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29. Ergonomics

Chapter Editors:  Wolfgang Laurig and Joachim Vedder

 


 

Table of Contents 

Tables and Figures

Overview
Wolfgang Laurig and Joachim Vedder

Goals, Principles and Methods

The Nature and Aims of Ergonomics
William T. Singleton

Analysis of Activities, Tasks and Work Systems
Véronique De Keyser

Ergonomics and Standardization
Friedhelm Nachreiner

Checklists
Pranab Kumar Nag

Physical and Physiological Aspects

Anthropometry
Melchiorre Masali

Muscular Work
Juhani Smolander and Veikko Louhevaara

Postures at Work
Ilkka Kuorinka

Biomechanics
Frank Darby

General Fatigue
Étienne Grandjean

Fatigue and Recovery
Rolf Helbig and Walter Rohmert

Psychological Aspects

Mental Workload
Winfried Hacker

Vigilance
Herbert Heuer

Mental Fatigue
Peter Richter

Organizational Aspects of Work

Work Organization
Eberhard Ulich and Gudela Grote

Sleep Deprivation
Kazutaka Kogi

Work Systems Design

Workstations
Roland Kadefors

Tools
T.M. Fraser

Controls, Indicators  and Panels
Karl H. E. Kroemer

Information Processing and Design
Andries F. Sanders

Designing for Everyone

Designing for Specific Groups
Joke H. Grady-van den Nieuwboer

     Case Study: The International Classification of Functional Limitation in People

Cultural Differences
Houshang Shahnavaz

Elderly Workers
Antoine Laville and Serge Volkoff

Workers with Special Needs
Joke H. Grady-van den Nieuwboer

Diversity and Importance of Ergonomics--Two Examples

System Design in Diamond Manufacturing
Issachar Gilad

Disregarding Ergonomic Design Principles: Chernobyl
Vladimir M. Munipov 

Tables

Click a link below to view table in article context.

1. Basic anthropometric core list

2. Fatigue & recovery dependent on activity levels

3. Rules of combination effects of two stress factors on strain

4. Differenting among several negative consequences of mental strain

5. Work-oriented principles for production structuring

6. Participation in organizational context

7. User participation in the technology process

8. Irregular working hours & sleep deprivation

9. Aspects of advance, anchor & retard sleeps

10. Control movements & expected effects

11. Control-effect relations of common hand controls

12. Rules for arrangement of controls

13. Guidelines for labels

Figures

Point to a thumbnail to see figure caption, click to see figure in article context.

ERG040T1ERG040F1ERG040F2ERG040F3ERG040T2ERG040F5ERG070F1ERG070F2ERG070F3ERG060F2ERG060F1ERG060F3ERG080F1ERG080F4ERG090F1ERG090F2ERG090F3ERG090F4ERG225F1ERG225F2ERG150F1ERG150F2ERG150F4ERG150F5ERG150F6ERG120F1ERG130F1ERG290F1ERG160T1ERG160F1ERG185F1ERG185F2ERG185F3ERG185F4ERG190F1ERG190F2ERG190F3ERG210F1ERG210F2ERG210F3ERG210F4ERG210T4ERG210T5ERG210T6ERG220F1ERG240F1ERG240F2ERG240F3ERG240F4ERG260F1ERG300F1ERG255F1

Monday, 14 March 2011 19:11

Mental Fatigue

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Mental strain is a normal consequence of the coping process with mental workload (MWL). Long-term load or a high intensity of job demands can result in short-term consequences of overload (fatigue) and underload (monotony, satiation) and in long-term consequences (e.g., stress symptoms and work-related diseases). The maintenance of the stable regulation of actions while under strain can be realized through changes in one’s action style (by variation of strategies of information-seeking and decision-making), in the lowering of the level of need for achievement (by redefinition of tasks and reduction of quality standards) and by means of a compensatory increase of psychophysiological effort and afterwards a decrease of effort during work time.

This understanding of the process of mental strain can be conceptualized as a transactional process of action regulation during the imposition of loading factors which include not only the negative components of the strain process but also the positive aspects of learning such as accretion, tuning and restructuring and motivation (see figure 2).

Figure 1. Components of the process of strain and its consequences

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Mental fatigue can be defined as a process of time-reversible decrement of behavioural stability in performance, mood and activity after prolonged working time. This state is temporarily reversible by changing the work demands, the environmental influences or stimulation and is completely reversible by means of sleep.

Mental fatigue is a consequence of performing tasks with a high level of difficulty that involve predominantly information processing and/or are of protracted duration. In contrast with monotony, the recovery of the decrements is time-consuming and does not occur suddenly after changing task conditions. Symptoms of fatigue are identified on several levels of behavioural regulation: dis-regulation in the biological homeostasis between environment and organism, dis-regulation in the cognitive processes of goal-directed actions and loss of stability in goal-oriented motivation and achievement level.

 

 

 

 

 

 

 

 

 

 

Symptoms of mental fatigue can be identified in all subsystems of the human information processing system:

  • perception: reduced eye movements, reduced discrimination of signals, threshold deterioration
  • information processing: extension of decision time, action slips, decision uncertainty, blockings, “risky strategies” in action sequences, disturbances in sensorimotor coordination of movements
  • memory functions: prolongation of information in ultrashort-term storages, disturbances in the rehearsal processes in short-term memory, delay in information transmission in long-term memory and in memory searching processes.

Differential Diagnostic of Mental Fatigue

Sufficient criteria exist to differentiate amongst menta fatigue, monotony, mental satiation and stress (in a narrow sense) (table 1).

Table 1. Differentiation among several negative consequences of mental strain

Criteria

Mental fatigue

Monotony

Satiation        

Stress

Key
condition

Poor fit in terms of overload
preconditions

Poor fit in terms
of underload
preconditions

Loss of perceived sense of tasks

Goals perceived
as threatening

Mood

Tiredness without
boredom exhaustion

Tiredness with
boredom

Irritability

Anxiety, threat
aversion

Emotional
evaluation

Neutral

Neutral

Increased affective aversion

Increased anxiety

Activation

Continuously
decreased

Not continuously
decreased

Increased

Increased

Recovery

Time-consuming

Suddenly after task alternation

?

Long-term
disturbances in recovery

Prevention

Task design,
training, short-break
system

Enrichment of job content

Goal-setting
programmes
and job
enrichment

Job redesign,
conflict and stress management

 

Degrees of Mental Fatigue

The well-described phenomenology of mental fatigue (Schmidtke 1965), many valid methods of assessment and the great amount of experimental and field results offer the possibility of an ordinal scaling of degrees of mental fatigue (Hacker and Richter 1994). The scaling is based on the individual’s capacity to cope with behavioural decrements:

Level 1: Optimal and efficient performance: no symptoms of decrement in performance, mood and activation level.

Level 2: Complete compensation characterized by increased peripheral psycho-physiological activation (e.g., as measured by electromyogram of finger muscles), perceived increase of mental effort, increased variability in performance criteria.

Level 3: Labile compensation additional to that described in level 2: action slips, perceived fatigue, increasing (compensatory) psycho-physiological activity in central indicators, heart rate, blood pressure.

Level 4: Reduced efficiency additional to that described in level 3: decrease of performance criteria.

Level 5: Yet further functional disturbances: disturbances in social relationships and cooperation at workplace; symptoms of clinical fatigue like loss of sleep quality and vital exhaustion.

Prevention of Mental Fatigue

The design of task structures, environment, rest periods during working time and sufficient sleep are the ways to reduce symptoms of mental fatigue in order that no clinical consequences will occur:

1. Changes in the structure of tasks. Designing of preconditions for adequate learning and task structuring is not only a means of furthering the development of efficient job structures, but is also essential for the prevention of a misfit in terms of mental overload or underload:

  • Information processing burdens can be relieved by developing efficient internal task representations and organization of information. The resulting enlargement of cognitive capacity will match information needs and resources more aptly.
  • Human-centred technologies with high compatibility between the order of information as it is presented and the required task (Norman 1993) will reduce the mental effort necessary for information recoding and, in consequence, relieve symptoms of fatigue and stress.
  • Well-balanced coordination of different levels of regulations (as they apply to skills, rules and knowledge) may reduce effort and, moreover, increase human reliability (Rasmussen 1983).
  • Training workers in goal-directed action sequences in advance of actual problems will lighten their sense of mental effort by making their jobs clearer, more predictable and more evidently under their control. Their psychophysiological activation level will be effectively reduced.

 

2. Introduction of systems of short-term breaks during work. The positive effects of such breaks depend on the observance of some preconditions. More short breaks are more efficient than fewer long breaks; effects depend on a fixed and therefore anticipatable time schedule; and the content of the breaks should have a compensatory function to the physical and mental job demands.

3. Sufficient relaxation and sleep. Special employee-assistant programmes and stress-management techniques may support the ability of relaxation and the prevention of the development of chronicle fatigue (Sethi, Caro and Schuler 1987).

 

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Monday, 14 March 2011 19:23

Work Organization

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Design of Production Systems

Many companies invest millions in computer-supported production systems and at the same time do not make full use of their human resources, whose value can be significantly increased through investments in training. In fact, the use of qualified employee potential instead of highly complex automation can not only, in certain circumstances, significantly reduce investment costs, it can also greatly increase flexibility and system capability.

Causes of Inefficient Use of Technology

The improvements which investments in modern technology are intended to make are frequently not even approximately achieved (Strohm, Kuark and Schilling 1993; Ulich 1994). The most important reasons for this are due to problems in the areas of technology, organization and employee qualifications.

Three main causes can be identified for problems with technology:

  1. Insufficient technology. Because of the rapidity of technological changes, new technology reaching the market has sometimes undergone inadequate continuous usability tests, and unplanned downtime can result.
  2. Unsuitable technology. Technology developed for large companies is often not suitable for smaller companies. When a small firm introduces a production planning and control system developed for a large company, it may deprive itself of the flexibility necessary for its success or even survival.
  3. Excessively complex technology. When designers and developers use their entire planning knowledge to realize what is technically feasible without taking into account the experience of those involved in production, the result can be complex automated systems which are no longer easy to master.

 

Problems with organization are primarily attributable to continuous attempts at implementing the latest technology in unsuitable organizational structures. For instance, it makes little sense to introduce third, fourth and fifth generation computers into second generation organizations. But this is exactly what many companies do (Savage and Appleton 1988). In many companies, a radical restructuring of the organization is a precondition for the successful use of new technology. This particularly includes an examination of the concepts of production planning and control. Ultimately, local self-control by qualified operators can in certain circumstances be significantly more efficient and economical than a technically highly developed production planning and control system.

Problems with the qualifications of employees primarily arise because a large number of companies do not recognize the need for qualification measures in conjunction with the introduction of computer-supported production systems. In addition, training is too frequently regarded as a cost factor to be controlled and minimized, rather than as a strategic investment. In fact, system downtime and the resulting costs can often be effectively reduced by allowing faults to be diagnosed and remedied on the basis of operators’ competence and system-specific knowledge and experience. This is particularly the case in tightly coupled production facilities (Köhler et al. 1989). The same applies to introducing new products or product variants. Many examples of inefficient excessive technology use testify to such relationships.

The consequence of the analysis briefly presented here is that the introduction of computer-supported production systems only promises success if it is integrated into an overall concept which seeks to jointly optimize the use of technology, the structure of the organization and the enhancement of staff qualifications.

From the Task to the Design of Socio-Technical Systems

Work-related psychological concepts of production design are based on the primacy of
the task
. On the one hand, the task forms the interface between individual and organization (Volpert 1987). On the other hand, the task links the social subsystem with the technical subsystem. “The task must be the point of articulation between the social and technical system—linking the job in the technical system with its correlated role behaviour, in the social system” (Blumberg 1988).

This means that a socio-technical system, for example a production island, is primarily defined by the task which it has to perform. The distribution of work between human and machine plays a central role, because it decides whether the person “functions” as the long arm of the machine with a function leftover in an automation “gap” or whether the machine functions as the long arm of the person, with a tool function supporting human capabilities and competence. We refer to these opposing positions as “technology-oriented” and “work-oriented” (Ulich 1994).

The Concept of Complete Task

The principle of complete activity (Hacker 1986) or complete task plays a central role in work-related psychological concepts for defining work tasks and for dividing up tasks between human and machine. Complete tasks are those “over which the individual has considerable personal control” and that “induce strong forces within the individual to complete or to continue them”. Complete tasks contribute to the “development of what has been described ... as ‘task orientation’—that is, a state of affairs in which the individual’s interest is aroused, engaged and directed by the character of the task” (Emery 1959). Figure 1 summarizes characteristics of completeness which must be taken into account for measures geared towards work-oriented design of production systems.

Figure 1. Characteristics of complete tasks

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Illustrations of concrete consequences for production design arising from the principle of the complete task are the following:
  1. The independent setting of objectives, which can be incorporated into higher-order goals, requires turning away from central planning and control in favour of decentralized shop-floor control, which provides the possibility of making self-determined decisions within defined periods of time.
  2. Self-determined preparation for action, in the sense of carrying out planning functions, requires the integration of work preparation tasks on the shop-floor.
  3. Selecting methods means, for example, allowing a designer to decide whether he or she wishes to use the drawing board instead of an automated system (such as a CAD application) to perform certain subtasks, provided that it is ensured that data required for other parts of the process are entered in the system.
  4. Performance functions with process feedback for correcting actions where appropriate require in the case of encapsulated work processes “windows to the process” which help to minimize process distance.
  5. Action control with feedback of results means that shop-floor workers take on the function of quality inspection and control.

 

These indications of the consequences arising from realizing the principle of the complete task make two things clear: (1) in many cases—probably even the majority of cases—complete tasks in the sense described in figure 1 can only be structured as group tasks on account of the resulting complexity and the associated scope; (2) restructuring of work tasks—particularly when it is linked to introducing group work—requires their integration into a comprehensive restructuring concept which covers all levels of the company.

The structural principles which apply to the various levels are summarized in table 1.

Table 1. Work-oriented principles for production structuring

Organizational level

Structural principle

Company

Decentralization

Organizational unit

Functional integration

Group

Self-regulation1

Individual

Skilled production work1

1 Taking into account the principle of differential work design.

Source: Ulich 1994.

Possibilities for realizing the principles for production structuring outlined in table 1 are illustrated by the proposal for restructuring a production company shown in figure 2. This proposal, which was unanimously approved both by those responsible for production and by the project group formed for the purpose of restructuring, also demonstrates a fundamental turning away from Tayloristic concepts of labour and authority divisions. The examples of many companies show that the restructuring of work and organization structures on the basis of such models is able to meet both work psychological criteria of promoting health and personality development and the demand for long-term economic efficiency (see Ulich 1994).

Figure 2. Proposal for restructuring a production company

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The line of argument favoured here—only very briefly outlined for reasons of space—seeks to make three things clear:

  1. Concepts like the ones mentioned here represent an alternative to “lean production” in the sense described by Womack, Jones and Roos (1990). While in the latter approach “every free space is removed” and extreme breaking down of work activities in the Tayloristic sense is maintained, in the approach being advanced in these pages, complete tasks in groups with wide-ranging self-regulation play a central role.
  2. Classical career paths for skilled workers are modified and in some cases precluded by the necessary realization of the functional integration principle, that is, with the reintegration on the shop-floor of what are known as indirectly productive functions, such as shop-floor work preparation, maintenance, quality control and so forth. This requires a fundamental reorientation in the sense of replacing the traditional career culture with a competence culture.
  3. Concepts such as those mentioned here mean a fundamental change to corporate power structures which must find their counterpart in the development of corresponding possibilities for participation.

 

Workers’ Participation

In the previous sections types of work organization were described that have as one basic characteristic the democratization at lower levels of an organization’s hierarchy through increased autonomy and decision latitude regarding work content as well as working conditions on the shop-floor. In this section, democratization is approached from a different angle by looking at participative decision-making in general. First, a definitional framework for participation is presented, followed by a discussion of research on the effects of participation. Finally, participative systems design is looked at in some detail.

Definitional framework for participation

Organizational development, leadership, systems design, and labour relations are examples of the variety of tasks and contexts where participation is considered relevant. A common denominator which can be regarded as the core of participation is the opportunity for individuals and groups to promote their interests through influencing the choice between alternative actions in a given situation (Wilpert 1989). In order to describe participation in more detail, a number of dimensions are necessary, however. Frequently suggested dimensions are (a) formal-informal, (b) direct-indirect, (c) degree of influence and (d) content of decision (e.g., Dachler and Wilpert 1978; Locke and Schweiger 1979). Formal participation refers to participation within legally or otherwise prescribed rules (e.g., bargaining procedures, guidelines for project management), while informal participation is based on non-prescribed exchanges, for example, between supervisor and subordinate. Direct participation allows for direct influence by the individuals concerned, whereas indirect participation functions through a system of representation. Degree of influence is usually described by means of a scale ranging from “no information to employees about a decision”, through “advance information to employees” and “consultation with employees” to “common decision of all parties involved”. As regards the giving of advance information without any consultation or common decision-making, some authors argue that this is not a low level of participation at all, but merely a form of “pseudo-participation” (Wall and Lischeron 1977). Finally, the content area for participative decision-making can be specified, for example, technological or organizational change, labour relations, or day-to-day operational decisions.

A classification scheme quite different from those derived from the dimensions presented so far was developed by Hornby and Clegg (1992). Based on work by Wall and Lischeron (1977), they distinguish three aspects of participative processes:

  1. the types and levels of interactions between the parties involved in a decision
  2. the flow of information between the participants
  3. the nature and degree of influence the parties exert on each other.

 

They then used these aspects to complement a framework suggested by Gowler and Legge (1978), which describes participation as a function of two organizational variables, namely, type of structure (mechanistic versus organic) and type of process (stable versus unstable). As this model includes a number of assumptions about participation and its relationship to organization, it cannot be used to classify general types of participation. It is presented here as one attempt to define participation in a broader context (see table 2). (In the last section of this article, Hornby and Clegg’s study (1992) will be discussed, which also aimed at testing the model’s assumptions.)

Table 2. Participation in organizational context

 

Organizational structure

 

Mechanistic

Organic

Organizational  processes

   

Stable

Regulated
Interaction: vertical/command
Information flow: non-reciprocal
Influence: asymmetrical

Open
Interaction: lateral/consultative
Information flow: reciprocal
Influence: asymmetrical

Unstable

Arbitrary
Interaction: ritualistic/random
Information flow:
non-reciprocal/sporadic
Influence: authoritarian

Regulated
Interaction: intensive/random
Information flow:
reciprocal/interrogative
Influence: paternalistic

Source: Adapted from Hornby and Clegg 1992.

An important dimension usually not included in classifications for participation is the organizational goal behind choosing a participative strategy (Dachler and Wilpert 1978). Most fundamentally, participation can take place in order to comply with a democratic norm, irrespective of its influence on the effectiveness of the decision-making process and the quality of the decision outcome and implementation. On the other hand, a participative procedure can be chosen to benefit from the knowledge and experience of the individuals involved or to ensure acceptance of a decision. Often it is difficult to identify the objectives behind choosing a participative approach to a decision and often several objectives will be found at the same time, so that this dimension cannot be easily used to classify participation. However, for understanding participative processes it is an important dimension to keep in mind.

Research on the effects of participation

A widely shared assumption holds that satisfaction as well as productivity gains can be achieved by providing the opportunity for direct participation in decision-making. Overall, research has supported this assumption, but the evidence is not unequivocal and many of the studies have been criticized on theoretical and methodological grounds (Cotton et al. 1988; Locke and Schweiger 1979; Wall and Lischeron 1977). Cotton et al. (1988) argued that inconsistent findings are due to differences in the form of participation studied; for instance, informal participation and employee ownership are associated with high productivity and satisfaction whereas short-term participation is ineffective in both respects. Although their conclusions were strongly criticized (Leana, Locke and Schweiger 1990), there is agreement that participation research is generally characterized by a number of deficiencies, ranging from conceptual problems like those mentioned by Cotton et al. (1988) to methodological issues like variations in results based on different operationalizations of the dependent variables (e.g., Wagner and Gooding 1987).

To exemplify the difficulties of participation research, the classic study by Coch and French (1948) is briefly described, followed by the critique of Bartlem and Locke (1981). The focus of the former study was overcoming resistance to change by means of participation. Operators in a textile plant where frequent transfers between work tasks occurred were given the opportunity to participate in the design of their new jobs to varying degrees. One group of operators participated in the decisions (detailed working procedures for new jobs and piece rates) through chosen representatives, that is, several operators of their group. In two smaller groups, all operators participated in those decisions and a fourth group served as control with no participation allowed. Previously it had been found in the plant that most operators resented being transferred and were slower in relearning their new jobs as compared with learning their first job in the plant and that absenteeism and turnover among transferred operators was higher than among operators not recently transferred.

This occurred despite the fact that a transfer bonus was given to compensate for the initial loss in piece-rate earnings after a transfer to a new job. Comparing the three experimental conditions it was found that the group with no participation remained at a low level of production—which had been set as the group standard—for the first month after the transfer, while the groups with full participation recovered to their former productivity within a few days and even exceeded it at the end of the month. The third group that participated through chosen representatives did not recover as fast, but showed their old productivity after a month. (They also had insufficient material to work on for the first week, however.) No turnover occurred in the groups with participation and little aggression towards management was observed. The turnover in the participation group without participation was 17% and the attitude towards management was generally hostile. The group with no participation was broken up after one month and brought together again after another two and one-half months to work on a new job, and this time they were given the opportunity to participate in the design of their job. They then showed the same pattern of recovery and increased productivity as the groups with participation in the first experiment. The results were explained by Coch and French on the basis of a general model of resistance to change derived from work by Lewin (1951, see below).

