Industrial shift systems

PII:S0003—6870(97)00059-8

Applied Ergonomics Vol. 29, No. 4, pp. 273—280, 1998 ( 1998 Elsevier Science Ltd All rights reserved. Printed in Great Britain 0003—6870/98 $19.00#0.00

Technical Report

Industrial shift systems Lawrence Smith,1 ,* Ian Macdonald,2 Simon Folkard 2 and Philip Tucker 2 1School of Psychology, ºniversity of ¸eeds, ¸eeds ¸S2 9J¹, ºK 2MRC Body Rhythms and Shiftwork Centre, Department of Psychology, ºniversity College of ¼ales Swansea, Singleton Park, Swansea, SA2 8PP, ºK (Received 13 October 1995; in revised form 13 August 1997)

This technical report describes the identification of shift systems worked by industrial shiftworkers in England, Scotland and Wales. A diverse range of shift systems were reported to be in operation across 27 industrial sectors. Companies employed up to 14 different shift systems at a particular site. The numbers of shiftworkers on a given shift schedule ranged from 1 to 2977. Most systems employed fewer than 100 people. The majority of rotas were regular, rotating systems. The most common shift durations were 8 or 12 h. Compared to earlier surveys of shiftwork prevalence in certain industries there appeared to be a substantial increase over the past 3 decades in the proportion of the workforce who work shifts. Information about the average numbers of hours worked per week on major system types is given. In addition, data for the range of shifts per cycle, the distribution of shifts and distributions of their start and end times are presented. ( 1998 Elsevier Science Ltd. All rights reserved.

Introduction

probably many thousands of rotating or permanent shift systems in operation all over the world (Knauth, 1993). Rotating systems may be subdivided into those with or without night work and systems with or without work on Sundays. There are also many other features that characterise a shift schedule. For example, the length of shifts, direction and speed of rotation, distribution and number of rest days or number of consecutive shifts. Permanent shifts may be organised as permanent days, afternoons, evenings or nights. Although there are recommendations for what may be termed least detrimental shift systems it is probably true to say that there is no single optimal system that is universally applicable across industrial settings and the huge diversity of task demands within and across these enterprises (Knauth, 1996). There have been a number of enquiries into the extent of shiftworking in industry since 1954. Two (1954 and 1964) were carried out by the then Ministry of Labour (now the Department for Education and Employment). A third was carried out in 1968 and was based on the New Earnings Survey conducted by the National Board for Prices and Incomes. Lastly, in 1978 the European Foundation for the Improvement of Living and Working Conditions compiled a report on the spread of shiftwork in the European Community. One section of this report focused on a number of areas including: the prevalence of shiftwork in the UK; the types of industries involved; the numbers of shiftworkers; the types of shift systems used; facilities available for shiftworkers and changes

In modern industrialised societies numerous and diverse shift systems are operated across a broad spectrum of industries in order to provide 24 h power, services and products, to maximise the useful life of expensive technologies and to increase profitability. Whatever the economic argument for shiftworking, this form of work scheduling can result in a range of difficulties. The problems associated with shiftwork are well documented (e.g. Monk and Folkard, 1985; Scott and Ladou, 1990) and fall into three main areas. Firstly, biological disruption to physiological processes, including the sleep-wake cycle (Tepas and Mahan, 1989; Akerstedt, 1990). Secondly, the impairment of physical health and psychological wellbeing (Bohle and Tilley, 1989; Waterhouse et al 1992), and thirdly, the disruption of social and domestic life (Walker, 1985; Volger et al. 1988). Today, we know roughly the proportion of national workforces exposed to some form of shiftwork. For example, around 20% of workforces in manufacturing and service sectors in the European Community work some form of shift system or non-standard work schedule (BEST, Issue No. 6, 1993; Statistics and News). There are

* Author to whom correspondence should be addressed. 273

¹echnical Report

274

over time through comparison with the studies mentioned above. The 1978 survey identified that the majority of shiftworkers (close to 1.5 millions) employed in 874 establishments were manual workers. In terms of global categories of shift system it was reported that 12% of shiftworkers were on continuous systems (24 h/d, 7 d/week); 35% worked discontinuous or semi-continuous systems (usually with weekend breaks in production). Both types included 8 and 12 h shift systems. A large proportion (47%) worked on systems on which there was no cover or production stopped for some period during the 24 h and 6% worked evening (twilight) shifts. More recently, there has been little published information on major industrial shift systems that are in operation in England and Wales. The aim of this study was to categorise industrial shift rotas according to specific system features that may impact upon the health and safety of those individuals having to work them.

