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8.7 Ergonomics and public health

8.7 Ergonomics and public health*
Oxford Textbook of Public Health

8.7
Ergonomics and public health*

Laura Punnett

Overview

Definition

Brief history

The ‘human–machine’ system

Ergonomics as an applied interdisciplinary field

The future of ergonomics
Relevant human characteristics

Anthropometry

Physical working capacity

Sensory perception

Cognitive capacity
Relevant work environment characteristics

Workstation and equipment design

Standing work

Seated work

Repetitive work and rest pauses

Manual handling

Presentation and communication of information

Physical environment

Work scheduling

Organizational design and management

Cost-effectiveness of ergonomic measures in the workplace
Ergonomics and public health

Musculoskeletal disorders

Acute traumatic injuries in the workplace

Cardiovascular and other work-related diseases

Ergonomic applications in transportation systems

Consumer product design

Design for the elderly and for people with physical or mental disability

Public health implications of complex technological environments: two case studies
Ergonomics in developing countries
Implementing change

Legislation, standards, and guidelines

Training

Participatory approaches
Conclusion
Chapter References

Overview
Definition
Ergonomics is the area of scientific research and application concerned with the design of engineered systems and environments to be compatible with human capacities and limitations. According to the International Ergonomics Association, the field ‘integrates knowledge derived from the human sciences to match jobs, systems, products and environments to the physical and mental abilities and limitations of people’. Clark and Corlett (1984) wrote that ‘ergonomics is the study of human abilities and characteristics which affect the design of equipment, systems and jobs and its aims are to improve efficiency, safety and well-being’.
Tools and systems that are badly designed, or not designed at all, often lead to fatigue, discomfort, injury, or chronic health disorders for the users. A system or device designed according to ergonomic principles should be easier to use, result in less fatigue and ill health, generate fewer errors, be more satisfying to the user, and improve work quality and productivity.
Brief history
Some of the health consequences of poor ergonomic design have been recognized for nearly three centuries, since the work of Ramazzini (1713). In modern times, the professional field was defined in 1949 with the establishment of the Ergonomics Society in the United Kingdom (Murrell 1965). Ergonomics research had begun as early as 1915 in this country with the establishment of the Industrial Fatigue Research Board. Human fatigue was to be prevented through proper allocation of breaks and suitable working hours, and thereby improved efficiency of production would be achieved. During the First World War, the productivity of the British ammunition factories was shown to increase in parallel with a reduction of weekly working hours (Vernon 1921).
Thus the first applications of ergonomics were in the defence industry, in both the United Kingdom and the United States. One important impetus to further development was the nature of the problems encountered during the Second World War with technological change, such as the introduction of new weapons. These new systems were found to perform poorly because of a mismatch between humans and technology. Previous attempts had been made to fit humans to new technology by means of training and information, but neither one could be used to their full capacity with this approach. When knowledge of human capabilities was employed in system design, efficiency and accuracy were vastly improved.
From productivity and safety in military systems, the focus of research and applications in ergonomics has broadened considerably over the years. After the Second World War, the concepts of ergonomics were applied to manufacturing and physically strenuous jobs in other sectors, such as mining and forestry. High aerobic demands and heavy manual handling characterized these jobs, and problems with general fatigue, accidents, and low back pain were widespread.
In modern manufacturing, many such tasks have been mechanized; work reorganization and the use of new technology have reduced aerobic demands in traditionally ‘heavy work’. However, these changes have also resulted in increased prevalence of static body positions and repetitive movements, with an accompanying pattern of musculoskeletal problems affecting the neck, shoulder, arm, and hand. Similar problems are encountered in the office environment, especially among people performing data entry work (Punnett and Bergqvist 1997). A substantial minority of the working population still perform physically strenuous jobs, even in developed countries, especially in mining, agriculture, transportation, and construction, and so-called service jobs in health care, food preparation, and cleaning. While the first four sectors are typically male dominated and recognized as hazardous, many employees in the latter jobs are women whose work is perceived as clean and safe, even when it requires a large proportion of their physical capacity.
Since the 1970s, issues such as human–computer interaction and health consequences of poor ergonomics, especially in the occupational setting, have grown in importance. Much more attention is given now than previously to work organization issues (‘macro-ergonomics’) and prevention of technological system failure, as well as techniques for implementing ergonomic improvements through worker participatory processes.
Geographically, there are some substantial differences in focus within the field. Many American practitioners have a background in engineering rather than in health sciences. The psychological aspects of ergonomics, especially cognitive and sensory perception issues, which are often referred to as ‘human factors’, dominated research in the United States for many years. Manufacturing systems and consumer issues have received much attention in research from the United Kingdom and Japan. Work physiology has dominated research in the rest of Europe, especially in the Nordic countries, while Francophone ergonomists emphasize the worker’s integrated, subjective experience. These varying emphases reflect differences in scientific traditions, industrial structures, and types of legislation related to occupational injuries.
The advantages of good ergonomics can now be seen in occupational settings, public life, and homes. Reduction of heavy lifting and handling of objects through lifting devices, the introduction of ergonomically designed office furniture and computer keyboards and pointing devices, and the improved design of transportation systems are examples that bear witness to these advances. Much remains to be done, however, to ensure safe, healthy, and productive workplaces, homes, and public spaces.
The ‘human–machine’ system
In the field of ergonomics, the interaction of the person with the environment has often been conceptualized as the ‘human–machine system’ (Fig. 1). In this system, the ‘machine’ presents information to the person, often via one or more displays, the information is perceived by the operator’s sensory apparatus (through vision or hearing), and the operator uses his or her cognitive capacity and memory to decide on a suitable response, which is transferred to the ‘machine’ as a motor activity such as pushing buttons or handling objects. The machine’s response involves additional information to the operator, and so on.

Fig. 1 The human–machine–environment system.

Although the first applications were aimed at machines and other technical equipment, in reality humans interact not only with devices but also with the physical and social environment, including with other humans. Now the term most often used is ‘human–machine–environment system’, and generally with a broader definition. The human operator may interact not only with a machine but also or instead with another human being, who feeds his or her response back via speech, signs (sign interpretation), or touch; alternatively, there may be other responses or inputs from society via road traffic signs, books, or other means. The operator’s response can then be via another form of motor activity, such as talking, writing, steering a car, or typing on a keyboard.
One important feature of the human–machine concept is that humans do not perform their actions in isolation, but as part of a system that is in dynamic equilibrium. The aim of the system is to perform efficiently and without mishap, which requires an optimization of the interface between the person and the ‘machine’ (now a metaphor for any other component of the system). Thus feedback or information must be presented in a way that can be perceived easily and without mistakes, and physical controls must be designed to comply with the person’s strength, body dimensions, and natural range of motion. The environment should be conducive to task performance, with attention to temperature, background noise, and psychosocial conditions. Efficiency also implies an optimal allocation of tasks between humans and ‘machines’, so that each component of the system performs the task for which he, she, or it is best suited (Chapanis 1965; Oborne et al. 1993; Mital et al. 1994). For example, humans are usually superior to machines in recognition of subtle patterns, decision-making requiring experience, and creativity, while machines are often superior in activities that require both precision and endurance, and/or high repeatability.
This system has traditionally been presented as a closed loop, where deviations from the desired ‘state’ of the system are corrected. Humans or operators were seen as elements of the system whose task is to respond to the feedback from the ‘machine’. The quality of the response depends on their individual physiological, anatomical, sensory, and cognitive capacity. In a complex system with high demands on safety, like a nuclear power plant or chemical processing industry, it is crucial that the operator does not deviate from the desired response to an anticipated situation. Nevertheless, in modern ergonomics it is acknowledged that the individual has a more central role. This ‘person-centred’ philosophy sees the operator as the one who initiates action, and controls and dominates the system. The human being contributes an ability to anticipate and predict what may happen within the system (Oborne et al. 1993), as well as his or her own concepts of the purpose of the system, which may build upon and improve the original design goals (Karasek and Theorell 1990). Training of the power-plant or chemical process operator need not only teach automatic responses to a variety of ‘standard’ situations but instead may seek to enhance critical thinking and problem-solving skills, while design of the process displays and controls should take account of the operators’ knowledge, expectations, and needed information.
Ergonomics as an applied interdisciplinary field
One important characteristic of ergonomics is that it is both a scientific area of research and a practical area of application. Another is that ergonomics is multidisciplinary and requires knowledge in three main areas: (a) anatomy and physiology, (b) psychology, and (c) technology. Although it is impossible to have extensive knowledge in all of these fields, the ergonomist must be able to integrate knowledge from areas other than that of his or her own basic training. In large ergonomic problem-solving projects, a teamwork approach, with representatives of several disciplines with a common ergonomics perspective, is often most successful.
In research, some basic questions have to be tackled separately by psychologists, physiologists, and engineers. However, most ergonomic research is applied to field settings, whether for occupational or consumer problems, and therefore requires a truly multidisciplinary approach. Dialogue among the disciplines is essential to establish common frames of reference. Joint training in ergonomics, where students with varying backgrounds can meet, develop a common outlook, and learn to appreciate the contributions of each other, is key to strengthening multidisciplinary research and problem-solving skills.
The future of ergonomics
In a short period of time, ergonomics has grown to become an important area of scientific research and practical applications. This is especially true for working life, but special ergonomic applications for consumers, for people with physical or mental disabilities and older people, for leisure and sports, and for developing countries are also emerging. Thus ergonomics, through its effects on health, safety, and well being, has a large impact on public health.
The International Ergonomics Association, which was formed by a number of national societies, has issued minimum requirements for training and practical experience in ergonomics, to be fulfilled by those researchers, consultants, and others who wish to be approved as European Ergonomists. Similar requirements have been developed for the United Kingdom, the United States, and Australia. Professional qualifications like these are likely to raise the quality of ergonomics work even further, although there are still geographical and professional differences regarding the areas of expertise considered most important.
Relevant human characteristics
Human capacity for work is a function of body size, strength and fitness, and sensory as well as cognitive capacity. These capacities vary widely by age, between the genders, and among individuals with different hereditary, nutritional, and educational backgrounds. Even within a specific subgroup of the population, individual capacity varies with health, training, and previous experience. Therefore work tasks, as well as tools and other items for use in both occupational and private life, must be designed to fit the capacities of a wide range of people. A strong inverse association exists between the relative capacity available for a task and its duration: the longer time over which a certain demand has to be met, the lower is the relative capacity that can be used without fatigue or injury. Human capacity is seldom taxed up to 100 per cent; the only exceptions are in all-out life-saving operations. More commonly, people use from a small percentage of capacity up to as much as 50 per cent in physically demanding jobs. (No similar estimates are available for sensory or mental capacity, which are more difficult to measure.)
Anthropometry
Workstations, tools, and machines should be designed with enough adjustability to individual differences in body size in order to include virtually all the population as potential users. The most common recommendation is to design workstations and tools to fit the range in body size from the 5th to the 95th percentile of the adult population. Anthropometric data for use in workstation design are available for most parts of the body and for some specific subsets of the population, for example, by gender (Pheasant 1986). Those anthropometric body segments most commonly used for design of workstations and furniture are illustrated in Fig. 2.