Bartlem and Locke (1981) argued that these findings could not be interpreted as support for the positive effects of participation because there were important differences between the groups as regards the explanation of the need for changes in the introductory meetings with management, the amount of training received, the way the time studies were carried out to set the piece rate, the amount of work available and group size. They assumed that perceived fairness of pay rates and general trust in management contributed to the better performance of the participation groups, not participation per se.

In addition to the problems associated with research on the effects of participation, very little is known about the processes that lead to these effects (e.g., Wilpert 1989). In a longitudinal study on the effects of participative job design, Baitsch (1985) described in detail processes of competence development in a number of shop-floor employees. His study can be linked to Deci’s (1975) theory of intrinsic motivation based on the need for being competent and self-determining. A theoretical framework focusing on the effects of participation on the resistance to change was suggested by Lewin (1951) who argued that social systems gain a quasi-stationary equilibrium which is disturbed by any attempt at change. For the change to be successfully carried through, forces in favour of the change must be stronger than the resisting forces. Participation helps in reducing the resisting forces as well as in increasing the driving forces because reasons for resistance can be openly discussed and dealt with, and individual concerns and needs can be integrated into the proposed change. Additionally, Lewin assumed that common decisions resulting from participatory change processes provide the link between the motivation for change and the actual changes in behaviour.

Participation in systems design

Given the—albeit not completely consistent—empirical support for the effectiveness of participation, as well as its ethical underpinnings in industrial democracy, there is widespread agreement that for the purposes of systems design a participative strategy should be followed (Greenbaum and Kyng 1991; Majchrzak 1988; Scarbrough and Corbett 1992). Additionally, a number of case studies on participative design processes have demonstrated the specific advantages of participation in systems design, for example, regarding the quality of the resulting design, user satisfaction, and acceptance (i.e., actual use) of the new system (Mumford and Henshall 1979; Spinas 1989; Ulich et al. 1991).

The important question then is not the if, but the how of participation. Scarbrough and Corbett (1992) provided an overview of various types of participation in the various stages of the design process (see table 3). As they point out, user involvement in the actual design of technology is rather rare and often does not extend beyond information distribution. Participation mostly occurs in the latter stages of implementation and optimization of the technical system and during the development of socio-technical design options, that is, options of organizational and job design in combination with options for the use of the technical system.

Table 3. User participation in the technology process

 

Type of participation

Phases of technology process

Formal

Informal

Design

Trade union consultation
Prototyping

User redesign

Implementation

New technology agreements
Collective bargaining

Skills bargaining
Negotiation
User cooperation

Use

Job design

Quality circles

Informal job redesign
and work practices

Adapted from Scarbrough and Corbett 1992.

Besides resistance in managers and engineers to the involvement of users in the design of technical systems and potential restrictions embedded in the formal participation structure of a company, an important difficulty concerns the need for methods that allow the discussion and evaluation of systems that do not yet exist (Grote 1994). In software development, usability labs can help to overcome this difficulty as they provide an opportunity for early testing by future users.

In looking at the process of systems design, including participative processes, Hirschheim and Klein (1989) have stressed the effects of implicit and explicit assumptions of system developers and managers about basic topics such as the nature of social organization, the nature of technology and their own role in the development process. Whether system designers see themselves as experts, catalysts or emancipators will greatly influence the design and implementation process. Also, as mentioned before, the broader organizational context in which participative design takes place has to be taken into account. Hornby and Clegg (1992) provided some evidence for the relationship between general organizational characteristics and the form of participation chosen (or, more precisely, the form evolving in the course of system design and implementation). They studied the introduction of an information system which was carried out within a participative project structure and with explicit commitment to user participation. However, users reported that they had had little information about the changes supposed to take place and low levels of influence over system design and related questions like job design and job security. This finding was interpreted in terms of the mechanistic structure and unstable processes of the organization that fostered “arbitrary” participation instead of the desired open participation (see table 2).

In conclusion, there is sufficient evidence demonstrating the benefits of participative change strategies. However, much still needs to be learned about the underlying processes and influencing factors that bring about, moderate or prevent these positive effects.

 

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Monday, 14 March 2011 19:35

Sleep Deprivation

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Healthy individuals regularly sleep for several hours every day. Normally they sleep during the night hours. They find it most difficult to remain awake during the hours between midnight and early morning, when they normally sleep. If an individual has to remain awake during these hours either totally or partially, the individual comes to a state of forced sleep loss, or sleep deprivation, that is usually perceived as tiredness. A need for sleep, with fluctuating degrees of sleepiness, is felt which continues until sufficient sleep is taken. This is the reason why periods of sleep deprivation are often said to cause a person to incur sleep deficit or sleep debt.

Sleep deprivation presents a particular problem for workers who cannot take sufficient sleep periods because of work schedules (e.g., working at night) or, for that matter, prolonged free-time activities. A worker on a night shift remains sleep-deprived until the opportunity for a sleep period becomes available at the end of the shift. Since sleep taken during daytime hours is usually shorter than needed, the worker cannot recover from the condition of sleep loss sufficiently until a long sleep period, most likely a night sleep, is taken. Until then, the person accumulates a sleep deficit. (A similar condition—jet lag—arises after travelling between time zones that differ by a few hours or more. The traveller tends to be sleep-deprived as the activity periods in the new time zone correspond more clearly to the normal sleep period in the originating place.) During the periods of sleep loss, workers feel tired and their performance is affected in various ways. Thus various degrees of sleep deprivation are incorporated into the daily life of workers having to work irregular hours and it is important to take measures to cope with unfavourable effects of such sleep deficit. The main conditions of irregular working hours that contribute to sleep deprivation are shown in table 1.

Table 1. Main conditions of irregular working hours which contribute to sleep deprivation of various degrees

Irregular working hours

Conditions leading to sleep deprivation

Night duty

No or shortened night-time sleep

Early morning or late evening duty

Shortened sleep, disrupted sleep

Long hours of work or working  two shifts together

Phase displacement of sleep

Straight night or early morning shifts

Consecutive phase displacement of sleep

Short between-shift period

Short and disrupted sleep

Long interval between days off

Accumulation of sleep shortages

Work in a different time zone

No or shortened sleep during the “night” hours in the originating place (jet lag)

Unbalanced free time periods

Phase displacement of sleep, short sleep

 

In extreme conditions, sleep deprivation may last for more than a day. Then sleepiness and performance changes increase as the period of sleep deprivation is prolonged. Workers, however, normally take some form of sleep before sleep deprivation becomes too protracted. If the sleep thus taken is not sufficient, the effects of sleep shortage still continue. Thus, it is important to know not only the effects of sleep deprivation in various forms but also the ways in which workers can recover from it.

Figure 1.  Perfomance, sleep ratings and physiological variables of a group of subjects exposed to two nights of sleep deprivation

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The complex nature of sleep deprivation is shown by figure 1, which depicts data from laboratory studies on the effects of two days of sleep deprivation (Fröberg 1985). The data show three basic changes resulting from prolonged sleep deprivation:

  1. There is a general decreasing trend in both objective performance and subjective ratings of performance efficiency.
  2. The decline in performance is influenced by the time of day. This cycling decline is correlated with those physiological variables which have a circadian cycling period. Performance is better in the normal activity phase when, for example, adrenaline excretion and body temperature are higher than those in the period originally assigned to a normal night’s sleep, when the physiological measures are low.
  3. Self-ratings of sleepiness increase with time of continuous sleep deprivation, with a clear cyclic component associated with time of day.

 

The fact that the effects of sleep deprivation are correlated with physiological circadian rhythms helps us to understand its complex nature (Folkard and Akerstedt 1992). These effects should be viewed as a result of a phase shift of the sleep-wakefulness cycle in one’s daily life.

The effects of continuous work or sleep deprivation thus include not only a reduction in alertness but decreased performance capabilities, increased probability of falling asleep, lowered well-being and morale and impaired safety. When such periods of sleep deprivation are repeated, as in the case of shift workers, their health may be affected (Rutenfranz 1982; Koller 1983; Costa et al. 1990). An important aim of research is thus to determine to what extent sleep deprivation damages the well-being of individuals and how we can best use the recovery function of sleep in reducing such effects.

Effects of Sleep Deprivation

During and after a night of sleep deprivation, the physiological circadian rhythms of the human body seem to remain sustained. For example, the body temperature curve during the first day’s work among night-shift workers tends to keep its basic circadian pattern. During the night hours, the temperature declines towards early morning hours, rebounds to rise during the subsequent daytime and falls again after an afternoon peak. The physiological rhythms are known to get “adjusted” to the reversed sleep-wakefulness cycles of night-shift workers only gradually in the course of several days of repeated night shifts. This means that the effects on performance and sleepiness are more significant during night hours than in the daytime. The effects of sleep deprivation are therefore variably associated with the original circadian rhythms seen in physiological and psychological functions.

The effects of sleep deprivation on performance depend on the type of the task to be performed. Different characteristics of the task influence the effects (Fröberg 1985; Folkard and Monk 1985; Folkard and Akerstedt 1992). Generally, a complex task is more vulnerable than a simpler task. Performance of a task involving an increasing number of digits or a more complex coding deteriorates more during three days of sleep loss (Fröberg 1985; Wilkinson 1964). Paced tasks that need to be responded to within a certain interval deteriorate more than self-paced tasks. Practical examples of vulnerable tasks include serial reactions to defined stimulations, simple sorting operations, the recording of coded messages, copy typing, display monitoring and continuous inspection. Effects of sleep deprivation on strenuous physical performance are also known. Typical effects of prolonged sleep deprivation on performance (on a visual task) is shown in figure 2 (Dinges 1992). The effects are more pronounced after two nights of sleep loss (40-56 hours) than after one night of sleep loss (16-40 hours).

Figure 2. Regression lines fit to response speed (the reciprocal of response times) on a 10-minute simple, unprepared visual task administered repeatedly to healthy young adults during no sleep loss (5-16 hours), one night of sleep loss (16-40 hours) and two nights of sleep loss (40-56 hours)

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The degree to which the performance of tasks is affected also appears to depend on how it is influenced by the “masking” components of the circadian rhythms. For example, some measures of performance, such as five-target memory search tasks, are found to adjust to night work considerably more quickly than serial reaction time tasks, and hence they may be relatively unimpaired on rapidly rotating shift systems (Folkard et al. 1993). Such differences in the effects of endogenous physiological body clock rhythms and their masking components must be taken into account in considering the safety and accuracy of performance under the influence of sleep deprivation.

One particular effect of sleep deprivation on performance efficiency is the appearance of frequent “lapses” or periods of no response (Wilkinson 1964; Empson 1993). These performance lapses are short periods of lowered alertness or light sleep. This can be traced in records of videotaped performance, eye movements or electroencephalograms (EEGs). A prolonged task (one-half hour or more), especially when the task is replicated, can more easily lead to such lapses. Monotonous tasks such as repetitions of simple reactions or monitoring of infrequent signals are very sensitive in this regard. On the other hand, a novel task is less affected. Performance in changing work situations is also resistant.

While there is evidence of a gradual arousal decrease in sleep deprivation, one would expect less affected performance levels between lapses. This explains why results of some performance tests show little influence of sleep loss when the tests are done in a short period of time. In a simple reaction time task, lapses would lead to very long response times whereas the rest of the measured times would remain unchanged. Caution is thus needed in interpreting test results concerning sleep loss effects in actual situations.

Changes in sleepiness during sleep deprivation obviously relate to physiological circadian rhythms as well as to such lapse periods. Sleepiness sharply increases with time of the first period of night-shift work, but decreases during subsequent daytime hours. If sleep deprivation continues to the second night sleepiness becomes very advanced during the night hours (Costa et al. 1990; Matsumoto and Harada 1994). There are moments when the need for sleep is felt to be almost irresistible; these moments correspond to the appearance of lapses, as well as to the appearance of interruptions in the cerebral functions as evidenced by EEG records. After a while, sleepiness is felt to be reduced, but there follows another period of lapse effects. If workers are questioned about various fatigue feelings, however, they usually mention increasing levels of fatigue and general tiredness persisting throughout the sleep deprivation period and between-lapse periods. A slight recovery of subjective fatigue levels is seen during the daytime following a night of sleep deprivation, but fatigue feelings are remarkably advanced in the second and subsequent nights of continued sleep deprivation.

During sleep deprivation, sleep pressure from the interaction of prior wakefulness and circadian phase may always be present to some degree, but the lability of state in sleepy subjects is also modulated by context effects (Dinges 1992). Sleepiness is influenced by the amount and type of stimulation, the interest afforded by the environment and the meaning of the stimulation to the subject. Monotonous stimulation or that requiring sustained attention can more easily lead to vigilance decrement and lapses. The greater the physiological sleepiness due to sleep loss, the more the subject is vulnerable to environmental monotony. Motivation and incentive can help override this environmental effect, but only for a limited period.

Effects of Partial Sleep Deprivation and Accumulated Sleep Shortages

If a subject works continuously for a whole night without sleep, many performance functions will have definitely deteriorated. If the subject goes to the second night shift without getting any sleep, the performance decline is far advanced. After the third or fourth night of total sleep deprivation, very few people can stay awake and perform tasks even if highly motivated. In actual life, however, such conditions of total sleep loss rarely occur. Usually people take some sleep during subsequent night shifts. But reports from various countries show that sleep taken during daytime is almost always insufficient to recover from the sleep debt incurred by night work (Knauth and Rutenfranz 1981; Kogi 1981; ILO 1990). As a result, sleep shortages accumulate as shift workers repeat night shifts. Similar sleep shortages also result when sleep periods are reduced on account of the need to follow shift schedules. Even if night sleep can be taken, sleep restriction of as little as two hours each night is known to lead to an insufficient amount of sleep for most persons. Such sleep reduction can lead to impaired performance and alertness (Monk 1991).

Examples of conditions in shift systems which contribute to accumulation of sleep shortages, or partial sleep deprivation, are given in table 1. In addition to continued night work for two or more days, short between-shift periods, repetition of an early start of morning shifts, frequent night shifts and inappropriate holiday allotment accelerate the accumulation of sleep shortages.

The poor quality of daytime sleep or shortened sleep is important, too. Daytime sleep is accompanied by an increased frequency of awakenings, less deep and slow-wave sleep and a distribution of REM sleep different from that of normal night-time sleep (Torsvall, Akerstedt and Gillberg 1981; Folkard and Monk 1985; Empson 1993). Thus a daytime sleep may not be as sound as a night sleep even in a favourable environment.

This difficulty of taking good quality sleep due to different timing of sleep in a shift system is illustrated by figure 3 which shows the duration of sleep as a function of the time of sleep onset for German and Japanese workers based on diary records (Knauth and Rutenfranz 1981; Kogi 1985). Due to circadian influence, daytime sleep is forced to be short. Many workers may have split sleep during the daytime and often add some sleep in the evening where possible.

Figure 3. Mean sleep length as a function of the time of sleep onset. Comparison of data from German and Japanese shift workers.

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In real-life settings, shift workers take a variety of measures to cope with such accumulation of sleep shortages (Wedderburn 1991). For example, many of them try to sleep in advance before a night shift or have a long sleep after it. Although such efforts are by no means entirely effective to offset the effects of sleep deficit, they are made quite deliberately. Social and cultural activities may be restricted as part of coping measures. Outgoing free-time activities, for example, are undertaken less frequently between two night shifts. Sleep timing and duration as well as the actual accumulation of sleep deficit thus depend on both job-related and social circumstances.

 

 

 

 

Recovery from Sleep Deprivation and Health Measures

The only effective means of recovering from sleep deprivation is to sleep. This restorative effect of sleep is well known (Kogi 1982). As recovery by sleep may differ according to its timing and duration (Costa et al. 1990), it is essential to know when and for how long people should sleep. In normal daily life, it is always the best to take a full night’s sleep to accelerate the recovery from sleep deficit but efforts are usually made to minimize sleep deficit by taking sleep at different occasions as replacements of normal night sleeps of which one has been deprived. Aspects of such replacement sleeps are shown in table 2.

Table 2. Aspects of advance, anchor & retard sleeps taken as replacement of normal night sleep

Aspect

Advance sleep

Anchor sleep

Retard sleep

Occasion

Before a night shift
Between night shifts
Before early
morning work
Late evening naps

Intermittent night
work
During a night shift
Alternate-day work
Prolonged freetime
Naps taken
informally

After a night shift
Between night shifts
After prolonged
evening work
Daytime naps

Duration

Usually short

Short by definition

Usually short but
longer after late
evening work

Quality

Longer latency of
falling asleep
Poor mood on rising
Reduced REM sleep
Slow-wave sleep
dependent on
prior wakefulness

Short latency
Poor mood on rising
Sleep stages similar
to initial part of a
normal night sleep

Shorter latency for
REM sleep
Increased
awakenings
Increased REM sleep
Increased slow-wave
sleep after long
wakefulness

Interaction with
circadian
rhythms

Disrupted rhythms;
relatively faster
adjustment

Conducive to
stabilizing
original rhythms

Disrupted rhythms;
slow adjustment

 

To offset night sleep deficit, the usual effort made is to take daytime sleep in “advance” and “retard” phases (i.e., before and after night-shift work). Such a sleep coincides with the circadian activity phase. Thus the sleep is characterized by longer latency, shortened slow-wave sleep, disrupted REM sleep and disturbances of one’s social life. Social and environmental factors are important in determining the recuperative effect of a sleep. That a complete conversion of circadian rhythms is impossible for a shift worker in a real-life situation should be borne in mind in considering the effectiveness of the recovery functions of sleep.

In this respect, interesting features of a short “anchor sleep” have been reported (Minors and Waterhouse 1981; Kogi 1982; Matsumoto and Harada 1994). When part of the customary daily sleep is taken during the normal night sleep period and the rest at irregular times, the circadian rhythms of rectal temperature and urinary secretion of several electrolytes can retain a 24-hour period. This means that a short night-time sleep taken during the night sleep period can help preserve the original circadian rhythms in subsequent periods.

We may assume that sleeps taken at different periods of the day could have certain complementary effects in view of the different recovery functions of these sleeps. An interesting approach for night-shift workers is the use of a night-time nap which usually lasts up to a few hours. Surveys show this short sleep taken during a night shift is common among some groups of workers. This anchor-sleep type sleep is effective in reducing night work fatigue (Kogi 1982) and may reduce the need of recovery sleep. Figure 4 compares the subjective feelings of fatigue during two consecutive night shifts and the off-duty recovery period between the nap-taking group and the non-nap group (Matsumoto and Harada 1994). The positive effects of a night-time nap in reducing fatigue was obvious. These effects continued for a large part of the recovery period following night work. Between these two groups, no significant difference was found upon comparing the length of the day sleep of the non-nap group with the total sleeping time (night-time nap plus subsequent day sleep) of the nap group. Therefore a night-time nap enables part of the essential sleep to be taken in advance of the day sleep following night work. It can therefore be suggested that naps taken during night work can to a certain extent aid recovery from the fatigue caused by that work and accompanying sleep deprivation (Sakai et al. 1984; Saito and Matsumoto 1988).

Figure 4. Mean scores for subjective feelings of  fatigue during two consecutive night shifts and the off-duty recovery period for nap and no-nap groups

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It must be admitted, however, that it is not possible to work out optimal strategies that each worker suffering from sleep deficit can apply. This is demonstrated in the development of international labour standards for night work that recommend a set of measures for workers doing frequent night work (Kogi and Thurman 1993). The varied nature of these measures and the trend towards increasing flexibility in shift systems clearly reflect an effort to develop flexible sleep strategies (Kogi 1991). Age, physical fitness, sleep habits and other individual differences in tolerance may play important roles (Folkard and Monk 1985; Costa et al. 1990; Härmä 1993). Increasing flexibility in work schedules in combination with better job design is useful in this regard (Kogi 1991).

Sleep strategies against sleep deprivation should be dependent on type of working life and be flexible enough to meet individual situations (Knauth, Rohmert and Rutenfranz 1979; Rutenfranz, Knauth and Angersbach 1981; Wedderburn 1991; Monk 1991). A general conclusion is that we should minimize night sleep deprivation by selecting appropriate work schedules and facilitate recovery by encouraging individually suitable sleeps, including replacement sleeps and a sound night-time sleep in the early periods after sleep deprivation. It is important to prevent the accumulation of sleep deficit. The period of night work which deprives workers of sleep in the normal night sleep period should be as short as possible. Between-shift intervals should be long enough to allow a sleep of sufficient length. A better sleep environment and measures to cope with social needs are also useful. Thus, social support is essential in designing working time arrangements, job design and individual coping strategies in promoting the health of workers faced with frequent sleep deficit.

 

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Monday, 14 March 2011 19:45

Workstations

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An Integrated Approach in the Design of Workstations

In ergonomics, the design of workstations is a critical task. There is general agreement that in any work setting, whether blue-collar or white-collar, a well-designed workstation furthers not only the health and well-being of the workers, but also productivity and the quality of the products. Conversely, the poorly designed workstation is likely to cause or contribute to the development of health complaints or chronic occupational diseases, as well as to problems with keeping product quality and productivity at a prescribed level.

To every ergonomist, the above statement may seem trivial. It is also recognized by every ergonomist that working life worldwide is full of not only ergonomic shortcomings, but blatant violations of basic ergonomic principles. It is clearly evident that there is a widespread unawareness with respect to the importance of workstation design among those responsible: production engineers, supervisors and managers.

It is noteworthy that there is an international trend with respect to industrial work which would seem to underline the importance of ergonomic factors: the increasing demand for improved product quality, flexibility and product delivery precision. These demands are not compatible with a conservative view regarding the design of work and workplaces.

Although in the present context it is the physical factors of workplace design that are of chief concern, it should be borne in mind that the physical design of the workstation cannot in practice be separated from the organization of work. This principle will be made evident in the design process described in what follows. The quality of the end result of the process relies on three supports: ergonomic knowledge, integration with productivity and quality demands, and participation. The process of implementation of a new workstation must cater to this integration, and it is the main focus of this article.