Method

Two hundred and thirty three companies were surveyed. The UK Health and Safety Executive (HSE) had identified these industrial companies as operating some form of shift system at their production sites. The companies were involved in a range of manufacturing operations and were spread throughout England, Scotland and Wales. Health and Safety, or Personnel Services Managers at these companies were sent letters explaining the background and objectives of the research programme as part of a HSE-commissioned project and were invited to participate by providing details of the shift system(s) in operation at the site using the Shift System Questionnaire. Within the scope of the research objectives and time frame, the identified companies were representative of the broad range of manufacturing industries in the UK (see ¹able 1). Clearly, this did not represent a random sample (those participating were self-selected), however, even with this cautionary note, the results do give a good indication of the types of shift systems in operation around the country.

Results

Shift system questionnaire The questionnaire used was based on one devised and used successfully by Barton et al (1993) for a study of Health Service shift systems. It was designed to provide information about the type of industry, the total number of workers at the site, the numbers employed on some form of shiftwork and details of the shift systems in operation (a copy of this questionnaire can be obtained from the authors). These details included information on the timing of shifts, duration, speed and direction of rotation, and temporal patterning of shifts and rest days.

3.1. Response to shift system questionnaire Shift system details were obtained from 73 companies (31.3% of those approached). A large number of companies did not reply, even after reminder letters, and many companies were unable to participate because of ongoing organisational changes or industrial relations negotiations. These respondents were spread nationwide and represented 27 sectors of manufacturing industry. ¹able 1 details the range of industries, the number of workers per industrial sector, the numbers of shift

Table 1 General information on industries, number employed and number of shift systems involved Industrial Sector Aircraft engineering Airline services Aluminium Auto. parts manufacturing Building and engineering Cable manufacturing Cement Chemicals Docks Engineering Food Gas Glass fibre Glass Heavy electrical Oil refining Paper Paper and board Parcel distribution Petro-chemicals Plastics Power generation Printing Refractory materials Rubber Semi-conductors Steel

Number of companies

Total number of shift systems

Number of different Workforce in each shift systems used sector

Total number of shift workers

Range of shift workers on systems

1

2

2

200

200

40—160

2 2 1

8 11 7

7 8 6

8418 1179 407

2536 930 203

19—1500 1—278 5—93

1

2

2

212

212

65—147

3 2 7 1 9 12 3 1 4 1 3 3 2 1 1 2 2 1 1 2 2 1

26 9 21 3 48 45 4 4 17 5 3 10 7 1 2 7 10 10 1 10 17 7

13 7 10 2 15 14 3 2 10 3 2 6 6 1 2 5 5 8 1 7 10 4

1602 381 3010 347 15,732 6558 382 379 1216 850 968 1239 452 240 505 440 8608 491 233 491 867 4041

1263 336 1793 290 8679 3959 93 379 933 148 544 952 198 224 324 424 2489 439 144 346 528 4031

2—251 3—80 2—600 53—181 1—2977 2—450 6—48 12—137 3—219 12—100 8—267 10—468 2—84 224 12—312 2—234 5—2200 1—225 144 2—114 1—274 202—1256

¹echnical Report

systems in operation, and the total numbers and ranges of shiftworkers involved. The total number of workers employed across all sites was 59,448 (ranging from 56 to 12,458 per site). The total number of shiftworkers was 32,394 (range "1!2977 per system) which was 54.5% of the workforce represented. Most shift systems (approximately 74%) employed fewer than 100 shiftworkers. Indeed, it was striking that 82 systems (27.5%) employed 10 or fewer shiftworkers while 50% of the systems employed 30 or fewer shiftworkers. Approximately 26% of the systems had 100 or more shiftworkers working them. Another notable feature is the large number of shift systems that may be employed by a single company. For example, the Aluminium manufacturers were represented by two companies (at two sites); these companies used a total of 11 shift rotas (eight of which differed from one another) to provide operational cover. The three cable manufacturing companies that provided information employed 26 systems in all, 13 of which were different. Earlier we mentioned that previous studies had examined the extent of shiftwork in industry. Like the present Table 2 Comparison of proportions of shiftworkers in selected industries Shiftworkers as % of workforce sampled Industry