Fig. 2 Commonly used anthropometric measures and their definitions: 1, body height, standing; 2, seated body height; 3, eye height; 4, shoulder height; 5, elbow height; 6, knuckle height; 7, thigh height; 8, seated knee height; 9, seat pan height. (Source: Hansson 1987.)

There are large variations among ethnic groups in body size, body proportions, and limb length as a proportion of body height. With the increased mobility of population groups around the world, it is no longer acceptable to design workstations only, for instance, for Caucasians in Europe and for the Japanese population in Japan. The wider range of workstation requirements caused by this mixture of population groups must be taken into account. This necessitates the continuous revision of anthropometric data. Unanticipated differences in body size can lead to poor fit of tools, equipment, workstations, gloves, and other personal protective equipment, with resulting increases in biomechanical disadvantage and postural strain.
In addition to the static anthropometric body measures available for workstation and tool design, there is also a need to consider functional or dynamic measures of the human capacity to reach, bend, and stretch (Pheasant 1986). Dynamic anthropometric data can be obtained when subjects are allowed to adopt natural postures and movements to perform a certain task, such as operating hand controls while sitting in a driver cabin. Such measurements are scarce, and the generalizability of the data from one setting to another is uncertain. Usually they have to be collected for each specific work situation.
Physical working capacity
Physical working capabilities relevant for ergonomics include cardiovascular, aerobic, and muscular strength capacity for maximal and submaximal, dynamic, and sustained (static) activity. Most physical capacities demonstrate a peak at around age 20 to 30 years and a gradual decline by about 30 per cent at least to the age of 60 (Åstrand and Rodahl 1986). Women usually have on average a 30 per cent lower maximal aerobic power (expressed in litres of oxygen uptake per minute) than men, and about 30 to 50 per cent lower maximal muscle strength. However, at a given level of relative submaximal exertion, there is no gender difference. The ratio in static strength ranges from 35 to 85 per cent, depending on the tasks and muscles involved (Chaffin et al. 1999); it is smaller when men and women have similar industrial experience or athletic training (Messing and Stevenson 1996). There are large interindividual differences in capacity, related to factors such as heredity, physical training, and health status. In all, gender, age, weight, and height together explain only about one-third of the variability in human strength.
Overall, the occupationally active population demonstrates higher capacities than the general population, since the latter includes those too ill to work or otherwise impaired. There are also differences between occupational groups, with higher values usually found in those who perform physically demanding tasks (Åstrand 1967a, 1988). This difference appears to be caused mainly by selection, since physically demanding jobs do not usually contain work tasks strenuous enough to introduce a training effect. Moreover, differences between occupations are most obvious in young age groups. In some (but not all) studies, muscle strength shows a larger decrease with age in blue collar than white collar workers, which may be attributable to a combination of musculoskeletal trauma and ‘wear and tear’ among those performing physically heavy work (Era et al. 1992).
Physically fit workers exhibit higher productivity and less fatigue in strenuous jobs than less fit workers (Åstrand 1967b). However, it is still an open question whether strong individuals are at a lower risk of musculoskeletal disorders than weaker ones. Among women performing electronics assembly work, there was no evidence that low muscle strength predicted upper-extremity musculoskeletal disorders (Jonsson et al. 1988). Other studies of whether or not muscle strength protected against back disorders have been similarly inconclusive (Biering-Sørensen 1984; Leino et al. 1987; Kujala et al. 1996); some have even shown high muscle force capacity to be a risk factor, rather than protective (Keyserling et al. 1980; Barnekow-Bergkvist et al. 1998). Stronger muscles are capable of generating higher internal forces, but they do not necessarily greater strength in vulnerable soft tissues such as nerves and spinal discs. Therefore pre-employment strength testing cannot be recommended on a scientific basis as a way of selecting workers unlikely to develop musculoskeletal disorders. Among people in jobs with substantial exposure to ergonomic stressors, individual factors like muscle strength appear to be of less importance for the risk of developing musculoskeletal disorders (Hagberg et al. 1995).
Neuromuscular function in precision tasks and the effect of motor control and skill training are areas of rapidly developing research, and these capacities may also become highly relevant to the risk of musculoskeletal disorders.
Sensory perception
Vision, hearing, and touch are primary factors in people’s perception of the environment, and thus in their ability to respond appropriately to cues from machines, displays, warning signs, and information received from other sources, including other people. Taste and smell are less important for ergonomics but may be life-saving in toxic environments.
Work with poorly presented sensory information requires an excessively high level of attention, leading to errors, stress, and/or fatigue. In order to enable humans to respond to sensory stimuli without missing information or over-reacting, the contrast between the relevant information and the ‘noise’ caused by irrelevant visual and hearing stimuli (i.e. the signal-to-noise ratio) must be high. One common example of inadequate signal-to-noise ratio is trying to read texts on computer screens with too little contrast or with bright lights surrounding the screen. In leisure time activities like jogging and cycling, music from earphones can camouflage important safety information from traffic.
Frequently the sensory input from vision is overemphasized in ergonomic design, when sound or touch stimuli might have fulfilled the same purpose. Ergonomics for handicapped individuals has many examples of successful switches from vision to hearing (e.g. traffic signals) and from vision to touch (e.g. Braille).
With advancing age, the sensitivity of the eye to light and of the ear to sound is reduced; therefore the elderly require higher signal-to-noise ratios in order to perceive important information easily and accurately.
Cognitive capacity
In accordance with the human–machine system model, information is perceived through the sensory organs and then processed in the brain, leading to a decision on what action to take. The capacity to process information and make decisions (cognitive capacity) requires short-term (working) memory for processing and long-term memory for storage of relevant experience and knowledge (Kroemer and Grandjean 1997).
Information perception and processing can be improved by presenting information in a form that makes it easy for the brain to code in the short-term memory. Information should be organized in such a way that it is easy to compare and relate to previous training and work experience, and so that it can be stored in the long-term memory and retrieved in a suitable form for use later (Sanders and McCormick 1992).
The capacity for information processing is gradually reduced with age, but it is usually not until the age of around 65 years that a noticeable change occurs (Rabbitt 1991). With increasing age the variation around mean values of cognitive capacities appears to increase, probably because of the training effects of different lifestyles, jobs, and levels of continuing mental exercise (Salthouse 1990; Rabbitt 1991). Neurophysiological and psychological research indicates that it is the brain’s ‘hardware’ (number of brain cells) that declines with age, rather than the ‘software’ (quality of processing). Even though the memory deteriorates slowly, experience can compensate for reduced capacity, especially in complex decision-making.
Relevant work environment characteristics
Workstation and equipment design
Workstations, equipment, tools, and other objects should be designed in a way that facilitates their use, permits variations in work routines, does not give fatigue, and leads to high efficiency. Common effects of poor workstation design are twisted and bent neck and trunk postures and elevated arms, leading to fatigue, musculoskeletal and other disorders (see below). In the office this applies to the computer and furniture, in industry it applies to machines and tools as well as to supports, and in a kitchen it applies to the layout and the usability of cleaning equipment.
For example, the correct height of a work surface depends on the nature of the task performed (Kroemer and Grandjean 1997). For precision work, the hands must be held relatively close to the eyes to allow sufficient accuracy of visuomotor co-ordination. However, since working with elevated arms is tiring, arm support must be provided. For light manual work with less visual precision, such as on an assembly line, the working area should be close to elbow height (standing or sitting). When lifting or other heavy work is performed, the working height should be even lower (Fig. 3). Frequent changes between sitting, standing, and walking reduce fatigue, and many modern workplaces have work surfaces where the height can be adjusted for both standing and sitting. A minimum requirement is that the height can be adjusted to fit both a tall man and a small woman.

Fig. 3 Recommended height for benches for standing work. The reference line (0) is the height of the elbows above the floor, which averages 1050 mm for men and 98 mm for women in Western populations. (Source: Kroemer nd Grandjean 1997.)