Design considerations

Workstations are meant for work. It must be recognized that the point of departure in the workstation design process is that a certain production goal has to be achieved. The designer—often a production engineer or other person at middle-management level—develops internally a vision of the workplace, and starts to implement that vision through his or her planning media. The process is iterative: from a crude first attempt, the solutions become gradually more and more refined. It is essential that ergonomic aspects be taken into account in each iteration as the work progresses.

It should be noted that ergonomic design of workstations is closely related to ergonomic assessment of workstations. In fact, the structure to be followed here applies equally to the cases where the workstation already exists or when it is in a planning stage.

In the design process, there is a need for a structure which ensures that all relevant aspects be considered. The traditional way to handle this is to use checklists containing a series of those variables which should be taken into account. However, general purpose checklists tend to be voluminous and difficult to use, since in a particular design situation only a fraction of the checklist may be relevant. Furthermore, in a practical design situation, some variables stand out as being more important than others. A methodology to consider these factors jointly in a design situation is required. Such a methodology will be proposed in this article.

Recommendations for workstation design must be based on a relevant set of demands. It should be noted that it is in general not enough to take into account threshold limit values for individual variables. A recognized combined goal of productivity and conservation of health makes it necessary to be more ambitious than in a traditional design situation. In particular, the question of musculoskeletal complaints is a major aspect in many industrial situations, although this category of problems is by no means limited to the industrial environment.

A Workstation Design Process

Steps in the process

In the workstation design and implementation process, there is always an initial need to inform users and to organize the project so as to allow for full user participation and in order to increase the chance of full employee acceptance of the final result. A treatment of this goal is not within the scope of the present treatise, which concentrates on the problem of arriving at an optimal solution for the physical design of the workstation, but the design process nonetheless allows the integration of such a goal. In this process, the following steps should always be considered:

  1. collection of user-specified demands
  2. prioritizing of demands
  3. transfer of demands into (a) technical specifications and (b) specifications in user terms
  4. iterative development of the workstation’s physical layout
  5. physical implementation
  6. trial period of production
  7. full production
  8. evaluation and identification of rest problems.

 

The focus here is on steps one through five. Many times, only a subset of all these steps is actually included in the design of workstations. There may be various reasons for this. If the workstation is a standard design, such as in some VDU working situations, some steps may duly be excluded. However, in most cases the exclusion of some of the steps listed would lead to a workstation of lower quality than what can be considered acceptable. This can be the case when economic or time constraints are too severe, or when there is sheer neglect due to lack of knowledge or insight at management level.

Collection of user-specified demands

It is essential to identify the user of the workplace as any member of the production organization who may be able to contribute qualified views on its design. Users may include, for instance, the workers, the supervisors, the production planners and production engineers, as well as the safety steward. Experience shows clearly that these actors all have their unique knowledge which should be made use of in the process.

The collection of the user-specified demands should meet a number of criteria:

  1. Openness. There should be no filter applied in the initial stage of the process. All points of view should be noted without voiced criticism.
  2. Non-discrimination. Viewpoints from every category should be treated equally at this stage of the process. Special consideration should be given to the fact that some persons may be more outspoken than others, and that there is a risk that they may silence some of the other actors.
  3. Development through dialogue. There should be an opportunity to adjust and develop the demands through a dialogue between participants of different backgrounds. Prioritizing should be addressed as part of the process.
  4. Versatility. The process of collection of user-specified demands should be reasonably economical and not require the involvement of specialist consultants or extensive time demands on the part of the participants.

 

The above set of criteria may be met by using a methodology based on quality function deployment (QFD) according to Sullivan (1986). Here, the user demands may be collected in a session where a mixed group of actors (not more than eight to ten people) is present. All participants are given a pad of removable self-sticking notes. They are asked to write down all workplace demands which they find relevant, each one on a separate slip of paper. Aspects relating to work environment and safety, productivity and quality should be covered. This activity may continue for as long as found necessary, typically ten to fifteen minutes. After this session, one after the other of the participants is asked to read out his or her demands and to stick the notes on a board in the room where everyone in the group can see them. The demands are grouped into natural categories such as lighting, lifting aids, production equipment, reaching requirements and flexibility demands. After the completion of the round, the group is given the opportunity to discuss and to comment on the set of demands, one category at a time, with respect to relevance and priority.

The set of user-specified demands collected in a process such as the one described in the above forms one of the bases for the development of the demand specification. Additional information in the process may be produced by other categories of actors, for example, product designers, quality engineers, or economists; however, it is vital to realize the potential contribution that the users can make in this context.

Prioritizing and demand specification

With respect to the specification process, it is essential that the different types of demands be given consideration according to their respective importance; otherwise, all aspects that have been taken into account will have to be considered in parallel, which may tend to make the design situation complex and difficult to handle. This is why checklists, which need to be elaborate if they are to serve the purpose, tend to be difficult to manage in a particular design situation.

It may be difficult to devise a priority scheme which serves all types of workstations equally well. However, on the assumption that manual handling of materials, tools or products is an essential aspect of the work to be carried out in the workstation, there is a high probability that aspects associated with musculoskeletal load will be at the top of the priority list. The validity of this assumption may be checked in the user demand collection stage of the process. Relevant user demands may be, for instance, associated with muscular strain and fatigue, reaching, seeing, or ease of manipulation.

It is essential to realize that it may not be possible to transform all user-specified demands into technical demand specifications. Although such demands may relate to more subtle aspects such as comfort, they may nevertheless be of high relevance and should be considered in the process.

Musculoskeletal load variables

In line with the above reasoning, we shall here apply the view that there is a set of basic ergonomic variables relating to musculoskeletal load which need to be taken into account as a priority in the design process, in order to eliminate the risk of work-related musculosketal disorders (WRMDs). This type of disorder is a pain syndrome, localized in the musculoskeletal system, which develops over long periods of time as a result of repeated stresses on a particular body part (Putz-Anderson 1988). The essential variables are (e.g., Corlett 1988):

  • muscular force demand
  • working posture demand
  • time demand.

 

With respect to muscular force, criteria setting may be based on a combination of biomechanical, physiological and psychological factors. This is a variable that is operationalized through measurement of output force demands, in terms of handled mass or required force for, say, the operation of handles. Also, peak loads in connection with highly dynamic work may have to be taken into account.

Working posture demands may be evaluated by mapping (a) situations where the joint structures are stretched beyond the natural range of movement, and (b) certain particularly awkward situations, such as kneeling, twisting, or stooped postures, or work with the hand held above shoulder level.

Time demands may be evaluated on the basis of mapping (a) short-cycle, repetitive work, and (b) static work. It should be noted that static work evaluation may not exclusively concern maintaining a working posture or producing a constant output force over lengthy periods of time; from the point of view of the stabilizing muscles, particularly in the shoulder joint, seemingly dynamic work may have a static character. It may thus be necessary to consider lengthy periods of joint mobilization.

The acceptability of a situation is of course based in practice on the demands on the part of the body that is under the highest strain.

It is important to note that these variables should not be considered one at a time but jointly. For instance, high force demands may be acceptable if they occur only occasionally; lifting the arm above shoulder level once in a while is not normally a risk factor. But combinations among such basic variables must be considered. This tends to make criteria setting difficult and involved.

In the Revised NIOSH equation for the design and evaluation of manual handling tasks (Waters et al. 1993), this problem is addressed by devising an equation for recommended weight limits which takes into account the following mediating factors: horizontal distance, vertical lifting height, lifting asymmetry, handle coupling and lifting frequency. In this way, the 23-kilogram acceptable load limit based on biomechanical, physiological and psychological criteria under ideal conditions, may be modified substantially upon taking into account the specifics of the working situation. The NIOSH equation provides a base for evaluation of work and workplaces involving lifting tasks. However, there are severe limitations as to the usability of the NIOSH equation: for instance, only two-handed lifts may be analysed; scientific evidence for analysis of one-handed lifts is still inconclusive. This illustrates the problem of applying scientific evidence exclusively as a basis for work and workplace design: in practice, scientific evidence must be merged with educated views of persons who have direct or indirect experience of the type of work considered.

The cube model

Ergonomic evaluation of workplaces, taking into account the complex set of variables which need to be considered, is to a large extent a communications problem. Based on the prioritizing discussion described above, a cube model for ergonomic evaluation of workplaces was developed (Kadefors 1993). Here the prime goal was to develop a didactic tool for communication purposes, based on the assumption that output force, posture and time measures in a great majority of situations constitute interrelated, prioritized basic variables.

For each one of the basic variables, it is recognized that the demands may be grouped with respect to severity. Here, it is proposed that such a grouping may be made in three classes: (1) low demands, (2) medium demands or (3) high demands. The demand levels may be set either by using whatever scientific evidence is available or by taking a consensus approach with a panel of users. These two alternatives are of course not mutually exclusive, and may well entail similar results, but probably with different degrees of generality.

As noted above, combinations of the basic variables determine to a large extent the risk level with respect to the development of musculoskeletal complaints and cumulative trauma disorders. For instance, high time demands may render a working situation unacceptable in cases where there are also at least medium level demands with respect to force and posture. It is essential in the design and assessment of workplaces that the most important variables be considered jointly. Here a cube model for such evaluation purposes is proposed. The basic variables—force, posture and time—constitute the three axes of the cube. For each combination of demands a subcube may be defined; in all, the model incorporates 27 such subcubes (see figure 1).

Figure 1. The "cube model" for ergonomics assessment. Each cube represents a combination of demands relating to force, posture and time. Light: acceptable combination; gray: conditionally acceptable; black: unacceptable

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An essential aspect of the model is the degree of acceptability of the demand combinations. In the model, a three-zone classification scheme is proposed for acceptability: (1) the situation is acceptable, (2) the situation is conditionally acceptable or (3) the situation is unacceptable. For didactic purposes, each subcube may be given a certain texture or colour (say, green-yellow-red). Again, the assessment may be user-based or based on scientific evidence. The conditionally acceptable (yellow) zone means that “there exists a risk of disease or injury that cannot be neglected, for the whole or a part of the operator population in question” (CEN 1994).

In order to develop this approach, it is useful to consider a case: the evaluation of load on the shoulder in moderately paced one-handed materials handling. This is a good example, since in this type of situation, it is normally the shoulder structures that are under the heaviest strain.

With respect to the force variable, classification may be based in this case on handled mass. Here, low force demand is identified as levels below 10% of maximal voluntary lifting capacity (MVLC), which amounts to approximately 1.6 kg in an optimal working zone. High force demand requires more than 30% MVLC, approximately 4.8 kg. Medium force demand falls in between these limits. Low postural strain is when the upper arm is close to the thorax. High postural strain is when humeral abduction or flexion exceeds 45°. Medium postural strain is when the abduction/flexion angle is between 15° and 45°. Low time demand is when the handling occupies less than one hour per working day on and off, or continuously for less than 10 minutes per day. High time demand is when the handling takes place for more than four hours per working day, or continuously for more than 30 minutes (sustained or repetitively). Medium time demand is when the exposure falls between these limits.

In figure 1, degrees of acceptability have been assigned to combinations of demands. For instance, it is seen that high time demands may only be combined with combined low force and postural demands. Moving from unacceptable to acceptable may be undertaken by reducing demands in either dimension, but reduction in time demands is the most efficient way in many cases. In other words, in some cases workplace design should be altered, in other cases it may be more efficient to change the organization of work.

Using a consensus panel with a set of users for definition of demand levels and classification of degree of acceptability may enhance the workstation design process considerably, as considered below.

Additional variables

In addition to the basic variables considered above, a set of variables and factors characterizing the workplace from an ergonomics point of view has to be taken into account, depending upon the particular conditions of the situation to be analysed. They include:

  • precautions to reduce risks for accidents
  • specific environmental factors such as noise, lighting and ventilation
  • exposure to climatic factors
  • exposure to vibration (from hand-held tools or whole body)
  • ease of meeting productivity and quality demands.

 

To a large extent these factors may be considered one at a time; hence the checklist approach may be useful. Grandjean (1988) in his textbook covers the essential aspects that usually need to be taken into account in this context. Konz (1990) in his guidelines provides for workstation organization and design a set of leading questions focusing on worker-machine interfacing in manufacturing systems.

In the design process followed here, the checklist should be read in conjunction with the user-specified demands.

A Workstation Design Example: Manual Welding

As an illustrative (hypothetical) example, the design process leading to implementation of a workstation for manual welding (Sundin et al. 1994) is described here. Welding is an activity frequently combining high demands for muscular force with high demands for manual precision. The work has a static character. The welder is often doing welding exclusively. The welding work environment is generally hostile, with a combination of exposure to high noise levels, welding smoke and optical radiation.

The task was to devise a workplace for manual MIG (metal inert gas) welding of medium size objects (up to 300 kg) in a workshop environment. The workstation had to be flexible since there was a variety of objects to be manufactured. There were high demands for productivity and quality.

A QFD process was carried out in order to provide a set of workstation demands in user terms. Welders, production engineers and product designers were involved. User demands, which are not listed here, covered a wide range of aspects including ergonomics, safety, productivity and quality.

Using the cube model approach, the panel identified, by consensus, limits between high, moderate and low load:

  1. Force variable. Less than 1 kg handled mass is termed a low load, whereas more than 3 kg is considered a high load.
  2. Postural strain variable. Working positions implying high strain are those involving elevated arms, twisted or deep forward-flexed positions, and kneeling positions, and also include situations where the wrist is held in extreme flexion/extension or deviation. Low strain occurs where the posture is straight upright standing or sitting and where hands are in optimal working zones.
  3. Time variable. Less than 10% of the working time devoted to welding is considered low demand, whereas more than 40% of total working time is termed high demand. Medium demands occur when the variable falls between the limits given above, or when the situation is unclear.

 

It was clear from assessment using the cube model (figure 1) that high time demands could not be accepted if there were concurrent high or moderate demands in terms of force and postural strain. In order to reduce these demands, mechanized object handling and tool suspension was deemed a necessity. There was consensus developed around this conclusion. Using a simple computer-aided design (CAD) program (ROOMER), an equipment library was created. Various workplace station layouts could be developed very easily and modified in close interaction with the users. This design approach has significant advantages compared with merely looking at plans. It gives the user an immediate vision of what the intended workplace may look like.

Figure 2.  A CAD version of a workstation for manual welding, arrived at in the design process

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Figure 2 shows the welding workstation arrived at using the CAD system. It is a workplace which reduces the force and posture demands, and which meets nearly all the residual user demands put forward.

 

 

 

 

 

Figure 3. The welding workstation implemented

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On the basis of the results of the first stages of the design process, a welding workplace (figure 3) was implemented. Assets of this workplace include:

  1. Work in the optimized zone is facilitated using a computerized handling device for welding objects. There is an overhead hoist for transportation purposes. As an alternative, a balanced lifting device is supplied for easy object handling.
  2. The welding gun and grinding machine are suspended, thus reducing force demands. They can be positioned anywhere around the welding object. A welding chair is supplied.
  3. All media come from above, which means that there are no cables on the floor.
  4. The workstation has lighting at three levels: general, workplace and process. The workplace lighting comes from ramps above the wall elements. The process lighting is integrated in the welding smoke ventilation arm.
  5. The workstation has ventilation at three levels: general displacement ventilation, workplace ventilation using a movable arm, and integrated ventilation in the MIG welding gun. The workplace ventilation is controlled from the welding gun.
  6. There are noise-absorbing wall elements on three sides of the workplace. A transparent welding curtain covers the fourth wall. This makes it possible for the welder to keep informed of what happens in the workshop environment.

 

In a real design situation, compromises of various kinds may have to be made, due to economic, space and other constraints. It should be noted, however, that licensed welders are hard to come by for the welding industry around the world, and they represent a considerable investment. Nearly no welders go into normal retirement as active welders. Keeping the skilled welder on the job is beneficial for all parties involved: welder, company and society. For instance, there are very good reasons why equipment for object handling and positioning should be an integral constituent of many welding workplaces.

Data for Workstation Design

In order to be able to design a workplace properly, extensive sets of basic information may be needed. Such information includes anthropometric data of user categories, lifting strength and other output force capacity data of male and female populations, specifications of what constitutes optimal working zones and so forth. In the present article, references to some key papers are given.

The most complete treatment of virtually all aspects of work and workstation design is probably still the textbook by Grandjean (1988). Information on a wide range of anthropometric aspects relevant to workstation design is presented by Pheasant (1986). Large amounts of biomechanical and anthropometric data are given by Chaffin and Andersson (1984). Konz (1990) has presented a practical guide to workstation design, including many useful rules of thumb. Evaluation criteria for the upper limb, particularly with reference to cumulative trauma disorders, have been presented by Putz-Anderson (1988). An assessment model for work with hand tools was given by Sperling et al. (1993). With respect to manual lifting, Waters and co-workers have developed the revised NIOSH equation, summarizing existing scientific knowledge on the subject (Waters et al. 1993). Specification of functional anthropometry and optimal working zones have been presented by, for example, Rebiffé, Zayana and Tarrière (1969) and Das and Grady (1983a, 1983b). Mital and Karwowski (1991) have edited a useful book reviewing various aspects relating in particular to the design of industrial workplaces.

The large amount of data needed to design workstations properly, taking all relevant aspects into account, will make necessary the use of modern information technology by production engineers and other responsible people. It is likely that various types of decision-support systems will be made available in the near future, for instance in the form of knowledge-based or expert systems. Reports on such developments have been given by, for example, DeGreve and Ayoub (1987), Laurig and Rombach (1989), and Pham and Onder (1992). However, it is an extremely difficult task to devise a system making it possible for the end-user to have easy access to all relevant data needed in a specific design situation.

 

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Monday, 14 March 2011 19:51

Tools

Written by

Commonly a tool comprises a head and a handle, with sometimes a shaft, or, in the case of the power tool, a body. Since the tool must meet the requirements of multiple users, basic conflicts can arise which may have to be met with compromise. Some of these conflicts derive from limitations in the capacities of the user, and some are intrinsic to the tool itself. It should be remembered, however, that human limitations are inherent and largely immutable, while the form and function of the tool are subject to a certain amount of modification. Thus, in order to effect desirable change, attention must be directed primarily to the form of the tool, and, in particular, to the interface between the user and the tool, namely the handle.

The Nature of Grip

The widely accepted characteristics of grip have been defined in terms of a power grip, a precision grip and a hook grip, by which virtually all human manual activities can be accomplished.

In a power grip, such as is used in hammering nails, the tool is held in a clamp formed by the partially flexed fingers and the palm, with counterpressure being applied by the thumb. In a precision grip, such as one uses when adjusting a set screw, the tool is pinched between the flexor aspects of the fingers and the opposing thumb. A modification of the precision grip is the pencil grip, which is self-explanatory and is used for intricate work. A precision grip provides only 20% of the strength of a power grip.

A hook grip is used where there is no requirement for anything other than holding. In the hook grip the object is suspended from the flexed fingers, with or without the support of the thumb. Heavy tools should be designed so that they can be carried in a hook grip.

Grip Thickness

For precision grips, recommended thicknesses have varied from 8 to 16 millimetres (mm) for screwdrivers, and 13 to 30 mm for pens. For power grips applied around a more or less cylindrical object, the fingers should surround more than half the circumference, but the fingers and thumb should not meet. Recommended diameters have ranged from as low as 25 mm to as much as 85 mm. The optimum, varying with hand size, is probably around 55 to 65 mm for males, and 50 to 60 mm for females. Persons with small hands should not perform repetitive actions in power grips of diameter greater than 60 mm.

Grip Strength and Hand Span

The use of a tool requires strength. Other than for holding, the greatest requirement for hand strength is found in the use of cross-lever action tools such as pliers and crushing tools. The effective force in crushing is a function of the grip strength and the required span of the tool. The maximum functional span between the end of the thumb and the ends of the grasping fingers averages about 145 mm for men and 125 mm for women, with ethnic variations. For an optimal span, which ranges from 45 to 55 mm for both men and women, the grip strength available for a single short-term action ranges from about 450 to 500 newtons for men and 250 to 300 newtons for women, but for repetitive action the recommended requirement is probably closer to 90 to 100 newtons for men, and 50 to 60 newtons for women. Many commonly used clamps or pliers are beyond the capacity of one-handed use, particularly in women.

When a handle is that of a screwdriver or similar tool the available torque is determined by the user’s ability to transmit force to the handle, and thus is determined by both the coefficient of friction between hand and handle and the diameter of the handle. Irregularities in the shape of the handle make little or no difference to the ability to apply torque, although sharp edges can cause discomfort and eventual tissue damage. The diameter of a cylindrical handle that allows the greatest application of torque is 50 to 65 mm, while that for a sphere is 65 to 75 mm.

Handles

Shape of handle

The shape of a handle should maximize contact between skin and handle. It should be generalized and basic, commonly of flattened cylindrical or elliptical section, with long curves and flat planes, or a sector of a sphere, put together in such a manner as to conform to the general contours of the grasping hand. Because of its attachment to the body of a tool, the handle may also take the form of a stirrup, a T-shape or an L-shape, but the portion that contacts the hand will be in the basic form.

The space enclosed by the fingers is, of course, complex. The use of simple curves is a compromise intended to meet the variations represented by different hands and different degrees of flexion. In this regard, it is undesirable to introduce any contour matching of flexed fingers into the handle in the form of ridges and valleys, flutings and indentations, since, in fact, these modifications would not fit a significant number of hands and might indeed, over a prolonged period, cause pressure injury to the soft tissues. In particular, recesses of greater that 3 mm are not recommended.

A modification of the cylindrical section is the hexagonal section, which is of particular value in the design of small calibre tools or instruments. It is easier to maintain a stable grip on a hexagonal section of small calibre than on a cylinder. Triangular and square sections have also been used with varying degrees of success. In these cases, the edges must be rounded to avert pressure injury.

