Tolerance of shift work

This study aimed to explore criteria for shift work tolerance and to investigate the relationships between personality traits and states and shift work tolerance. Eighty-nine policemen and police women completed a questionnaire, once during consecutive night shifts and again during rotating shifts, and their responses were used to assess anxiety, emotional control, positive and negative affect, health complaints, sleep quality, difficulties in social and domestic life, and perceptions about shift work. Both the criteria for tolerance and the relationship between tolerance and personality varied according to shift type. Night shift tolerance involved four factors--somatic health, flexibility, sleep and sleep need--while rotating shift tolerance involved three factors--somatic health, flexibility and fatigue. Tolerance of shift work was associated with anxiety, repressive emotional style and mood. During night shifts, anxiety was the most influential personality factor for the somatic health and sleep dimensions of shift tolerance. During rotating shifts, positive and negative moods, rather than trait personality factors, were important predictors of the somatic health and fatigue shift tolerance dimensions. These results suggest a mechanism for more effective matching of workers to suitable shift schedules.     

Experimental Changes in Shift Schedules—Their Effects on Well-Being

A questionnaire was given to 400 workers on different shift schedules (day, 2 shift, 3 shift (weekly rotation) and 4 shift (2-3 day rotation)), shortly before, and in the year after the work schedules of 131 of them had been changed to accommodate an overall reduction in the total amount of shift working. Those workers who had to change from 3 or 4 shift working to 2 shift working (without night work) showed a significant increase in well-being with respect lo sleep/mood, gastrointestinal functioning, and social factors, along with an improvement in attitude to their work schedules. Those who were switched from shift to day work reported greatly increased social well-being, a shortening of sleep-length during free days, and considerably improved altitudes towards their work schedule; their sickness absence rates were also reduced. Attitudes towards the change from fast rotation to slow rotation of shift cycles in those whose schedule was altered from 4 shift to 3 shift working were mainly negative. Questionnaire scores remained at their original levels in the 269 workers whose schedules were left unchanged, It is concluded that the abolition of night work results in a substantial improvement in mental, physical and social well-being.     

Designing better shift systems

The results of some intervention studies on the effects of the change from weekly rotating to quicker rotating shift systems are presented. Consequently, the following recommendations for the design of shift systems according to physiological, psychological and social criteria are discussed: (1) Nightwork should be reduced as much as possible. If this is not possible, quickly rotating shift systems are preferable to slowly rotating ones. Permanent nightwork does not seem to be recommendable for the majority of shiftworkers. (2) Extended workdays (9-12 hours) should only be contemplated when the nature of work and the workload are suitable for extended working hours, and the shift system is designed to minimize the accumulation of fatigue and toxic exposure is limited. (3) An early start for the morning shift should be avoided. Flexible working time arrangements can be achieved in all shift systems. The highest flexibility is possible in the so-called 'time autonomous groups'. (4) Quick changeovers (e.g. from night shift to afternoon shift on the same day) should be avoided. The number of consecutive working days should be limited to five-seven. Every shift system should include some free weekends with at least two consecutive days off. (5) The forward rotation (phase delay, clockwise rotation: morning/evening/night shift) would seem to be most preferred.     

Influence of shift work in process industry on workers' occupational health,productivity, and family and social life: An ergonomic approach

Shift work is a major feature of modern work practices. It involves working at times considered unconventional for most workers, such as at night. Although the community often benefits from such work practices, shift work can be hazardous for both the workers and the community. There are increased risks for accidents and errors, increased sleepiness and fatigue due to difficulties sleeping, increased health problems, and disruptions to family and social life. More shift workers complained of sleep disturbance, poor sleep quality, tiredness at awakening, and sleepiness in work than did non‐shift workers. More shift workers also complained of gastrointestinal disturbances than did non‐shift workers. The aim of this article is to provide general information on shift work, work schedules, and the effects of work schedules on sleep, fatigue, performance, the health of the human operator, and productivity. © 2010 Wiley Periodicals, Inc.     