Standing work
The advantage of a standing posture is that the combined mobility of the trunk and arms permits a much larger reach and work area than is possible in the sitting position. Another advantage is that much larger forces can be exerted, especially if the work area is relatively low so that the arms can be held straight and the trunk weight can be used. Conversely, standing work is tiring for the legs, especially for older people and for those with peripheral circulatory problems in the legs. Static standing for at least half the work day is also a risk factor for spontaneous abortion and premature labour among pregnant workers (Gold and Tomich 1994). The horizontal area in front of a standing person that is optimal for arm work is small (Hansson 1987) (Fig. 4). When work is performed standing and walking, it can be made less fatiguing if shoes are changed a few times a day and if the floor is not hard—concrete floors are extremely tiring.

Fig. 4 Optimal work area for the hands in standing work. (Source: Hansson 1987.)

Seated work
Sitting is preferred by most people for prolonged tasks because it is less tiring for the legs. Conversely, in many jobs sitting implies confined and static postures with elevated shoulders and arms, and frequent or sustained twisting and bending of the neck. The optimal horizontal work area in front of a seated person is even smaller than for standing work. In general, commonly occurring work tasks should not be performed beyond forearm reach, to avoid postural strain and because much less force can be exerted. The basic posture in sitting (Hansson 1987) requires the following:

the shoulders are relaxed, the upper arms are nearly vertical alongside the torso, and the forearms are flexed about 100° at the elbows (that is, angled slightly below horizontal)

the forearm and hand form a straight line, or alternatively the hand can be slightly extended (angled upward) but should not be bent sideways towards the little finger.
The head posture in seated work is frequently static, especially when fine manual tasks or visually intensive work, such as computer tasks, are performed. The line of vision should be horizontal, or somewhat below horizontal, and the seated workplace must also provide sufficient leg space, because sitting with the trunk twisted to accommodate the legs requires static muscle exertion and is very tiring. For the seated worker, no equipment is more important than a well-padded fully adjustable chair. However, no seated posture—even with good furniture—can be maintained for prolonged periods.
Repetitive work and rest pauses
Lack of recovery time after performance of repetitive work or sustained loading is believed to be an important factor in the aetiology of work-related musculoskeletal disorders, especially of the arm, wrist, and hand. Prolonged repetitive tasks should be avoided by providing frequent breaks and alternative tasks that do not tax the same tissues. Repetitive tasks should not be machine-paced; the individual should be allowed to set his or her own pace and to vary it over the course of the day, as fatigue sets in. Tasks that require precision, force exertion, and speed in combination with repetitiveness imply particularly high risk (Kilbom 1994).
Manual handling
Manual handling of loads—lifting, lowering, holding, carrying, pushing, and pulling—is an important risk factor for low back and other musculoskeletal disorders. The American National Institute of Occupational Safety and Health has developed an equation for estimating the acceptability of a two-handed lift based on the weight of the object, its horizontal distance from the body, the degree of asymmetry, the height of the object, the vertical distance that it is moved, and the frequency of lifting (Waters et al. 1993). Although this equation does not apply to all lifting situations, its dissemination has increased awareness about the interactions among these factors in manual handling and how to prioritize them for intervention. Apart from minimizing object weight and distance from the body, manual handling tasks should be designed to eliminate trunk bending and twisting, remove obstructions, provide good coupling of the load and the worker, and eliminate uneven or slippery surfaces.

Case study: Manual handling in nursing (Ljungberg et al. 1989) The importance of workstation design, technical lifting aides, and work organization was studied among nursing aides in two hospital geriatric wards. The traditional ward had cramped work spaces, narrow corridors, and small lavatories with room for only one nursing aide to help the patient. Mobile hoists were available but the space was so cramped that they were seldom used. In the modern ward, both corridors and rooms were spacious and about 50 per cent of the beds had motorized overhead hoists for lifting patients. Moreover, the modern ward had a new work organization incorporating ‘group-care’, in which a senior nurse and two aides shared the responsibility for 12 patients, whereas work at the traditional ward was more like an ‘assembly line’.
Patient-handling workload was compared between the two wards. The vertical force in each lifting and carrying manoeuvre, as well as the time for each lift, was measured using wooden shoes instrumented with strain gauges. The work performed in lifting was considerably less in the modern ward, whether expressed as total weight lifted per hour, the duration of each lift, or the proportion of lifts with uneven distribution of weight between right and left leg (Table 1).

Table 1 Workload in lifting and carrying: comparison of two geriatric hospital wards

It was not possible to distinguish whether the differences in work organization, use and availability of technical aids, or workstation layout most accounted for these large differences; most likely it was a combination of all three. The important point is that physical stresses due to manual handling can be substantially reduced.

Presentation and communication of information
Unfortunately, large-scale accidents bring to public attention the need to present information, in both workplaces and public places, in a way that is easily understandable and compatible with human comprehension (see case studies below). Warning signs must use symbols and icons familiar to people: the colour red signifies something forbidden while green means acceptable or safe to proceed, and the symbol for radio-activity is well known to most. Deficiencies in such conceptual compatibility are especially noteworthy in many computer programs. Movement compatibility implies that there is a concordance between the movement of a control or a lever, and the ensuing movement of a machine or tool—you turn the wheel to the right when you want to make a right turn (Sanders and McCormick 1992). Spatial compatibility reflects human expectations with regard to the relative positioning of displays and controls and the understanding of ‘high’ versus ‘low’ measurements; high values are expected to be at the top of, or at the right-handed side of, a display, whereas low values are expected to be represented at the bottom or the left side.
Good quality visual display is important to avoid both fatigue and error. Work at a visual display terminal, especially for prolonged periods, requires that the screen be of high quality with good contrast, no flicker, and adjustable in height (see section on seated work above).
The information on a display or a warning sign (auditory or visual) needs to be coded in a way that accentuates the crucial information, while redundant information is suppressed. Recommendations for the design of warning signs and labels have been given by Lehto (1992). The schematic representation of the very complex London Underground is a good example of a simplified, schematic, yet easily understandable system.
The quality of information processing can be further improved by undivided attention to the task and high motivation. Thus care should be taken when presenting information so that attention is not divided between simultaneous or conflicting demands.
Physical environment
Extremes of temperature and humidity, poor lighting, vibrations, noise, low frequency sound, and slippery or unstable ground conditions can all severely influence working capacity, endurance, and reliability. This is partly because these factors require additional physiological resources in addition to the work task; for instance, heat reduces blood circulation available for working muscles, cold reduces motor precision, and vibrations and slippery ground require extra muscle exertion to stabilize the body. Poor lighting and low frequency background noise impair mental concentration and communication between people. The International Standards Organization has standards on heat and vibration, but their main aim is to prevent ill health; they are not intended for safety purposes or to maintain general well being or productivity.
Work scheduling
Work schedules other than a standard 5-day working week are utilized in hospitals, emergency services, food processing, transportation, communications, steel working, petroleum and paper manufacturing, law enforcement, and other public agencies. In the United States, approximately 16 million people are classified as shiftworkers; up to 45 per cent of the labour force works a designated shift or at least 4 h per week outside of the standard working week (NIOSH 1997). Specific schedules vary tremendously; some have worse consequences than others for fatigue, psychological health, and family and leisure time. Sleep disorders are the most obvious and consistent health consequences. Many shiftworkers also experience gastrointestinal and digestive disorders (Rosa and Colligan 1992). Shiftworkers are at greater risk of coronary heart disease and associated risk factors, including poor diet and tendency to male central obesity, than day workers (Knutsson 1989; Nakamura et al. 1997; Tenkanen et al. 1998; Steenland 2000). Women with child-care responsibilities often experience additional stress; mental health was worse among female hospital workers who were dissatisfied with their work schedules (Estryn-Behar et al. 1990).
Organizational design and management
Work organization—the leadership style (democratic or authoritarian), the hierarchical structure of the organization (flat or high pyramid), the influence of employees on decision-making, the distribution of work tasks among employees, the industrial relations within the organization, the wage/salary negotiating system, the level of technology, and skill utilization—all influence productivity, well being, and health in an organization. These features of the work environment are also referred to as organizational design and management or ‘macro-ergonomics’ (Hendricks 1986).
The organization of work generates technical constraints on individual workers and thus influences physical load as well as psychological job content and potential ‘stress’. Psychological job demands reflect both the physical pace of work and time pressure in processing or responding to information. Decision latitude is based on the worker’s decision authority and discretion over skill use, i.e. the ability to control one’s own work process and decide which skills to utilize to accomplish the job. According to one widely used model (Karasek and Theorell 1990), high psychological job demands in combination with low decision latitude result in residual job strain and, over time, chronic adverse health effects. This model has proved a powerful predictor of risk of cardiovascular morbidity in numerous countries and industrial sectors; recent research suggests that it is probably also relevant for musculoskeletal disorders, acute occupational injury, and adverse reproductive outcomes related to work demands during pregnancy (see below). The relationship of work organization factors with psychosocial strain has also been demonstrated by intervention studies showing that interventions which increase worker participation in decision-making can resolve strain linked to high levels of demands over which the worker had no control.
Organizations that promote employee initiatives, support development of skills and experience, and let employees exercise choice regarding quality and quantity of work adapt more easily to structural changes in society and appear to maintain a higher level of innovation. The underlying philosophy is that humans not only need bread and clothing for satisfaction and full development; when the above additional demands are met, people can contribute more to the aims of the organization.
The full consequences of work organized along these lines are not yet fully realized; for example, some disadvantages may follow for people with little initiative. Moreover, stress levels may increase above acceptable levels when individuals feel pressured to be as creative and productive as possible. There is no doubt, however, that work organization has a profound influence on productivity and health.
Cost-effectiveness of ergonomic measures in the workplace
Well-designed ergonomic systems often improve efficiency and productivity in industry, both directly and as a result of improved employee health (Simpson 1988; Oxenburgh 1991). In the workplace, productivity, safety, and health may not always be parallel outcomes (Frick 1997). However, there are many situations in which these goals go hand in hand, at least over the longer term.
To evaluate cost-effectiveness, the costs of ergonomic improvements like re-engineering of workstations and tools, introduction of new production methods, and work reorganization can be compared with the past or expected costs of leaving the work system unchanged. Factors that should be balanced against the costs for improvements include high sick-leave rate, compensation claims, staff turnover, and low-quality production such as many rejected products.