Grip Surface and Texture

It is not by accident that for millennia wood has been the material of choice for tool handles other than those for crushing tools like pliers or clamps. In addition to its aesthetic appeal, wood has been readily available and easily worked by unskilled workers, and has qualities of elasticity, thermal conductivity, frictional resistance and relative lightness in relation to bulk that have made it very acceptable for this and other uses.

In recent years, metal and plastic handles have become more common for many tools, the latter in particular for use with light hammers or screwdrivers. A metal handle, however, transmits more force to the hand, and preferably should be encased in a rubber or plastic sheath. The grip surface should be slightly compressible, where feasible, nonconductive and smooth, and the surface area should be maximized to ensure pressure distribution over as large an area as possible. A foam rubber grip has been used to reduce the perception of hand fatigue and tenderness.

The frictional characteristics of the tool surface vary with the pressure exerted by the hand, with the nature of the surface and contamination by oil or sweat. A small amount of sweat increases the coefficient of friction.

Length of handle

The length of the handle is determined by the critical dimensions of the hand and the nature of the tool. For a hammer to be used by one hand in a power grip, for example, the ideal length ranges from a minimum of about 100 mm to a maximum of about 125 mm. Short handles are unsuitable for a power grip, while a handle shorter than 19 mm cannot be properly grasped between thumb and forefinger and is unsuitable for any tool.

Ideally, for a power tool, or a hand saw other than a coping or fret saw, the handle should accommodate at the 97.5th percentile level the width of the closed hand thrust into it, namely 90 to 100 mm in the long axis and 35 to 40 mm in the short.

Weight and Balance

Weight is not a problem with precision tools. For heavy hammers and power tools a weight between 0.9 kg and 1.5 kg is acceptable, with a maximum of about 2.3 kg. For weights greater than recommended, the tool should be supported by mechanical means.

In the case of a percussion tool such as a hammer, it is desirable to reduce the weight of the handle to the minimum compatible with structural strength and have as much weight as possible in the head. In other tools, the balance should be evenly distributed where possible. In tools with small heads and bulky handles this may not be possible, but the handle should then be made progressively lighter as the bulk increases relative to the size of the head and shaft.

Significance of Gloves

It is sometimes overlooked by tool designers that tools are not always held and operated by bare hands. Gloves are commonly worn for safety and comfort. Safety gloves are seldom bulky, but gloves worn in cold climates may be very heavy, interfering not only with sensory feedback but also with the ability to grasp and hold. The wearing of woollen or leather gloves can add 5 mm to hand thickness and 8 mm to hand breadth at the thumb, while heavy mittens can add as much as 25 to 40 mm respectively.

Handedness

The majority of the population in the western hemisphere favours the use of the right hand. A few are functionally ambidextrous, and all persons can learn to operate with greater or less efficiency with either hand.

Although the number of left-handed persons is small, wherever feasible the fitting of handles to tools should make the tool workable by either left-handed or right-handed persons (examples would include the positioning of the secondary handle in a power tool or the finger loops in scissors or clamps) unless it is clearly inefficient to do so, as in the case of screw-type fasteners which are designed to take advantage of the powerful supinating muscles of the forearm in a right-handed person while precluding the left-hander from using them with equal effectiveness. This sort of limitation has to be accepted since the provision of left-hand threads is not an acceptable solution.

Significance of Gender

In general, women tend to have smaller hand dimensions, smaller grasp and some 50 to 70% less strength than men, although of course a few women at the higher percentile end have larger hands and greater strength than some men at the lower percentile end. As a result there exists a significant although undetermined number of persons, mostly female, who have difficulty in manipulating various hand tools which have been designed with male use in mind, including in particular heavy hammers and heavy pliers, as well as metal cutting, crimping and clamping tools and wire strippers. The use of these tools by women may require an undesirable two-handed instead of single-handed function. In a mixed-gender workplace it is therefore essential to ensure that tools of suitable size are available not only to meet the requirements of women, but also to meet those of men who are at the low percentile end of hand dimensions.

Special considerations

The orientation of a tool handle, where feasible, should allow the operating hand to conform to the natural functional position of the arm and hand, namely with the wrist more than half-supinated, abducted about 15° and slightly dorsiflexed, with the little finger in almost full flexion, the others less so and the thumb adducted and slightly flexed, a posture sometimes erroneously called the handshake position. (In a handshake the wrist is not more than half-supinated.) The combination of adduction and dorsiflexion at the wrist with varying flexion of the fingers and thumb generates an angle of grasp comprising about 80° between the long axis of the arm and a line passing through the centre point of the loop created by the thumb and index finger, that is, the transverse axis of the fist.

Forcing the hand into a position of ulnar deviation, that is, with the hand bent towards the little finger, as is found in using a standard pliers, generates pressure on the tendons, nerves and blood vessels within the wrist structure and can give rise to the disabling conditions of tenosynovitis, carpal tunnel syndrome and the like. By bending the handle and keeping the wrist straight, (that is, by bending the tool and not the hand) compression of nerves, soft tissues and blood vessels can be avoided. While this principle has been long recognized, it has not been widely accepted by tool manufacturers or the using public. It has particular application in the design of cross-lever action tools such as pliers, as well as knives and hammers.

Pliers and cross-lever tools

Special consideration must be given to the shape of the handles of pliers and similar devices. Traditionally pliers have had curved handles of equal length, the upper curve approximating the curve of the palm of the hand and the lower curve approximating the curve of the flexed fingers. When the tool is held in the hand, the axis between the handles is in line with the axis of the jaws of the pliers. Consequently, in operation, it is necessary to hold the wrist in extreme ulnar deviation, that is, bent towards the little finger, while it is being repeatedly rotated. In this position the use of the hand-wrist-arm segment of the body is extremely inefficient and very stressful on the tendons and joint structures. If the action is repetitive it may give rise to various manifestations of overuse injury.

To counter this problem a new and ergonomically more suitable version of pliers has appeared in recent years. In these pliers the axis of the handles is bent through approximately 45° relative to the axis of the jaws. The handles are thickened to allow a better grasp with less localized pressure on the soft tissues. The upper handle is proportionately longer with a shape that fits into, and around the ulnar side of, the palm. The forward end of the handle incorporates a thumb support. The lower handle is shorter, with a tang, or rounded projection, at the forward end and a curve conforming to the flexed fingers.

While the foregoing is a somewhat radical change, several ergonomically sound improvements can be made in pliers relatively easily. Perhaps the most important, where a power grip is required, is in the thickening and slight flattening of the handles, with a thumb support at the head-end of the handle and a slight flare at the other end. If not integral to the design, this modification can be achieved by encasing the basic metal handle with a fixed or detachable non-conductive sheath made of rubber or an appropriate synthetic material, and perhaps bluntly roughened to improve the tactile quality. Indentation of the handles for fingers is undesirable. For repetitive use it may be desirable to incorporate a light spring into the handle to open it after closing.

The same principles apply to other cross-lever tools, particularly with respect to change in the thickness and flattening of the handles.

Knives

For a general purpose knife, that is, one that is not used in a dagger grasp, it is desirable to include a 15° angle between handle and blade to reduce the stress on joint tissues. The size and shape of handles should conform in general to that for other tools, but to allow for different hand sizes it has been suggested that two sizes of knife handle should be supplied, namely one to fit the 50th to 95th percentile user, and one for the 5th to 50th percentile. To allow the hand to exert force as close to the blade as possible the top surface of the handle should incorporate a raised thumb rest.

A knife guard is required to prevent the hand from slipping forward onto the blade. The guard may take several forms, such as a tang, or curved projection, about 10 to 15 mm in length, protruding downwards from the handle, or at right angles to the handle, or a bail guard comprising a heavy metal loop from front to rear of the handle. The thumb rest also acts to prevent slippage.

The handle should conform to general ergonomic guidelines, with a yielding surface resistant to grease.

Hammers

The requirements for hammers have been largely considered above, with the exception of that relating to bending the handle. As noted above, forced and repetitive bending of the wrist may cause tissue damage. By bending the tool instead of the wrist this damage may be reduced. With respect to hammers various angles have been examined, but it would appear that bending the head downward between 10° and 20° may improve comfort, if it does not actually improve performance.

Screwdrivers and scraping tools

The handles of screwdrivers and other tools held in a somewhat similar manner, such as scrapers, files, hand chisels and so on, have some special requirements. Each at one time or another is used with a precision grip or a power grip. Each relies on the functions of the fingers and the palm of the hand for stabilization and the transmission of force.

The general requirements of handles have already been considered. The most common effective shape of a screwdriver handle has been found to be that of a modified cylinder, dome-shaped at the end to receive the palm, and slightly flared where it meets the shaft to provide support to the ends of the fingers. In this manner, torque is applied largely by way of the palm, which is maintained in contact with the handle by way of pressure applied from the arm and the frictional resistance at the skin. The fingers, although transmitting some force, occupy more of a stabilizing role, which is less fatiguing since less power is required. Thus the dome of the head becomes very important in handle design. If there are sharp edges or ridges on the dome or where the dome meets the handle, then either the hand becomes callused and injured, or the transmission of force is transferred towards the less efficient and more readily fatigued fingers and thumb. The shaft is commonly cylindrical, but a triangular shaft has been introduced which provides better support for the fingers, although its use may be more fatiguing.

Where the use of a screwdriver or other fastener is so repetitive as to comprise an overuse injury hazard the manual driver should be replaced with a powered driver slung from an overhead harness in such a manner as to be readily accessible without obstructing the work.

Saws and power tools

Hand saws, with the exception of fret saws and light hacksaws, where a handle like that of a screwdriver is most appropriate, commonly have a handle which takes the form of a closed pistol grip attached to the blade of the saw.

The handle essentially comprises a loop into which the fingers are placed. The loop is effectively a rectangle with curved ends. To allow for gloves it should have internal dimensions of approximately 90 to 100 mm in the long diameter and 35 to 40 mm in the short. The handle in contact with the palm should have the flattened cylindrical shape already mentioned, with compound curves to reasonably fit the palm and the flexed fingers. The width from outer curve to inner curve should be about 35 mm, and the thickness not more than 25 mm.

Curiously, the function of grasping and holding a power tool is very similar to that of holding a saw, and consequently a somewhat similar type of handle is effective. The pistol grip common in power tools is akin to an open saw handle with the sides being curved instead of being flattened.

Most power tools comprise a handle, a body and a head. Placement of the handle is significant. Ideally handle, body and head should be in line so that the handle is attached at the rear of the body and the head protrudes from the front. The line of action is the line of the extended index finger, so that the head is eccentric to the central axis of the body. The centre of mass of the tool, however, is in front of the handle, while the torque is such as to create a turning movement of the body which the hand must overcome. Consequently it would be more appropriate to place the primary handle directly under the centre of mass in such a way that, if necessary, the body juts out behind the handle as well as in front. Alternatively, particularly in a heavy drill, a secondary handle can be placed underneath the drill in such a manner that the drill can be operated with either hand. Power tools are normally operated by a trigger incorporated into the upper front end of the handle and operated by the index finger. The trigger should be designed to be operated by either hand and should incorporate an easily reset latching mechanism to hold the power on when required.

 

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Monday, 14 March 2011 19:54

Controls, Indicators and Panels

Written by

Karl H. E. Kroemer

In what follows, three of the most important concerns of ergonomic design will be examined: first, that of controls, devices to transfer energy or signals from the operator to a piece of machinery; second, indicators or displays, which provide visual information to the operator about the status of the machinery; and third, the combination of controls and displays in a panel or console.

Designing for the Sitting Operator

Sitting is a more stable and less energy-consuming posture than standing, but it restricts the working space, particularly of the feet, more than standing. However, it is much easier to operate foot controls when sitting, as compared to standing, because little body weight must be transferred by the feet to the ground. Furthermore, if the direction of the force exerted by the foot is partly or largely forward, provision of a seat with a backrest allows the exertion of rather large forces. (A typical example of this arrangement is the location of pedals in an automobile, which are located in front of the driver, more or less below seat height.) Figure 1 shows schematically the locations in which pedals may be located for a seated operator. Note that the specific dimensions of that space depend on the anthropometry of the actual operators.

Figure 1. Preferred and regular workspace for feet (in centimetres)

ERG210F1

The space for the positioning of hand-operated controls is primarily located in front of the body, within a roughly spherical contour that is centred at either the elbow, at the shoulder, or somewhere between those two body joints. Figure 2 shows schematically that space for the location of controls. Of course, the specific dimensions depend on the anthropometry of the operators.

 

Figure 2. Preferred and regular workspace for hands (in centimetres)

ERG210F2

The space for displays and for controls that must be looked at is bounded by the periphery of a partial sphere in front of the eyes and centred at the eyes. Thus, the reference height for such displays and controls depends on the eye height of the seated operator and on his or her trunk and neck postures. The preferred location for visual targets closer than about one metre is distinctly below the height of the eye, and depends on the closeness of the target and on the posture of the head. The closer the target, the lower it should be located, and it should be in or near the medial (mid-sagittal) plane of the operator.

It is convenient to describe the posture of the head by using the “ear-eye line” (Kroemer 1994a) which, in the side view, runs through the right ear hole and the juncture of the lids of the right eye, while the head is not tilted to either side (the pupils are at the same horizontal level in the frontal view). One usually calls the head position “erect” or “upright” when the pitch angle P (see figure 3) between the ear-eye line and the horizon is about 15°, with the eyes above the height of the ear. The preferred location for visual targets is 25°–65° below the ear-eye line (LOSEE in figure 3), with the lower values preferred by most people for close targets that must be kept in focus. Even though there are large variations in the preferred angles of the line of sight, most subjects, particularly as they become older, prefer to focus on close targets with large LOSEE angles.

Figure 3. Ear-eye line

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Designing for the Standing Operator

Pedal operation by a standing operator should be seldom required, because otherwise the person must spend too much time standing on one foot while the other foot operates the control. Obviously, simultaneous operation of two pedals by a standing operator is practically impossible. While the operator is standing still, the room for the location of foot controls is limited to a small area below the trunk and slightly in front of it. Walking about would provide more room to place pedals, but that is highly impractical in most cases because of the walking distances involved.

The location for hand-operated controls of a standing operator includes about the same area as for a seated operator, roughly a half sphere in front of the body, with its centre near the shoulders of the operator. For repeated control operations, the preferred part of that half sphere would be its lower section. The area for the location of displays is also similar to the one suited to a seated operator, again roughly a half sphere centred near the operator’s eyes, with the preferred locations in the lower section of that half sphere. The exact locations for displays, and also for controls that must be seen, depends on the posture of the head, as discussed above.

The height of controls is appropriately referenced to the height of the elbow of the operator while the upper arm is hanging from the shoulder. The height of displays and controls that must be looked at is referred to the eye height of the operator. Both depend on the operator’s anthropometry, which may be rather different for short and tall persons, for men and women, and for people of different ethnic origins.

Foot-operated Controls

Two kinds of controls should be distinguished: one is used to transfer large energy or forces to a piece of machinery. Examples of this are the pedals on a bicycle or the brake pedal in a heavier vehicle that does not have a power-assist feature. A foot-operated control, such as an on-off switch, in which a control signal is conveyed to the machinery, usually requires only a small quantity of force or energy. While it is convenient to consider these two extremes of pedals, there are various intermediate forms, and it is the task of the designer to determine which of the following design recommendations apply best among them.

As mentioned above, repeated or continual pedal operation should be required only from a seated operator. For controls meant to transmit large energies and forces, the following rules apply:

  • Locate pedals underneath the body, slightly in front, so that they can be operated with the leg in a comfortable position. The total horizontal displacement of a reciprocating pedal should normally not exceed about 0.15 m. For rotating pedals, the radius should also be about 0.15 m. The linear displacement of a switch-type pedal may be minimal and should not exceed about 0.15 m.
  • Pedals should be so designed that the direction of travel and the foot force are approximately in the line extending from the hip through the ankle joint of the operator.
  • Pedals that are operated by flexion and extension of the foot in the ankle joint should be so arranged that in the normal position the angle between the lower leg and the foot is approximately 90°; during operation, that angle may be increased to about 120°.
  • Foot-operated controls that simply provide signals to the machinery should normally have two discrete positions, such as ON or OFF. Note, however, that tactile distinction between the two positions may be difficult with the foot.

 

Selection of Controls

Selection among different sorts of controls must be made according to the following needs or conditions:

  • Operation by hand or foot
  • Amounts of energies and forces transmitted
  • Applying “continuous” inputs, such as steering an automobile
  • Performing “discrete actions,” for example, (a) activating or shutting down equipment, (b) selecting one of several distinct adjustments, such as switching from one TV or radio channel to another, or (c) carrying out data entry, as with a keyboard.

 

The functional usefulness of controls also determines selection procedures. The main criteria are as follows:

  • The control type shall be compatible with stereotypical or common expectations (for instance, using a push-button or toggle switch to turn on an electric light, not a rotary knob).
  • Size and motion characteristics of the control shall be compatible with stereotypical experience and past practice (for instance, providing a large steering wheel for the two-handed operation of an automobile, not a lever).
  • The direction of operation of a control shall be compatible with stereotypical or common expectations (for instance, an ON control is pushed or pulled, not turned to the left).
  • Hand operation is used for controls that require small force and fine adjustment, while foot operation is suitable for gross adjustments and large forces (however, consider the common use of pedals, particularly accelerator pedals, in automobiles, which does not comply with this principle).
  • The control shall be “safe” in that it cannot be operated inadvertently nor in ways that are excessive or inconsistent with its intended purpose.

 

Table 1. Control movements and expected effects

Direction of control movement

Function

Up

Right

Forward

Clockwise

Press,
Squeeze

Down

Left

Rearward

Back

Counter-
clockwise

Pull1

Push2

On

+3

+

+

+

+3

       

+

 

Off

         

+

 

+

 

Right

 

+

 

               

Left

           

+

 

     

Raise

+

           

       

Lower

   

   

+

           

Retract

           

+

   

 

Extend

   

+

   

         

Increase

+

               

Decrease

         

+

 

   

Open Value

         

     

+

   

Close Value

     

+

 

           

Blank: Not applicable; + Most preferred; – less preferred. 1 With trigger-type control. 2 With push-pull switch. 3 Up in the United States, down in Europe.

Source: Modified from Kroemer 1995.

 

Table 1 and table 2 help in the selection of proper controls. However, note that there are few “natural” rules for selection and design of controls. Most current recommendations are purely empirical and apply to existing devices and Western stereotypes.

Table 2. Control-effect relations of common hand controls

Effect

Key-
lock

Toggle
switch

Push-
button

Bar
knob

Round
knob

Thumbwheel
discrete

Thumbwheel
continuous

Crank

Rocker switch

Lever

Joystick
or ball

Legend
switch

Slide1

Select ON/OFF

+

+

+

=

       

+

   

+

+

Select ON/STANDBY/OFF

 

+

+

         

+

 

+

+

Select OFF/MODE1/MODE2

 

=

+

         

+

 

+

+

Select one function of several  related functions

 

+

         

     

=

Select one of three or more  discrete alternatives

     

+

               

+

Select operating condition

 

+

+

       

+

+

   

Engage or disengage

                 

+

     

Select one of mutually
exclusive functions

   

+

               

+

 

Set value on scale

       

+

 

=

 

=

=

 

+

Select value in discrete steps

   

+

+

 

+

           

+

Blank: Not applicable; +: Most preferred; –: Less preferred; = Least preferred. 1 Estimated (no experiments known).

Source: Modified from Kroemer 1995.

 

Figure 4 presents examples of “detent” controls, characterized by discrete detents or stops in which the control comes to rest. It also depicts typical “continuous” controls where the control operation may take place anywhere within the adjustment range, without the need to be set in any given position.

Figure 4. Some examples of "detent" and "continuous" controls

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The sizing of controls is largely a matter of past experiences with various control types, often guided by the desire to minimize the needed space in a control panel, and either to allow simultaneous operations of adjacent controls or to avoid inadvertent concurrent activation. Furthermore, the choice of design characteristics will be influenced by such considerations as whether the controls are to be located outdoors or in sheltered environments, in stationary equipment or moving vehicles, or may involve the use of bare hands or of gloves and mittens. For these conditions, consult readings at the end of the chapter.

Several operational rules govern the arrangement and grouping of controls. These are listed in table 3. For more details, check the references listed at the end of this section and Kroemer, Kroemer and Kroemer-Elbert (1994).

Table 3. Rules for arrangement of controls

Locate for the
ease of
operation

Controls shall be oriented with respect to the operator. If the
operator uses different postures (such as in driving and
operating a backhoe), the controls and their associated
displays shall move with the operator so that in each posture
their arrangement and operation is the same for the operator.

Primary controls
first

The most important controls shall have the most advantageous
locations to make operation and reaching easy for the
operator.

Group related
controls
together

Controls that are operated in sequence, that are related to a
particular function, or that are operated together, shall be
arranged in functional groups (together with their associated
displays). Within each functional group, controls and displays
shall be arranged according to operational importance and
sequence.

Arrange for
sequential
operation

If operation of controls follows a given pattern, controls shall
be arranged to facilitate that sequence. Common
arrangements are left-to-right (preferred) or top-to-bottom,
as in printed materials of the Western world.

Be consistent

The arrangement of functionally identical or similar controls
shall be the same from panel to panel.

Dead-operator
control

If the operator becomes incapacitated and either lets go of a
control, or continues to hold on to it, a “deadman” control
design shall be utilized which either turns the system to a
non-critical operation state or shuts it down.

Select codes
appropriately

There are numerous ways to help identify controls, to indicate
the effects of the operation and to show their status.
Major coding means are:
–Location–Shape–Size–Mode of operation– Labels
–Colours–Redundancy

Source: Modified from Kroemer, Kroemer and Kroemer-Elbert 1994.
Reproduced by permission of Prentice-Hall. All rights reserved.