The design of shift systems

All shift systems have advantages and drawbacks. There is no single ‘optimum shift system’ which can be used in industry or commerce at all work places. However, there are shift systems which are more favourable, and others which are less favourable, in the context of physiological, psychological, and social recommendations for the design of shift systems. This article discusses the following recommendations:

(1) Nightwork should be reduced as much as possible. If this is not possible, quickly rotating shift systems are preferable to slowly rotating ones. Permanent nightwork does not seem to be advisable for the majority of shiftworkers.

(2) Extended workdays (9-12 h) should only be contemplated, if the nature of work and the workload are suitable; the shift system is designed to minimize the accumulation of fatigue; there are adequate arrangements for cover of absentees; overtime will not be added; toxic exposure is limited; and if it is likely that a complete recovery after work and a high acceptance of the working time arrangement are possible.

(3) An early start for the morning shift should be avoided. In all shiftsystems flexible working time arrangements- are realizable. The highest flexibility is possible in ‘time autonomous groups’.

(4) Quick changeovers (e.g., from night to afternoon shift at the same day or from afternoon to morning shift) must be avoided. The number of consecutive working days should be limited to 5-7 days. Every shift system should include some free weekends with at least two successive full days off.

(5) The forward rotation of shifts (phase delay, clockwise rotation) would seem to be recommendable at least in continuous shift systems.

Besides the design of a shift system, implementation strategy is of particular importance for the acceptance of the shift system.     

Using a circadian rhythms model to evaluate shift schedules

As long as the need for shiftwork exists, so will the demand for an optimal scheduling strategy that balances the needs of both industry and the shiftworker. One aim is for schedules that require workers to be on duty during the times that they are most naturally alert and awake. Czeisler et al. (1982) developed a set of circadian rhythm based guidelines intended to aid in designing such shiftwork schedules. This paper takes research one step further by testing such empirical criteria in a mathematical setting. The two-oscillator model of free-run human circadian rhythms developed by Kronauer et al. (1982) was modified to represent the circadian rhythms of a shiftworker on a pre-selected shiftwork schedule. Numerical simulations were used to compare the circadian rhythms produced from a variety of shiftwork schedules to the free-run rhythms. Shift schedules that resulted in circadian rhythms closest to the free-run rhythms were identified as preferred schedules. The numerical results supported Czeisler's findings (1982), indicating the best shift schedules adopt a slow, forward-shifting rotation pattern, rotate shifts after 2-week periods and allow an average of 2 days off per week.     

Changing the shift system in a mining company: An intervention study

The aim of this study is to determine the shift system that allows for sustainable time management, considering the characteristics of the mining company analyzed. Regarding the methodology, the Standard Shiftwork Index was used to characterize the workers perceptions of the shift system. In order to increase the chances of changing the shift system, the Besiak method of shifts was applied to the following: modified 4 × 4 (current shift); 6 × 6 modified and 7 × 7. Furthermore, with input from company representatives, the method seeks to jointly identify the company's strengths, weaknesses, opportunities, and threats of the different shift systems. The main results show that the level in which the shift system (modified 4 × 4) interferes with leisure, social, and domestic life is associated with the city of residence. The application of Besiak concluded that the order of the highest risk to the lowest risk is as follows: 7 × 7, modified 6 × 6, and modified 4 × 4. Once the 7 × 7 shift work was discarded, a second level of analysis was performed between the two remaining shift work systems. Both have strengths, but the worker's place of residence on the days off became the determining factor. Hence, the 6 × 6 modified model met the biopsychosocial factors and favored residence in other cities during the days off. Finally, it was clear that during the shift system change, it is very important to involve workers, labor unions, and managers in the process of designing and introducing a new shift system.     

Development of a hybrid expert system for nurse shift scheduling

In this article, we discuss the effect of nurse shift job on circadian rhythm, work stress, and some important ergonomics criteria. We also review and compare different nurse shift scheduling methodologies via the criteria of flexibility, consideration of nurse preference, and consideration of ergonomics principles. A hybrid expert system, entitled NURSE-HELP, is developed to facilitate the nurse scheduling process with an emphasis on considering ergonomics criteria. Moreover, the combination of a linear zero-one goal programming and an expert system program reduces the program run time while maintaining the quality of the schedule. The evaluation of the system is done by comparing 18 sets of four-week schedules generated by the head nurses manually and by NURSE-HELP. Concerning the amount of time to generate the schedules, NURSE-HELP averages less than 20 minutes while the head nurses spend about two to four hours. The quality of the schedules is measured by the following four criteria; minimum staff level not satisfied, day off request not granted, backward rotation, and maximum consecutive work periods on the night shift. The results show that NURSE-HELP is superior than the head nurses in preparing schedules, both in terms of time and quality.     

