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9 Design, Practice, and Standards for VDT Equipment and Work Many video display terminals have been designed and introduced into workplaces with little attention to existing data and well- established principles of design and practice. There is a large base of knowledge about image quality, lighting and reflections, workplace design, and industrial and organizational psychology that has often been disregarded or inappropriately applied. It is likely that problems with and concerns about the comfort and performance of workers using VDTs would be greatly alleviated by the appropriate application of this knowledge to the design of VDT equipment and VDT jobs. The first section of this chapter discusses specific ways in which this knowledge can be applied to enhance the comfort, performance, and job satisfaction of VDT workers. The second section examines guidelines and standards for VDT design that have been proposed or enacted into law in several European countries and Canada and discusses whether useful and appro- priate standards should be established in the United States on the basis of present data. PRINCIPLES OF GOOD DESIGN AND PRACTICE Image Quality and Display Design A number of display parameters that are known to influence visual performance (discussed in Chapter 4) may also influence operator comfort, but the relationships have not been quantitatively established. As a minimum, the following eight parameters should be considered in the design of displays: 1. Modulation transfer function (NITF) or other quality measures; 194
195 2. Acceptable color ranges (specified either as dominant wavelength and purity or as Commission Internationale de l'Eclairage [C1E] x,y coordinates); 3. Luminance and contrast for positive- and negative~ontrast displays; 4. Dot-matrix and character sizes; 5. Character fonts; 6. Display jitter and geometric fidelity; 7. Specular and diffuse reflection coefficients; and 8. Number, spacing, and luminance profiles of video scan lines. The use of existing data on visual processes and visual perfor- mance to determine appropriate values for these parameters could do much to prevent workplace problems. The complex considera- tions discussed in Chapter 4 preclude simply listing here a set or range of preferred values for these parameters. For many of them, compromises between ideal values and ergonomic and technological constraints are necessary; for others, existing data are not adequate to establish appropriate values, and further research is needed. Specific detailed procedures for measuring parameters of image quality should be established so that mean- ingful comparisons between VDT sets can be made. Lighting and Reflections The use of VDTs in workplaces in which the lighting is designed for traditional desk-top tasks is likely to adversely affect the comfort and performance of VDT operators. Virtually all of the problems associated with lighting and reflections in VDT workplaces can be eliminated or prevented by applying established principles of illuminating engineering, including lighting specification systems, in systematic workplace lighting design (discussed in Chapter 5~. Problems caused by inappropriate lighting can be classified into three general categories: (1) those caused by direct glare, (2) those caused by successive viewing of different luminances (trans- ient adaptation), and (3) those caused by reflected glare and veiling reflections. Minimizing Problems Caused by Direct Glare and Transient Adaptation It is not possible to specify exact numerical values for lighting parameters for workplaces because of the enormous diversity of
196 VDT workplaces. We suggest that the values discussed in this section and in the references cited be treated as rough guidelines; a flexible approach is needed to optimize lighting conditions for particular tasks at particular workstations. Discomfort glare and disability glare can be minimized in several ways (Stewart, 1980b; Christensen, 1981; Cole, 1981; see also Chapter 5~. Direct glare problems caused by a bright light source, such as a window or luminaire, near a VDT screen can be solved simply by repositioning the screen; if repositioning is not possible, the light source should be screened. Workplace lighting should be designed so that the ratio of the luminance of the dis- play to the luminance of the areas immediately surrounding the display is no higher than approximately 1:3. Areas not immedi- ately surrounding the display but still within the operator's visual field should have luminances of approximately 5 to 10 times that of the display. Because the luminance of most displays is either fixed or can be adjusted only within a fairly narrow range, ambi- ent illumination should be much lower than that typically used in offices; 300-500 lux of ambient illumination allows adequate visibility of both the display and hard-copy materials. It may be useful in some situations to lower ambient illumination still further; in this case it may be necessary to provide secondary lighting of hard-copy materials. Measures that reduce direct glare also minimize the likelihood of problems with transient adaptation. In addition, the use of negative-contrast displays can reduce the likelihood of difficulty with transient adaptation. The use of negative-contrast displays