Preventing Accidental Operation

The following are the most important means to guard against inadvertent activation of controls, some of which may be combined:

  • Locate and orient the control so that the operator is unlikely to strike it or move it accidentally in the normal sequence of control operations.
  • Recess, shield or surround the control by physical barriers.
  • Cover the control or guard it by providing a pin, a lock or other means that must be removed or broken before the control can be operated.
  • Provide extra resistance (by viscous or coulomb friction, by spring-loading or by inertia) so that an unusual effort is required for actuation.
  • Provide a “delaying” means so that the control must pass through a critical position with an unusual movement (such as in the gear shift mechanism of an automobile).
  • Provide interlocking between controls so that prior operation of a related control is required before the critical control can be activated.

 

Note that these designs usually slow the operation of controls, which may be detrimental in case of an emergency.

Data Entry Devices

Nearly all controls can be used to enter data on a computer or other data storage device. However, we are most used to the practice of using a keyboard with push-buttons. On the original typewriter keyboard, which has become the standard even for computer keyboards, the keys were arranged in a basically alphabetic sequence, which has been modified for various, often obscure, reasons. In some cases, letters which frequently follow each other in common text were spaced apart so that the original mechanical type bars might not entangle if struck in rapid sequence. “Columns” of keys run in roughly straight lines, as do the “rows” of keys. However, the fingertips are not aligned in such manners, and do not move in this way when digits of the hand are flexed or extended, or moved sideways.

Many attempts have been made over the last hundred years to improve keying performance by changing the keyboard layout. These include relocating keys within the standard layout, or changing the keyboard layout altogether. The keyboard has been divided into separate sections, and sets of keys (such as numerical pads) have been added. Arrangements of adjacent keys may be changed by altering spacing, offset from each other or from reference lines. The keyboard may be divided into sections for the left and right hand, and those sections may be laterally tilted and sloped and slanted.

The dynamics of the operation of push-button keys are important for the user, but are difficult to measure in operation. Thus, the force-displacement characteristics of keys are commonly described for static testing, which is not indicative of actual operation. By current practise, keys on computer keyboards have fairly little displacement (about 2 mm) and display a “snap-back” resistance, that is, a decrease in operation force at the point when actuation of the key has been achieved. Instead of separate single keys, some keyboards consist of a membrane with switches underneath which, when pressed in the correct location, generate the desired input with little or no displacement felt. The major advantage of the membrane is that dust or fluids cannot penetrate it; however, many users dislike it.

There are alternatives to the “one key-one character” principle; instead, one can generate inputs by various combinatory means. One is “chording”, meaning that two or more controls are operated simultaneously to generate one character. This poses demands on the memory capabilities of the operator, but requires the use of only very few keys. Other developments utilize controls other than the binary tapped push button, replacing it by levers, toggles or special sensors (such as an instrumented glove) which respond to movements of the digits of the hand.

By tradition, typing and computer entry have been made by mechanical interaction between the operator’s fingers and such devices as keyboard, mouse, track ball or light pen. Yet there are many other means to generate inputs. Voice recognition appears one promising technique, but other methods can be employed. They might utilize, for example, pointing, gestures, facial expressions, body movements, looking (directing one’s gaze), movements of the tongue, breathing or sign language to transmit information and to generate inputs to a computer. Technical development in this area is very much in flux, and as the many nontraditional input devices used for computer games indicate, acceptance of devices other than the traditional binary tap-down keyboard is entirely feasible within the near future. Discussions of current keyboard devices have been provided, for example, by Kroemer (1994b) and McIntosh (1994).

Displays

Displays provide information about the status of equipment. Displays may apply to the operator’s visual sense (lights, scales, counters, cathode-ray tubes, flat panel electronics, etc.), to the auditory sense (bells, horns, recorded voice messages, electronically generated sounds, etc.) or to the sense of touch (shaped controls, Braille, etc.). Labels, written instructions, warnings or symbols (“icons”) may be considered special kinds of displays.

The four “cardinal rules” for displays are:

  1. Display only that information which is essential for adequate job performance.
  2. Display information only as accurately as is required for the operator’s decisions and actions.
  3. Present information in the most direct, simple, understandable and usable form.
  4. Present information in such a way that failure or malfunction of the display itself will be immediately obvious.

 

The selection of either an auditory or visual display depends on the prevailing conditions and purposes. The objective of the display may be to provide:

  • historical information about the past state of the system, such as the course run by a ship
  • status information about the current state of the system, such as the text already input into a word processor or the current position of an airplane
  • predictive information, such as on the future position of a ship, given certain steering settings
  • instructions or commands telling the operator what to do, and possibly how to do it.

 

A visual display is most appropriate if the environment is noisy, the operator stays in place, the message is long and complex, and especially if it deals with the spatial location of an object. An auditory display is appropriate if the workplace must be kept dark, the operator moves around, and the message is short and simple, requires immediate attention, and deals with events and time.

Visual Displays

There are three basic types of visual displays: (1)The check display indicates whether or not a given condition exists (for example a green light indicates normal function). (2)The qualitative display indicates the status of a changing variable or its approximate value, or its trend of change (for example, a pointer moves within a “normal” range). (3) The quantitative display shows exact information that must be ascertained (for example, to find a location on a map, to read text or to draw on a computer monitor), or it may indicate an exact numerical value that must be read by the operator (for example, a time or a temperature).

Design guidelines for visual displays are:

  • Arrange displays so that the operator can locate and identify them easily without unnecessary searching. (This usually means that the displays should be in or near the medial plane of the operator, and below or at eye height.)
  • Group displays functionally or sequentially so that the operator can use them easily.
  • Make sure that all displays are properly illuminated or illuminant, coded and labelled according to their function.
  • Use lights, often coloured, to indicate the status of a system (such as ON or OFF) or to alert the operator that the system, or a subsystem, is inoperative and that special action must be taken. Common meanings of light colours are listed in figure 5. Flashing red indicates an emergency condition that requires immediate action. An emergency signal is most effective when it combines sounds with a flashing red light.

Figure 5. Colour coding of indicator lights

ERG210T4

For more complex and detailed information, especially quantitative information, one of four different kinds of displays are traditionally used: (1) a moving pointer (with fixed scale), (2) a moving scale (with fixed pointer), (3) counters or (4) “pictorial” displays, especially computer-generated on a display monitor. Figure 6 lists the major characteristics of these display types.

Figure 6. Characteristics of displays

ERG210T5

It is usually preferable to use a moving pointer rather than a moving scale, with the scale either straight (horizontally or vertically arranged), curved or circular. Scales should be simple and uncluttered, with graduation and numbering so designed that correct readings can be taken quickly. Numerals should be located outside the scale markings so that they are not obscured by the pointer. The pointer should end with its tip directly at the marking. The scale should mark divisions only so finely as the operator must read. All major marks should be numbered. Progressions are best marked with intervals of one, five or ten units between major marks. Numbers should increase left to right, bottom to top or clockwise. For details of dimensions of scales refer to standards such as those listed by Cushman and Rosenberg 1991 or Kroemer 1994a.

Starting in the 1980s, mechanical displays with pointers and printed scales were increasingly replaced by “electronic” displays with computer-generated images, or solid-state devices using light-emitting diodes (see Snyder 1985a). The displayed information may be coded by the following means:

  • shapes, such as straight or circular
  • alphanumeric, that is, letters, numbers, words, abbreviations
  • figures, pictures, pictorials, icons, symbols, in various levels of abstraction, such as the outline of an airplane against the horizon
  • shades of black, white or gray
  • colours.

 

Unfortunately, many electronically generated displays have been fuzzy, often overly complex and colourful, hard to read, and required exact focusing and close attention, which may distract from the main task, for example, driving a car. In these cases the first three of the four “cardinal rules” listed above were often violated. Furthermore, many electronically generated pointers, markings and alphanumerics did not comply with established ergonomic design guidelines, especially when generated by line segments, scan lines or dot matrices. Although some of these defective designs were tolerated by the users, rapid innovation and improving display techniques allows many better solutions. However, the same rapid development leads to the fact that printed statements (even if current and comprehensive when they appear) are becoming obsolete quickly. Therefore, none are given in this text. Compilations have been published by Cushman and Rosenberg (1991), Kinney and Huey (1990), and Woodson, Tillman and Tillman (1991).

The overall quality of electronic displays is often wanting. One measure used to assess the image quality is the modulation transfer function (MTF) (Snyder 1985b). It describes the resolution of the display using a special sine-wave test signal; yet, readers have many criteria regarding the preference of displays (Dillon 1992).

Monochrome displays have only one colour, usually either green, yellow, amber, orange or white (achromatic). If several colours appear on the same chromatic display, they should be easily discriminated. It is best to display not more than three or four colours simultaneously (with preference being given to red, green, yellow or orange, and cyan or purple). All should strongly contrast with the background. In fact, a suitable rule is to design first by contrast, that is, in terms of black and white, and then to add colours sparingly.

In spite of the many variables that, singly and interacting with each other, affect the use of complex colour display, Cushman and Rosenberg (1991) compiled guidelines for use of colour in displays; these are listed in figure 7.

Figure 7. Guidelines for use of colours in displays

ERG210T6

Other suggestions are as follows:

  • Blue (preferably desaturated) is a good colour for backgrounds and large shapes. However, blue should not be used for text, thin lines or small shapes.
  • The colour of alphanumeric characters should contrast with that of the background.
  • When using colour, use shape as a redundant cue (e.g., all yellow symbols are triangles, all green symbols are circles, all red symbols are squares). Redundant coding makes the display much more acceptable for users who have colour-vision deficiencies.
  • As the number of colours is increased, the sizes of the colour-coded objects should also be increased.
  • Red and green should not be used for small symbols and small shapes in peripheral areas of large displays.
  • Using opponent colours (red and green, yellow and blue) adjacent to one another or in an object/background relationship is sometimes beneficial and sometimes detrimental. No general guidelines can be given; a solution should be determined for each case.
  • Avoid displaying several highly saturated, spectrally extreme colours at the same time.

 

Panels of Controls and Displays

Displays as well as controls should be arranged in panels so they are in front of the operator, that is, close to the person’s medial plane. As discussed earlier, controls should be near elbow height, and displays below or at eye height, whether the operator is sitting or standing. Infrequently operated controls, or less important displays, can be located further to the sides, or higher.

Often, information on the result of control operation is displayed on an instrument. In this case, the display should be located close to the control so that the control setting can be done without error, quickly and conveniently. The assignment is usually clearest when the control is directly below or to the right of the display. Care must be taken that the hand does not cover the display when operating the control.

Popular expectancies of control-display relations exist, but they are often learned, they may depend on the user’s cultural background and experience, and these relationships are often not strong. Expected movement relationships are influenced by the type of control and display. When both are either linear or rotary, the stereotypical expectation is that they move in corresponding directions, such as both up or both clockwise. When the movements are incongruent, in general the following rules apply:

  • Clockwise for increase. Turning the control clockwise causes an increase in the displayed value.
  • Warrick’s gear-slide rule. A display (pointer) is expected to move in the same direction as does the side of the control close to (i.e., geared with) the display.

 

The ratio of control and display displacement (C/D ratio or D/C gain) describes how much a control must be moved to adjust a display. If much control movement produces only a small display motion, once speaks of a high C/D ratio, and of the control as having low sensitivity. Often, two distinct movements are involved in making a setting: first a fast primary (“slewing”) motion to an approximate location, then a fine adjustment to the exact setting. In some cases, one takes as the optimal C/D ratio that which minimizes the sum of these two movements. However, the most suitable ratio depends on the given circumstances; it must be determined for each application.

Labels and Warnings

Labels

Ideally, no label should be required on equipment or on a control to explain its use. Often, however, it is necessary to use labels so that one may locate, identify, read or manipulate controls, displays or other equipment items. Labelling must be done so that the information is provided accurately and rapidly. For this, the guidelines in table 4 apply.

Table 4. Guidelines for labels

Orientation

A label and the information printed on it shall be oriented
horizontally so that it can be read quickly and easily.
(Note that this applies if the operator is used to reading
horizontally, as in Western countries.)

Location

A label shall be placed on or very near the item that it
identifies.

Standardization

Placement of all labels shall be consistent throughout the
equipment and system.

Equipment
functions

A label shall primarily describe the function (“what does it
do”) of the labelled item.

Abbreviations

Common abbreviations may be used. If a new abbreviation is
necessary, its meaning should be obvious to the reader.
The same abbreviation shall be used for all tenses and for
the singular and plural forms of a word. Capital letters
shall be used, periods normally omitted.

Brevity

The label inscription shall be as concise as possible without
distorting the intended meaning or information. The texts
shall be unambiguous, redundancy minimized.

Familiarity

Words shall be chosen, if possible, that are familiar to the
operator.

Visibility and
legibility

The operator shall be able to be read easily and accurately at
the anticipated actual reading distances, at the anticipated
worst illumination level, and within the anticipated
vibration and motion environment. Important factors are:
contrast between the lettering and its background; the
height, width, strokewidth, spacing and style of letters;
and the specular reflection of the background, cover or
other components.

Font and size

Typography determines the legibility of written information;
it refers to style, font, arrangement and appearance.

Source: Modified from Kroemer, Kroemer and Kroemer-Elbert 1994
(reproduced by permission of Prentice-Hall; all rights reserved).

 

Font (typeface) should be simple, bold and vertical, such as Futura, Helvetica, Namel, Tempo and Vega. Note that most electronically generated fonts (formed by LED, LCD or dot matrix) are generally inferior to printed fonts; thus, special attention must be paid to making these as legible as possible.

  • The height of characters depends on the viewing distance:

viewing distance 35 cm, suggested height 22 mm

viewing distance 70 cm, suggested height 50 mm

viewing distance 1 m, suggested height 70 mm

viewing distance 1.5 m, suggested height at least 1 cm.

  • The ratio of strokewidth to character height should be between 1:8 to 1:6 for black letters on white background, and 1:10 to 1:8 for white letters on black background.
  • The ratio of character width to character height should be about 3:5.
  • The space between letters should be at least one stroke width.
  • The space between words should be at least one character width.
  • For continuous text, mix upper- and lower-case letters; for labels, use upper-case letters only.

 

Warnings

Ideally, all devices should be safe to use. In reality, often this cannot be achieved through design. In this case, one must warn users of the dangers associated with product use and provide instructions for safe use to prevent injury or damage.

It is preferable to have an “active” warning, usually consisting of a sensor that notices inappropriate use, combined with an alerting device that warns the human of an impending danger. Yet, in most cases, “passive” warnings are used, usually consisting of a label attached to the product and of instructions for safe use in the user manual. Such passive warnings rely completely on the human user to recognize an existing or potential dangerous situation, to remember the warning, and to behave prudently.

Labels and signs for passive warnings must be carefully designed by following the most recent government laws and regulations, national and international standards, and the best applicable human engineering information. Warning labels and placards may contain text, graphics, and pictures—often graphics with redundant text. Graphics, particularly pictures and pictograms, can be used by persons with different cultural and language backgrounds, if these depictions are selected carefully. However, users with different ages, experiences, and ethnic and educational backgrounds, may have rather different perceptions of dangers and warnings. Therefore, design of a safe product is much preferable to applying warnings to an inferior product.

 

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Monday, 14 March 2011 20:21

Information Processing and Design

Written by

In designing equipment it is of the utmost importance to take full account of the fact that a human operator has both capabilities and limitations in processing information, which are of a varying nature and which are found on various levels. Performance in actual work conditions strongly depends on the extent to which a design has either attended to or ignored these potentials and their limits. In the following a brief sketch will be offered of some of the chief issues. Reference will be made to other contributions of this volume, where an issue will be discussed in greater detail.

It is common to distinguish three main levels in the analysis of human information processing, namely, the perceptual level, the decision level and the motor level. The perceptual level is subdivided into three further levels, relating to sensory processing, feature extraction and identification of the percept. On the decision level, the operator receives perceptual information and chooses a reaction to it which is finally programmed and actualized on the motor level. This describes only the information flow in the simplest case of a choice reaction. It is evident, though, that perceptual information may accumulate and be combined and diagnosed before eliciting an action. Again, there may arise a need for selecting information in view of perceptual overload. Finally, choosing an appropriate action becomes more of a problem when there are several options some of which may be more appropriate than others. In the present discussion, the emphasis will be on the perceptual and decisional factors of information processing.

Perceptual Capabilities and Limits

Sensory limits

The first category of processing limits is sensory. Their relevance to information processing is obvious since processing becomes less reliable as information approaches threshold limits. This may seem a fairly trivial statement, but nonetheless, sensory problems are not always clearly recognized in designs. For example, alphanumerical characters in sign posting systems should be sufficiently large to be legible at a distance consistent with the need for appropriate action. Legibility, in turn, depends not only on the absolute size of the alphanumericals but also on contrast and—in view of lateral inhibition—also on the total amount of information on the sign. In particular, in conditions of low visibility (e.g., rain or fog during driving or flying) legibility is a considerable problem requiring additional measures. More recently developed traffic signposts and road markers are usually well designed, but signposts near and within buildings are often illegible. Visual display units are another example in which sensory limits of size, contrast and amount of information play an important role. In the auditory domain some main sensory problems are related to understanding speech in noisy environments or in poor quality audio transmission systems.

Feature extraction

Provided sufficient sensory information, the next set of information processing issues relates to extracting features from the information presented. Most recent research has shown ample evidence that an analysis of features precedes the perception of meaningful wholes. Feature analysis is particularly useful in locating a special deviant object amidst many others. For instance, an essential value on a display containing many values may be represented by a single deviant colour or size, which feature then draws immediate attention or “pops out”. Theoretically, there is the common assumption of “feature maps” for different colours, sizes, forms and other physical features. The attention value of a feature depends on the difference in activation of the feature maps that belong to the same class, for example, colour. Thus, the activation of a feature map depends on the discriminability of the deviant features. This means that when there are a few instances of many colours on a screen, most colour feature maps are about equally activated, which has the effect that none of the colours pops out.

In the same way a single moving advertisement pops out, but this effect disappears altogether when there are several moving stimuli in the field of view. The principle of the different activation of feature maps is also applied when aligning pointers that indicate ideal parameter values. A deviation of a pointer is indicated by a deviant slope which is rapidly detected. If this is impossible to realize, a dangerous deviation might be indicated by a change in colour. Thus, the general rule for design is to use only a very few deviant features on a screen and to reserve them only for the most essential information. Searching for relevant information becomes cumbersome in the case of conjunctions of features. For example, it is hard to locate a large red object amidst small red objects and large and small green objects. If possible, conjunctions should be avoided when trying to design for efficient search.

Separable versus integral dimensions

Features are separable when they can be changed without affecting the perception of other features of an object. Line lengths of histograms are a case in point. On the other hand, integral features refer to features which, when changed, change the total appearance of the object. For instance, one cannot change features of the mouth in a schematic drawing of a face without altering the total appearance of the picture. Again, colour and brightness are integral in the sense that one cannot change a colour without altering the brightness impression at the same time. The principles of separable and integral features, and of emergent properties evolving from changes of single features of an object, are applied in so-called integrated or diagnostic displays. The rationale of these displays is that, rather than displaying individual parameters, different parameters are integrated into a single display, the total composition of which indicates what may be actually wrong with a system.

Data presentation in control rooms is still often dominated by the philosophy that each individual measure should have its own indicator. Piecemeal presentation of the measures means that the operator has the task of integrating the evidence from the various individual displays so as to diagnose a potential problem. At the time of the problems in the Three Mile Island nuclear power plant in the United States some forty to fifty displays were registering some form of disorder. Thus, the operator had the task of diagnosing what was actually wrong by integrating the information from that myriad of displays. Integral displays may be helpful in diagnosing the kind of error, since they combine various measures into a single pattern. Different patterns of the integrated display, then, may be diagnostic with regard to specific errors.

A classical example of a diagnostic display, which has been proposed for nuclear control rooms, is shown in figure 1. It displays a number of measures as spokes of equal length so that a regular polygon always represents normal conditions, while different distortions may be connected with different types of problems in the process.

Figure 1. In the normal situation all parameter values are equal, creating a hexagon. In the deviation, some of the values have changed creating a specific distortion.

ERG220F1Not all integral displays are equally discriminable. To illustrate the issue, a positive correlation between the two dimensions of a rectangle creates differences in surface, while maintaining an equal shape. Alternatively, a negative correlation creates differences in shape while maintaining an equal surface. The case in which variation of integral dimensions creates a new shape has been referred to as revealing an emergent property of the patterning, which adds to the operator’s ability to discriminate the patterns. Emergent properties depend upon the identity and arrangement of parts but are not identifiable with any single part.

Object and configural displays are not always beneficial. The very fact that they are integral means that the characteristics of the individual variables are harder to perceive. The point is that, by definition, integral dimensions are mutually dependent, thus clouding their individual constituents. There may be circumstances in which this is unacceptable, while one may still wish to profit from the diagnostic patternlike properties, which are typical for the object display. One compromise might be a traditional bar graph display. On the one hand, bar graphs are quite separable. Yet, when positioned in sufficiently close vicinity, the differential lengths of the bars may together constitute an object-like pattern which may well serve a diagnostic aim.

Some diagnostic displays are better than others. Their quality depends on the extent that the display corresponds to the mental model of the task. For example, fault diagnosis on the basis of distortions of a regular polygon, as in figure 1, may still bear little relationship to the domain semantics or to the concept of the operator of the processes in a power plant. Thus, various types of deviations of the polygon do not obviously refer to a specific problem in the plant. Therefore, the design of the most suitable configural display is one that corresponds to the specific mental model of the task. Thus it should be emphasized that the surface of a rectangle is only a useful object display when the product of length and width is the variable of interest!