1954

1964

1978

1994

Chemicals Metal manufacture Engineering Food Cement/bricks/pottery Paper

24 42 6 13 17 14

29 44 11 19 23 24

39 44 36 32 23 32

60 95 56 60 88 68

Table 3 General system details System type

Proportion of Range of shift total number of durations (h) systems (%)

Rotating 2-shift and 3-shift systems Rotating 12 h systems Permanent morning shifts Permanent afternoon shifts Permanent evening shifts Permanent night shifts 12 h days 12 h nights Permanent weekends Permanent days

39.6

8h

13.1 6.6 4.0 2.3 11.4 2.2 1.3 2.2 17.3

12 h 4—8 h mode"8 h 4—9 h mode"8 h 4—10 h mode"4 h 4—11 h mode"8 h 12 h 12 h 12 h 6—11 h mode"8 h

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study, these studies targeted companies that employed shiftworkers and provided information on the proportion of the workforce in given manufacturing industries that worked some form of shift system. As a point of comparison ¹able 2 shows these figures as well as those for the percentages of shiftworkers in similar industrial categories for the present study. Similar to this study, previous inquiries into shiftworking in industry focused on those sectors in which shiftwork was known to occur. Thus, assuming that the information provided for this study was fairly representative it appears that the proportion of shiftworkers in the workforces of these industries shows a substantial increase to the present day. With the rationalisation of manufacturing industry that has occurred in recent years this increase is probably a result of a combination of a loss of standard day work jobs and a move towards shiftworking. 3.2. Range of shift systems and system details In total 298 shift systems were reported (range 1—14 systems/company). 103 (34.5%) systems provided continuous cover over 7 d. In contrast, 195 (65.5%) of the systems were discontinuous (with a break in production at some time during the week; usually at weekends). The majority (221; 74.2%) of the systems had regularly repeating cycles, i.e. the same sequencing of shifts and rest days was worked over successive cycles of the rota. In 245 (82.2%) of the systems work hours were covered by equal numbers of each type of shift on each cycle (e.g. 5 d, 5 afternoons and 5 nights distributed over the cycle). The general breakdown of system types and shift durations is shown in ¹able 3. There is little variation in shift durations. That is, these industrial shift systems tended to employ either 8 h or 12 h shifts. ¹able 4 provides system details in terms of the numbers of systems containing shifts of a particular kind, the range of these shifts per cycle, the range of blocks of these shifts per cycle, the range of blocks of rest days per cycle and the start/end time boundaries of the majority of shifts. The shift cycle here refers to that drawn out on the shift system survey form by the respondents. Later we use 28 d as a convenient period with which to compare the distributions of work-shifts and rest days in 8 h and 12 h systems. 3.3. Distribution of shift start and end times There was some variation in the distributions of the start and end times of the major shift types but by and large the majority of shifts started and ended within fairly

Table 4 Details for all systems Shift type

Numbers of systems containing given shifts

Range of shift per cycle

Range of blocks of shifts per cycle

Start time boundaries of shifts

% of systems with these start times

End time boundaries of shifts

% of systems with these end times

Morning Afternoon Night Evening 12 h day 12 h night Perm. days Rest days

137 125 105 8 55 54 76 298

1—44 5—30 1—28 5—7 2—32 2—28 1—38 1—64

1—15 1—9 1—9 1—3 1—14 1—12 1—8 1—17

0600—0730 1300—1500 2100—2300 1600—1800 0600—0800 1800—2000 0600—0900

(90.4) (90.4) (91.4) (87.5) (98.2) (94.4) (97.4)

1300—1500 2100—2300 0600—0730 2200—2400 1800—2000 0600—0800 1500—1730

(95.6) (86.8) (89.5) (87.5) (98.2) (96.3) (90.8)

276

¹echnical Report

standard boundaries. Figures 1 and 2 show the distributions of start and end times for all systems that include morning, afternoon or night shifts, i.e. predominantly 8 h shift systems (excluding 12 h systems, permanent day schedules and permanent evening schedules). The majority of morning shifts started and night shifts ended between 0600 and 0700. Similarly, most morning shifts ended and afternoon shifts started between 1400 and 1500. Lastly, the bulk of the afternoon shifts ended and night shifts started between 2200 and 2300. The start and end times of the 12 h systems also demonstrated a general consistency. Figure 3 shows the distribution of start and end times for 12 h day and night shifts (including permanent 12 h day or night shifts). The day and night shift distributions are not equal as might be expected. This is because diferent numbers of permanent 12 h day and 12 h night shifts were reported.

