Performance, alertness, and sleep after 3·5 years of 12 h shifts: A follow-up study

Rostering in Air Traffic Control: A Narrative Review

Most Air Traffic Controllers (ATCOs) must cover uninterrupted work shifts for 24 h a day, seven days a week. The proper planning of a shift schedule requires consideration of at least three elements: the specific characteristics of the controller task, the physiological needs of the operator, and the definition of rest periods within rostering. We reviewed the literature for providing comprehensive guidance on the main requirements for the construction of a shift schedule for ATCOs. Our considerations are organized according to a rationale reflecting the most important criteria for the construction of the schedule: namely, the organization of rest periods conceptualized as intervals between cycles of shifts, intervals between individual shifts, and breaks within the shift. The suggested parameters could be used to construct shift schedules within a variation margin that depends on individual contexts of application.

Burnout, Sleep, and Sleepiness during Day and Night Shifts in Transition from 8- to 12-Hour Shift Rosters among Airline Ground Crew Managers

Organizational changes in shift scheduling provide rare opportunities for field studies aimed at investigating the effects of such changes on health and wellbeing. We studied the effects of a transition from 8-hour (8-h) to 12-hour (12-h) shift rosters in 39 airline ground crew managers on burnout, sleep quality, and sleepiness. Assessments were collected during the 8-h and were repeated three months after the transition to 12-h shift rosters. These assessments included the Shirom-Melamed Burnout Measure (SMBM), the Pittsburgh Sleep Quality Index (PSQI), actigraphy, the Karolinska Sleepiness Scale (KSS) completed hourly during one day and two night shifts, and caffeine intake. Findings demonstrated lower burnout, improved sleep quality, improved quality of naps, and increased afternoon sleepiness during the 12-h day shift. Napping was reported during 12-h night shifts by 36% of the sample. In nappers, increased night shift sleepiness was associated with increased caffeine intake on 8- and 12-h shifts. In non-nappers, increased night shift sleepiness was associated with decreased caffeine intake on the 8-h shift only. Change in shift length affects other structural and behavioral parameters in the workplace, making it challenging to isolate distinct characteristics of the two rosters and their relative effects on study outcomes. Individual differences in adaptation to shiftwork may also play a role.

The distribution of sleepiness, sleep and work hours during a long distance morning trip: a comparison between night- and non-night workers

Few studies have examined the extent of driver sleepiness during a long distance morning trip. Sleepiness at this time may be high because of night work, waking early to commence work or travel, sleep disorders and the monotony of driving long distances. The objective of this study was to estimate the prevalence of chronic sleepiness (Epworth sleepiness score ≥10) and sleep restriction (≤5h) in a sample of 649 drivers. Participants driving between 08:00 and 10:00 on three highways in regional Australia participated in a telephone interview. Approximately 18% of drivers reported chronic sleepiness. The proportions of night workers (NW) and non-night workers (NNW) with chronic sleepiness were not significantly different but males reported a significantly greater proportion of chronic sleepiness than females. The NW group had a significantly greater proportion of drivers with ≤5h of sleep in the previous 24 and 48h, fewer nights of full sleep (≤4), acute sleepiness and longer weekly work hours. The NW group reported driving a significantly longer distance at Time 1 (Mean=140.29±72.17km, versus 117.55±89.74km) and an additional longer distance to complete the journey (Mean=89.33±95.23km, versus 64.77±94.07km). The high proportions of sleep restriction and acute sleepiness among the NW group, and the amount of chronic sleepiness in the NW and NNW groups reported during a long distance morning trip may be of concern for driver safety.