Interesting object displays stem from three-dimensional representations. For instance, a three-dimensional representation of air traffic—rather than the traditional two-dimensional radar representation—may provide the pilot with a greater “situational awareness” of other traffic. The three-dimensional display has been shown to be much superior to a two-dimensional one since its symbols indicate whether another aircraft is above or below one’s own.

Degraded conditions

Degraded viewing occurs under a variety of conditions. For some purposes, as with camouflage, objects are intentionally degraded so as to prevent their identification. On other occasions, for example in brightness amplification, features may become too blurred to allow one to identify the object. One research issue has concerned the minimal number of “lines” required on a screen or “the amount of detail” needed in order to avoid degradation. Unfortunately, this approach to image quality has not led to unequivocal results. The problem is that identifying degraded stimuli (e.g., a camouflaged armoured vehicle) depends too much on the presence or absence of minor object-specific details. The consequence is that no general prescription about line density can be formulated, except for the trivial statement that degradation decreases as the density increases.

Features of alphanumeric symbols

A major issue in the process of feature extraction concerns the actual number of features which together define a stimulus. Thus, the legibility of ornate characters like Gothic letters is poor because of the many redundant curves. In order to avoid confusion, the difference between letters with very similar features—like the i and the l, and the c and the e—should be accentuated. For the same reason, it is recommended to make the stroke and tail length of ascenders and descenders at least 40% of the total letter height.

It is evident that discrimination among letters is mainly determined by the number of features which they do not share. These mainly consist of straight line and circular segments which may have horizontal, vertical and oblique orientation and which may differ in size, as in lower- and upper-case letters.

It is obvious that, even when alphanumericals are well discriminable, they may easily lose that property in combination with other items. Thus, the digits 4 and 7 share only a few features but they do not do well in the context of larger otherwise identical groups (e.g., 384 versus 387) There is unanimous evidence that reading text in lower case is faster than in capitals. This is usually ascribed to the fact that lower case letters have more distinct features (e.g., dog, cat versus DOG, CAT). The superiority of lower case letters has not only been established for reading text but also for road signs such as those used for indicating towns at the exits of motorways.

Identification

The final perceptual process is concerned with identification and interpretation of percepts. Human limits arising on this level are usually related to discrimination and finding the appropriate interpretation of the percept. The applications of research on visual discrimination are manifold, relating to alphanumerical patterns as well as to more general stimulus identification. The design of brake lights in cars will serve as an example of the last category. Rear-end accidents account for a considerable proportion of traffic accidents, and are due in part to the fact that the traditional location of the brake light next to the rear lights makes it poorly discriminable and therefore extends the driver’s reaction time. As an alternative, a single light has been developed which appears to reduce the accident rate. It is mounted in the centre of the rear window at approximately eye level. In experimental studies on the road, the effect of the central braking light appears to be less when subjects are aware of the aim of the study, suggesting that stimulus identification in the traditional configuration improves when subjects focus on the task. Despite the positive effect of the isolated brake light, its identification might still be further improved by making the brake light more meaningful, giving it the form of an exclamation mark, “!”, or even an icon.

Absolute judgement

Very strict and often counterintuitive performance limits arise in cases of absolute judgement of physical dimensions. Examples occur in connection with colour coding of objects and the use of tones in auditory call systems. The point is that relative judgement is far superior to absolute judgement. The problem with absolute judgement is that the code has to be translated into another category. Thus a specific colour may be linked with an electrical resistance value or a specific tone may be intended for a person for which an ensuing message is meant. In fact, therefore, the problem is not one of perceptual identification but rather of response choice, which will be discussed later in this article. At this point it suffices to remark that one should not use more than four or five colours or pitches so as to avoid errors. When more alternatives are needed one may add extra dimensions, like loudness, duration and components of tones.

Word reading

The relevance of reading separate word units in traditional print is demonstrated by various widely experienced evidence, such as the fact that reading is very much hampered when spaces are omitted, printing errors remain often undetected, and it is very hard to read words in alternating cases (e.g., ALTeRnAtInG). Some investigators have emphasized the role of word shape in reading word units and suggested that spatial frequency analysers may be relevant in identifying word shape. In this view meaning would be derived from total word shape rather than by letter-by-letter analysis. Yet, the contribution of word shape analysis is probably limited to small common words—articles and endings—which is consistent with the finding that printing errors in small words and endings have a relatively low probability of detection.

Text in lower case has an advantage over upper case which is due to a loss of features in the upper case. Yet, the advantage of lower case words is absent or may even be reversed when searching for a single word. It could be that factors of letter size and letter case are confounded in searching: Larger-sized letters are detected more rapidly, which may offset the disadvantage of less distinctive features. Thus, a single word may be about equally legible in upper case as in lower case, while continuous text is read faster in lower case. Detecting a SINGLE capital word amidst many lower case words is very efficient, since it evokes pop-out. An even more efficient fast detection can be achieved by printing a single lower case word in bold, in which case the advantages of pop-out and of more distinctive features are combined.

The role of encoding features in reading is also clear from the impaired legibility of older low-resolution visual display unit screens, which consisted of fairly rough dot matrices and could portray alphanumericals only as straight lines. The common finding was that reading text or searching from a low-resolution monitor was considerably slower than from a paper-printed copy. The problem has largely disappeared with the present-day higher-resolution screens. Besides letter form there are a number of additional differences between reading from paper and reading from a screen. The spacing of the lines, the size of the characters, the type face, the contrast ratio between characters and background, the viewing distance, the amount of flicker and the fact that changing pages on a screen is done by scrolling are some examples. The common finding that reading is slower from computer screens—although comprehension seems about equal—may be due to some combination of these factors. Present-day text processors usually offer a variety of options in font, size, colour, format and style; such choices could give the false impression that personal taste is the major reason.

Icons versus words

In some studies the time taken by a subject in naming a printed word was found to be faster than that for a corresponding icon, while both times were about equally fast in other studies. It has been suggested that words are read faster than icons since they are less ambiguous. Even a fairly simple icon, like a house, may still elicit different responses among subjects, resulting in response conflict and, hence, a decrease in reaction speed. If response conflict is avoided by using really unambiguous icons the difference in response speed is likely to disappear. It is interesting to note that as traffic signs, icons are usually much superior to words, even in the case where the issue of understanding language is not seen as a problem. This paradox may be due to the fact that the legibility of traffic signs is largely a matter of the distance at which a sign can be identified. If properly designed, this distance is larger for symbols than for words, since pictures can provide considerably larger differences in shape and contain less fine details than words. The advantage of pictures, then, arises from the fact that discrimination of letters requires some ten to twelve minutes of arc and that feature detection is the initial prerequisite for discrimination. At the same time it is clear that the superiority of symbols is only guaranteed when (1) they do indeed contain little detail, (2) they are sufficiently distinct in shape and (3) they are unambiguous.

Capabilities and Limits for Decision

Once a precept has been identified and interpreted it may call for an action. In this context the discussion will be limited to deterministic stimulus-response relations, or, in other words, to conditions in which each stimulus has its own fixed response. In that case the major problems for equipment design arise from issues of compatibility, that is, the extent to which the identified stimulus and its related response have a “natural” or well-practised relationship. There are conditions in which an optimal relation is intentionally aborted, as in the case of abbreviations. Usually a contraction like abrvtin is much worse than a truncation like abbrev. Theoretically, this is due to the increasing redundancy of successive letters in a word, which allows “filling out” final letters on the basis of earlier ones; a truncated word can profit from this principle while a contracted one cannot.

Mental models and compatibility

In most compatibility problems there are stereotypical responses derived from generalized mental models. Choosing the null position in a circular display is a case in point. The 12 o’clock and 9 o’clock positions appear to be corrected faster than the 6 o’clock and 3 o’clock positions. The reason may be that a clockwise deviation and a movement in the upper part in the display are experienced as “increases” requiring a response that reduces the value. In the 3 and 6 o’clock positions both principles conflict and they may therefore be handled less efficiently. A similar stereotype is found in locking or opening the rear door of a car. Most people act on the stereotype that locking requires a clockwise movement. If the lock is designed in the opposite way, continuous errors and frustration in trying to lock the door are the most likely result.

With respect to control movements the well-known Warrick’s principle on compatibility describes the relation between the location of a control knob and the direction of the movement on a display. If the control knob is located to the right of the display, a clockwise movement is supposed to move the scale marker up. Or consider moving window displays. According to most people’s mental model, the upward direction of a moving display suggests that the values go up in the same way in which a rising temperature in a thermometer is indicated by a higher mercury column. There are problems in implementing this principle with a “fixed pointer-moving scale” indicator. When the scale in such an indicator moves down, its value is intended to increasing. Thus a conflict with the common stereotype occurs. If the values are inverted, the low values are on the top of the scale, which is also contrary to most stereotypes.

The term proximity compatibility refers to the correspondence of symbolic representations to people’s mental models of functional or even spatial relationships within a system. Issues of proximity compatibility are more pressing as the mental model of a situation is more primitive, global or distorted. Thus, a flow diagram of a complex automated industrial process is often displayed on the basis of a technical model which may not correspond at all with the mental model of the process. In particular, when the mental model of a process is incomplete or distorted, a technical representation of the progress adds little to develop or correct it. A daily-life example of poor proximity compatibility is an architectural map of a building that is intended for viewer orientation or for showing fire escape routes. These maps are usually entirely inadequate—full of irrelevant details—in particular for people who have only a global mental model of the building. Such convergence between map reading and orientation comes close to what has been called “situational awareness”, which is particularly relevant in three-dimensional space during an air flight. There have been interesting recent developments in three-dimensional object displays, representing attempts to achieve optimal proximity compatibility in this domain.

Stimulus-response compatibility

An example of stimulus-response (S-R) compatibility is typically found in the case of most text processing programs, which assume that operators know how commands correspond to specific key combinations. The problem is that a command and its corresponding key combination usually fail to have any pre-existing relation, which means that the S-R relations must be learned by a painstaking process of paired-associate learning. The result is that, even after the skill has been acquired, the task remains error-prone. The internal model of the program remains incomplete since less practised operations are liable to be forgotten, so that the operator can simply not come up with the appropriate response. Also, the text produced on the screen usually does not correspond in all respects to what finally appears on the printed page, which is another example of inferior proximity compatibility. Only a few programs utilize a stereotypical spatial internal model in connection with stimulus-response relations for controlling commands.

It has been correctly argued that there are much better pre-existing relations between spatial stimuli and manual responses—like the relation between a pointing response and a spatial location, or like that between verbal stimuli and vocal responses. There is ample evidence that spatial and verbal representations are relatively separate cognitive categories with little mutual interference but also with little mutual correspondence. Hence, a spatial task, like formatting a text, is most easily performed by spatial mouse-type movement, thus leaving the keyboard for verbal commands.

This does not mean that the keyboard is ideal for carrying out verbal commands. Typing remains a matter of manually operating arbitrary spatial locations which are basically incompatible with processing letters. It is actually another example of a highly incompatible task which is only mastered by extensive practise, and the skill is easily lost without continuous practice. A similar argument can be made for shorthand writing, which also consists of connecting arbitrary written symbols to verbal stimuli. An interesting example of an alternative method of keyboard operation is a chording keyboard.

The operator handles two keyboards (one for the left and one for the right hand) both consisting of six keys. Each letter of the alphabet corresponds to a chording response, that is, a combination of keys. The results of studies on such a keyboard showed striking savings in the time needed for acquiring typing skills. Motor limitations limited the maximal speed of the chording technique but, still, once learned, operator performance approached the speed of the conventional technique quite closely.

A classical example of a spatial compatibility effect concerns the traditional arrangements of stove burner controls: four burners in a 2 ´ 2 matrix, with the controls in a horizontal row. In this configuration, the relations between burner and control are not obvious and are poorly learned. However, despite many errors, the problem of lighting the stove, given time, can usually be solved. The situation is worse when one is faced with undefined display-control relations. Other examples of poor S-R compatibility are found in the display-control relations of video cameras, video recorders and television sets. The effect is that many options are never used or must be studied anew at each new trial. The claim that “it is all explained in the manual”, while true, is not useful since, in practice, most manuals are incomprehensible to the average user, in particular when they attempt to describe actions using incompatible verbal terms.

Stimulus-stimulus (S-S) and response-response (R-R) compatibility

Originally S-S and R-R compatibility were distinguished from S-R compatibility. A classical illustration of S-S compatibility concerns attempts in the late forties to support auditory sonar by a visual display in an effort to enhance signal detection. One solution was sought in a horizontal light beam with vertical perturbations travelling from left to right and reflecting a visual translation of the auditory background noise and potential signal. A signal consisted of a slightly larger vertical perturbation. The experiments showed that a combination of the auditory and visual displays did not do better than the single auditory display. The reason was sought in a poor S-S compatibility: the auditory signal is perceived as a loudness change; hence visual support should correspond most when provided in the form of a brightness change, since that is the compatible visual analogue of a loudness change.

It is of interest that the degree of S-S compatibility corresponds directly to how skilled subjects are in cross-modality matching. In a cross-modality match, subjects may be asked to indicate which auditory loudness corresponds to a certain brightness or to a certain weight; this approach has been popular in research on scaling sensory dimensions, since it allows one to avoid mapping sensory stimuli to numerals. R-R compatibility refers to correspondence of simultaneous and also of successive movements. Some movements are more easily coordinated than others, which provides clear constraints for the way a succession of actions—for example, successive operation of controls—is most efficiently done.

The above examples show clearly how compatibility issues pervade all user-machine interfaces. The problem is that the effects of poor compatibility are often softened by extended practice and so may remain unnoticed or underestimated. Yet, even when incompatible display-control relations are well-practised and do not seem to affect performance, there remains the point of a larger error probability. The incorrect compatible response remains a competitor for the correct incompatible one and is likely to come through on occasion, with the obvious risk of an accident. In addition, the amount of practice required for mastering incompatible S-R relations is formidable and a waste of time.

Limits of Motor Programming and Execution

One limit in motor programming was already briefly touched upon in the remarks on R-R compatibility. The human operator has clear problems in carrying out incongruent movement sequences, and in particular, changing from the one to another incongruent sequence is hard to accomplish. The results of studies on motor coordination are relevant to the design of controls in which both hands are active. Yet, practice can overcome much in this regard, as is clear from the surprising levels of acrobatic skills.

Many common principles in the design of controls derive from motor programming. They include the incorporation of resistance in a control and the provision of feedback indicating that it has been properly operated. A preparatory motor state is a highly relevant determinant of reaction time. Reacting to an unexpected sudden stimulus may take an additional second or so, which is considerable when a fast reaction is needed—as in reacting to a lead car’s brake light. Unprepared reactions are probably a main cause of chain collisions. Early warning signals are beneficial in preventing such collisions. A major application of research on movement execution concerns Fitt’s law, which relates movement, distance and the size of the target that is aimed at. This law appears to be quite general, applying equally to an operating lever, a joystick, a mouse or a light pen. Among others, it has been applied to estimate the time needed to make corrections on computer screens.

There is obviously much more to say than the above sketchy remarks. For instance, the discussion has been almost fully limited to issues of information flow on the level of a simple choice reaction. Issues beyond choice reactions have not been touched upon, nor problems of feedback and feed forward in the ongoing monitoring of information and motor activity. Many of the issues mentioned bear a strong relation to problems of memory and of planning of behaviour, which have not been addressed either. More extensive discussions are found in Wickens (1992), for example.

 

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Monday, 14 March 2011 20:28

Designing for Specific Groups

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In designing a product or an industrial process, one focuses on the “average” and “healthy” worker. Information regarding human abilities in terms of muscular strength, bodily flexibility, length of reach, and many other characteristics is for the most part derived from empirical studies carried out by military recruitment agencies, and reflects measured values valid for the typical young male in his twenties. But working populations, to be sure, consist of people of both sexes and a broad range of ages, to say nothing of a variety of physical types and abilities, levels of fitness and health, and functional capacities. A classification of the varieties of functional limitation among people as outlined by the World Health Organization is given in the accompanying article "Case Study: The International Classifcation of Functional Limitation in People." At present, industrial design for the most part takes insufficient account of the general abilities (or inabilities, for that matter) of workers at large, and should take as its point of departure a broader human average as a basis for design. Clearly, a suitable physical load for a 20-year-old may exceed the capacity to manage of a 15-year-old or a 60-year-old. It is the business of the designer to consider such differences not only from the point of view of efficiency, but with a eye to the prevention of job-related injury and illness.

The progress of technology has brought about the state of affairs that, of all the workplaces in Europe and North America, 60% involve the seated position. The physical load in work situations is now on average far less than before, but many worksites, nonetheless, call for physical loads that cannot be sufficiently reduced to fit human physical capabilities; in some developing countries, the resources of current technology are simply not available to relieve the human physical burden to any appreciable extent. And in technologically advanced countries, it is still a common problem that a designer will adapt his or her approach to constraints imposed by product specifications or production processes, either slighting or leaving out human factors related to disability and the prevention of harm due to the workload. With respect to these aims, designers have to be educated to devote attention to all such human factors, expressing the results of their study in a product requirements document (PRD). The PRD contains the system of demands which the designer has to meet in order to achieve both the expected product quality level and the satisfaction of human capability needs in the production process. While it is unrealistic to demand a product that matches a PRD in every respect, given the need of unavoidable compromises, the design method suited to the closest approach to this goal is the system ergonomic design (SED) method, to be discussed following a consideration of two alternative design approaches.

Creative Design

This design approach is characteristic of artists and others involved in the production of work of a high order of originality. The essence of this design process is that a concept is worked out intuitively and through “inspiration”, allowing problems to be dealt with as they arise, without conscious deliberation beforehand. Sometimes, the outcome will not resemble the initial concept, but nonetheless represents what the creator regards as his or her authentic product. Not seldom, too, the design is a failure. Figure 1 illustrates the route of creative design.

Figure 1. Creative design

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System Design

System design arose from the need to predetermine the steps in design in a logical order. As design becomes complex, it has to be subdivided into subtasks. Designers or subtask teams thus become interdependent, and design becomes the job of a design team rather than an individual designer. Complementary expertise is distributed through the team, and design assumes an interdisciplinary character.

System design is oriented to the optimal realization of complex and well-defined product functions through the selection of the most appropriate technology; it is costly, but the risks of failure are considerably reduced as compared with less organized approaches. The efficacy of the design is measured against the goals formulated in the PRD.

The way in which the specifications formulated in the PRD are of the first importance. Figure 2 illustrates the relationship between the PRD and other parts of the system design process.

Figure 2. System design

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As this scheme shows, the input of the user is neglected. Only at the end of the design process can the user criticize the design. This is unhelpful to both producer and user, since one has to wait for the next design cycle (if there is one) before errors can be corrected and modifications made. Furthermore, user feedback is seldom systematized and imported into a new PRD as a design influence.

 

 

 

 

 

 

 

 

System ergonomic design (SED)

SED is a version of system design adapted to ensure that the human factor is accounted for in the design process. Figure 3 illustrates the flow of user input into the PRD.

Figure 3. System ergonomic design

ERG240F3In system ergonomic design, the human being is considered part of the system: design specification changes are, in fact, made in consideration of the worker’s abilities with respect to cognitive, physical and mental aspects, and the method lends itself as an efficient design approach for any technical system where human operators are employed.

For example, to examine the implications of the worker’s physical abilities, task-allocation in the design of the process will call for a careful selection of tasks to be performed by the human operator or by the machine, each task being studied for its aptness to machine or human treatment. Clearly, the human worker will be more effective at interpreting incomplete information; machines however calculate much more rapidly with prepared data; a machine is the choice for lifting heavy loads; and so forth. Furthermore, since the user-machine interface can be tested at the prototype phase, one can eliminate design errors that would otherwise untimely manifest                                                                                                                                         themselves at the phase of technical functioning.

Methods in User Research

No “best” method exists, nor any source of formulae and sure and certain guidelines, according to which design for disabled workers ought to be undertaken. It is a rather a common-sense business of making as exhaustive search of all obtainable knowledge relevant to the problem and of implementing it to its most evident best effect.

Information can be assembled from sources such as the following:

  • The literature of research results.
  • Direct observation of the disabled person at work and description of his or her particular work difficulties. Such observation should be made at a point in the worker’s schedule when he or she can be expected to be subject to fatigue—the end of a work shift, perhaps. The point is that any design solutions should be adapted to the most arduous phase of the work process, or else such phases may fail to be performed adequately (or at all) owing to the worker’s capacity having been physically exceeded.
  • The interview. One has to be aware of the possibly subjective responses which the interview per se may have the effect of eliciting. It is a far better approach that the interview technique be combined with observation. Disabled persons sometimes hesitate to discuss their difficulties, but when workers are aware that the investigator is willing to exert special thoroughness on their behalf, their reticence will diminish. This technique is time-consuming, but quite worthwhile.
  • Questionnaires. An advantage of the questionnaire is that it can be distributed to large groups of respondents and at the same time gather data of as specific a sort as one wishes to provide for. The questionnaire must, however, be constructed upon the basis of representative information pertaining to the group to which it will be administered. This means that the type of information to be sought must be obtained on the basis of interviews and observations carried out among a sample of workers and specialists that ought to be reasonably restricted as to size. In the case of disabled persons, it is sensible to include among such a sample the physicians and therapists who are involved with prescribing special aids for disabled persons and have examined them regarding their physical capabilities.
  • Physical measurements. Measurements obtained from instruments in the field of bio-instrumentation (e.g., the activity level of muscles, or the amount of oxygen consumed in a given task) and by anthropometrical methods (e.g., the linear dimensions of body elements, the range of motion of limbs, muscular strength) are of indispensable value in human-oriented work designs.