The majority of 12 h systems’ day shifts started and night shifts ended between 0600 and 0800. The 12 h morning shifts ended and night shifts started between 1800 and 2000. A number of permanent evening shift rotas were also reported. The distribution of their start and end times is shown in Figure 4. The majority (87.5%) of evening shifts started between 1600 and 1800 inclusive, and ended between 2200 and 2400. Figure 5 gives the distribution of start and end times for the permanent day schedules reported. As might be expected most start times fell between 0700 and 0900 whereas work period end times tended to fall between 1500 and 1800. Finally, the average numbers of hours worked per week for the major system categories is presented in ¹able 5. In concordance with the diversity of systems identified, there is also great variation in the numbers of hours worked each week on particular systems.

Figure 1 Distribution of start times for systems with morning, afternoon and night shifts

Figure 2 Distribution of end times for systems with morning, afternoon and night shifts

¹echnical Report

Figure 3 Distribution of 12 h shift system start and end times

Figure 4 Distribution of start and end times for permanent evening shifts

Figure 5 Distribution of start and end times for permanent day schedules

277

¹echnical Report

278

3.4. Distribution of work-shifts and rest days in 8 h and 12 h systems per 28 d The majority of systems operated either 8 h or 12 h shifts (¹able 2). This enables a reasonable grouping of systems. The figures below provide details of the distributions of work-shifts and rest days in both 8 h and 12 h shift Table 5 Average hours worked per week on major categories of systems System category

Average number Range of h/week

Rotating 8 h systems Rotating 12 h systems Permanent morning shifts Permanent afternoon shifts Permanent evening shifts Permanent night shifts 12 h days 12 h nights Permanent weekends Permanent days All systems

38.96 42.03 36.79 36.89 29.14 39.87 44.50 39.00 19.78 41.17 39.03

24.17—51.00 h/week 28.00—60.00 h/week 20.00—42.50 h/week 20.00—42.50 h/week 19.50—47.50 h/week 17.50—60.00 h/week 36.00—71.50 h/week 36.00—42.00 h/week 05.00—28.25 h/week 33.78—48.85 h/week 05.00—71.50 h/week

systems. The period of 28 d gives a standard time-span to enable comparison between the global categories (cf. Knauth et al 1983). Figure 6 shows the distributions of total numbers of work-shifts per 28 d for both system types. The mode for all 8 h systems was 20/28 while that for all 12 h systems was 16/28 which implies greater numbers of work hours for those on 12 h systems (192 h) compared to those on 8 h systems (160 h). However, it is worth noting that if the average hours for rotating 8 h and 12 h systems are examined the above discrepancy is not so stark (i.e. just over 155 h/28 d on rotating 8 h systems and 168 h/28 d for rotating 12 h systems). Approximately half of the 12 h systems had 15 or fewer workshifts per 28 d period compared to a tiny minority of 8 h systems (about 3%). The number of successive work-shifts before a rest day has implications for the degree of build up of work fatigue. The distributions of maximum numbers of successive work-shifts before a rest day are shown in Figure 7. A block of 5 successive work periods (40 h) is commonest for 8 h systems compared to blocks of 4 successive shifts (48 h) in 12 h systems. On continuous

Figure 6 Distribution of total number of work-shifts per 28 d in 8 h and 12 h shift systems

Figure 7 Distribution of largest blocks of successive work-shifts before a rest day per 28 d in 8 h and 12 h shift systems

¹echnical Report

3]8 shift systems blocks of 7 successive shifts are also fairly frequent (Figure 7). Nearly a third of successive shifts in 12 h systems are arranged into blocks of 2 or 3. Figure 8 illustrates the distribution of maximum numbers of rest days per 28 d. A rest day is defined as a period in excess of 24 h during which no work takes place. A greater proportion of 12 h systems have 12 or more rest days per 28 d. One reason for this is the need to compensate for extra fatigue induced by longer work periods. Eight rest days in 28 is the mode for 8 h systems. This reflects the tendency for there to be two successive rest days per week (commonly at the weekend on discontinuous 3]8 systems). Figure 9 shows this tendency. For 12 h systems the commonest organisation of rest days is 4 successive days usually following four 12 h periods in work.