12-h or 8-h shifts? It depends

Since 12-h shifts were first implemented, the question has been asked - are 'twelves' better than 'eights'? People trying to answer this question invariably refer to the limited literature at their disposal, often piecemeal, small-scale studies comparing 8-h versus 12-h shifts in isolated groups of workers in which many other factors vary concurrently. The narrow perspective and sometimes 'vested interests' of the organizations, researchers, publishers and individual workers can influence both the choice of measures, the analysis of results and their interpretation. The current review suggests that it is not sufficient to evaluate a shift pattern on the basis of a single dimension of a working time arrangement, such as shift length. Numerous factors associated with the work practice influence the outcome of a shift pattern including start times, pattern of shifts and amount of overtime. Moreover, the type of work being done and the demographics or characteristics of the workforce are additional mediating factors. Finally, and perhaps most critically, the relative importance assigned to different outcome measures is an important consideration. There are situations where total sleep time might increase following a change to 12-h shifts, whereas domestic life for some workers may deteriorate. Additionally, safety measures may show improvements on 8-h shifts but physical or psychological health outcomes may be worse. The myriad combinations of work pattern, work task, worker and outcome measure under investigation mean that the best way to take account of these complexities may be to use an approach that manages 'system' risk. Given the non-linearities in the system, and the fact that current approaches either ignore, or privilege a subset of outcomes, it is perhaps more appropriate to conceptualize working time arrangements as an 'ecosystem' and to address the risks in the overall system as opposed to a single dimension such as shift length.

Demographic factors, fatigue, and driving accidents: An examination of the published literature

This article reviews the literature pertaining to the association between demographic variables (e.g., age, sex, race, socio-economic status) with fatigue, and when feasible, accident risk. It also explores their potential influence and interaction with some working arrangements, commute time, personality characteristics, and circadian chronotype. Fatigue has been implicated in a range of impairments that can have detrimental effects on individuals, and it is differentially associated with conventional demographic variables. However, several major methodological limitations prevent clear conclusions. First, there is absence of a shared definition both within and across disciplines. Second, although fatigue has been investigated using a variety of diverse designs, they have either been too weak to substantiate causality or lacked ecological validity. Third, while both subjective and objective measures have been used as dependent variables, fatigue has been more often found to be more strongly linked with the former. Fourth, with the exception of age and sex, the influence of other demographic variables is unknown, since they have not yet been concomitantly assessed. In instances when they have been assessed and included in statistical analyses, they are considered as covariates or confounders; thus, their contribution to the outcome variable is controlled for, rather than being a planned aspect of investigation. Because the interaction of demographic factors with fatigue is largely a neglected area of study, we recommend greater interdisciplinary collaborations, incorporation of multiple demographic variables as independent factors, and use of within-participant analyses. These recommendations would provide meaningful results that may be used to inform public policy and preventive strategies.

Changes in physical performance among construction workers during extended workweeks with 12-hour workdays

PURPOSE

To investigate changes of physical performance during long working hours and extended workweeks among construction workers with temporary accommodation in camps.

METHODS

Nineteen construction workers with 12-h workdays and extended workweeks participated. Physical performance in the morning and evening of the second and eleventh workdays was tested by endurance, ability to react to a sudden load, flexibility of the back, handgrip strength and sub-maximal HR during a bicycle test. HR was registered throughout two separate workdays.

RESULTS

HR during each of the two separate workdays corresponded to a relative workload of 25%. Sub-maximal HR was lower, reaction time faster and handgrip strength higher in the end of each test day. In the end of the work period, sub-maximal HR was lower, reaction time faster and sitting balance was better.

CONCLUSION

No trends of decreased physical performance were found after a workday or a work period.

Toward a “Risk Index” to Assess Work Schedules

This article describes our preliminary attempt to develop a Risk Index to estimate the risk of human error on different work schedules based on trends in the relative risk of accidents and injuries, rather than on hypothetical intervening variables such as alertness, fatigue, or performance on interpolated tasks. We briefly review trends in risk from the published epidemiological studies that have ensured that the a priori risk was constant. A simple Risk Index based on an additive model is developed on the basis of these trends, and we illustrate how it may be used to assess work schedules. Finally, we compare the results from this Risk Index with those from the UK HSE's Fatigue Index and point out the discrepancies that emerge. We conclude that our risk-based modeling approach may assist in developing safer work schedules and also increase our understanding of this complex, multifaceted area.