Fatigue assessment among onshore oil rig shift workers in Thailand

This study aimed to assess fatigue among onshore oil rig shift workers in a petroleum company working in swing shifts. The work schedule consisted of 12 h of night shifts for one week followed by 12 h of day shifts for one week. Fatigue was assessed using both subjective and objective measurements which were visual analogue fatigue scale (VAFS) and simple reaction time (SRT) test, respectively. A total of 38 male onshore oil rig shift workers participated in this study. Fatigue assessment was conducted at the start and at the end of workdays on nights 1, 4 and 7, and days 1, 4 and 7. The results showed that there were significant differences of VAFS and SRT at the end of workdays, compared with at the start of workdays (p < 0.001). The fatigue level assessed by both SRT and VAFS was highest on the rotating day (p < 0.001). In conclusion, swing shifts might affect fatigue levels in shift workers. The fatigue level increased over the two-week work period. Further studies on fatigue assessment and management among onshore oil rig shift workers are still needed.     

Optimization of shift work: physiological contributions

Abstract

Healthy subjects (n= 62) with different circadian phase positions worked up to six weeks in different shift systems. Rotation speed was experimentally varied. On shift days all subjects worked in the Institute but spent their leisure time as usual.

In order to minimize bias through masking effects, ‘control days’ were interpolated (twice a week) into the shift periods. On these control days subjects remained on bedrest for 24 hours under constant conditions.

Results were as follows:

(i) The earlier the circadian phase position the poorer the adaptation to night-shifts. In particular, morning types were not able to adapt even to permanent night-shifts.

(ii) Evening types were able to adjust their circadian systems to a slowly rotating shift system (rotation speed seven days) and a 25 h-sliding system though they failed to do so with more quickly rotating systems. Whereas indifferent subjects were not able to adjust to even the slowly rotating system.

(iii) When stable phase shifts occurred in response to altered working hours they always amounted to about one hour per day if the working hours were not coherent with the usual environmental zeitgebers.

It is concluded that, on physiological criteria, very slow rotating shift systems or permanent night-shifts seem to be acceptable for evening types, but not for morning types who may require special health care in these conditions.     

Changing the speed of shift rotation: a field study

Abstract

A group of 33 controllers of an emergency service were studied before and after a change in shift roster. The original roster was the traditional weekly rotating type of three shifts, morning, afternoon and night in that direction, in which controllers worked seven consecutive shifts of the same type. This was changed to a rapidly rotating roster of shifts with no more than three consecutive night shifts. The direction of shift change remained the same. Sleep and meal diaries were kept by all controllers for 2 weeks before the roster change. Self-report measures were taken of health, social drug consumption and work variables, an anxiety inventory, the State-Train Anxiety Inventory and the Work Environment Scale were administered both before and 5 months after the roster change. Significant improvements were found after the shift roster change on almost all measures with the exception of self-reported nervousness and loss of appetite and a number of items in the Work Environment Scale. This finding provides some evidence from the field for the argument that rapidly rotating shifts may be the optimal form of shift system.     

The importance of individual preferences when evaluating the associations between working hours and indicators of health and well-being

Previous studies indicate that the effect of a given shift schedule may depend on individual factors. The aim of the present study was to investigate whether a misfit between individual preferences and actual working hours affected the association between working hours and self-reported indicators of health and well-being. The study population consisted of 173 female eldercare workers who mainly worked day or evening shifts. We combined self-reported questionnaire data on preferences with actual work schedules during a four-week period. The study showed that a misfit between preferences on one hand and “non-day work”, “weekend work” or “only a few consecutive days off” on the other hand was associated with an increased dissatisfaction with working hours and/or an increase in the intention to leave the workplace due to one's working hours.     