 

The methods described above are some of the various ways of gathering data about people. Methods exist, too, to evaluate user-machine systems. One of these—simulation—is to construct a realistic physical copy. The development of a more or less abstract symbolic representation of a system is an example of modelling. Such expedients, of course, are both useful and necessary when the actual system or product is not in existence or not accessible to experimental manipulation. Simulation is more often used for training purposes and modelling for research. A mock-up is a full-size, three-dimensional copy of the designed workplace composed, where necessary, of improvised materials, and is of great use in testing design possibilities with the proposed disabled worker: in fact, the majority of design problems can be identified with the aid of such a device. Another advantage to this approach is that the motivation of the worker grows as he or she participates in the design of his or her own future workstation.

Analysis of Tasks

In the analysis of tasks, different aspects of a defined job are subject to analytical observation. These manifold aspects include posture, routing of work manipulations, interactions with other workers, handling tools and operating machines, the logical order of subtasks, the efficiency of operations, static conditions (a worker may have to perform tasks in the same posture over a long time or with high frequency), dynamic conditions (calling for numerous varying physical conditions), material environmental conditions (as in a cold slaughterhouse) or non-material conditions (as with stressful work surroundings or the organization of the work itself).

Work design for the disabled person has, then, to be founded on a thorough task analysis as well as a full examination of the functional abilities of the disabled person. The basic design approach is a crucial issue: it is more efficient to elaborate all possible solutions for the problem in hand without prejudice than to produce a single design concept or a limited number of concepts. In design terminology, this approach is called making a morphological overview. Given the multiplicity of original design concepts, one can proceed to an analysis of the pro and con features of each possibility with respect to material use, construction method, technical production features, ease of manipulation, and so on. It is not unprecedented that more than one solution reaches the prototype stage and that a final decision is made at a relatively late phase in the design process.

Although this may seem a time-consuming way to realize design projects, in fact the extra work it entails is compensated for in terms of fewer problems encountered in the developmental stage, to say nothing that the result—a new workstation or product—will have embodied a better balance between the needs of the disabled worker and the exigencies of the working environment. Unfortunately, the latter benefit rarely if ever reaches the designer in terms of feedback.

Product Requirements Document (PRD) and Disability

After all information relating to a product has been assembled, it should be transformed into a description not only of the product but of all those demands which may be made of it, regardless of source or nature. These demands may of course be divided along various lines. The PRD should include demands relating to user-operator data (physical measurements, range of motion, range of muscular strength, etc.), technical data (materials, construction, production technique, safety standards, etc.), and even conclusions arising out of market feasibility studies.

The PRD forms the designer’s framework, and some designers regard it as an unwelcome restriction of their creativity rather than as a salutary challenge. In view of the difficulties at times accompanying the execution of a PRD, it should always be borne steadily in mind that a design failure causes distress for the disabled person, who may relinquish his or her efforts to succeed in the employment arena (or else fall helpless victim to the progress of the disabling condition), and additional costs for redesign as well. To this end, technical designers should not operate alone in their design work for the disabled, but should cooperate with whatever disciplines are needed for securing the medical and functional information to set up an integrated PRD as a framework for the design.

Prototype Testing

When a prototype is built, it should be tested for errors. Error testing should be carried out not only from the point of view of the technical system and subsystems, but also with a view to its usability in combination with the user. When the user is a disabled person, extra precautions have to be taken. An error to which an unimpaired worker may successfully respond in safety may not afford the disabled worker the opportunity of avoiding harm.

Prototype testing should be carried out on a small number of disabled workers (except in the case of a unique design) according to a protocol matched to the PRD. Only by such empirical testing can the degree to which the design meets the demands of the PRD be adequately judged. Although results on small numbers of subjects may not be generalizable to all cases, they do supply valuable information for the designer’s use in either the final design or in future designs.

Evaluation

The evaluation of a technical system (a work situation, machine or tool) should be judged on its PRD, not by questioning the user or even by attempting comparisons of alternative designs with respect to physical performance. For instance, the designer of a specific knee brace, basing his or her design on research results that show unstable knee joints to exhibit a delayed hamstring reaction, will create a product that compensates for this delay. But another brace may have different design aims. Yet present evaluation methods show no insight as to when to prescribe what kind of knee brace to which patients under what conditions—precisely the sort of insight a health professional needs when prescribing technical aids in the treatment of disabilities.

Current research aims at making this sort of insight possible. A model used to obtain insight into those factors which actually determine whether or not a technical aid ought to be used, or whether or not a worksite is well designed and equipped for the disabled worker is the Rehabilitation Technology Useability Model (RTUM). The RTUM model offers a framework to use in evaluations of existing products, tools or machines, but can also be used in combination with the design process as shown in figure 4.

Figure 4. Rehabilitation Technology Useability Model (RTUM) in combination with the system ergonomic design approach

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Evaluations of existing products reveal that as regards technical aids and worksites, the quality of PRDs is very poor. At some times, the product requirements are not recorded properly; at others they are not developed to a useful extent. Designers simply must learn to start documenting their product requirements, including those relevant to disabled users. Note that, as figure 4 shows, RTUM, in conjunction with SED, offers a framework that includes the requirements of disabled users. Agencies responsible for prescribing products for their users must request industry to evaluate those products before marketing them, a task in essence impossible in the absence of product requirement specifications; figure 4 also shows how provision can be made to ensure that the end result can be evaluated as it should (on a PRD) with the help of the disabled person or group for whom the product is intended. It is up to national health organizations to stimulate designers to abide by such design standards and to formulate appropriate regulations.

 

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Monday, 14 March 2011 20:33

Cultural Differences

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Culture and technology are interdependent. While culture is indeed an important aspect in technology design, development and utilization, the relationship between culture and technology is, however, extremely complex. It needs to be analysed from several perspectives in order to be considered in the design and application of technology. Based on his work in Zambia, Kingsley (1983) divides technological adaptation into changes and adjustments at three levels: that of the individual, of the social organization and of the cultural value system of the society. Each level possesses strong cultural dimensions which require special design considerations.

At the same time, technology itself is an inseparable part of culture. It is built, wholly or in part, around the cultural values of a particular society. And as part of culture, technology becomes an expression of that society’s way of life and thinking. Thus, in order for technology to be accepted, utilized and acknowledged by a society as its own, it must be congruent to the overall image of that society’s culture. Technology must complement culture, not antagonize it.

This article will deal with some of the intricacies concerning cultural considerations in technology designs, examining the current issues and problems, as well as the prevailing concepts and principles, and how they can be applied.

Definition of Culture

The definition of the term culture has been debated at length amongst sociologists and anthropologists for many decades. Culture can be defined in many terms. Kroeber and Kluckhohn (1952) reviewed over a hundred definitions of culture. Williams (1976) mentioned culture as one of the most complicated words in the English language. Culture has even been defined as the entire way of life of people. As such, it includes their technology and material artefacts—anything one would need to know to become a functioning member of the society (Geertz 1973). It may even be described as “publicly available symbolic forms through which people experience and express meaning” (Keesing 1974). Summing it up, Elzinga and Jamison (1981) put it aptly when they said that “the word culture has different meanings in different intellectual disciplines and systems of thought”.

Technology: Part and Product of Culture

Technology can be considered both as part of culture and its product. More than 60 years ago the noted sociologist Malinowsky included technology as part of the culture and gave the following definition: “culture comprises inherited artefacts, goods, technical processes, ideas, habits and values.” Later, Leach (1965) considered technology as a cultural product and mentioned “artefacts, goods and technical processes” as “products of culture”.

In the technological realm, “culture” as an important issue in the design, development and utilization of technical products or systems has been largely neglected by many suppliers as well as receivers of technology. One major reason for this neglect is the absence of basic information on cultural differences.

In the past, technological changes have led to significant changes in social life and organization and in people’s value systems. Industrialization has made deep and enduring changes in the traditional lifestyles of many previously agricultural societies since such lifestyles were largely regarded as incompatible with the way industrial work should be organized. In situations of large cultural diversity, this has led to various negative socio-economic outcomes (Shahnavaz 1991). It is now a well-established fact that simply to impose a technology on a society and believe that it will be absorbed and utilized through extensive training is wishful thinking (Martin et al. 1991).

It is the responsibility of the technology designer to consider the direct and indirect effects of the culture and to make the product compatible with the cultural value system of the user and with its intended operating environment.

The impact of technology for many “industrially developing countries” (IDCs) has been much more than improvement in efficiency. Industrialization was not just modernization of the production and service sectors, but to some extent Westernization of the society. Technology transfer is, thus, also cultural transfer.

Culture, in addition to religion, tradition and language, which are important parameters for technology design and utilization, encompasses other aspects, such as specific attitudes towards certain products and tasks, rules of appropriate behaviour, rules of etiquette, taboos, habits and customs. All these must be equally considered for optimum design.

It is said that people are also products of their distinctive cultures. Nevertheless, the fact remains that world cultures are very much interwoven due to human migration throughout history. It is small wonder that there exist more cultural than national variations in the world. Nevertheless, some very broad distinctions can be made regarding societal, organizational and professional culture-based differences that could influence design in general.

Constraining Influences of Culture

There is very little information on both theoretical and empirical analyses of the constraining influences of culture on technology and how this issue should be incorporated in the design of hardware and software technology. Even though the influence of culture on technology has been recognized (Shahnavaz 1991; Abeysekera, Shahnavaz and Chapman 1990; Alvares 1980; Baranson 1969), very little information is available on the theoretical analysis of cultural differences with regard to technology design and utilization. There are even fewer empirical studies that quantify the importance of cultural variations and provide recommendations on how cultural factors should be considered in the design of product or system (Kedia and Bhagat 1988). Nevertheless, culture and technology can still be studied with some degree of clarity when viewed from different sociological viewpoints.

Culture and Technology: Compatibility and Preference

Proper application of a technology depends, to a large extent, on the compatibility of the user’s culture with the design specifications. Compatibility must exist at all levels of culture—at the societal, organizational and professional levels. In turn, cultural compatibility can have strong influence on a people’s preferences and aptness to utilize a technology. This question involves preferences relating to a product or system; to concepts of productivity and relative efficiency; to change, achievement and authority; as well as to the manner of technology utilization. Cultural values can thus affect people’s willingness and ability to select, to use and to control technology. They have to be compatible in order to be preferred.

Societal culture

As all technologies are inevitably associated with sociocultural values, the cultural receptivity of the society is a very important issue for the proper functioning of a given technological design (Hosni 1988). National or societal culture, which contributes to the formation of a collective mental model of people, influences the entire process of technology design and application, which ranges from planning, goal setting and defining design specifications, to production, management and maintenance systems, training and evaluation. Technology design of both hardware and software should, therefore, reflect society-based cultural variations for maximum benefit. However, defining such society-based cultural factors for consideration in the design of technology is a very complicated task. Hofstede (1980) has proposed four dimensional framework variations of national-based culture.

  1. Weak versus strong uncertainty avoidance. This concerns a people’s desire to avoid ambiguous situations and to what extent their society has developed formal means (such as rules and regulations) to serve this purpose. Hofstede (1980) gave, for example, high uncertainty avoidance scores to countries like Japan and Greece, and low scores to Hong Kong and Scandinavia.
  2. Individualism versus collectivism. This pertains to the relationship between individuals and organizations in the society. In individualistic societies, the orientation is such that each person is expected to look after his or her own interests. In contrast, in a collectivist culture, social ties between people are very strong. Some examples of individualistic countries are the United States and Great Britain while Colombia and Venezuela can be considered as having collectivist cultures.
  3. Small versus large power distance. A large “power distance” characterizes those cultures where the less powerful individuals accept the unequal distribution of power in a culture, as well as the hierarchies in the society and its organizations. Examples of large power distance countries are India and the Philippines. Small power distances are typical of countries like Sweden and Austria.
  4. Masculinity versus femininity. Cultures that put more emphasis on material achievements are regarded as belonging to the former category. Those giving more value to quality of life and other less tangible outcomes belong to the latter.

 

Glenn and Glenn (1981) have also distinguished between “abstractive” and “associative” tendencies in a given national culture. It is argued that when people of an associative culture (like those from Asia) approach a cognitive problem, they put more emphasis on context, adapt a global thinking approach and try to utilize association among various events. Whereas in the Western societies, a more abstractive culture of rational thinking predominates. Based on these cultural dimensions, Kedia and Bhagat (1988) have developed a conceptual model for understanding cultural constraints on technology transfer. They have developed various descriptive “propositions” which provide information on different countries’ cultural variations and their receptivity with regard to technology. Certainly many cultures are moderately inclined to one or the other of these categories and contain some mixed features.

Consumers’ as well as producers’ perspectives upon technological design and utilization are directly influenced by the societal culture. Product safety standards for safeguarding consumers as well as work-environment regulations, inspection and enforcement systems for protecting the producers are to a large extent the reflection of the societal culture and value system.

Organizational culture

A company’s organization, its structure, value system, function, behaviour, and so on, are largely cultural products of the society in which it operates. This means that what happens within an organization is mostly a direct reflection of what is happening in the outside society (Hofstede 1983). The prevailing organizations of many companies operating in the IDCs are influenced both by the characteristics of the technology producer country as well as those of the technology recipient environment. However, the reflection of the societal culture in a given organization can vary. Organizations interpret the society in terms of their own culture, and their degree of control depends, among other factors, on the modes of technology transfer.

Given the changing nature of organization today, plus a multicultural, diverse workforce, adapting a proper organizational programme is more important than ever before to a successful operation (an example of a workforce diversity management programme is described in Solomon (1989)).

Professional culture

People belonging to a certain professional category may use a piece of technology in a specific fashion. Wikström et al. (1991), in a project aimed to develop hand tools, have noted that despite the designers’ assumption of how plate shares are to be held and used (i.e., with a forward holding grip and the tool moving away from one’s own body), the professional tinsmiths were holding and using the plate share in a reversed manner, as shown in figure 1. They concluded that tools should be studied in the actual field conditions of the user population itself in order to acquire relevant information on the tools characteristics.

Figure 1. The use of plate share tools by professional tinsmiths in practice (the reversed grip)

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Using Cultural Features for Optimum Design

As implied by the foregoing considerations, culture provides identity and confidence. It forms opinions about the objectives and characteristics of a “human-technology system” and how it should operate in a given environment. And in any culture, there are always some features that are valuable with regard to technological progress. If these features are considered in the design of software and hardware technology, they can act as the driving force for technology absorption in the society. One good example is the culture of some southeast Asian countries largely influenced by Confucianism and Buddhism. The former emphasizes, among other things, learning and loyalty, and considers it a virtue to be able to absorb new concepts. The latter teaches the importance of harmony and respect for fellow human beings. It is said that these unique cultural features have contributed to the provision of the right environment for the absorption and implementation of advanced hardware and organizational technology furnished by the Japanese (Matthews 1982).

A clever strategy would thus make the best use of the positive features of a society’s culture in promoting ergonomic ideas and principles. According to McWhinney (1990) “the events, to be understood and thus used effectively in projection, must be embedded in stories. One must go to varying depths to unleash founding energy, to free society or organization from inhibiting traits, to find the paths along which it might naturally flow. . . . Neither planning nor change can be effective without embedding it consciously in a narrative.”

A good example of cultural appreciation in designing management strategy is the implementation of the “seven tools” technique for quality assurance in Japan. The “seven tools” are the minimum weapons a samurai warrior had to carry with him whenever he went out to fight. The pioneers of “quality control circles”, adapting their nine recommendations to a Japanese setting, reduced this number in order to take advantage of a familiar term—“the seven tools”—so as to encourage the involvement of all employees in their quality work strategy (Lillrank and Kano 1989).

However, other cultural features may not be beneficial to technological development. Discrimination against women, the strict observation of a caste system, racial or other prejudice, or considering some tasks as degrading, are a few examples that can have a negative influence on technology development. In some traditional cultures, men are expected to be the primary wage-earners. They become accustomed to regarding the role of women as equal employees, not to mention as supervisors, with insensitivity or even hostility. Withholding equal employment opportunity from women and questioning the legitimacy of women’s authority is not appropriate to the current needs of organizations, which require optimum utilization of human resources.

With regard to task design and job content, some cultures consider tasks like manual labour and service as degrading. This may be attributed to past experiences linked to colonial times regarding “master-slave relationships”. In some other cultures, strong biases exist against tasks or occupations associated with “dirty hands”. These attitudes are also reflected in lower-than-average pay scales for these occupations. In turn, these have contributed to shortages of technicians or inadequate maintenance resources (Sinaiko 1975).

Since it usually takes many generations to change cultural values with respect to a new technology, it would be more cost-effective to fit the technology to the technology recipient’s culture, taking cultural differences into consideration in the design of hardware and software.

Cultural Considerations in Product and System Designing

By now it is obvious that technology consists both of hardware and software. Hardware components include capital and intermediary goods, such as industrial products, machinery, equipment, buildings, workplaces and physical layouts, most of which chiefly concern the micro-ergonomics domain. Software pertains to programming and planning, management and organizational techniques, administration, maintenance, training and education, documentation and services. All these concerns fall under the heading of macro-ergonomics.

A few examples of cultural influences that require special design consideration from the micro- and macro-ergonomic point of view are given below.

Micro-ergonomic issues

Micro-ergonomics is concerned with the design of a product or system with the objective of creating a “usable” user-machine-environment interface. The major concept of product design is usability. This concept involves not only the functionality and reliability of the product, but issues of safety, comfort and enjoyment as well.

The user’s internal model (i.e., his or her cognitive or mental model) plays an important role in usability design. To operate or control a system efficiently and safely, the user must have an accurate representative cognitive model of the system in use. Wisner (1983) has stated that “industrialization would thus more or less require a new kind of mental model.” In this view, formal education and technical training, experience as well as culture are important factors in determining the formation of an adequate cognitive model.

Meshkati (1989), in studying the micro- and macro-ergonomic factors of the 1984 Union Carbide Bhopal accident, highlighted the importance of culture on the Indian operators’ inadequate mental model of the plant operation. He stated that part of the problem may have been due to “the performance of poorly trained Third World operators using advanced technological systems designed by other humans with much different educational backgrounds, as well as cultural and psychosocial attributes.” Indeed, many design usability aspects at the micro-interface level are influenced by the user’s culture. Careful analyses of the user’s perception, behaviour and preferences would lead to a better understanding of the user’s needs and requirements for designing a product or system that is both effective and acceptable.

Some of these culture-related micro-ergonomic aspects are the following:

  1. Interface design. Human emotion is an essential element of product design. It is concerned in such factors as colour and shape (Kwon, Lee and Ahn 1993; Nagamachi 1992). Colour is regarded as the most important factor to do with human emotions with regard to product design. The product’s colour treatment reflects the psychological and sentimental dispositions of the users, which differ from country to country. The symbolism of colour may also differ. For example, the colour red, which indicates danger in Western countries, is an auspicious token in India (Sen 1984) and symbolizes joy or happiness in China. 
  2. Pictorial signs and symbols that are used in many different applications for public accommodations are strongly culture related. Western pictorial information, for example, is difficult to interpret by non-Western people (Daftuar 1975; Fuglesang 1982).
  3. Control/display compatibility. Compatibility is a measure of how well spatial movements of control, display behaviour or conceptual relationships meet human expectations (Staramler 1993). It refers to the user’s expectation of the stimulus-response relationship, which is a fundamental ergonomic issue for safe and efficient operation of a product or system. A compatible system is one which considers people’s common perceptual-motor behaviour (i.e., their population-stereotype). However, like other human behaviour, perceptual-motor behaviour may also be influenced by culture. Hsu and Peng (1993) compared American and Chinese subjects regarding control/burner relationships in a four-burner stove. Different population-stereotype patterns were observed. They conclude that population stereotypes regarding control/burner linkages were culturally different, probably as a result of differences in reading or scanning habits.
  4. Workplace design. An industrial workstation design aims to eliminate harmful postures and improve user performance in relation to the user’s biological needs, preferences and task requirements. People from different cultures may prefer different types of sitting posture and work heights. In Western countries, work heights are set near the seated elbow height for maximum comfort and efficiency. However, in many parts of the world people sit on the floor. Indian workers, for example, prefer squatting or sitting cross-legged to standing or to sitting on a chair. In fact it has been observed that even when chairs are provided, the operators still prefer to squat or sit cross-legged on the seats. Daftuar (1975) and Sen (1984) have studied the merits and implications of the Indian sitting posture. After describing the various advantages of sitting on the floor, Sen stated that “as a large population of the world market covers societies where squatting or sitting on the ground predominate, it is unfortunate that up to now no modern machines have been designed to be used in this way.” Thus, variations in preferred posture should be considered in machine and workplace design in order to improve the operator’s efficiency and comfort.
  5. Design of protective equipment. There exist both psychological and physical constraints with regard to wearing protective clothing. In some cultures, for example, jobs requiring the use of protective wear may be regarded as common labour, suitable only for unskilled workers. Consequently, protective equipment is usually not worn by engineers at workplaces in such settings. Regarding physical constraints, some religious groups, obliged by their religion to wear a head covering (like the turbans of Indian Sikhs or the head covers of Muslim women) find it difficult to wear, for example, protective helmets. Therefore, special designs of protective wear are needed to cope with such cultural variations in protecting people against work-environmental hazards.

 

Macro-ergonomic issues

The term macro-ergonomics refers to the design of software technology. It concerns the proper design of organizations and management systems. Evidence exists showing that because of differences in culture, sociopolitical conditions and educational levels, many successful managerial and organizational methods developed in industrialized countries cannot be successfully applied to developing countries (Negandhi 1975). In most IDCs, an organizational hierarchy characterized by a down-flow of authority structure within the organization is a common practice. It has little concern for Western values such as democracy or power sharing in decision-making, which are regarded as key issues in modern management, being essential for proper utilization of human resources as regards intelligence, creativity, problem solving potential and ingenuity.