Case study: A railway maintenance workshop (Oxenburgh 1991) In a workshop for the maintenance and repair of diesel engines, there were problems with low productivity and unacceptably high injury rates. The workstations required awkward postures because of problems with access, reach, and visibility, and the risk of injury was high because of temporary, makeshift support for engine parts during repair.
A new management style was adopted to encourage worker participation in the change process. Improvements in work systems and practices were introduced via teams of workers and engineers, informed by visits to other workshops, consultants’ inputs, and their own experience. Quality control was improved by allowing workers to take responsibility for their work and encouraging customer feedback as to acceptability of the work. The cost for the physical improvements was about 6 per cent of yearly payroll. The injury rate did not decrease, but severity was reduced and injury absenteeism was halved. The productivity gain was very high and throughput of engines increased by 80 per cent. Altogether, the costs of improvements were paid back in 4 months.

Ergonomics and public health
Musculoskeletal disorders
Musculoskeletal disorders are widespread in many countries, with substantial costs and impact on quality of life. In the United States, Canada, and Finland, more people are disabled from working as a result of musculoskeletal disorders than from any other group of diseases (Pope et al. 1991; Badley et al. 1994; Riihimäki 1995; Rempel and Punnett 1997). Musculoskeletal disorders also constitute a major proportion of all registered and/or compensatable work-related diseases in many countries. Criteria for diagnosis and for evaluating work-relatedness and completeness of reporting vary among countries, making statistical comparisons difficult. However, where record-keeping systems have been developed, musculoskeletal disorders are often the single largest group of conditions, representing a third or more of all registered occupational diseases in the United States, the Nordic countries, and Japan (Pope et al. 1991; Vaaranen et al. 1994; Bernard 1997). For the Nordic countries in 1991, it was estimated that from 15 to 49 per cent of all musculoskeletal disorders were due to work, and their cost represented approximately 1 per cent of gross national product (Hansen 1993).
Some industries and occupations have musculoskeletal disorder rates up to three or four times higher than the overall frequency. High-risk sectors include nursing facilities, air transportation, mining, food processing, leather tanning, and heavy and light manufacturing of vehicles, furniture, appliances, electrical equipment, electronic products, textiles, clothing, and shoes (Bernard 1997). Upper-extremity musculoskeletal disorders are highly prevalent in manual-intensive occupations such as clerical work, postal service, cleaning, industrial inspection, and packaging (Rempel and Punnett 1997). Back and lower-limb disorders occur disproportionately among truck drivers, warehouse workers, airplane baggage handlers, construction trades, nurses, nursing aides and other patient-care workers, and operators of cranes and other large vehicles (Pope et al. 1991).
The work-relatedness of many musculoskeletal disorders has been discussed extensively (Armstrong et al. 1993; Bongers et al. 1993; Hagberg et al. 1995; Scientific Committee for Musculoskeletal Disorders 1996; Bernard 1997; Buckle and Devereaux 1999; Sluiter et al. 2000). Both experimental science and epidemiology indicate that job features which increase the risk of work-related musculoskeletal disorders are heavy lifting, repetitive hand motion, static work in which the body is maintained in a fixed posture, vibration, and any of these in combination with each other or with an undesirable psychosocial work environment.
Work-related musculoskeletal disorders cover a wide range of inflammatory and degenerative diseases, including some less well-described states of pain and functional impairment. Clinically, the most common disease entities are tendinitis and related conditions, myalgia, nerve-entrapment syndromes, low back pain, sciatica, and arthrosis. Body regions most commonly involved are the low back, neck, shoulder, forearm, and hand, although recently the lower extremity has received more attention.
Inflammations of tendons and surrounding tissues (tendinitis, peritendinitis, tenosynovitis), especially in the forearm and wrist, elbow, and shoulder, have a high prevalence and incidence in occupations with prolonged periods of repetitive and static work loads (Kurppa et al. 1991). Tendon strain accumulates as a function of work pace (the frequency and duration of mechanical loading), the level of muscular effort, and recovery time between exertions (Goldstein et al. 1987). Tendon disorders may have an acute or insidious onset, depending on the intensity of the loading. Recovery is usually complete, but some workers develop chronic disorders.
Myalgia, meaning pain and functional impairment of muscles, occurs especially in the shoulder and neck region in occupations with large static demands, when performing precision work with the hands, or in work with the arms elevated (Kilbom et al. 1986; Winkel and Westgaard 1992). The forearm muscles may also be affected in hand-intensive tasks (Ranney et al. 1995).
Nerve-entrapment syndromes cause pain or other symptoms and loss of sensibility and strength. The most common of these is carpal tunnel syndrome (Hagberg et al. 1992; Viikari-Juntura and Silverstein 1999). It occurs in work tasks that require prolonged, repetitive, and forceful gripping or wrist bending, especially if combined with exposure to local vibration. With continued exposure, functional impairment may become permanent.
Degenerative disorders commonly occur in the spine, especially in the neck and low back region, as well as in the hip and knee joints. Such disorders are common in the general population at older ages. However, several factors at work, especially heavy physical work, manual handling of objects, forward bending and twisting of the trunk, and exposure to whole-body vibration (especially while seated) accelerate the degenerative joint process (Riihimäki 1991; Vingård et al. 1991; Kirkeskov Jensen and Eenberg 1996). The course of these disorders is chronic, and usually exposure to risk factors at work has lasted for many years before symptoms occur.
In some countries work-related disorders of the upper extremity are referred to as repetition strain injury or cumulative trauma disorders. These terms are intended to convey that the cause is repetitive work or the accumulation of microtrauma over a period of time, but they are clinically imprecise, and sometimes even misleading, since musculoskeletal disorders can also occur as a result of high-intensity exposure for relatively brief periods. It is generally acknowledged that the aetiology of these disorders in the population is multifactorial and may involve risk factors both on and off the job. A more useful term is ‘work-related musculoskeletal disorders’, which reflects the idea that the work environment contributes substantially to causation in the population, although with varying importance among individuals (WHO 1985). Work-related disorders are thus distinguished from specific ‘occupational’ disorders where a single factor is both necessary and sufficient to cause the disease (e.g. mesothelioma from asbestos exposure).
Accurate data on the incidence and prevalence of musculoskeletal disorders are difficult to obtain, and the true magnitude is probably underestimated. In addition, regional differences have been noted in the relative frequency of different diagnoses and affected body regions. These may be related to variations in clinical practice, the circumstances under which the disorders were first noted, or the occupational health legislation and compensation systems in each jurisdiction. Nevertheless, there is international agreement that musculoskeletal disorders are a serious problem and that many can be prevented by improved work design.
Acute traumatic injuries in the workplace
Both acute injury and chronic disorders have essentially the same aetiological agents, namely, physical energy transmitted to the human body in doses harmful to tissues. Despite the traditional focus on individual behaviour as the ’cause’ of accidents, it is increasingly recognized that factors in the workplace, such as poor machine and tool design and lack of adequate maintenance and care, contribute to many occupational accidents. Instructions and warning signs are often not designed in accordance with ergonomic principles regarding visual perception and information processing. Physical work load is relevant in several ways: fatigue may lead to reduced attention and motor co-ordination, or musculoskeletal trauma may itself manifest as an acute incident (e.g. low back strain) or may lead to an acute episode (e.g. inability to handle a heavy load may result in loss of balance and a slip or fall). The contributions of the physical and psychosocial environment to injury risk have been little studied to date, with a few exceptions (Sundström-Frisk 1984; Moll van Charante and Mulder 1990; Melamed et al. 1999). Therefore prevention requires attention to all aspects of ergonomics: technical redesign, information processing demands, physical work environment, and reorganization of work procedures. For these reasons, some have now rejected the term ‘accident’ altogether, because it implies an unforeseeable or random occurrence, in favour of ‘acute injury’ or ‘incident’—terms more compatible with the public health approach of identifying preventable risk factors.
A high incidence of occupational injuries in industry has been the original impetus for occupational health and safety legislation in many countries. Table 2 summarizes some official statistics on occupational ‘accidents’ in Sweden (Statistics Sweden 1994). A very large proportion occurred while handling machines, tools, and other technical devices, and much of the cost resulted from relatively long periods of sick-leave for a relatively small number of cases. The two most common ‘main events’ were ‘fall on same level’ and ‘overexertion of body part’, with annual incidence rates of 3.2 and 2.7 per 1000 men and 2.1 and 2.5 per 1000 women respectively.