Extended work periods

A literature review of 105 studies on the effects of extended daily working hours was conducted. Potential negative effects of extended working hours are discussed: More accidents on the job; more accidents off the job; reduced duration and quality of sleep due to moonlighting; sleepiness; reduced alertness; fatigue; adverse effects on performance; prolonged toxic exposure; adverse effects on health; increased absenteeism; problems communicating with managers; and problems while driving home. Potential positive effects of extended working hours are discussed: Less travel time and costs; more time for the family, social life, and domestic duties; increased satisfaction with working hours; fewer handovers; and less overtime. No firm conclusions can be drawn because of the partly contradictory results and the methodological problems of many studies. However, caution is advised when considering the introduction of extended work shifts, particularly where public safety is at stake. A checklist is provided (concerning work load, breaks, staffing level, systematic assessments of health and safety factors) to support decisions for or against the use of extended work shifts.

Modeling the impact of the components of long work hours on injuries and "accidents"

BACKGROUND

Many of the industrial disasters of the last few decades, including Three Mile island, Chernobyl, Bhopal, Exxon Valdez, and the Estonia ferry, have occurred in the early hours of the morning. Follow-up investigations concluded that they were at least partially attributable to human fatigue and/or error. The potential impact of long work hours on health and safety is a major concern that has resulted in various work hour regulations.

METHODS

The risk of injuries and "accidents" (incidents) associated with features of work schedules from published epidemiological studies are pooled using an additive model to form a "Risk Index." The estimated risks of an incident for various standard work schedules are presented using the proposed model.

RESULTS

The estimated risk of an injury or accident associated with any given number of weekly work hours varies substantially depending on how work hours are comprised. The risk depends on the length and type of shift, as well as the frequency of rest breaks.

CONCLUSIONS

We conclude that placing a limit on the risk associated with a particular work schedule is likely more effective than setting daily, weekly or monthly work hour regulations in keeping workplace safety within acceptable limits.

The effects of sleep debt and monotonous work on sleepiness and performance during a 12-h dayshift

The study examined the effects of the amount of preceding sleep and work pace on sleepiness and cognitive performance during a 12-h dayshift. Twelve process operators (aged 28-56 years) completed a study with four single 12-h dayshifts and preceding night sleep in the laboratory. A simulated distillation process served as a work task. The 12-h shifts differed from each other in terms of the amount of preceding night sleep (23:00-06:30 hours or 2:30-6:30 hours) and work pace (slow or fast). All shifts contained four work simulation sessions of 1.5 h, and each of them included a 15-min alarm session. Cognitive performance was also measured with a 10-choice reaction time test and a mental subtraction test. Objective sleepiness was measured with a continuous electroencephalography/electro-oculography (EEG/EOG) recording during the work periods and with a sleep latency test. Subjective sleepiness at work was measured with the Karolinska Sleepiness Scale. Sleep debt increased the proportion of EEG/EOG-defined and subjective sleepiness at work, but did not impair work or test performance. The fatiguing effect of monotonous work as indicated by EEG/EOG-defined sleepiness was comparable with the effect of sleep debt. The alarm epochs in the middle of monotonous work temporarily decreased EEG/EOG-defined sleepiness. Sleep debt or monotonous work did not have a significant effect on the results of the sleep latency test. None of the sleepiness or performance measures indicated the impairment of a subject's functional capacity at the end of the 12-h shift. Our results suggest that monotonous work is at least as harmful as moderate sleep debt for alertness at work. The results support the view that the last hours of a single 12-h dayshift with frequent pauses are not associated with an increase in sleepiness or performance errors.

