Maintaining safety and high performance on shiftwork

Applied

Ergonomics

ooo3-6870(95)ooo48-8

I. pp.

Vol 27, No. 17-23, 1996 Elsevier Science Ltd Printed in Great Bntain WO3-687086 $10.00 + 0.00

ELSEVIER

Maintaining safety and high performance on shiftwork’ Timothy H. Monk*, Simon Folkard+ and Alexander I. Wedderburn$ *Sleep and Chronobiology Center, University of Pittsburgh School of Medicine, Western Psychiatric Institute h Clinic, 3811 O’Hara St., Pittsburgh, PA 15213, USA ‘Body Rhythms and Shiftwork Centre, Department of Psychology, University of Wales, Swansea, Singleton Park, Swansea SA2 8PP, Wales, UK *Department of Business Organization, Heriot-Watt University, PO Box 807, Riccarton, Edinburgh, EH14 4AT, Scotland, UK

This review of lthe shiftwork area focuses on aspects of safety and productivity. It discusses the situations in which shiftworker performance is critical, the types of problem that can develop and the reasons why shiftworker performance can be impaired. The review ends with a discussion of the various advantages and disadvantages of several shift rotation systems, and of other possible solutions to the problem. Keywords:

human.

circadian

rhythm,

shiftwork,

night work,

category approach: ‘. . . accidents are caused by failures of control. They are not, as is so often believed, the result of straightforward failures of technology; social, organizational and technical problems interact to produce them’ (Accident Prevention Advisory Unit, 1981). Landy (1989) has outlined a similar division of ways of reducing accidents, into the personnel, and industrial-social engineering, approaches (Landy, 1989, p. 642). The relevant point about these distinctions is that the contribution of error by the human operator, which has often been shown to exhibit clear time-of-day effects, may at times be concealed by, or confounded with, problems of technology or work organization.

The aim of this paper is to explore the various situations in which the performance of shiftworkers is critical, to gain an understanding of the biological and social reasons why there i,s a problem, to explain what the problems are, and to begin to put forward an approach as to how the problems might be ameliorated. Historically, there has often been an unfortunate misunderstanding about the study of shiftworker performance. Some have regarded it as a rather hardnosed profit-oriented enterprise, designed to squeeze the greatest productivity out of the hapless shiftworker. We regard that view as a rather unhelpful caricature of a complex area which has much more to do with the safety and well-being of the shiftworker, rather than the number of ‘widgets’ that he or she can produce per hour. We believe that a worker-oriented strategy, which addresses the various problems connected with safety and well-being in shiftwork, is a much more sensitive approach that is generally acceptable to the workforce. While for some organizations there will inevitably be a trade-off between safety and wellbeing on one hand, and profitability on the other, there will be many others for which both aspects can be improved. We espouse the view that improvements in shiftwork coping are, in general, likely to enhance not only the workers’ safety and well-being, but also their effectiveness and productivity. From some viewpoints, not all accidents are most usefully attributed to human error. The United Kingdom Health and Safely Executive suggests a three ’ This paper was presented at the mini-symposium the 24th International Congress on Occupational France, September 1993

shift, performance

When is on-shift performance

critical?

In certain situations it is very important that shiftworkers perform at their optimum. There are four basic situations, related to a 2 X 2 classification of ‘error’ versus ‘failure to respond’ and ‘danger to society’ versus ‘danger to self. First there is the case where a work error is dangerous to society, such as, for example, an airline pilot who lands on the wrong runway, a nuclear power station operator who opens the wrong valve, or a chemical worker who allows a temperature or a pressure to become critical. These errors may have catastrophic implications for society which far outweigh the simple slip of judgement or mistake of the worker. Second, there is the situation where a work error is dangerous to the worker or workers themselves. This often (but not always) includes the first category since the pilot is involved in the plane crash and the power station operator is closest to the power station.

on Shiftwork at Health, Nice,

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Maintaining safety and high performance

However, there are many other situations where making an error will be dangerous only to a worker himself or herself. Thus, for example, in the meat packing industry, an error could result in injury to a limb; in hospital laboratory situations it could result in infection of the worker, possibly by something as critical as HIV-tainted blood. Again, the consequences may far outweigh the magnitude of the error, but only a single individual (and perhaps his or her immediate colleagues) is involved. Thirdly, we have the situation when a failure to respond is dangerous to society. Here, we are not talking about the shiftworker doing something incorrectly; we are talking about the shiftworker failing to do something. Usually, of course, this is because on the night shift, in particular, the shiftworker may be asleep. The most obvious situation here, in regard to danger to society, is a long distance bus or passenger train driver falling asleep at the wheel. Equally though, we have documented situations in the nuclear power industry, for example, where nuclear power operators have literally been asleep while they were supposed to be controlling the power station. Fourthly, we have the situation where failure to respond is dangerous to the worker or workers themselves. Here, of course, the most obvious and sadly the most frequent situation is the long distance truck or lorry driver who falls asleep and is killed by running off the road.