Adaptation to permanent night work: the number of consecutive work nights and motivated choice

To study the effects of different patterns of days on and days off duty within a permanent night shift schedule, we studied two groups of female permanent night nurses, one (n=42) working‘many’ nights in a row, and the other (n=36) working ‘few’ nights in a row. The groups were matched for several important moderating variables. All nurses were interviewed individually, and they answered several questionnaires. A MANOVA revealed no statistically significant differences in subjective health between the two groups. Nor was any difference found for satisfaction measures. The many-night group however seemed to put more effort into dealing with their schedule; they used more active coping, had a higher cigarette consumption, and engaged more in sport. They also stayed one hour less in bed during the day after the last night shift. It is concluded that neither schedule was a clear threat to subjective health because the acceptance of permanent night work was the result of a motivated choice and because social support was high. The differences between the two schedules were not large enough to suggest that one of them should be favoured over the other.     

Using a circadian rhythms model to evaluate shift schedules

As long as the need for shiftwork exists, so will the demand for an optimal scheduling strategy that balances the needs of both industry and the shiftworker. One aim is for schedules that require workers to be on duty during the times that they are most naturally alert and awake. Czeisler et al. (1982) developed a set of circadian rhythm based guidelines intended to aid in designing such shiftwork schedules. This paper takes research one step further by testing such empirical criteria in a mathematical setting. The two-oscillator model of free-run human circadian rhythms developed by Kronauer et al. (1982) was modified to represent the circadian rhythms of a shiftworker on a pre-selected shiftwork schedule. Numerical simulations were used to compare the circadian rhythms produced from a variety of shiftwork schedules to the free-run rhythms. Shift schedules that resulted in circadian rhythms closest to the free-run rhythms were identified as preferred schedules. The numerical results supported Czeisler's findings (1982), indicating the best shift schedules adopt a slow, forward-shifting rotation pattern, rotate shifts after 2-week periods and allow an average of 2 days o^ff per week.     

Worktime control-dependent reductions in fatigue, sleep problems, and depression

We investigated the association between worktime control and fatigue, sleep problems, and depressive symptoms in a sample of daytime and shift workers. A total of 3681 permanent daytime workers and 599 shift workers completed a questionnaire designed to assess the above variables. Worktime control was evaluated in terms of both “control over daily working hours” and “control over days off”. Worktime control × work schedule × gender analysis of covariance, adjusted for age and employment status, showed overall reductions in incomplete recovery, insomnia symptoms, daytime sleepiness, and depressive symptoms with increasing levels of worktime control. However, no associations between control over daily working hours and insomnia symptoms were observed in women. The reductions appeared to be more evident for control over days off. These results remained consistent after adjustments for other potential covariates. The present findings indicate that increased worktime control and enhanced control over days off in particular, may be associated with favorable health outcomes.     

Do we want to keep working in 12-h shifts? The follow-up of the work schedule change in a Portuguese industrial company

BackgroundIn Europe, atypical work schedules assume an increasing position, framed by the so-called “adaptability regime”. Despite being seen as a “temporary” option, this regime supports the extension of the working hours up to 12 h per shift.ObjectiveThe purpose of this study was to analyse how the workers from a Portuguese industrial company perceive the impacts of a 12-h schedule, after replacing the former 8-h shift schedule.MethodsThe sample included a total of 87 shiftworkers of an industrial company. A mixed method research was followed based on the ergonomic work analysis, using observations; a self-report instrument describing a week working on 2 × 12 h; and a questionnaire.ResultsField study findings are consistent in showing that, in 2 × 12 h, the workers perceive the risks as resized, both physical risk factors (e.g., noise) and factors related to the work organization (e.g., work pace). The results also reveal a perceived aggravation of the main health outcomes: “sleep debt”, feeling of chronic fatigue, and muscles pains. Despite this, most workers prefer the new 12-h schedule, but not until their retirement age.ConclusionAt present, it is noticed that the new schedule receives collective acceptance and is considered the least-worst option; the advantages outside work seem to compensate the higher costs imposed by this schedule.Relevance to industryOur findings highlight ergonomics' contribution to the sustainability of the work in 12-h shifts, establishing the conditions that enable a technical-scientific opinion supporting the company's decision on the exposure length of the workers to these work schedules.     