does, however, involve some tradeoffs and issues that are not yet resolved (see Chapters 4 and 5~. Minimizing Reflected Glare and Veiling Reflections Several steps can be taken to minimize reflected glare and veiling reflections (Stewart, 1980b; Christensen, 1981; Cole, 1981; see also Chapter 5~. Reflected glare from light sources such as windows and luminaires can be reduced by positioning the VDT screen perpendicular to the plane of the light sources. When such positioning is not possible, windows and lunninaires should be shielded or screened: for example, parabolic wedge louvres can be used to reduce side light from luminaires. The use of VDTs in which the screen angle can be adjusted can also help in reducing reflections; a hood placed around the screen can help minimize veiling reflections. Reflections off the front surface of a VDT screen can reduce the contrast and thus the visibility of the display image. Such reflections can also act as additional visual targets, which may
197 promote fluctuations in accommodation and convergence. The use of negative-contrast displays may help to reduce these effects. The luminance of reflected images and thus their effect on the visibility of the display image can be reduced by reducing the reflectance of materials in the area surrounding the VDT. The luminance of reflected images can also be reduced by using filters of various types. While filters reduce the luminance of the reflected image with respect to the luminance of the display image, they also tend to diffuse the display image to varying degrees (see the discussion in Chapter 4~. Systematic Design of VDT Workstations General Considerations To achieve an ergonomically satisfactory workstation design, the multiple interactions between task, environment, and workplace elements must be considered (see the discussion in Chapter 6~. The system components of the workstation include the display and its support, the keyboard and its support, the work seat, and the needed leg space in which foot controls may be located. All of these system elements are integrated through an operator, who determines system output and system dimensions. A VDT must be located at the proper distance and elevation with respect to the human eye. The screen is usually located in front of the operator near the source document and possibly near the keyboard. Design parameters for the location of a VDT and its support are primarily determined by the operator Is preferred viewing distance and preferred inclination of the line of sight (below the horizontal). The same principal considerations apply to the source docu- ment (and its holder). Its distance from the operator is largely dependent on the operator's ability to focus clearly on the visual target, and its height depends on the operator's preferred incli- nation of the line of sight. These parameters are also influenced by the quality of illumination on the source document. Manual work areas include the keyboard and writing surfaces. The keyboard itself should be detachable from the screen so that it can be located for the convenience and preference of the VDT operator. It therefore needs a separate support, adjustable independently of the screen support. While there is de facto agreement on the standard (QWERTY) keyboard with straight lines of keys arranged behind each other on a flat slope, current data indicate that other designssuch as a lateral tilt of separate left- and right-hand keyboards, including built-in wrist rests -may be preferable. Writing surfaces should be provided as needed, at
198 an operator's preferred height and distance for ease of manipula- tion, support of the forearm, and convenience of seeing the target. Leg room for a seated operator must provide ample space to accommodate variations in posture in the lower extremities, particularly knees and feet. Severe reductions in the height, width, or depth of leg room lead to confined postures that may be uncomfortable and unhealthful. Hand, wrist, and arm supports are often said to be desirable, particularly for long-term periods of VDT operation, but there is little data on their presumed advantages. Guidelines have not yet been developed for support of hands and forearms. The work seat is needed to support the body of a seated oper- ator. While the seat pan carries most of the body weight, a properly designed backrest will also support some of the body weight. The main function of the backrest is to stabilize the body trunk and to provide suitable curvature of the spinal column. A high backrest with a properly incorporated neck support allows relaxation of neck and trunk muscles, particularly during work breaks. The backrest should be firmly attached to the seat pan and should have adjustable depth, height, and angle with respect to the seat pan. The seat pan itself should have a slight cavity in its center and should be well rounded along its front edge. Like the backrest, it should be firmly upholstered to evenly distribute the body weight. A footrest is needed if the height adjustments of the supports for display, keyboard, and chair are not sufficiently variable to allow a comfortable posture for every operator who uses a given workstation. The footrest should have a large surface, and it should be slightly inclined with adjustable height. The five-legged chair provides a more stable base with a shorter radius than the traditional four-legged chair; thus an operator's feet are kicked against the base less frequently. Over all, a five-legged chair seems to be more suitable than the four-legged chair and is now required in many European countries. Specific Design and Use Guidelines The following design guidelines apply primarily to a VDT workstation at which a person works many hours per day. As discussed in Chapter 6, this work situation probably imposes the most stringent requirements; if they are met, the workstation would also be suitable for occasional use. four design guidelines are largely derived from Ridder (1959~; Kroemer (1970, 1971, 1981~; Grandjean and Hunting, 1977; -