The feudal system of social hierarchy and its value system are also widely practised in most industrial workplaces in the developing countries. These make a participatory management approach (which is essential for the new production mode of flexible specialization and the motivation of the workforce) a difficult endeavour. However, there are reports confirming the desirability of introducing autonomous work systems even in these cultures Ketchum 1984).

  1. Participatory ergonomics. Participatory ergonomics is a useful macro-ergonomics approach for solving various work-related problems (Shahnavaz, Abeysekera and Johansson 1993; Noro and Imada 1991; Wilson 1991). This approach, mostly used in industrialized countries, has been applied in different forms depending on the organizational culture in which it has been implemented. In a study, Liker, Nagamachi and Lifshitz (1988) compared participatory ergonomics programmes in two US and two Japanese manufacturing plants which were aiming to reduce physical stress on workers. They concluded that an “effective participatory ergonomics programme can take many forms. The best programme for any plant in any culture may depend on its own unique history, structure and culture.”
  2. Software systems. Societal and organizational culture-based differences should be considered in designing a new software system or introducing a change in the organization. With respect to information technology, De Lisi (1990) indicates that networking capabilities will not be realized unless the networks fit the existing organizational culture.
  3. Work organization and management. In some cultures, the family is so important an institution that it plays a prominent role in work organization. For example, among some communities in India, a job is generally regarded as a family responsibility and is collectively performed by all family members (Chapanis 1975).
  4. Maintenance system. Design of maintenance programmes (both preventive and regular) as well as housekeeping are other examples of areas in which work organization should be adapted to cultural constraints. The traditional culture among the sort of agricultural societies predominant in many IDCs is generally not compatible with the requirements of industrial work and how activities are organized. Traditional agricultural activity does not require, for example, formal maintenance programming and precision work. It is for the most part not carried out under time pressure. In the field, it is usually left to the recycling process of nature to take care of maintenance and housekeeping work. The design of maintenance programmes and housekeeping manuals for industrial activities should thus take these cultural constraints into account and provide for adequate training and supervision.

 

Zhang and Tyler (1990), in a case study related to the successful establishment of a modern telephone cable production facility in China supplied by a US firm (the Essex Company) stated that “both parties realize, however, that the direct application of American or Essex management practices was not always practical nor desirable due to cultural, philosophical, and political differences. Thus the information and instructions provided by Essex was often modified by the Chinese partner to be compatible with the conditions existing in China.” They also argued that the key to their success, despite cultural, economic and political differences, was both parties’ dedication and commitment to a common goal as well as the mutual respect, trust, and friendship which transcended any differences between them.

Design of shift and work schedules are other examples of work organization. In most IDCs there are certain sociocultural problems associated with shift work. These include poor general living and housing conditions, lack of support services, a noisy home environment and other factors, which require the design of special shift programmes. Furthermore, for female workers, a working day is usually much longer than eight hours; it consists of not only the actual time spent working, but also the time spent on travelling, working at home and taking care of children and elderly relatives. In view of the prevailing culture, shift and other work design requires special work-rest schedules for effective operation.

Flexibility in work schedules to allow cultural variances such as an after-lunch nap for Chinese workers and religious activities for Muslims are further cultural aspects of work organization. In the Islamic culture, people are required to break from work a few times a day to pray, and to fast for one month each year from sunrise to sunset. All these cultural constraints require special work organizational considerations.

Thus, many macro-ergonomic design features are closely influenced by culture. These features should be considered in the design of software systems for effective operation.

Conclusion: Cultural Differences in Design

Designing a usable product or system is not an easy task. There exists no absolute quality of suitability. It is the designer’s task to create an optimum and harmonic interaction between the four basic components of the human-technology system: the user, the task, the technological system and the operating environment. A system may be fully usable for one combination of user, task and environmental conditions but totally unsuitable for another. One design aspect which can greatly contribute to the design’s usability, whether it is a case of a single product or a complex system, is the consideration of cultural aspects which have a profound influence on both the user and the operating environment.

Even if a conscientious engineer designs a proper human-machine interface for use in a given environment, the designer is often unable to foresee the effects of a different culture on the product’s usability. It is difficult to prevent possible negative cultural effects when a product is used in an environment different from that for which it was designed. And since there exist almost no quantitative data regarding cultural constraints, the only way the engineer can make the design compatible with regard to cultural factors is to actively integrate the user population in the design process.

The best way to consider cultural aspects in design is for the designer to adapt a user-centred design approach. True enough, the design approach adapted by the designer is the essential factor that will instantly influence the usability of the designed system. The importance of this basic concept must be recognized and implemented by the product or system designer at the very beginning of the design life cycle. The basic principles of user-centred design can thus be summarized as follows (Gould and Lewis 1985; Shackel 1986; Gould et al. 1987; Gould 1988; Wang 1992):

  1. Early and continual focus on user. The user should be an active member of the design team throughout the whole product development life cycle (i.e., predesign, detail design, production, verification and product improvement phase).
  2. Integrated design. The system should be considered as a whole, ensuring a holistic design approach. This means that all aspects of the system’s usability should be evolved in parallel by the design team.
  3. Early and continuous user testing. User reaction should be tested using prototypes or simulations while carrying out real work in the real environment from early development stage to the final product.
  4. Iterative design. Designing, testing and redesigning are repeated in regular cycles until satisfactory usability results are achieved.

 

In the case of designing a product on a global scale, the designer has to consider the needs of consumers around the world. In such a case, access to all actual users and operating environments may not be possible for the purpose of adopting a user-centred design approach. The designer has to use a broad range of information, both formal and informal, such as literature reference material, standards, guidelines, and practical principles and experience in making an analytical evaluation of the design and has to provide sufficient adjustability and flexibility in the product in order to satisfy the needs of a wider user population.

Another point to consider is the fact that designers can never be all-knowing. They need input from not only the users but also other parties involved in the project, including managers, technicians, and repair and maintenance workers. In a participatory process, people involved should share their knowledge and experiences in developing a usable product or system and accept collective responsibility for its functionality and safety. After all, everyone involved has something at stake.

 

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Monday, 14 March 2011 20:37

Elderly Workers

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The status of ageing workers varies according to their functional condition, which itself is influenced by their past working history. Their status also depends on the work post that they occupy, and the social, cultural and economic situation of the country in which they live.

Thus, workers who have to perform much physical labour are also, most often, those who have had the least schooling and the least occupational training. They are subject to exhausting work conditions, which can cause disease, and they are exposed to the risk of accidents. In this context, their physical capacity is very likely to decline towards the end of their active life, a fact that makes them more vulnerable at work.

Conversely, workers who have had the advantage of lengthy schooling, followed by occupational training that equips them for their work, in general practise trades where they can put to use the knowledge thus acquired and progressively widen their experience. Often they do not work in the most harmful occupational environments and their skills are recognized and valued as they grow older.

During a period of economic expansion and shortage of labour, ageing workers are recognized as having the qualities of “occupational conscientiousness”, being regular in their work, and being able to keep up their know-how. In a period of recession and unemployment, there will be greater emphasis on the fact that their work performance falls short of that of younger people and on their lower capacity to adapt to changes in work techniques and organization.

Depending on the countries concerned, their cultural traditions and their mode and level of economic development, consideration for ageing workers and solidarity with them will be more or less evident, and their protection will be more or less assured.

The time dimensions of the age/work relationship

The relationship between ageing and work covers a great diversity of situations, which can be considered from two points of view: on the one hand, work appears to be a transformation factor for the worker throughout his or her active life, the transformations being either negative (e.g., wear and tear, decline in skills, illnesses and accidents) or positive (e.g., acquisition of knowledge and experience); on the other hand, work reveals the changes connected with age, and this results in marginalization and even exclusion from the production system for older workers exposed to demands at work that are too great for their declining capacity, or on the contrary allows for progress in their working career if the content of the work is such that a high value is placed on experience.

Advancing age therefore plays the role of a “vector” on which events in life are registered chronologically, both at and outside work. Around this axis are hinged processes of decline and building, which are very variable from one worker to another. In order to take into account the problems of ageing workers in the design of work situations, it is necessary to take into account both the dynamic characteristics of changes connected with age and the variability of these changes among individuals.

The age/work relationship can be considered in the light of a threefold evolution:

  1. Work evolves. Techniques change; mechanization, automation, computerization and methods of information transfer, among other factors, tend or will tend to become more generalized. New products make their appearance, others disappear. New risks are revealed or extended (e.g., radiation and chemical products), others become less prominent. Work organization, labour management, the distribution of tasks and the work schedules are transformed. Some production sectors develop, while others decline. From one generation to another, the work situations encountered during the active life of the worker, the demands that they make and the skills that they require are not the same.
  2. Working populations change. Age structures are modified in accordance with demographic changes, the means of entering or retiring from work and attitudes towards employment. Women’s share in the working population continues to evolve. Genuine upheavals are occurring in the field of education, occupational training and access to the health system. All these transformations are at the same time producing generation-related and period-related effects which obviously influence the age/work relationship and which can to a certain extent be anticipated.
  3. Finally—a point that deserves emphasis—individual changes are in progress throughout one’s working life, and the adjustment between the characteristics of particular work and those of the people who carry it out is therefore frequently called into question.

 

Some processes of organic ageing and their relationship to work

The main organic functions involved in work decline in an observable way from the ages of 40 or 50, after some of them have undergone development up to the ages of 20 or 25.

In particular, a decline with age is observed in maximum muscular strength and range of joint movement. The reduction in strength is in the order of 15 to 20% between the ages of 20 and 60. But this is only an overall trend, and the variability among individuals is considerable. Moreover, these are maximum capacities; the decline is much less for more moderate physical demands.

One function that is very sensitive to age is regulation of posture. This difficulty is not very apparent for common and stable working positions (standing or sitting) but it becomes obvious in situations of disequilibrium that require precise adjustments, strong muscular contraction or joint movements at extreme angles. These problems become more severe when the work has to be carried out on unstable or slippery supports, or when the worker suffers a shock or unexpected jolt. The result is that accidents due to loss of balance become more frequent with age.

Sleep regulation becomes less reliable from the ages of 40 to 45 onwards. It is more sensitive to changes in working schedules (such as night work or shift work) and to disturbing environments (e.g., noise or lighting). Changes in the length and quality of sleep follow.

Thermoregulation also becomes more difficult with age, and this causes older workers to have specific problems with regard to work in heat, particularly when physically intense work has to be carried out.

Sensory functions begin to be affected very early, but the resulting deficiencies are rarely marked before the ages of 40 to 45. Visual function as a whole is affected: there is a reduction in the amplitude of accommodation (which can be corrected with appropriate lenses), and also in the peripheral visual field, perception of depth, resistance to glare and light transmission through the crystalline lens. The resulting inconvenience is noticeable only in particular conditions: in poor lighting, near sources of glare, with objects or texts of very small size or badly presented, and so on.

The decline in auditory function affects the hearing threshold for high frequencies (high-pitched sounds), but it reveals itself particularly as difficulty in discriminating sound signals in a noisy environment. Thus, the intelligibility of the spoken word becomes more difficult in the presence of ambient noise or strong reverberation.

The other sensory functions are, in general, little affected at this time of life.

It can be seen that, in a general way, organic decline with age is noticeable particularly in extreme situations, which should in any case be modified to avoid difficulties even for young workers. Moreover, ageing workers can compensate for their deficiencies by means of particular strategies, often acquired with experience, when the work conditions and organization permit: the use of additional supports for unbalanced postures, lifting and carrying loads in such a way as to reduce extreme effort, organizing visual scanning so as to pinpoint useful information, among other means.

Cognitive ageing: slowing down and learning

As regards cognitive functions, the first thing to note is that work activity brings into play basic mechanisms for receiving and processing information on the one hand, and on the other, knowledge acquired throughout life. This knowledge concerns mainly the meaning of objects, signals, words and situations (“declarative” knowledge), and ways of doing things (“procedural” knowledge).

Short-term memory allows us to retain, for some dozens of seconds or for some minutes, useful information that has been detected. Processing of this information is carried out by comparing it with knowledge that has been memorized on a permanent basis. Ageing acts on these mechanisms in various ways: (1) by virtue of experience, it enriches knowledge, the capacity to select in the best way both useful knowledge and the method of processing it, especially in tasks that are carried out fairly frequently, but (2) the time taken to process this information is lengthened owing both to ageing of the central nervous system, and to more fragile short-term memory.

These cognitive functions depend very much on the environment in which the workers have lived, and therefore on their past history, their training, and the work situations which they have had to face. The changes that occur with age are therefore manifested in extremely varied combinations of phenomena of decline and reconstruction, in which each of these two factors may be more or less accentuated.

If in the course of their working lives workers have received only brief training, and if they have had to carry out relatively simple and repetitive tasks, their knowledge will be limited and they have difficulties when confronted with new or relatively unfamiliar tasks. If, moreover, they have to perform work under marked time constraints, the changes that have occurred in their sensory functions and the slowing down of their information processing will handicap them. If, on the other hand, they have had lengthy schooling and training, and if they have had to carry out a variety of tasks, they will thereby have been able to enhance their skills so that the sensory or cognitive deficiencies associated with age will be largely compensated for.

It is therefore easy to understand the role played by continued training in the work situation of ageing workers. Changes in work make it necessary more and more often to have recourse to periodic training, but older workers rarely receive it. Firms frequently do not consider it worthwhile to give training to a worker nearing the end of his or her active life, particularly as learning difficulties are thought to increase with age. And the workers themselves hesitate to undergo training, fearing that they will not succeed, and not always seeing very clearly the benefits that they could derive from training.

In fact, with age, the manner of learning is modified. Whereas a young person records the knowledge transmitted to him, an older person needs to understand how this knowledge is organized in relation to what he or she already knows, what is its logic, and what is its justification for work. He or she also needs time to learn. Therefore one response to the problem of training older workers is, in the first place, to use different teaching methods, according to each person’s age, knowledge and experience, with, in particular, a longer training period for older people.

Ageing of men and women at work

Age differences between men and women are found at two different levels. At the organic level, life expectancy is generally greater for women than for men, but what is called life expectancy without disability is very close for the two sexes—up to 65 to 70 years. Beyond that age, women are generally at a disadvantage. Moreover, women’s maximum physical capacity is on average 30% less than men’s, and this difference tends to persist with advancing age, but the variability in the two groups is wide, with some overlap between the two distributions.

At the level of the working career there are great differences. On average, women have received less training for work than men when they start their working life, they most often occupy posts for which fewer qualifications are needed, and their working careers are less rewarding. With age they, therefore, occupy posts with considerable constraints, such as time constraints and repetitiveness of the work. No sexual difference in the development of cognitive capacity with age can be established without reference to this social context of work.

If the design of work situations is to take account of these gender differences, action must be taken especially in favour of the initial and continuing vocational training of women and constructing work careers that increase women’s experiences and enhance their value. This action must, therefore, be taken well before the end of their active lives.

Ageing of working populations: the usefulness of collective data

There are at least two reasons for adopting collective and quantitative approaches with respect to the ageing of the working population. The first reason is that such data will be necessary in order to evaluate and foresee the effects of ageing in a workshop, a service, a firm, a sector or a country. The second reason is that the main components of ageing are themselves phenomena subject to probability: all workers do not age in the same way or at the same rate. It is therefore by means of statistical tools that various aspects of ageing will sometimes be revealed, confirmed or assessed.

The simplest instrument in this field is the description of age structures and of their evolution, expressed in ways relevant to work: economic sector, trade, group of jobs, and so on.

For example, when we observe that the age structure of a population in a workplace remains stable and young, we may ask which characteristics of the work could play a selective role in terms of age. If, on the contrary, this structure is stable and older, the workplace has the function of receiving people from other sectors of the firm; the reasons for these movements are worth studying, and we should equally verify whether the work in this workplace is suited to the characteristics of an ageing workforce. If, finally, the age structure shifts regularly, simply reflecting recruitment levels from one year to another, we probably have a situation where people “grow old on site”; this sometimes requires special study, particularly if the annual number of recruitments is tending to decline, which will shift the overall structure towards higher age groups.

Our understanding of these phenomena can be enhanced if we have quantitative data on working conditions, on the posts currently occupied by the workers and (if possible) on the posts that they no longer occupy. The work schedules, the repetitiveness of work, the nature of the physical demands, the work environment, and even certain cognitive components, can be the subject of queries (to be asked of the workers) or of evaluations (by experts). It is then possible to establish a connection between the characteristics of the present work and of past work, and the age of the workers concerned, and so to elucidate the selection mechanisms to which the work conditions can give rise at certain ages.

These investigations can be further improved by also obtaining information on the health status of the workers. This information can be derived from objective indicators such as the work accident rate or sickness absence rate. But these indicators often require considerable care as regards methodology, because although they do indeed reflect health conditions that may be work-related, they also reflect the strategy of all those concerned with occupational accidents and absence due to illness: the workers themselves, the management and the physicians can have various strategies in this regard, and there is no guarantee that these strategies are independent of the worker’s age. Comparisons of these indicators between ages are therefore often complex.

Recourse will therefore be had, when possible, to data arising from self-evaluation of health by the workers, or obtained during medical examinations. These data may relate to diseases whose variable prevalence with age needs to be better known for purposes of anticipation and prevention. But the study of ageing will rely above all on the appreciation of conditions that have not reached the disease stage, such as certain types of functional deterioration: (e. g., of the joints—pain and limitation of sight and hearing, of the respiratory system) or else certain kinds of difficulty or even incapacity (e. g. in mounting a high step, making a precise movement, maintaining equilibrium in an awkward position).

Relating data concerning age, work and health is therefore at the same time a useful and complex matter. Their use permits various types of connections to be revealed (or their existence to be presumed). It may be a case of simple causal relationships, with some requirement of the work accelerating a type of decline in the functional state as age advances. But this is not the most frequent case. Very often, we shall be led to appreciate simultaneously the effect of an accumulation of constraints on the a set of health characteristics, and at the same time the effect of selection mechanisms in accordance with which workers whose health has declined may find that they are excluded from certain kinds of work (what the epidemiologists call the “healthy worker effect”).

In this way we can evaluate the soundness of this collection of relationships, confirm certain fundamental knowledge in the sphere of psychophysiology, and above all obtain information that is useful for devising preventive strategies as regards ageing at work.

Some types of action

Action to be undertaken to maintain ageing workers in employment, without negative consequences for them, must follow several general lines:

  1. One must not consider this age group as a category apart, but must instead consider age as one factor of diversity among others in the active population; protective measures that are too targeted or too accentuated tend to marginalize and weaken the position of the populations concerned.
  2. One should anticipate individual and collective changes related to age, as well as changes in work techniques and organization. The management of human resources can be effectively carried out only over time, so as to prepare appropriate adjustments in work careers and training. The design of work situations can then take account at the same time of the available technical and organizational solutions and the characteristics of the (future) population concerned.
  3. The diversity of individual development throughout working life should be taken into consideration, so as to create conditions of equivalent diversity in work careers and situations.
  4. Attention should be devoted to favouring the process of building up skills and attenuating the process of decline.

 

On the basis of these few principles, several types of immediate action can first be defined. The highest priority of action will concern working conditions that are capable of posing particularly acute problems for older workers. As mentioned earlier, postural stresses, extreme exertion, strict time constraints (e.g., as with assembly-line work or the imposition of higher output goals), harmful environments (temperature, noise) or unsuitable environments (lighting conditions), night work and shift work are examples.

Systematic pinpointing of these constraints in posts that are (or may be) occupied by older workers allows an inventory to be drawn up and priorities to be established for action. This pinpointing can be carried out by means of empirical inspection checklists. Of equal use will be analysis of worker activity, which will permit observation of their behaviour to be linked with the explanations that they give of their difficulties. In these two cases, measures of effort or of environmental parameters may complete the observations.

Beyond this pinpointing, the action to be taken cannot be described here, since it will obviously be specific to each work situation. The use of standards may sometimes be useful, but few standards take account of specific aspects of ageing, and each one is concerned with a particular domain, which tends to give rise to thinking in an isolated fashion about each component of the activity under study.

Apart from the immediate measures, taking ageing into account implies longer-range thinking directed towards working out the widest possible flexibility in the design of work situations.

Such flexibility must first be sought in the design of work situations and equipment. Restricted space, nonadjustable tools, rigid software, in short, all the characteristics of the situation that limit the expression of human diversity in the carrying out of the task are very likely to penalize a considerable proportion of older workers. The same is true of the more constraining types of organization: a completely predetermined distribution of tasks, frequent and urgent deadlines, or too numerous or too strict orders (these, of course, must be tolerated when there are essential requirements relating to the quality of production or the safety of an installation). The search for such flexibility is, therefore, the search for varied individual and collective adjustments that can facilitate the successful integration of ageing workers into the production system. One of the conditions for the success of these adjustments is obviously the establishment of work training programmes, provided for workers of all ages and geared to their specific needs.

Taking ageing into account in the design of work situations thus entails a series of coordinated actions (overall reduction in extreme stresses, using all possible strategies for work organization, and continuous efforts to increase skills), which are all the more efficient and all the less expensive when they are taken over the long term and are carefully thought out in advance. The ageing of the population is a sufficiently slow and foreseeable phenomenon for appropriate preventive action to be perfectly feasible.

 

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Contents

Preface
Part I. The Body
Part II. Health Care
Part III. Management & Policy
Part IV. Tools and Approaches
Part V. Psychosocial and Organizational Factors
Part VI. General Hazards
Part VII. The Environment
Part VIII. Accidents and Safety Management
Part IX. Chemicals
Part X. Industries Based on Biological Resources
Part XI. Industries Based on Natural Resources
Part XII. Chemical Industries
Part XIII. Manufacturing Industries
Part XIV. Textile and Apparel Industries
Part XV. Transport Industries
Part XVI. Construction
Part XVII. Services and Trade
Part XVIII. Guides