Table 2 Distribution and average sick-leave due to cases of reported occupational accidents involving some important ‘principal external agencies’ (Sweden 1992)

Although acute injuries are still a major source of mortality and morbidity at work, over the past 10 to 20 years their incidence has been reduced in many Western countries. For example, in Sweden the incidence of reported occupational injuries per 1000 people in the workforce has come down from 40 in 1980 to 16 in 1992 for men and from 11.5 to 7.5 for women over the same period.
Cardiovascular and other work-related diseases
The impact of psychosocial ‘job strain’ on physiological stress response, mental strain, coronary heart disease, hypertension, and other heart disease risk factors is well established (Karasek and Theorell 1990; Kristensen 1996). While estimates of the proportion of heart disease possibly due to ‘job strain’ vary greatly between studies, perhaps up to 23 per cent of heart disease (over 150 000 deaths per year in the United States) could potentially be prevented if the level of ‘job strain’ in all jobs was reduced to the average level of all occupations. The economic costs of job stress in general (absenteeism, lost productivity) are difficult to estimate but could be as high as several hundred billion dollars per year in the United States alone (Karasek and Theorell 1990).
For the pregnant worker, physically demanding tasks such as heavy lifting interfere with uteroplacental blood flow and may precipitate uterine contractility later in pregnancy. Such work has been associated with preterm birth (before 37 weeks gestation) and hypertension or pre-eclampsia (Gold and Tomich 1994; Mozurkewich et al. 2000). Prolonged standing and shiftwork increase the risk of preterm birth; psychosocial strain is also physiologically relevant (Omer and Everly 1988), although the epidemiology is not conclusive (Hedegaard et al. 1996).
Ergonomic applications in transportation systems
Traffic accidents are one of the leading causes of death and disability today. In the United States, traffic injury is second only to cancer in the total financial cost to the community of major disabilities and deaths. Even in some developing countries where infectious disease is still a significant cause of death, traffic injury accounts for a percentage of all deaths similar to that in some highly motorized countries (Trinca et al. 1988).
Traffic incidents are often blamed on ‘human error’. The car driver ‘disregarded’ the warning sign, the truck driver stepped on the breaks ‘too late’, the signal-box attendant ‘forgot’ the coming train, and so on. What if the warning sign was obscured because of the car design and the position of the sign, the truck driver was just entering a tunnel with sudden (relative) darkness, and the signal-box attendant was tired because of having to work double shifts? Transportation systems can be designed in a way that takes human limitations into consideration, instead of relying on unrealistic instructions, rules, and regulations that do not comply with human capacity.
Traffic incidents have a complex causality, and ergonomics can play an important role for prevention through the design of vehicles and traffic signs, and the engineering of roads and railways. Because of the high speed of movement in traffic, the design of transportation systems has special requirements. Speed places excessive demands on reaction time, short-term memory, and vision of both drivers and pedestrians, although these demands can be moderated by the design of the system (Lay 1986; Ogden 1990).
Reaction time can be reduced by encouraging familiarity, because drivers reset faster to a familiar situation, and by reducing the number of alternatives. For example, unusual intersection layouts and a large number of exits from a roundabout require longer response times.
Short-term memory is crucial for driver performance because most of the driving task relies on information that is never stored in long-term memory. Therefore warning signs should require an immediate response, drivers should be frequently reminded of control information which varies along the road (e.g. speed limits), and the driver should be allowed to respond to one stimulus before the next is imposed.
Of all information required by a vehicle driver, 90 per cent is supplied by vision. As the amount of visual information is almost limitless, the driver must continuously select the most important cues to help in his or her driving. As the data-processing demands increase, the driver tends to be overloaded and to miss some information or to shed part of it. This situation also takes place immediately after a situation of overload. Thus the departure side of an intersection may be relatively more accident prone than the approach side, which also implies that pedestrian crossings and bus stops should not be placed after intersections. Only 1 to 1.5 fixations of vision per second are realistic in driving. Therefore road traffic signs must be separated in time and space and must only be used for the most necessary information. They must be within the field of vision of the driver which, when moving at a certain speed, implies a narrower field both horizontally and vertically than for a stationary observer. Delineation (i.e. markings of road alignment immediately ahead) is especially important at the approach to curves and crests, and for elderly drivers whose visual capacity is often reduced.
The design of the driver cabin directly influences traffic safety by the degree of visibility that it affords to the driver. Cabin design should provide a comfortable seated posture in which the driver can reach all the hand and foot controls and is protected from vibration (Pheasant 1991). Traffic safety is also influenced by circumstances like fatigue, medication, and ill health of the driver, training of drivers and pedestrians, legislation, traffic density, and weather conditions (Ogden 1990; Sanders and McCormick 1992).
Consumer product design
The design of products, implements, and entire systems for use by the general population increasingly involves ergonomics. Some important applications that influence the health or safety of the consumer include the design of furniture and kitchen utensils, floor coverings, handheld tools, and containers. As in the workplace, injuries often happen as a consequence of several factors simultaneously—consider slipping and falling due to a combination of slippery floors and carrying a bulky wobbly object that obscures one’s vision. In the kitchen, problems may occur due to unsuitable working heights, poor lighting, and ambiguous labelling of stove controls. Examples of poor ergonomic design of consumer products include carrying purchases in plastic bags with handles which cut into the fingers, trying to open containers that require excessive pinch force, and sorting paper money of different denominations but the same size and colour. In all of these situations, better design would reduce discomfort and fatigue, make the task less time-consuming, and reduce the risk of mistakes.
Devices should be designed to fit the anthropometry, strength, and endurance of the entire population. Information and warning signs must similarly be understandable to populations with large variations in sensory and cognitive capacity, cultural background, and level of schooling. All areas of design must be considered: a product or an implement must be shaped and marked in a way that explains its function, safety devices must be designed without demands on previous training and experience, and size, weight, and grips must fit a wide variety of human body sizes. Therefore design for the public requires even more sophisticated considerations than design for the workplace, where the user population is better defined in terms of physical and psychological capacities and where additional training can be given to selected groups.
This area is becoming increasingly important, partly as a consequence of product liability legislation enacted in many Western countries. The manufacturer of any product can be made economically responsible for a user’s injury if it can be demonstrated that deficient design of the product was responsible or that the user could not have been expected to know of the risk. There are also market considerations; since a consumer device is purchased by the end-user, that user (unlike most workers) has the opportunity to choose among available designs, and comfort and ease of use are usually important criteria for the purchaser.
Although usually not described in ergonomic terms, many implements and tools used in sports and leisure time have been developed with an ergonomics approach, emphasizing high levels of achievement and absence of accidents and injuries. Some examples are hand-grip fit in golf clubs and tennis rackets to improve force output and reduce the risk of epicondylitis, and the development of sports shoes to reduce impact forces and periostial and tendon inflammation.
Design for the elderly and for people with physical or mental disability
In recent years there have been advances in design for rehabilitation and for people with physical or mental disabilities, with primary emphasis on compensating for reduced physical capacity such as muscle strength and precision, hearing, vision, and mobility. In the future, more emphasis should also be put on compensating for longer reaction times and reduced cognitive capacity. Computer use, for example, is often out of reach for both people with disabilities and elderly people because of poor visibility, demands on rapid information processing, and the introduction of unfamiliar symbols. In the same way as a handicap may affect only one out of several functional capacities, an elderly person may have most functions well preserved. Therefore there is no need to distinguish between ergonomics for people with physical or mental disabilities and the elderly. In fact, it would make more economic sense if products were designed for use by those with limited abilities, as well as by the more able-bodied (Haigh 1993).
In a recent survey of commercially available products intended for elderly people, it was found that many of them were inappropriate or inadequate to perform the task for which they were intended (Gardner et al. 1993). Some did not perform the intended job; others introduced hazards that could have led to serious accidents, but which could have been avoided after simple consumer trials and redesign. One group of ergonomists and designers in Sweden, Ergonomi-Design Gruppen, have successfully designed a range of products for people with disabilities and the elderly (Benktzon 1993). Modification of products such as knives, walking sticks, and cutlery have made people with reduced strength and mobility of the hand or arm more self-sufficient in their everyday life.
The design process is stepwise, starting with thorough documentation of the functional ability of groups with different types of disabilities, preparing a range of test tools, prototype testing, and finally manufacturing. The same approach has been used in the redesign of products for craftsworkers and others with repeated and prolonged use of tools and implements. Small design details can be of vital importance for safety, comfort, and usability. Pliers, screwdrivers, and butcher’s knives with improved grip surface and grip diameter, and a coffee pot with its centre of gravity closer to the hand, are other commercial products developed by the group. These all reduce the load on the forearm and hand, improving comfort and decreasing fatigue, and therefore have been widely adopted. Solutions originally created for the elderly or for people with physical or mental disabilities have frequently been found acceptable to a broader range of users (Benktzon 1993).
Public health implications of complex technological environments: two case studies
Disasters in high-tech environments, such as the nuclear power plants in Japan, Chernobyl (Russia), and Three Mile Island (United States), are well known. Such disasters can be ascribed to the combined effects of design defects, conflicts between safety and productivity goals, poor operating and maintenance procedures, and inadequate training (Reason 1990). Ergonomics is central in the causality of many of these accidents because of poor system design, which is not compatible with human capacity and its limitations. The operators or workers involved are often victims, but the reason that these disasters are widely publicized and analysed is that the public—the third party—is exposed to risks without the ability to protect itself. The following two case studies illustrate that serious ‘accidents’ can and will happen when technical systems have been designed and implemented without ample consideration of human limitations.