4. Discussion The aim of this technical report was to present information about some of the major shift systems in operation in

279

British industry. The study focused on companies that used some form of shiftwork. A diverse range of systems spanning many industrial sectors were identified. While not exhaustive, this diversity is wholly consistent with the contentions of other shiftwork researchers who have noted that there are many thousands of shift systems in use worldwide (e.g. Knauth, 1996). The systems identified were generally regular in nature in terms of the sequencing of shifts, their timing and their durations. The night shift is commonly reported to be the most problemmatic for shiftworkers, therefore, how night cover is organised is an important health and safety issue. A sizable proportion of permanent night shifts were reported in this study, however, it was clear that the industries surveyed tended to favour the use of night shifts within some form of rotating system. In a review of the area, Wilkinson (1992) concluded that sleep, health and performance on permanent and slowly rotating (long spans of successive nights) night shifts are probably marginally better than on rapidly rotating systems because of

Figure 8 Distribution of total number of rest days per 28 d in 8 h and 12 h shift systems

Figure 9 Distribution of largest blocks of successive rest days per 28 d in 8 h and 12 h shift systems

280

¹echnical Report

acceptable levels of adjustment of shiftworkers’ body clocks. However, Folkard (1988), for example, has argued that the degree to which individuals adjust their body clocks to night work may be over-estimated. While not denying that some people may adjust well to a night-time activity routine, it is highly likely that most individuals do not do so. A large proportion of the systems identified in this study were 12 h systems. There has been considerable debate in the shiftwork literature with respect to the pros and cons of operating 12 h systems and their potential effects on the individuals having to work (e.g. Rosa et al, 1986). A major advantage of 12 h systems is that they compress the work week and free up more highly valued time off for family or leisure pursuits. Twelve-hour shifts, on the other hand, may be inherently more fatiguing for the individual who has to sustain alertness and appropriately allocate resources to their job for 50% longer than a traditional 8 h shift. Over the night shift this may have serious implications for personal and public safety. Knauth (1993, 1996) suggested that such extended workdays should only be contemplated if the nature of the work and workload are appropriate; the system is designed to minimize fatigue; overtime is restricted; toxic exposure is limited; that there is adequate post-work recovery and that there is high acceptance of the schedule by the workforce. The differences between the 8 h and 12 h systems can be summarised as follows. The majority of 3]8 systems had shift start times as follows: Morning/Early shift 0600—0700; Afternoon/Late/Evening Shift 1400 —1500 and Night shift 2200—2300. In comparison there was a broader range of start times on 12 h systems: Day shifts 0600—0800 and Night shifts 1800—2000. The systems differed in the average number of hours worked per week and thereby per 28 d. Rotating 8 h systems averaged 155.84 h/28 d compared to an average of 168.12 h on 12 h systems. On 8 h systems the mode was 5 work-shifts before a rest day compared to a mode of 4 successive work-shifts on 12 h systems, i.e. 12 h systems tend to have shorter runs of successive shifts. A block of 7 successive shifts was not uncommon on 8 h schedules while the next most common configuration on 12 h systems were blocks of 3 shifts in a row. The majority of 8 h systems had 7 or 8 rest days per 28 d arranged, by and large, in blocks of 2 or 3 successive days off. In comparison, the majority of 12 h systems contained 12 to 14 rest days organised mainly as blocks of 3 or 4 successive days off. A fair number of 12 h systems also had between 15 and 20 rest days rostered. To conclude, two issues that warrant further investigation are highligted. The first concerns flexibility of working hours. In this study rotas tended to be fixed and organised well in advance of being worked. This situation is very different from the rostering arrangements found within the Health Service. Barton et al (1993) found that 82% of systems in a study of Health Service shift systems were irregular. Most of these irregular systems were also flexible in that they offered shiftworkers the opportunity to influence their roster and thereby the timing of their work. In theory, flexibility should allow a better fit between work-time and home life requirements (Smith and Barton, 1994). The regularity and inflexibility of industrial systems reflect a traditional approach to work scheduling and while they offer control in terms of predictability, shiftworkers are impelled to structure their lives around their work roster far more rigidly. Thus, the