199 +5 ~ +15 = ~ approx. 50 high (cm) ~0-20 (cm) ~ ~= X Ao | N+15 40-50 (cm) < > 140x401_ (cm )_ , O C -O O' ~ - `;\+15° ' - :10-30 ~15 (cm ) 65-80 (cm) FIGURE 9.1 Design recommendations for VDT workstation components. SOURCE: Kroemer and Price (1982~. Reprinted with permission of ndustrial Engineering magazine, July, 1982. Copyright ° Institute of Industrial Engineers, Inc., 25 Technology Park/Atlanta, Norcross, GA 30092. The seat, keyboard, display, and foot support are interacting system components in the design of the workstation. Detailed design guidelines are shown in Figure 9.1, which gives suggested height ranges, angles, and other accommodations. The chair should be securely supported on four legs (or five casters as required in many European countries), and it should have adjust- able seat pan and backrest heights. The angles of the seat pan and backrest should be adjustable relative to each other, and the backrest should also be adjustable front and back with respect to the seat pan. In some situations the writing surface and the support surface Grandjean (1980, 1981); Easterby et al., (1981); Grandjean and coworkers (1981); and National Institute for Occupational Safety and Health (1981). Van Cott and Kinkade (1972); Churchill et al. (1 978); International Business Machines (1979); Cakir and coworkers (1980);Grandjean and Vigliani (1980); Mandal (1981); Olsen (1981); Rupp (1981); and Woodson (1981) summarize research results and present design recommendations.
200 1 1 ~1 30° 1 1 ~ (cm ) ~ \ ~ \ A\ hi\ ~~ ( ~~ 10-25 10-20 (cm) - JL 'O O O O O' 35-50 (cm) FIGURE 9.2 Design recommendations for a large work seat. for the keyboard may need to be adjustable in height, front and back distance, and angulation. Finally, the footrest, if needed, may need to be adjustable in height, angulation, and front and back distance. Figure 9.2 illustrates a chair that is larger than those usually used, with its dimensions increased in order to allow more flexi- bility in body position and support of upper back and neck. Several approaches may be taken to designing backrests that combine adequate support and mobility (see the discussion in Kroemer, 1983~. Job Design and Organizational Variables There are a number of potential healthrelated outcomes asso- ciated with psychosocial stressors that may occur with improper
201 ,/DT use. Lack of control, low social support, heavy (quantitative) workload, and underutilization of skills and abilities can all occur within the context of VDT-related tasks (see Chapter 8~. The literature we reviewed indicates that these stressors can affect mental and physical states. Variation in the Task and Task Environment There are a number of strategies for reducing workers' strain. Two of them are job rotation and rest breaks, to allow variety in the work and recovery from intense exposure to psychosocial stressors. With regard to work breaks, the National Institute for Occupational Safety and Health (1981:70) has recommended that 1. A 15-minute work-rest break should be taken after two hours of continuous VDT work for operators under moderate visual demands and/or moderate workload. 2. A 1 5-minute work-rest break should be taken after one hour of continuous VDT work for operators under high visual demands, high workload and/or those engaged in repetitive work tasks. We note, however, that "moderate" and "high" visual demands and workloads are not defined by NIOSH, and no comparison is made between VDT jobs and comparable non-VDT jobs on these parameters. A report issued by the Department of Health of New Zealand (Coe et al., 1980) finds that although fatiguelike complaints about the eyes are not alleviated by mandated formal breaks, they are alleviated by informal breaks, that is, time spent not viewing the screen, which may include time spent performing other work tasks. These findings support two major principles in Chapter 8: (1 ) low stress can be thought of as the goodness of fit between individuals and their environment, rather than the standardization of environments regardless of individual needs and abilities; and (2) participation in decision making or some degree of individual control over the nature and pace of the work allows people to exercise maximum person-environment fit because each person is assumed to be the best judge of the needs for rest breaks. The recommendation of a fixed rest break is not supported by those principles. (The NIOSH recommendations need to be reconciled with such findings.) One can imagine instances in which an imposed rest break might prove very strain-producing for an operator who is highly involved in a task and who wants to finish the task without interruption.