Case study: Tram collision In a tram accident in Sweden, 13 people died and 29 were taken to hospital when a tram raced downhill along the track with the brakes disconnected. All those killed or injured were waiting at the next stop, or were pedestrians or car passengers happening to pass further down. The tram had been taken out of service because of a breakdown in the overhead power supply. As the electric power had been cut, the normal electrodynamic brakes did not function and mechanical brakes had automatically taken over. The traffic supervisor in charge of the removal of the tram decided to use the downslope to move the tram further down where the power was intact. However, the mechanical brakes first had to be released, which could be done by a simple handgrip from the outside of each carriage. The intention was to use the mechanical brakes again further down. However, for the mechanical brakes to be functional again they had to be refilled with pressurized air, which could only be done when under electrical power. As a consequence, the tram driver could not stop the tram from racing down the track.
This incident appears to be a typical example of so-called ‘human error’. However, the subsequent investigation revealed several errors in the design of the system (Haverikommission 1992). The drivers and supervisors knew that the mechanical brakes must not be released unless the tram was secured by other means, but they did not know why; nor did they know how the brakes were constructed or what the consequences might be of disconnecting the mechanical brakes. Moreover, they had been given no formal training in emergency procedures of this nature. The mechanical brakes had been designed with an external release mechanism that was easily accessible but without any warning signs. This case is an unfortunate example of the combined effects of deficiencies in technical design, training, and emergency procedures that could have been avoided by the application of ergonomic principles.

Case study: Haemodialysis incident In 1983, three patients died and 12 others nearly died while undergoing haemodialysis in a Swedish hospital. The haemodialysis unit fed sterile water to the patients instead of physiological saline. The nurse on duty was charged and later sentenced for negligence, since she had switched off the alarm system of the haemodialysis unit.
In order to understand the sequence of events it is necessary to know the design of the haemodialysis unit alarm panel (Fig. 5). It had six horizontal rows of lamps and switches, for the conductivity (ion concentration) of the haemodialysis fluid, for its temperature, for the level of fluid in the tanks, and for the amount of concentrated saline available for diluting with water to create the haemodialysis fluid. Two more rows (1 and 2) were available but not in use. The vertical row of switches was for turning the alarm system on or off, and the first column of lamps (from the right) had yellow warning lamps that were lit when the alarm was in the ‘off’ position. Since rows 1 and 2 were not in use their alarms had been turned off and therefore the corresponding lamps were lit yellow, i.e. they were constantly indicating a warning. The second vertical column of lamps had green lamps that were lit when the alarm was on and when conductivity, temperature, etc. were within given acceptable levels. The vertical column of lamps to the extreme left had red lamps that were lit when the ion concentration, temperature, tank level, or amount of concentrate were below or above the set ‘safe’ levels. The main switch at the bottom of the panel was connected to an acoustic alarm that was common for all four alarm functions.

Fig. 5 Control panel of the haemodialysis unit before it was disconnected. (Adapted from Lundberg 1992.)

In a retrospective analysis, the most likely series of events was determined as follows (Lundberg 1992). The nurse was experienced in the treatment of haemodialysis patients and with the particular system, which had been in use for several years. Normally the nurses did not have to use the six alarm switches; they had been left on the panel because the unit had needed occasional adjustments by technicians, and the system had to be operational even when one of the circuits was out of function (albeit with intensified surveillance). On the day of the accident, however, the nurse demonstrated the haemodialysis unit to a visitor and explained its function. She noted that the main switch was ‘on’, i.e. turned up, whereas the four top switches were turned down, i.e. they appeared to be turned off (Fig. 5). Consequently, she turned up the four top switches, believing that she had turned the alarms on. She did not know that the main switch and the other switches had their ‘on’ and ‘off’ positions in different directions, and that she was actually disconnecting the alarms. Neither did she know that the emergency stop of the system was disconnected with the same switch. The haemodialysis unit continued working even though the alarms were disconnected. When the concentrated saline solution ran out, it continued with mere distilled water, with disastrous consequences for the patients. The nurse might have been alerted by the fact that the four yellow warning lamps lit up when the alarms were turned off; however, she was used to two of the yellow lights always being on, and said during the trial that she thought they should be on.
Sentencing this duty nurse caused considerable discussion and was widely considered unjust. Obviously the design of the haemodialysis unit, as well as the nurse’s understanding of its function, was poor. Insufficient oral information about the system had been provided to the users. Surveillance of the system was done by technicians for whom its function was obvious, but they did not convey their understanding to the nurses operating the system. This case emphasizes the need for unambiguous designs of control panels with consistent markings, for proper training, and for clear written procedures for both routine operation and emergencies. Why then blame only one person? Were not the designers at fault, and the head of the haemodialysis unit for not providing instruction and training? The application of ergonomic principles in the design of this haemodialysis system, as well as for similar surveillance systems used in hospitals, is necessary for the avoidance of ‘accidents’.

Ergonomics in developing countries
In developing countries, especially with high rates of unemployment, it is tempting for employers who build up small and middle-sized industries to disregard safety and health (Kogi and Sen 1987). Labour inspectors are scarce and have limited resources, and surveillance of occupational conditions is often lacking. Therefore ergonomics must be promoted not only as a means to improve safety, but also to fulfil other management goals, such as high productivity, and must stem from local initiatives to be effective.
According to Kogi (1991), support from international organizations and states should be organized so as to enable people to identify priority problems and effective solutions using locally available materials and skills. The support should provide for:

practical advice on how to identify priority problems and how to find solutions

practical guidance, particularly through ‘learning-by-doing’, about ways to implement immediate improvements.
The International Labour Organization has developed a training programme targeting entrepreneurs and workers of small and medium-sized enterprises (Louzine 1982) because of the great need for improvements and the scarcity of ergonomists in developing countries. The training programme focuses on the simultaneous improvement of working conditions and productivity, and encourages low-cost voluntary measures using a participatory approach. The following eight themes have been selected for the programme because of their importance for both working conditions and productivity:

materials storage and handling

workstation design

machine safety

control of hazardous substances

lighting

welfare facilities and services

work premises

work organization.
During the programme, local examples are used and the participants are encouraged to find practical improvements by means of self-help and sharing of experience. If managers and workers do not see any likelihood of a productivity gain and do not learn to use their own ideas and skills, they will quickly lose interest.
Implementing change
Legislation, standards, and guidelines
National legislation concerning ergonomic factors varies widely between different countries. Traditionally, legislation in occupational health focuses on quantitative data, for example concentrations of chemical substances, or minimum physical dimensions of barriers and guardrails as safety measures. The application of strict quantitative risk assessment in ergonomics has proved controversial for several reasons especially related to the multiplicity of physical risk factors, lack of standardized assessment protocols for each of them, and uncertainties in quantifying the interactions among them for different health outcomes (Viikari-Juntura 1997; Kilbom 1998). At the same time, regulations are desirable because voluntary actions by forward-thinking employers only cover a small proportion of the workforce in any single country, and because those measures generally lag behind technological changes rather than anticipating future health effects.
As an alternative approach, some countries have adopted performance standards based on functional requirements and desired outcomes, for example, that a certain work process must not produce injuries and must comply with safe handling (Kilbom 1995). Such an approach could more feasibly address work organization as well, rather than focusing only on micro-ergonomic issues (Kilbom 1998). Intense effort is under way in the European Community to develop directives relevant for ergonomics (Buckle and Devereaux 1999); some have already been presented for machine work, manual handling (EEC/90/269 Directive), and work at visual display terminals (Dul and de Flaming 1994). In the United States an ergonomics programme standard for prevention of musculoskeletal disorders was proposed by OSHA (1999) but did not stand.
International occupational standards are also continually being developed and refined, but these are usually not legally binding. The International Standardization Organization issues standards complementary to the European Community directives; for example, both whole-body and hand–arm vibration are covered by International Standardization Organization standards. Other examples are the American National Standards Institute proposed standard (2000) on prevention of upper-limb disorders and the American Conference of Government Industrial Hygienists proposal for a threshold limit value on hand activity level.
Large manufacturing or scientific organizations often develop codes of practice or guidelines for the specific area of their activity. These can be made more precise, relating to the conditions at hand at a certain organization, and are therefore useful for the practitioner (Mital and Kilbom 1992; Winkel and Westgaard 1992; Kilbom 1994).
In the public sector, intensification of product liability legislation in many countries has provided better tools for consumers in pursuing safety.
Training
Effective ergonomics programmes in the workplace emphasize engineering controls, especially the ergonomic design of workstations, equipment, tools, and work reorganization, together with a participatory process that engages the workers’ knowledge and empowers them to identify and remedy hazards (Hagberg et al. 1995). Thus both professional expertise and worker education are required.
In most countries, the labour inspectorate is responsible for the follow-up of ergonomics legislation. Since inspectors are usually poorly trained in ergonomics, this surveillance is often ineffective. In countries with a well-developed occupational health service (e.g. the Nordic countries), physiotherapists and safety engineers are usually well trained in ergonomics and perform valuable work. In the United States, plant nurses frequently provide such services in large companies.
Sometimes the occupational health service is unable to influence sufficiently the development of new workstations—the effort is reactive rather than proactive. For improved ergonomic conditions, both at workplaces and for the public, those responsible for developing technical systems need more training in ergonomics. Thus production engineers, designers, architects, systems engineers (in computing), and personnel managers need more training, which is seldom provided by technical universities. Since few universities provide postgraduate degrees in ergonomics there is so far an unfulfilled need for training, which is even more pronounced in developing countries.
Education of workers to recognize hazards and participate in work redesign processes is essential, although there is little consensus on the specific goals or methods for worker education in occupational health and safety. To be effective, worker education should involve two-way dialogue, value experiential knowledge, recognize the organizational nature of many hazards, and assist workers to develop strategies for corrective action (Wallerstein and Weinger 1992).
Participatory approaches
In recent years it has been proved repeatedly that improvements of ergonomic conditions are most efficiently achieved when all those using a particular system are also involved in its improvement. For example, ‘expert’ advice from a short-term consultant frequently results in failure if not supported by the experience of those manufacturing or using the product. The knowledge of the consumer or the worker is often unspoken but can be used for product and system improvement in practical trials. The group of people involved in a workplace should include not only the product designer and manufacturing engineer but also the workers, the occupational health staff, those who sell and promote the product, and its users (Gjessing et al. 1994; Moir and Buchholz 1996). However, such participatory approaches should not be used to the exclusion of technical expertise, since it is not easy for the worker or consumer to predict new hazards that may arise from a change in design.
Conclusion
The design of tools, equipment, and complex systems to be compatible with human needs, abilities, and expectations is increasingly important in the modern world. Failure to apply these principles impacts negatively on people in their workplaces, in transit, and at home. The necessary knowledge base already exists, although the extent to which it is utilized varies widely among countries and types of applications. Legal requirements appear to be necessary to achieve protection from occupational injury and illness, while market incentives may motivate improved design of many consumer devices.