Why is there a problem? There are several different facets to the shiftwork coping problem: that we are a diurnal species; that society expects us to be asleep at night and recreating in the evening and weekends; that daylight is a powerful time cue; and that the human circadian system (or biological clock) is a timekeeping system inside our head that has a momentum of its own and is slow to adjust to a night work routine. We shall discuss these in turn. First, Homo Sapiens is a diurnal creature accustomed to being asleep at night, and awake and active during the day. This is shown in Figure 2 which represents a collection of circadian rhythms in various measures. The details of these rhythms are not important. What is important is that, under normal conditions, these rhythms are aligned so as to set the stage for wakefulness during the day and for sleep at night. Working together, these rhythms have the effect of shutting down some processes so that the individual can have a restful night of sleep and to warming up others in the morning so that the individual can be alert and active during the day. This is apparent in Figure 2; when subjects are given opportunities for sleep at different times around the clock, then we see that there are definite times when they are much more likely to be asleep. Also, there are times when they find it very difficult to sleep. This is because the biological clock has not prepared their mind and their body for sleep at that time of day. Accident peaks can occur at less vulnerable times of day as well. One of the great paradoxes about accidents is that human beings can to some extent adjust their risk-taking to their abilities. So both

TEMPERATURE

on shiftwork: T. H. Monk et al

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road traffic accidents and industrial accidents (in the UK) show pronounced peaks for males between 16 and 25 years old, the decade when both mental and physical abilities are at their peak (Accident Prevention Advisory Unit, 1981). Even at the 0300 hrs trough, Chiles et al (1968) found that the dip in

Maintaining

safety and high performance

on shiftwork: T. H. Monk et al

performance of trainee astronauts could be eliminated after these’extremely fit and highly motivated personnel were informed about it. The second cause of the problem is that because society is made up of hulman beings who are diurnal creatures, society itself is a diurnal culture. Regulations and social taboos are in place to protect the nocturnal sleep of the day-working majority. Because night workers lack that protlection (and because their biological clocks are unlikely to be fully adjusted) shiftworkers who try to sleep at times other than at night, are often woken early and do not get the satisfactory amount of sleep. Kogi (1985) has plotted the results of very large-scale survey studies of the sleep of many thousands of German and Japanese shiftworkers, showing how much sleep they obtained as a function of the time of day (Figure 3). We can see that whereas 8 hours of sleep was obtained when sleep was attempted at night, when sleep was attempted towards the middle of the day, very little sleep was obtained. Some of this was due to the society intruding on these people’s ability to sleep, while in other situations it was the natural biological clock not having prepared the individual for restful sleep. Society not only expects people to do their sleeping at night, but also expects community and family interaction to take place in the evenings and at weekends. This creates problems for shiftworkers, who often have to be at work during these times. Tepas (Tepas and Monk, 1.987) asked several thousand workers whether they were satisfied with the time they had available for family and friends. Over half of the morning shift were satisfiled, but only 20-30% of the respondents from the evening and night shifts were satisfied with this aspect of their lives. We can also consider this in terms of the weekend. Figure 4 reports the data from a study of accidents to mineworkers in the US Lake Superior iron ore mining region (Monk and Wagner, 1989). We looked at the weekly trend in accidents on the night shift. These were miners who always had the same schedule which started

0

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Figure 3 Mean and standard deviation of the diary measured

sleep lengths of 2332 German workers (solid circles) and 3240 Japanese workers (open circles). From Kogi (1985)

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Figure 4 Total number of accidents in the US Lake Superior mining region for the period 1975-1984 occurring to workers under 30 years. From Monk and Wagner (1988)