202 If rest breaks should be flexible, are there any other principles that should govern them? In the 1920s and 1930s much of the research in industrial psychology was directed toward finding optimal placement and duration of rest periods; the research was summarized in the first edition of the text by Ghiselli and Brown (1 948:249): 1. Rest should be introduced when performance is at a maximum, just before a reduction in productivity. lee timing of rest is more important than the length of the rest period, although optimal rest period lengths can also be determined for individual jobs. 2. Rest periods may be more useful for relatively ineffective workers; better workers seem to develop more efficient procedures and therefore have less need for rest. [It would be valuable to know whether this finding applies to performance of near-,risual work, a question not asked in this early research.] 3. Rest periods are most effective with work requiring concentration than on jobs that are more or less automatic and leave the employee free to daydream, converse with others, or follow similar monotony reducing strategies. In the many years since most of the research was done, rest periods have been determined more by negotiation than by empirical research. However, it would again be useful to determine, independently for data entry or for more screen- intensive work, the curves showing productivity, performance decrements, and optimal rest period timing to attempt to relieve visual discomfort. Over Strategies for Good Employee Management Another strategy for reducing workers' strain is allowing a VDT user the authority to delegate workload under conditions of overload or to pace the input of workload according to his or he r tolerances. Supervisors can also be framed to seek feedback on the input, production, and output of work (Katz and Kahn, 1978) so that work can be allocated according to a worker's ability to process it. Reward systems can be instituted that provide a supervisor with incentives for promoting workers' well-being, low turnover, and low absenteeism, as well as for promoting high productivity. Similarly, reward systems can be instituted that provide VDT users with incentives to give feedback when they experience excessive strain and when they perceive poor person-environment fite
203 General principles of employee participation should be used to maximize the quality of strain-reducing strategies and adherence to them (Vroom and Yetton t19733 discuss decision points in determining whether participation is appropriate). Otherwise, even well-intentioned changes in work procedures, such as job rotation, delegation of work to others, and feedback to super- visors may be resisted both because employees want to maintain a sense of control and because they perceive genuine penalties in adopting the changes. For example, it is unlikely that feedback to supervisors about excessive workload can be unilaterally man- dated: with only a simple mandate from management, an experienced worker may wisely decide that exercising the feedback option could threaten a possible future pay increase. It is obviously difficult to make specific suggestions about employee management for all possible VDT work situations in which such advice might be applied. In general, humane manage- ment techniques should be applied to the design of VDT work as they should for any other type of work. There is a large body of knowledge in industrial and organizational psychology on the determinants of employee satisfaction (see, e.g., Katzell and Yankelovich, 1975; Kahn, 1981~.2 An organ Cation planning to integrate VDT-related technology into the larger design of jobs should examine some of the suggestions that derive from that literature. We also suggest that organizations that are making a major commitment to VDT technology consider initiating their own investigations of the psychosocial components of the job design. In this way, organizations can supplement the existing knowledge regarding psychosocial stressors and their relation to the use of VDTs. If organizations do undertake such research, they could make significant advances in knowledge by adopting research designs that are specifically intended to test causal models over time and are intended to evaluate simultaneously several competing explanations for hypothesized health outcomes (for detailed discussions of such designs, see, e.g., Cooke and Campbell, 1976; Joreskog and Sorbom, 1979; Kenny, 1979~. - ZKatzell and Yankelovich (1975) summarize research that shows that the basic conditions of good working circumstances for both an employee's emotional well-being and high productivity include competent supervision, fair pay, job security, good working conditions with regard to the physical parameters of work and the fit between the nature of the work and the person's needs and abilities, and good relationships with employers and employer representatives. '>