potential for conflict between work and home life may be accentuated. The second issue is that surrounding the increased use of 12 h shifts. Despite the apparent advantages of a compressed work week on 12 h systems, these shiftworkers tended to work longer hours per 28 d than their 8 h system peers. While the long-term impact of 12 h shifts remains to be systematically examined, on the basis of this observation the introduction of these rotas should be carefully considered from a health and safety perspective.

Acknowledgement The authors gratefully acknowledge the support of the Health and Safety Executive for this study. In particular, our thanks go to Chris Kelly for his interest and guidance throughout.

References Akerstedt, T. (1990) Psychological and psychophysiological effects of shiftwork. Scandinavian Journal of ¼ork and Environmental Health. 16, 67—73 Barton, J., Smith, L., Spelten, E., Totterdell, P. and Folkard, S. (1993) Does individual choice determine shift system acceptability? Ergonomics, 36(1—3), 93—100 Barton, J., Spelten, E., Smith, L., Totterdell, P. and Folkard, S. (1993) A classification of nursing and midwifery shift systems. International Journal of Nursing Studies 30(1), 65—80 Bohle, P. and Tilley, A.J. (1989) The impact of nightwork on psychological well-being. Ergonomics 32, 1089—1099 B.E.S.T. (1993) Bulletin of European Studies on Time No. 6, Statistics and News. European Foundation for the Improvement of Living and Working Conditons. Loughlinstown House, Shankill, Dublin, Ireland Folkard, S. (1988) Circadian rhythms and shiftwork: Adjustment or masking? Advances in the biosciences 73, 173—182 Folkard, S. and Monk, T. (1985) Hours of ¼ork: ¹emporal Factors in ¼ork Scheduling. Wiley, Chichester Knauth, P. (1993) The design of shift systems. Applied Ergonomics, 36(1—3), 15—28 Knauth, P. (1996) Designing border shift systems. Applied Ergonomics, 27(1), 39—44 Minors, D. and Waterhouse, J. (1985) Introduction to circadian rhythms in Folkard, S., and Monk, T. (eds) Hours of ¼ork: ¹emporal Factors in ¼ork Scheduling. Wiley, Chichester Rosa, R., Colligan, M. and Lewis, P. (1986) Extended workdays: effects of 8 h and 12 h rotating shift schedules on test performance, subjective alertness, sleep patterns and psychosocial variables in Proceedings of the Human Factors Society 30th Annual Meeting. Human Factors Society, Santa Monica, CA, pp. 882—884 Scott, A.J. and Ladou, J. (1990) Shiftwork: effects on sleep and health with recommendations for medical surveillance and screening in Scott, A.J., (ed) Occupational Medicine: State of the art reviews — Shiftwork Vol 5, No. 2. Hanley and Belfus, Philadelphia Shade, P. (1988) Flexible friend. Nursing ¹imes 84(44) 32—34 Smith, L. and Barton, J. (1995) Shiftwork and personal control. European ¼ork and Organisational Psychologist 4(2), 101—120 Tepas, D.I. and Mahan, R.P. (1989) The many meanings of sleep. ¼ork and Stress. 3(1), 93—102 Verhaegen, P., Cober, R., De Smedt, M., Dirkx, J., Kerstens, J., Ryvers, D. and Van Daele, P. (1987) The adaptation of night nurses to different work schedules. Ergonomics 30(9), 1301—1309 Volger, A., Ernst, G., Nachreiner, F. and Hanecke, K. (1988) Common free time of family members under different shift systems. Applied Ergonomics 19(3), 213—218 Walker, J. (1985) Social problems of shiftwork. in Folkard, S., and Monk, T. (eds) Hours of ¼ork: ¹emporal Factors in ¼ork Scheduling. Wiley, Chichester Waterhouse, J., Folkard, S. and Minors, D. (1992) Shiftwork, health and safety: an overview of the scientific literature 1978—1990. HMSO, London Wilkinson, R.T. (1992) How fast should the night shift rotate? Ergonomics. 35, 1425—1446