on a Thursday night and ran for seven consecutive nights. It shows the beginnings of a decreasing trend as the workers’ biological clocks adjusted to the night work. However, on Sunday night there was a large peak in accidents with again a gradual recovery. There seemed to be no organizational reasons for this trend. Although hard off-work data were not available, the most plausible explanation appeared to be that these shiftworkers were living in communities which expected them, particularly on Sunday, to go to church and do family-oriented activities which then prevented them getting enough sleep for their Sunday night shift. Thus, the demands of society can directly impact the safety of the shiftworker. The third factor causing problems for the shiftworker is that daylight is an extremely powerful time cue. Unlike the transmeridianal traveller whose biological clock adjustment is assisted by natural daylight, the shiftworker must always regard natural daylight as an enemy to nocturnal circadian orientation. Some authors (e.g. Czeisler et al, 1990) argue that it is the reason why complete circadian phase adjustment to night work is almost never found in field studies (Knauth and Rutenfranz, 1976). Data to support this are available from many different authors. Even permanent night workers, after a weekend break where the daylight and other time cues are encouraging a reversion to a day oriented schedule, will show the same circadian properties as those who have never worked nights (Van Loon, 1963; Monk, 1986). The fourth source of problems for the shiftworker is that the human biological clock or circadian system is slow to adjust to night work. One can regard the circadian system as having a momentum of its own, a momentum at a particular circadian orientation. Again, there is a wealth of data for this. Figure 5 (from Monk et al, 1978) presents an example of a phase adjustment curve of temperature rhythms from two volunteers who worked 21 consecutive night shifts. It took well over a week for their circadian systems to become in tune with the night work routine. Between them, these four factors make it increasingly likely that the shiftworker’s on-shift performance and off-shift sleep will be compromised. Both biology and society are often working against the best

Maintaining safety and high performance

20

on shiftwork: T. H. Monk et al

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What are the problem areas?

MINOR IN

Essentially, there are five different problem areas: (1) errors, (2) sleep and excessive fatigue, (3) moodiness, irritability and disruptiveness, (4) absence, and (5) off-work accidents - the most serious being traffic accidents on the drive home. The fifth point represents an issue that has often been neglected, but is one that may be vitally important to the safety of those involved. We shall deal with the five issues in turn, starting with the problem of making errors or being slow to respond, particularly on the night shift. Figure 6 represents a composite graph from many different studies that have been published several times (Folkard and Monk, 1979). Plotted is the ‘real-life’ performance of how well somebody did their job: how quickly they answered a switchboard, how accurately they could read a meter, how they could avoid sleep while driving, how many times they missed warning signals as a train driver, and how many times they had hospital accidents on a genera1 hospital ward. When all of these performance scores are transformed using a Z score, one can calculate and plot a composite curve, up being good, down being bad (Figure 7). To illustrate the rhythm, each point is plotted twice. There is a major trough indicating a disruption in performance during the night shift. Also, there is a secondary drop during the early afternoon, the ‘postlunch dip’. Thus, the biological and societal problems for the shiftworker outlined above, do indeed produce impairments in performance at night. People make more errors, they also fall asleep more often. Sadly, as mentioned earlier, one common effect of this in reallife is when single vehicle accidents occur, usually somebody driving off the road in the early hours of the morning after driving all night. We can see this again in a second graph from Simon Folkard (Figure 8),

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Figure 7 A meta-analysis of the Figure 6 data by Folkard. Increases on the y-axis indicate better performance. Each point is double plotted

which is a composite curve of falling asleep at the wheel. As well as the late night peak, there is again a post-lunch dip indicating the two times of day at which human beings have a propensity to fall asleep. Thirdly, we have the situation of being irritable

Maintaining safety and high performance

on shiftwork: T. H. Monk et al

a statistical likelihood that almost every one of these respondents would have had at least one accident or near miss. Although the high-profile events such as Chernobyl, Three-Mile Island and Exxon Valdez, may make the headlines, in terms of people killed, in terms of human misery, and of course, in terms of financial cost, it is quite likely that these many uncounted traffic accidents are far more important. When added up, they may have a much greater impact on society than do the big high profile accidents.

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of studies indicating incidence of falling asleep at the wheel. Increases on the y-axis indicate better performance (less sleepiness). Each point is double plotted

disruptive at work. This is something that has been neglected. Under certain circumstances, an angry shiftworker may be as dangerous as a sleepy shiftworker. This is illustrated very nicely by Dr John Lauber’s description of a fatal bus accident. Far from being drowsy, in this case, the driver was being very aggressive, muttering to himself and generally being angry. Although tlhis was not officially listed as the cause of the accident, when Lauber looked at this bus driver’s work schedule it was clear that he had had very little sleep and had good reason to be angry; it is argued that perhaps this anger had contributed to the possible accident (Lauber and Kayten, 1988). Being absent on the night shift is very important to safety because if somebody is absent from their work then typically somebody else is asked to do it, often someone less able (either through less training or because they are being asked to work ‘a doubler’, work on at the end of their shift without notice, and are naturally tired. The alternatives are to run with light staffing, perhaps over-stretching the work team, or to call out a stand-by replacement from home. The use and consequences of working ‘doublers’ has never been reported in the published literature, although anecdotal reports suggest that it is quite frequent, and is usually considered to be hazardous. While the new European directive on the organization of working time proposes that working overtime on night shift should be completely banned, problems can be expected in trying to monitor and enforce such a ban. The fifth topic, accidents on the journey home, probably represents the major risk for bodily harm in shiftworkers whose actual work is inherently fairly safe. Richardson et al (1990) compared rotating shiftworkers with permanent dayworkers. When asked the question ‘Have you had any automobile accidents or near misses in the past year due to sleepiness?‘, more than 20% of the rotating shiftworkers replied ‘yes’. That means, on average over a five year period, there is and

21

solutions?