The impact of shift and night work on health

Shift work, in particular night work, can have a negative impact on health and well-being of workers as it can cause: (a) disturbances of the normal circadian rhythms of the psychophysiological functions, beginning with the sleep/wake cycle; (b) interferences with work performance and efficiency over the 24 hour span, with consequent errors and accidents; (c) difficulties in maintaining the usual relationships both at family and social level, with consequent negative influences on marital relations, care of children and social contacts; (d) deterioration of health that can be manifested in disturbances of sleeping and eating habits and, in the long run, in more severe disorders that deal prevalently with the gastrointestinal (colitis, gastroduodenitis and peptic ulcer), neuro-psychic (chronic fatigue, anxiety, depression) and, probably, cardiovascular (hypertension, ischemic heart diseases) functions. Besides, shift and night work may have more specific adverse effects on women's health both in relation to their particular hormonal and reproductive function, and their family roles. It has been estimated that about 20% of all workers have to leave shift work in a very short time because of serious disturbances; those remaining in shift work show different levels of (mal)adaptation and (in)tolerance, that can become more or less manifest in different times, and with different intensity. In fact, the effects of such stress condition can vary widely among the shift workers in relation to many 'intervening variables' concerning both individual factors (e.g. age, personality traits, physiological characteristics), as well as working situations (e.g. work loads, shift schedules) and social conditions (e.g. number and age of children, housing, commuting).     

Internal locus of control and choice in health service shift workers

This study examined the relationship between shift work-specific locus of control (SH-LOC), active choice of work schedule and health outcomes, personal initiatives and coping behaviours in 1611 Danish Health Service shift workers. The 20-item SH-LOC scale was administered as part of a battery of measures. Multivariate analysis of covariance (controlling for age, workplace experience and weekly work hours) tested for differential responses to shift working and coping strategies. Interactive effects of internality and type of work rota were examined. Higher internality was linked to better tolerance to shift work. This did not appear to be a result of greater personal action in higher internals. The importance of control as a potential moderating factor to shift work exposure and the possible use of this measure in the process of shift worker monitoring is highlighted.     

Internal locus of control and choice in health service shift workers

This study examined the relationship between shift work-specific locus of control (SH-LOC), active choice of work schedule and health outcomes, personal initiatives and coping behaviours in 1611 Danish Health Service shift workers. The 20-item SH-LOC scale was administered as part of a battery of measures. Multivariate analysis of covariance (controlling for age, workplace experience and weekly work hours) tested for differential responses to shift working and coping strategies. Interactive effects of internality and type of work rota were examined. Higher internality was linked to better tolerance to shift work. This did not appear to be a result of greater personal action in higher internals. The importance of control as a potential moderating factor to shift work exposure and the possible use of this measure in the process of shift worker monitoring is highlighted.     

Night shift paralysis in air traffic control officers

Abstract

In an earlier paper (Folkard et al. 1984) we reported on the incidence of a temporary but incapacitating paralysis known as ‘night shift paralysis’. This appeared to be a special form of sleep paralysis that occurs when night workers manage to maintain a state of wakefulness despite considerable pressures to sleep. The incidence of this paralysis might thus be assumed to reflect the level of sleep deprivation associated with different shift systems or individuals. The present survey was designed to examine this possibility in a sample of 435 Air Traffic Control Officers (ATCOs) from 17 different countries who were on a variety of different work schedules. The incidence of this paralysis was found to be affected by four main factors, all of which might reasonably be assumed to influence the night-worker's level of sleep deprivation or sleepiness. These were the time of night, the number of consecutive night shifts, the requirement to work both a morning and a night shift starting on the same day and individual differences in the flexibility of sleeping habits. These results suggest that the incidence of this paralysis may indeed prove to be a useful ‘critical incident’ for comparing the level of sleep deprivation associated with different shift systems or individuals.