2.4.3 Usage of Handbook Data

With reference to the above background, the operator will be allocated certain tasks and these will form the basis for determining the quantity and quality of person­nel staffing levels. Factors such as educational background, practical experience, skills, personality variables, and choice of the technical principles, job aids, and information presentation and controllability would be used to assess these levels. Given this background, concrete ‘knobs and dials’ recommendations can be given on ergonomic grounds. This can be divided into the following sections:

1. General layout of information presentation and control devices.

2. Design of individual display devices and control devices (e. g., VDU screens, pointers, instruments, keyboards, knobs, buttons).

3. Design of workplaces, including work surfaces, rest surfaces, storage sur­faces, secondary communications devices (e. g., telephones), and support in the form of lighting.

4. Room design.

5. General environmental design (e. g., climate, acoustics, air quality, windows).

On the first point, it is usual to start by determining the relative importance of the various tasks in the job from different viewpoints. One may attempt, for example, to define the information and the controls that are especially important and that require rapid attention or rapid corrective measures. This information and/or control device must thus be placed centrally and be clearly accessible.

The positioning of instruments and controls is usually determined by a cursory breakdown of the process into main functions (for example, well-defined process stages). Within these main functions, information/display devices are then posi­tioned on the basis of frequency of use and sequence of use. In certain cases it may also be suitable to position the control and information devices on some form of function flow diagram. This type of function flow diagram is practically always required to complement the general overview of the process. In addition, some form of simplified technically orientated process model is also required, with signal lights for showing the current state of the process, perhaps also connected up to a general alarm panel.

The Ris0 group in Denmark mentions three main ways of presenting informa­tion (Rasmussen, 1979a; Goodstein, 1982):

1. Data/number presentation

2. Information connected with physical components in the process (e. g., tanks, pumps, reactors, condensers)

3. Functionally orientated information

Based on this classification, display systems have begun to be designed that are related to the functional presentation method (for example, Goodstein, 1982). The operator is thus working on a more abstract functional plane, and only when nec­essary will he or she go down to the more concrete and physical component level. Although this is an interesting approach, it can be questioned to some extent. It is absolutely correct to state that human beings build up abstract mental models (as discussed earlier in this chapter) of how an actual physical industrial process works. This abstract and mental model of the process does not require any direct agreement with the physical reality, but it is functional in the real meaning of the word. The operator needs the best available information about the actual system to enable him or her to build up a mental model quickly and effectively and to update it efficiently during continuous work. However, caution must be used when designing abstract models for the operator based on some form of theoretical working method. It is not certain that such models would help the operator to build and update his or her own mental process model more simply or more efficiently.

It is doubtful whether presenting this form of theoretically designed functional model to the operator is the right approach. The reason for doubt relates to the dif­ferences between individuals. Different operators work with widely differing models of how the process operates. Each individual operator probably builds up a personal model of a process on the basis of intellectual abilities, training, experience, and so on. What is typical for the model built up by an individual operator is that it suits his or her own ability to handle the system efficiently. In order to design an abstract functional model in advance to be presented directly to the operator, it is necessary to take into account the types of operators who will handle the system, and their abstract and functional model requirements. It is not certain, or even probable, that the functional models that are natural and suitable for system design are suitable for the operator, as system designers are probably accustomed to thinking in abstrac­tions and will thus start from a completely different type of process model from that of most operators.

It was found in Ergolab’s studies on the project of Computerisation in the Pro­cess Industries that the primary requirement of the operators was a set of simplified models of the physical design of the process (Ivergard, Istance, and Gunther, 1980). Therefore, to a large extent, the requirement was for information presentation more closely related to the types of jobs, which the operators had to do. If the opera­tors were expected to work with more cognitively-orientated tasks—for example, for optimisation of operation—they would probably want a more functionally orientated model. If, on the other hand, the work was combined with maintenance work, for example, the physically-orientated models would be more suitable.

The following chapter describes detailed information on the design of informa­tion and control devices.