As with any other area, it is easier in shiftwork to outline the problems than to put forward solutions. There are, however, five areas in which improvements can be made: the elimination or reduction of night work, the selection of appropriate shiftworkers, the education of shiftworkers, the adoption of correct shift rotation schedules, and the improvement of the working environment. As Knauth (1993) has clearly demonstrated, night work can often be reduced or eliminated. While there are some processes such as glass and steel making which are relatively time of day independent, there are others in which much of the work can be quite easily moved to the morning or evening shift. It is often a useful exercise to aggressively probe management as to why each task for the night shift cannot be moved to a different time of day. After such an exercise it may become apparent that many tasks can be removed from the night shift, allowing a much smaller night team (perhaps small enough to be staffed by permanent volunteers) to do the work. It is worth remembering that a small proportion of the workforce do actually seek night work, and might thus be (within the limits of their biological and social constraints) relatively happy and productive in this role. However, one should exercise caution in embracing such a solution, since the long term consequences of permanent night work are largely unknown. Second, there is the selection issue. Here there is need for much caution. Our knowledge is not so sufficiently developed that we can arbitrarily rule people out and deny them the ability to do shiftwork. Moreover, most test instruments that one might use have very obvious ‘right’ or ‘wrong’ answers for those who want the job. Certainly, however, there are interindividual differences in shiftwork suitability. Tepas and Monk (1987) came up with the following list of potential problem areas: those over 50 years of age, those who are doing a lot of moonlighting (unofficial second jobs); somebody who has a heavy domestic workload, neurotic introverts, people who are the ‘morning lark’ rather than the ‘night-owl’ or who are ‘rigid’ rather than ‘flexible’ sleepers, those with a history of sleep disorders, psychiatric illness, alcohol or drug abuse, gastrointestinal complaints, epilepsy, diabetes or heart disease. Although the predictive validity of most scores (e.g. sleep flexibility) in later shiftwork tolerance is only 0.3, this equals that of many widely used selection devices. There are many other conditions that one can add to this, but there are certain individuals who should certainly be counselled against shiftwork though we would hesitate to forbid them from doing shiftwork.

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Maintaining safety and high performance

Third. we can educate night workers, and shiftworkers in general. Human error is most likely to occur in shiftworkers who are failing to cope and so, helping shiftworkers to cope with their work schedules and domestic situations will inevitably reflect favourably on performance and safety. We would emphasize here that the ability to cope is due to a triad of coping factors: circadian factors relating to the biological clock, sleep factors relating to sleep hygiene and sleep practice, and the social and domestic factors. All three of these are mutually interactive and all three serve to determine how well the individual copes with the shiftwork (Monk, 1988). Fourth, we can improve or optimize the schedule. Unfortunately, there are no simple ‘cook book’ answers with regard to selection of the best schedule. Just as the shiftwork problems are multifactorial, so one must take into account many factors when seeking to improve the shift rota or schedule. Different schedules have different factors working for and against them. For weekly rotation we have in favour of it; that the work schedule is predictable and that the misery is shared. But there is a lot working against it: The biological clock never adjusts; as shown in Figure 5, the process of adjustment is very slow. Although the biological clock aspects get better over time, there is a sleep debt being built up (Tilley et al, 1982). There is sleepiness at work because of the inappropriate circadian rhythm and there is very often continuous jet lag with the circadian system never fully adapting to any of the schedules worked. For permanent, or fixed night shifts, evidence fur them is that there is time for the circadian rhythm, at least in theory, to achieve a nocturnal orientation. Work and sleep times are predictable, and there is ability for the worker to make a commitment to a nocturnal way of life, and workers can arrange their life around a nocturnal working schedule (Folkard, et al, 1978; Alward and Monk, 1990; Barton, 1994). Working against fixed night shifts, as mentioned above, there is daylight and a diurnal society, both of which will conflict very much with this nocturnal orientation. Regression to a day-orientation on weekend breaks is very easy (Van Loon, 1968; Monk, 1986), and there is also a potential for a buildup of sleep debt which then has to be dissipated over the weekend break. The other option is rapid rotation where all three shift timings are worked within a given week. In favour of rapid rotation is that there are no residual jet-lag effects; essentially, the biological clock does not go anywhere. Misery is shared among the work force. Rapid rotation is particularly good when the task is arousing because the individuals can keep their alertness up, and there are only a few bad day-sleeps in a row. Working against rapid rotation, though, is that the work schedule is less easily predictable which many workers take a while to get used to. There is excessive sleepiness on the night shift which can be a problem if the task is a monotonous, sleep-inducing one, and there is less incentive to make a commitment to a nocturnal lifestyle. Finally, one has the ability to improve the workplace. Some of these improvements are obvious: the provision of canteen facilities, and the making of a pleasant, stimulating environment. Bright light is a