204 STANDARDS AND GUIDELINES FOR VDT DESIGNS Standards that specify values for various workstation and work- place design parameters have been enacted or proposed in several countries. Individual and group~uthored papers in the technical literature have also recommended guideline values for various parameters. Several of the more widely known guidelines and standards are summarized in Tables 9.1-9~8. There is considerable disagreement in the specifications of some design parameters in these guidelines and standards (see Brown et al., 1982), and some authors have criticized some standards as inappropriate or untimely (see, e.g., Rupp, 1981~. The various guidelines and standards differ considerably in their underlying assumptions. Some specifications are oriented toward issues of performance; others are more concerned with issues of comfort. Because the relationship between comfort and performance is unknown for most tasks (but is likely to be com- plex) and because comfort and performance are not necessarily positively correlated, recommended specifications differ among various guidelines and standards. Research is needed to establish the relationships between comfort and performance in VDT- related work; such research would assist efforts to develop guidelines for the design of VDTs that take account of both factors. The various specifications may also conflict because some guidelines and standards include considerations of interactions between variables and others do not. For example, few of the standards take into account the well-established and quantified interaction between contrast and character size in determining character legibility. Another reason for conflicting specifications is that research on requirements for VDTs in office use is a relatively new research area, and the best approaches have yet to be established. (Some researchers who have been active in other areas have turned their attention to needs in this area without becoming adept at human performance research in VDT applica- 3We use standards to refer to specifications of values for design parameters to which strict adherence is expected. The term includes legally binding specifications, such as the German Safety Standards; specifications written into contracts, such as the U.S. Military Standards 1472B and 1472C; and specifications volun- tarily adopted by industry, such as those promulgated by the American National Standards Institute. In contrast, we use guidelines to refer to specifications that are suggested with the understanding that implementation be flexible, depending on circumstances and needs.
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213 tions; this is another factor in conflicting specifications among various guidelines and standards.) Examples of topics on which further study is needed are image characteristics, keyboard height, and needs for wristrests. Because there are many types of VOT applications, the number and variety of applications are growing rapidly, and there are major differences in VDT workstation operations, different guide- lines or standards are likely to be required for significantly dif- ferent applications and operations. Simplified specifications or guidelines can be misleading and seductively comforting. Blind compliance with guidelines or attemping to purchase a VDT for use for any task under any circumstances can lead to obvious difficulties. Both research and careful deliberation will be required to deal with the heterogeneity of applications. In this situation, we believe it is too early to establish man- datory standards. In particular there is a danger that rigid standards would stifle technological improvements and new approaches. Thus we recommend that the United States not now attempt to establish mandatory standards for VDT design. Rather, we urge three concurrent courses of action. First, users and manufacturers should become familiar with the technical literature in this area and solicit the advice and assistance of knowledgeable professionals in the design and installation of VDT equipment and the layout of workstations. Second, there should be continued dialogue between scientists, manufacturers, and users in efforts to evolve guidelines and minimum standards appropriate to particular applications. Third, research should be directed at unresolved questions about the effects of display and workstation parameters on worker comfort and performance. At the same time, judicious use of guidelines to suggest reasonable values for design parameters is useful and desirable.