* This chapter in the previous edition was written by Dr Åsa Kilbom. The current revision was undertaken with her consent but without her review of specific changes.
Chapter References
Armstrong, T.J., Buckle, P., Fine, L.J., et al. (1993). A conceptual model for work-related neck and upper-limb musculoskeletal disorders. Scandinavian Journal of Work Environment and Health, 19, 73–84.
Åstrand, I. (1967a). Aerobic working capacity in men and women in some professions. Forsvarsmedicin, 3, 163–70.
Åstrand, I. (1967b). Degree of strain during building work as related to individual aerobic work capacity. Ergonomics, 10, 293–303.
Åstrand, I. (1988). Physical demands in worklife. Scandinavian Journal of Work Environment and Health, 14, 10–13.
Åstrand, P.O. and Rodahl, K. (1986). Textbook of work physiology. McGraw-Hill, New York.
Badley, E.M., Rasooly, I., and Webster, G.K. (1994). Relative importance of musculoskeletal disorders as a cause of chronic health problems, disability, and health care utilization: Findings from the 1990 Ontario Health Survey. Journal of Rheumatology, 21, 505–14.
Barnekow-Bergkvist, M., Hedberg, G.E., Janlert, U., et al. (1998). Determinants of self-reported neck–shoulder and low back symptoms in a general population. Spine, 23, 235–43.
Benktzon, M. (1993). Designing for our future selves: the Swedish experience. Applied Ergonomics, 24, 19–27.
Bergqvist, U., Wolgast, E., Nilsson, B., and Voss, M. (1995). The influence of VDT work on musculoskeletal disorders. Ergonomics, 38, 754–62.
Bernard, B.P. (ed.) (1997). Musculoskeletal disorders and workplace factors: a critical review of epidemiologic evidence for work-related musculoskeletal disorders of the neck, upper extremity, and low back. Department of Health and Human Services, National Institute for Occupational Safety and Health, Cincinnati, OH.
Biering-Sørensen, F. (1984). Physical measurements as risk indicators for low-back trouble over a one-year period. Spine, 9, 106–18.
Bongers, P.M., de Winter, C.R., Kompier, M.A.J., and Hildebrandt, V.H. (1993). Psychosocial factors at work and musculoskeletal disease. Scandinavian Journal of Work Environment and Health, 19, 297–312.
Buckle, P.W. and Devereaux, J. (1999). Work-related neck and upper limb musculoskeletal disorders. European Agency for Safety and Health at Work, Luxembourg.
Chaffin, D.B., Andersson, G.B.J., and Martin, B.J. (1999). Occupational biomechanics (3rd edn). Wiley, New York.
Chapanis, A. (1965). On the allocation of functions between men and machines. Occupational Psychology, 39, 1–11.
Clark, T.S. and Corlett, E.N. (1984). The ergonomics of workspaces and machines—a design manual. Taylor & Francis, London.
Dul, J. and de Flaming, P. (1994). A review of ISO and CEN standards on ergonomics. Proceedings of the 12th Triennial Congress of the International Ergonomics Association, pp. 131–3. Human Factors Association of Canada, Toronto.
Era, P., Lyyra, A.L., Viitasalo, J.T., and Heikkinen, E. (1992). Determinants of isometric muscle strength in men of different ages. European Journal of Applied Physiology, 64, 84–91.
Estryn-Behar, M., Kaminski, M., Peigne, E., et al. (1990). Stress at work and mental health status among female hospital workers. British Journal of Industrial Medicine, 47, 20–8.
Frick, K. (1997). Can managers see any profit in health and safety? New Solutions, 7, 32–40.
Gardner, L., Powell, L., and Page, M. (1993). An appraisal of a selection of products currently available to older consumers. Applied Ergonomics, 24, 35–9.
Gjessing, G.C., Schoenborn, T.F., and Cohen, A. (1994). Participatory ergonomic interventions in meatpacking plants. NIOSH Publication 94–124, Department of Health and Human Services, Cincinnati, OH.
Gold, E.B. and Tomich, E. (1994). Occupational hazards to fertility and pregnancy outcome. Occupational Medicine, 9, 435–69.
Goldstein, S.A., Armstrong, T.J., Chaffin, D.B., et al. (1987). Analysis of cumulative strain in tendons and tendon sheaths. Journal of Biomechanics, 20, 1–6.
Grandjean, E. (1988). Fitting the task to the man. A textbook of occupational ergonomics. Taylor & Francis, London.
Hagberg, M., Morgenstern, H., and Kelsh, M. (1992). Impact of occupations and job tasks on the prevalence of carpal tunnel syndrome: a review. Scandinavian Journal of Work Environment and Health, 18, 337–45.
Hagberg, M., Hendricks, H., Silverstein, B., Smith, M., Welsh, R., and Carayon, P. (1995). Work related musculoskeletal disorders (WMSDs): a reference book for prevention. Taylor & Francis, London.
Haigh, R. (1993). The ageing process: a challenge for design. Applied Ergonomics, 24, 9–14.
Hansen, S.M. (1993). Arbeidsmiljo og samfundsokonomi. Nordisk Ministerråd, Nord.
Hansson, J.-E. (1987). Funktionell anatomi, antropometri och biomekanik. In Människan i arbete (ed. N. Lundgren, G. Luthman, and K. Elgstrand), pp. 92–118. Almqvist and Wiksell, Stockholm.
Haverikommissionen (1992). Spårvägnsolycka 1992–03–12. Report J 1992:1, Swedish Board of Accident Investigation, Stockholm.
Hedegaard, M., Henriksen, T.B., Secher, N.J., Hatch, M.C., and Sabroe, S. (1996). Do stressful life events affect duration of gestation and risk of preterm delivery? Epidemiology, 7, 339–45.
Hendricks, H.W. (1986). Macroergonomics: a conceptual model for integrating human factors with organizational design. In Proceedings of the human factors in organizational design and management II (ed. O. Brown and H. Hendricks), pp. 467–77. North-Holland, Amsterdam.
Jonsson, R.G., Persson, I., and Kilbom, A. (1988). Disorders of the cervicobrachial region among female workers in the electronics industry. A two-year follow up. International JournaI of lndustrial Ergonomics, 3, 1–12.
Karasek, R.A. and Theorell, T. (1990). Healthy work. Stress, productivity and the reconstruction of working life. Basic Books, New York.
Keyserling, W.M., Herrin, G.D., and Chaffin, D.B. (1980). Isometric strength testing as a means of controlling medical incidents on strenuous jobs. Journal of Occupational Medicine, 22, 332–6.
Kilbom, Å. (1994). Repetitive work of the upper extremity: Part 1—Guidelines for the practitioner. Part II—The scientific basis (knowledge base) for the guide. International Journal of lndustrial Ergonomics, 14, 51–86.
Kilbom, Å. (1995). Prevention of musculoskeletal disorders through standards and guidelines: possibilities and limitations. In From research to prevention (ed. J. Rantanen, S. Lehtinen, S. Hernberg, et al.), pp. 178–86. Finnish Institute of Occupational Health, Helsinki.
Kilbom, Å. (1998). Possibilities of regulatory actions in prevention of musculoskeletal disorders. Abstracts of PREMUS-ISEOH ’98: 3rd International Scientific Conference on Prevention of Work-Related Musculoskeletal Disorders/13th International Symposium on Epidemiology in Occupational Health, p. 87. Finnish Institute of Occupational Health, Helsinki, Finland.
Kilbom, Å., Persson, J., and Jonsson, B.G. (1986). Disorders of the cervicobrachial region among female workers in the electronics industry. International Journal of lndustrial Ergonomics, 1, 37–47.
Kirkeskov Jensen, L. and Eenberg, W. (1996). Occupation as a risk factor for knee disorders. Scandinavian Journal of Work Environment and Health, 22, 165–75.
Knutsson, A. (1989). Shift work and coronary heart disease. Scandinavian Journal of Social Medicine, 44 (Supplement), 1–36.
Kristensen, T.S. (1996). Job stress and cardiovascular disease: a theoretical critical review. Journal of Occupational Health Psychology, 1, 246–60.
Kogi, K. (1991). Participatory training for low-cost improvements in small enterprises in developing countries. In Participatory ergonomics (ed. K. Noro and A. Imada), pp. 73–80. Taylor & Francis, London.
Kogi, K. and Sen, R. (1987). Third world ergonomics. International Reviews of Ergonomics, 1, 77–118.
Kroemer, K.H.E. and Grandjean, E. (1997). Fitting the task to the human: a textbook of occupational ergonomics (5th edn). Taylor & Francis, London.
Kujala, U.M., Taimela, S., Viljanen, T., et al. (1996). Physical loading and performance as predictors of back pain in healthy adults: a 5-year prospective study. European Journal of Applied Physiology, 73, 452–8.