on shiftwork: T. H. Monk et al

manipulation that can perhaps more quickly reset the biological clock and certainly bright lights can improve alertness during the night shift (Czeisler et al, 1990). In both a laboratory study, and in an enclosed workplace (astronaut crew quarters), Czeisler et al (1990; 1991) have shown that extremely bright levels of illumination for the duration of the night shift can work quite well, especially when combined with complete darkness in bedrooms, and strict adherence to daytime bedtimes. However, the cost of such manipulations can be enormous, and for many applications (e.g. truck drivers) they are simply infeasible.

Conclusion:

A conceptual

model

We will finish with a recent model (Figure 9, taken from Folkard, 1993). This model illustrates all of the various interacting factors affecting the on-shift performance of the night- and shiftworker, and thus his or her safety and ability to perform well. The ‘take home’ message is that shiftwork is not a simple problem and thus it does not have a simple, single solution. We have to look at many different facets of the work situation, the individuals who are taking part in that work and the task that they are being asked to do before we can make conclusions about how we can make the shiftwork environment safe and productive. 1

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SAFETY & EFFICIENCY

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ance by Folkard (1993)

1

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perform-

Maintaining safety and high performance

on shiftwork: T. H. Monk et al

Acknowledgements Financial support of NASA contract NAS-9-18404 and NIMH grant MH-01235 is acknowledged (T.H.M.) as is that of the British Medical Research Council(S.F.).

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Kugl, K. 1985 ‘Introduction to the problems of shift work’ in Folkard, S. and Monk, T.H. (eds) Hours of Work - Temporal Factors in Work Scheduling John Wiley, New York, pp 165184 Landy, F. 1989 The Psychology of Work Behaviour, Brooks/Cole, Pacific Grove Lauber, J.K. and Kayten, P.J. 1988 ‘Keynote address: sleepiness, circadian dysrhythmia, and fatigue in transportation system accidents’ Sleep 11, 503-5 12 Lavie, P. 1991 ‘The 24-hour sleep propensity function (SPF): practical and theoretical implications’ in Monk, T.H. (ed) Sleep, Sleepiness and Performance John Wiley, Chichester, pp 65-93 Mitler, M.M., Carskadon, M.A., Czeisler, C.A., Dement, W.C., Dinges, D.F. and Graeber, R.C. 1988 ‘Catastrophes, sleep and public policy: Consensus report’ Sleep 11 (l), 100-109 Monk, T.H. 1986 ‘Advantages and disadvantages of rapidly rotating shift schedules - A circadian viewpoint’ Human Factors 28, 553557 Monk, T.H. 1988 ‘Coping with the stress of shift work’ Work and Stress 2, 169-172 Monk, T.H., Knautb, P., Folkard, S. and Rutenfranz, J. 1978 ‘Memory based performance measures in studies of shiftwork’ Ergonomics 21, 819-826 Monk, T.H. and Wagner, J.A. 1989 ‘Social factors can outweigh biological ones in determining night shift safety’ Human Factors 31,121-724 Richardson, G.S., Miner, J.D. and Czeisler, C.A. 1990 ‘Impaired driving performance in shiftworkers: the role of the circadian system in a multifactorial model’ Alcohol, Drugs and Driving 5 (4) & 6 (1) 265-273 Tepas, D.I. and Monk, T.H. 1987 ‘Work schedules’ in Salvendy, G. (ed) Handbook of Human Factors, John Wiley, New York, pp 819-843 Tilley, A.J., Wilkinson, R.T., Warren, P.&G., Watson, B. and Drud, M. 1982 ‘The sleep and performance of shift workers’ Human Factors 24, 629-641 Van Leon, J.H. 1963 ‘Diurnal body temperature curves in shift workers’ Ergonomics 6, 267-272