademaker (1987). It is suggested here that future studies should incorporate both objective and subjective measures while evaluating the effects of different workday durations. It has frequently been reported that most workers favour longer work durations because of perceived benefits mentioned earlier (Duchon & Smith, 1993; Nelson & Holland, 1999). This greater satisfaction with the longer work durations might sometimes have affected the results of subjective measures, making them less reliable as indicators of the overall desirability of 12-h shifts. At the same time, there is evidence from several studies listed in Table 1 that workers' performance capacities decrease and that they experience more fatigue with 12-h than 8-h shifts. It appears that workers are often willing to tolerate the greater fatigue because of the associated benefits. However, those perceived benefits need to be considered along with indications of negative consequences in terms of impaired alertness and performance capacities, and the consequent possibility of longer-term negative effects on health and well-being. The negative effects attributed to 12-h workdays found in several studies suggest that 12-h workdays may have long-term negative effects on workers' health and well-being if not implemented and managed properly. Unfortunately little is known currently on these possible long-term effects of the higher fatigue levels, which may result from a combination of high workload and 12-h shifts in terms of its implications for workers' health and wellbeing. In a rare case, an investigation of the long-term effects of a 12-hour shift roster on control panel operators was done 7 months (Rosa et al., 1989) and then 3.5 years (Rosa, 1991) after the introduction of this roster. Both studies revealed persistent decrements in performance on certain battery measures and in alertness, and 1-3 h reduction in total sleep after 12-h shifts. The importance of studying long-term effects of longer work shift rosters is also illustrated in a study by Ivancevich and Lyon (1977). The authors found positive effects attributed to changing from the regular 8-h workdays to 10-h workdays 13 months after the change, revealed through increased satisfaction and productivity and reduced anxiety and stress. However, these positive effects were not observed 25 months after the change. Although this study was concerned with 10-h workdays, its findings might also be applicable to 12-h workdays. It is worth mentioning that neither Rosa (1991) nor Ivancevich and Lyon (1977) measured the workload experienced by their participants. Relying solely on subjective preferences while deciding on varying shift duration could be misleading. This is because the perceived advantages of 12-h shifts to workers and operators (as has also been indicated by Colligan and Tepas, 1986) may outweigh any possible long-term negative effects of these shifts on their safety, health and well-being. The possible conflict between workers' preferences and some objective measures (of system effectiveness and workers' health and well-being) highlights the complexity of deciding upon appropriate shift durations for particular types of work and workload levels. As indicated earlier, shift design factors, namely shift rotation pattern, number of consecutive shifts worked, rest break regime and shift starting and finishing times, may affect fatigue experienced by workers and alter their opinion on shift duration. Future research should further explore the possibility of these factors affecting work performance and workers' health and well-being. Furthermore, more research is recommended to help 12-h workdays: current knowledge and future directions 333 in determining which level of each of these factors suits any given work type and workload level. Most standards, regulations and codes of practice on hazardous materials exposure are concerned with 8-h workdays. Little is done to this date to update these standards and regulations to accommodate exposure in 12-h shifts. Future research should aim at developing standards and regulations for hazardous materials exposure for extended work shifts such as 12-h shifts. This will help in minimizing short and long-term health problems due to this exposure in 12-h shifts and give decision makers a useful tool that will help them in deciding on suitable shift durations. Finally, current knowledge cannot provide a sufficient basis for clear guidelines as to the types of work and related workload levels for which 12-h workdays are appropriate. 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YAMADA, Y. & KAMEDA, M. (2001). Excessive fatigue and weight gain among cleanroom workers after changing from an 8-hour to a 12-hour shift. Scandinavian Journal of Work Environment and Health , 27 , 318 \u0001/326. 0405301 Ergonomics and Work & Process Improvement Assignment 3 Read the paper titled "12-h workdays: current knowledge and future directions" and, if felt necessary, search the internet for more information on 12-h workdays. 1. List and explain five potentially positive and five potentially negative consequences of 12-h workdays from section 4 (2-3 lines each). 2. Why do employees prefer 12-h workdays in general? List five reasons from sections 4 and 5 (2-3 lines each). 3. Give five recommendations to decision makers on what to take into consideration when deciding on introducing or not introducing 12-h workdays from section 5 (2-3 lines each). The assignment can be done individually or in groups of two students and should be written on a computer and printed (i.e. hand written assignments will not be accepted). Due date: Thursday 5 May 2016. Weight: 4%