Evaluation of an 8 hour versus a 12 hour shift roster on employees at a power station

Several studies exist that have conducted research into the effects of different shiftwork patterns on the individual, especially regarding 8 and 12 h rosters. The findings of these studies have been largely supportive of longer shifts, however, the effects on work performance are not as clear cut. This study aimed to examine the changeover from an 8 h roster to a 12 h roster in a power station via monitoring on-shift performance, general health and well-being, sleep and mood behaviour, as well as absence and accident data. Results suggest that the domestic and social life of workers was markedly improved under the 12 h roster. Improvements in physical health, sleeping behaviour and mood state of employees were also documented. On-shift performance measures showed an increase in error rates at the end of a 12 h shift. Ways of reducing the risk of error towards the end of a 12 h shift should be explored. The results of this study suggest that 12 h shifts are a valid alternative to 8 h shifts in this particular workplace, although tasks that require error-free activities should not be performed towards the end of a 12 h shift.

Work shift duration: a review comparing eight hour and 12 hour shift systems

OBJECTIVES

Shiftwork is now a major feature of working life across a broad range of industries. The features of the shift systems operated can impact on the wellbeing, performance, and sleep of shiftworkers. This paper reviews the current state of knowledge on one major characteristic of shift rotas-namely, shift duration. Evidence comparing the relative effects of eight hour and 12 hour shifts on fatigue and job performance, safety, sleep, and physical and psychological health are considered. At the organisational level, factors such as the mode of system implementation, attitudes towards shift rotas, sickness absence and turnover, overtime, and moonlighting are discussed.

METHODS

Manual and electronic searches of the shiftwork research literature were conducted to obtain information on comparisons between eight hour and 12 hour shifts.

RESULTS

The research findings are largely equivocal. The bulk of the evidence suggests few differences between eight and 12 hour shifts in the way they affect people. There may even be advantages to 12 hour shifts in terms of lower stress levels, better physical and psychological wellbeing, improved durations and quality of off duty sleep as well as improvements in family relations. On the negative side, the main concerns are fatigue and safety. It is noted that a 12 hour shift does not equate with being active for only 12 hours.

CONCLUSIONS

There can be considerable extension of the person's time awake either side of the shift. However, the effects of longer term exposure to extended work days have been relatively uncharted in any systematic way. Longitudinal comparative research into the chronic impact of the compressed working week is needed.

Work schedule and task factors in upper-extremity fatigue

We tested the combined effects of work schedule and task factors on upper-extremity fatigue in the laboratory during 8-h and 12-h shift schedules. Participants performed a simulated manual assembly task at three repetition rates and three torque loads and self-adjusted their work cycle duration to maintain fatigue at moderate levels. Work cycle durations decreased with increases in both load level and repetition rate. Fatigue was observed more quickly with increasing time on shifts and during night shifts compared with day shifts. Work schedule effects were most apparent at lighter workloads, with minimal differences at higher workloads. The highest fatigue levels were observed during 12-h night shifts, with similar levels reached by the end of both the week of 8-h night shifts and the week of 12-h day shifts. Overall durations were 20%-30% shorter than in previous short-term studies, which was likely a result of the more realistic work schedules used in this study. Results from this study could be applied to the design of work-rest schedules for manual tasks involving the upper extremities.

Rescheduling a three shift system at a steel rolling mill: effects of a one hour delay of shift starting times on sleep and alertness in younger and older workers

OBJECTIVE

To evaluate a new work schedule at a Finnish steel mill with special attention to effects on older workers. The schedule was designed to improve sleep before the morning shift, and alertness during the morning shift, by delaying shift start and end times.

METHODS

Evaluation was by a shiftwork health and safety questionnaire, recordings of work-rest-sleep cycles with activity monitors worn on the wrist, daily diaries, and on site computerised testing of fatigue and alertness by the NIOSH fatigue test battery.