Kurppa, K., Viikari-Juntura, E., Kuosma, E., Huuskonen, M., and Kivi, P. (1991). Incidence of tenosynovitis or peritendinitis and epicondylitis in a meat-processing factory. Scandinavian Journal of Work Environment and Health, 17, 32–7.
Lay, M. (1986). Handbook of road technology. Gordon & Breach, London.
Lehto, M. (1992). Designing warning signs and warning labels. Part I: Guidelines for the practitioner. Part II: The scientific basis for the guide. International Journal of Industrial Ergonomics, 10, 78–95.
Leino, P., Aro, S., and Hasan, J. (1987). Trunk muscle function and low back disorders: a ten-year follow-up study. Journal of Chronic Diseases, 40, 289–96.
Ljungberg, A.-S., Kilbom, Å., and Hägg, G. (1989). Occupational lifting by nursing aides and warehouse workers. Ergonomics, 32, 59–78.
Louzine, A. (1982). Improving working conditions in small enterprises in developing countries. International Labour Review, 121, 443–54.
Lundberg, A. (1992). Dialysmålet–ett öppet såt i svensk rättskipning. Private report.
Melamed, S., Yekutieli, D., Froom, P., Kristal-Boneh, E., and Ribak, J. (1999). Adverse work and environmental conditions predict occupational injuries. American Journal of Epidemiology, 150, 18–26.
Messing, K. and Stevenson, J. (1996). Women in Procrustean beds: strength testing and the workplace. Gender, Work and Organization, 3, 156–67.
Mital, A. and Kilbom, Å. (1992). Design, selection and use of hand tools to alleviate trauma of the upper extremities. International Journal of Industrial Ergonomics, 10, 1–21.
Mital, A., Motorwala, A., Kulkarni, M., Sinclair, M., and Siemieniuch, C. (1994). Allocation of functions to humans and machines in a manufacturing environment. Part I: Guidelines for the practitioner. International Journal of lndustrial Ergonomics, 14, 3–29.
Moir, S. and Buchholz, B.O. (1996). Emerging participatory approaches to ergonomic interventions in the construction industry. American Journal of Industrial Medicine, 29, 425–30.
Moll van Charante, A.W. and Mulder, P.G.H. (1990). Perceptual acuity and the risk of industrial accidents. American Journal of Epidemiology, 131, 652–63.
Mozurkewich, E.L., Luke, B., Avni, M., and Wolf, F.M. (2000). Working conditions and adverse pregnancy outcome: a meta-analysis. Obstetrics and Gynecology, 95, 623–35.
Murrell, K.F.H. (1965). Ergonomics—man in his working environment. Chapman & Hall, London.
Nakamura, K., Shimai, S., Kikuchi, S., et al. (1997). Shift work and risk factors for coronary heart disease in Japanese blue-collar workers: serum lipids and anthropometric characteristics. Occupational Medicine, 47, 142–6.
NIOSH (National Institute for Occupational Safety and Health) (1997). Plain language about shiftwork. NIOSH Publication 97-145, Department of Health and Human Services, Cincinnati, OH.
Oborne, D.J., Branton, R., Leal, F, Shipley, P., and Stewart, T (1993). Person-centred ergonomics. A Brantonian view of human factors. Taylor & Francis, London.
Ogden, K. (1990). Human factors in traffic engineering. Institute of Transportation Engineers Journal, 60, 41–6.
Omer, H. and Everly, G.S. (1988). Psychological factors in preterm labor: Critical review and theoretical synthesis. American Journal of Psychiatry, 145, 1507–13.
Oxenburgh, M. (1991). Increasing productivity and profit through health and safety. CCH Australia, Chicago, IL.
Pheasant, S. (1986). Bodyspace. Taylor & Francis, London.
Pheasant, S. (1991). Ergonomics, work and health. Macmillan, London.
Pope, M.H., Andersson, G.B.J., Frymoyer, J.W., and Chaffin, D.B. (ed). (1991). Occupational low back pain: assessment, treatment and prevention. Mosby–Year Book, St Louis, MO.
Punnett, L. and Bergqvist, U. (1997). Visual display unit work and upper extremity musculoskeletal disorders. A review of epidemiological findings. National Institute of Working Life, Solna, Sweden.
Rabbitt, P. (1991). Management of the working population. Ergonomics, 34, 775–90.
Ramazzini, B. (1713). Diseases of workers. Reprinted by O & H Press, Thunder Bay, Ontario, 1993.
Ranney, D., Wells, R., and Moore, A. (1995). Upper limb musculoskeletal disorders in highly repetitive industries: precise anatomical physical findings. Ergonomics, 38, 1408–23.
Reason, J. (1990). Human error. Cambridge University Press.
Rempel, D.M. and Punnett, L. (1997). Epidemiology of wrist and hand disorders. In Musculoskeletal disorders in the workplace: principles and practice (ed. M. Nordin, G.B. Andersson, and M.H. Pope), pp. 421–30. Mosby–Year Book, St. Louis, MO.
Riihimäki, H. (1991). Low-back pain, its origin and risk indicators. Scandinavian Journal of Work Environment and Health, 17, 81–90.
Riihimäki, H. (1995). Back and limb disorders. Epidemiology of work related diseases (ed. C. McDonald), pp. 207–38. BMJ Publishing, London.
Rosa, R.R. and Colligan, M.J. (1992). Shift work: health and performance effects. In Environmental and occupational medicine (ed. W.N. Rom), pp. 1173–6. Little, Brown, Boston, MA.
Salthouse, T.A. (1990). Influence of experience on age differences in cognitive functioning. Human Factors, 32, 551–69.
Sanders, M. and McCormick, E. (1992). Human factors in engineering and design. McGraw-Hill, New York.
Scientific Committee for Musculoskeletal Disorders of the International Commission on Occupational Health (1996). Musculoskeletal disorders: work-related risk factors and prevention. International Journal of Occupational and Environmental Health, 2, 239–46.
Simpson, G. (1988). The economic justification for ergonomics. International Journal of Industrial Ergonomics, 2, 157–63.
Sluiter, J.K., Rest, K.M., and Frings-Dresen, M.H.W. (2000). Criteria document for evaluation of the work-relatedness of upper extremity musculoskeletal disorders. SALTSA Joint Programme for Working Life Research in Europe and Academic Medical Center, University of Amsterdam.
Statistics Sweden (SCB) (1994). Arbetssjukdomar och arbetsolyckor 1992. Sveriges Officiella Statistik, Stockholm.
Steenland, K. (2000). Shift work, long hours, and cardiovascular disease: a review. Occupational Medicine, 15, 7–17.
Sundström-Frisk, C. (1984). Behavioural control through piece-rate wages. Journal of Occupational Accidents, 6, 49–59.
Tenkanen, L., Sjoblom, T., and Harma, M. (1998). Joint effect of shift work and adverse life-style factors on the risk of coronary heart disease. Scandinavian Journal of Work Environment and Health, 24, 351–7.
Trinca, G., Johnston, I., Campbell, F., et al. (1988). Reducing traffic injury—a global challenge. Royal Australasian College of Surgeons, Melbourne.
Vaaranen, V., Vasama, M., Toikkanen, J., Jolanki, R., and Kaupinen, T. (1994). Ammattitauditi 1993 (Occupational diseases in Finland l993). Institute of Occupational Health, Helsinki.
Vernon, H.M. (1921). Industrial fatigue and efficiency. Routledge, London.
Viikari-Juntura, E. (1997). The scientific basis for making guidelines and standards to prevent work-related musculoskeletal disorders. Ergonomics, 40, 1097–117.
Viikari-Juntura, E. and Silverstein, B.A. (1999). Role of physical load factors in carpal tunnel syndrome. Scandinavian Journal of Work Environment and Health, 25, 163–85.
Vingård, E., Hogstedt, C., Alfredsson, L., Fellenius, E., Goldie, I., and Köster, M. (1991). Coxarthrosis and physical work load. Scandinavian Journal of Work Environment and Health, 17, 14–19.
Wallerstein, N. and Weinger, M. (1992). Health and safety education for worker empowerment. American Journal of Public Health, 22, 619–35.
Waters, T.W., Putz-Anderson, V., Garg, A., and Fine, L.J. (1993). Revised NIOSH equation for the design and evaluation of manual lifting tasks. Ergonomics, 36, 749–76.
WHO (World Health Organization) (1985). Identification and control of work related diseases, Technical Report Series 714. WHO, Geneva.
Winkel, J. and Westgaard, R. (1992). Occupational and individual risk factors for shoulder–neck complaints. Part I: Guidelines for the practitioner. Part II: The scientific basis (literature review) for the guide. International Journal of Industrial Ergonomics, 10, 79–104.

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