RESULTS

The one hour delay in shift starting times improved sleep before the morning shift, and improved waking fatigue, sleepiness, and performance during the morning shift. Evening and night shift sleep and fatigue or sleepiness, however, were affected negatively by the new work schedule, but the results for those shifts were less consistent across the various measures. Despite the improvements, most workers were not satisfied with the new schedule because of social concerns. Few interactions of age with the new work schedule were found, suggesting that the effects of the work schedule were uniform across age groups.

CONCLUSION

A change of as little as one hour in shift starting times can improve morning shift sleep and alertness, but there are trade offs from these improvements in terms of night shift effects and social considerations. It seems, then, that optimal shift start and end times for an entire organisation are difficult to institute on a wide scale. Tailoring shift schedules to subgroups within an organisation is suggested.

Speed and direction of shift rotation

This review paper deals with the issue of shift rotation, i.e. the number of consecutive shifts of the same type and the order of change between shifts. To minimize the disturbances of the circadian system and the accumulation of sleep deficits, rapidly and clockwise-rotating shift systems would seem to be preferable. Regarding consecutive night shifts, a week of night shifts seems to be the worst system with regard to performance and accidents. There is a lack of reliable data on the effects of permanent vs. rotating-shift systems on alertness, performance and accidents. This is also true for the comparison of forward (delaying) and backward (advancing) rotating-shift systems, although the former would seem to be associated with fewer problems. For both systems, controlled longitudinal studies are necessary.

Extended workshifts and excessive fatigue

Studies of overtime have pointed to fatigue as a potential factor producing, for example, a three-fold increase in accident rate after 16 h of work, increases in back injuries, hospital outbreaks of bacterial infection, or nuclear-power plant safety compromises. Fatigue has been measured more directly in studies of scheduled long workshifts, where performance decrements in both work-related tasks and laboratory-type behavioural tests have been observed, and significant loss of sleep and increases in subjective sleepiness have been reported. Analyses of accidents or injuries during scheduled extended workshifts, however, have produced equivocal results. Factors which could compound the fatiguing effects of extended workshifts, such as workload, noise, chemical exposure, or duties and responsibilities outside of the workplace, rarely have been studied systematically. It is concluded that extended workshift schedules should be instituted cautiously and evaluated carefully, with appropriate attention given to staffing levels, workload, job rotation, environmental exposures, emergency contingencies, rest breaks, commuting time, and social or domestic responsibilities.

Sleep patterns, shiftwork, and individual differences: a comparison of onshore and offshore control-room operators

The sleep patterns of offshore control-room operators were compared with those of personnel carrying out similar work onshore, taking into account individual differences in age, number of years of shiftwork, and neuroticism. The dependent variables were self-reported sleep quality and duration for day-shift (D-S) and night-shift (N-S) work, and during leave periods (L-P). Offshore workers reported longer N-S sleep duration, and lower D-S sleep quality than those onshore, but the two groups did not differ in L-P measures. The effects of environmental differences (onshore versus offshore) on sleep patterns were more marked than those of the two different shift systems (weekly rotation and fast rotation) in operation onshore. Age was negatively related to both duration and quality of sleep; over and above age, number of years of shiftwork was negatively related to sleep duration. Neuroticism was also negatively related to sleep duration and, more strongly, to sleep quality. These findings are discussed in relation to the literature on shiftwork and sleep in general, and the characteristics of the offshore environment in particular.

Performance and alertness on 8 h and 12 h rotating shifts at a natural gas utility

An 8 h/5-7 day shift schedule was compared with a newly instituted 12 h/2-4 day schedule in this, our second worksite study of extended workshifts. Workers completed a performance/alertness test battery, and a questionnaire on sleep patterns and other personal habits, 2-4 times a week on all shifts. After 10 months adaptation to the 12 h shift schedule, there were decrements in performance/alertness attributable to the extra 4 h on the extended shift. There were also reductions in sleep across the workweek which were most apparent on 12 h night shifts. The results are consistent with our first worksite study of 12 h shifts and indicate extra caution should be exercised when scheduling critical activities for extended workshifts, especially extended night shifts.