Hierarchical task analysis

Job and task analysis. This involves applying techniques such as hierarchical task analysis (see Chapter 4) to provide a comprehensive description of the work for which training is required. The task analysis provides essential information on the content of training. 

It is often assumed that TA cannot be applied during design, because until the plant has been fabricated the tasks to be performed by workers cannot be defined in sufficient detail. In fact, many TA techniques can be used to specify the nature of the tasks to achieve the required process plant functions, even before the exact configuration of the system has been finalized. This point will be elaborated later in the context of hierarchical task analysis. 

Hierarchical Task Analysis commences by stating the overall objective that the person has to achieve. This is then redescribed into a set of suboperations and the plan specifying when they are carried out. The plan is an essential component of HTA since it describes the information sources that the worker must attend to, in order to signal the need for various activities. Each suboperation can be redescribed further if the analyst requires, again in terms of other operations and plans. 

By visual inspection of an OAET it is possible to identify the elements of a process control task which are critical in responding to an initiating event. An important issue in the construction of OAETs is the level of task breakdown. If the overall task is redescribed to very small subtasks it might be difficult to gain insights from the OAET because it Ccin become relatively unwieldy. Hierarchical Task Analysis provides a useful framework for the... 

The task analysis techniques described in the previous section are mainly oriented toward observable actions, although hierarchical task analysis (HTA) allows it to address functional requirements as well as the specific actions that are required to satisfy these requirements. 

The particular type of task analysis used in this example is hierarchical task analysis (HTA) (see Chapter 4). This has the advantage that it has been applied extensively in the chemical and other industries. As described in Chapter 4, HTA breaks down the overall objective of a task by successively describing it in increasing detail, to whatever level of description is required by the analysis. At each of the levels, a "plan" is produced that describes how the steps or functions at that level are to be executed. 

QUALITATIVE ERROR PREDICTION. The first Stage of quantitative prediction is a task analysis. THERP is usually applied at the level of specific tasks and the steps within these tasks. The form of task analysis used therefore focuses on the operations which would be the lowest level of a hierarchical task analysis... 

This section illustrates how the techniques described in Chapter 4 can be used to develop a procedure for the job of the top floor operator in the batch plant considered earlier. Two techniques are illustrated (i) a hierarchical task analysis (HTA) of the job, and (ii) a predictive human error analysis (PHEA) of the operations involved. HTA provides a description of how the job is actually done while PHEA identifies critical errors which can have an impact on the system in terms of safety or quality. The basic structure of the procedure is derived from the HTA which specifies in increasing detail the goals to be achieved. To emphasize critical task steps, various warnings and cautions can be issued based on the likely errors and recovery points generated by the PHEA. 

FIGURE 7.16. Hierarchical Task Analysis of the Task of Increasing Furnace Load. 

Shepherd, A. (1985). Hierarchical Task Analysis and Training Decisions. Programmed Learning and Educational Technology 22,162-176. 

The results of CTA are usually cast in the form of graphical representations that incorporate the work demands and user strategies. For cognitive tasks that have been encountered in the past, operators may have developed well-established responses that may need some modifications but nevertheless provide a starting framework. For unfamiliar tasks that have not been encountered in the past or are beyond the design-basis of the system, operators are required to develop new methods or combine old methods in new ways. To illustrate how the results of CTA can be merged in a graphical form, two techniques are presented hierarchical task analysis and the critical decision method. 

The human factors literature is rich in task analysis techniques for situations and jobs requiring rule-based behavior (e.g., Kirwan and Ainsworth 1992). Some of these techniques can also be used for the analysis of cognitive tasks where weU-practiced work methods must be adapted to task variations and new circumstances. This can be achieved provided that task analysis goes beyond the recommended work methods and explores task variations that can cause failures of human performance. Hierarchical task analysis (Shepherd 1989), for instance, can be used to describe how operators set goals and plan their activities in terms of work methods, antecedent conditions, and expected feedback. When the analysis is expanded to cover not only normal situations but also task variations or changes in circumstances, it would be possible to record possible ways in which humans may fail and how they could recover from errors. Table 2 shows an analysis of a process control task where operators start up an oil refinery furnace. This is a safety-critical task because many safety systems are on manual mode, radio communications between control room and on-site personnel are intensive, side effects are not visible (e.g., accumulation of fuel in the fire box), and errors can lead to furnace explosions. 

TABLE 2. Extract from the Analysis of Starting an Oil Refinery Furnace (a variant of hierarchical task analysis)... 

The human inspection models of visual search and human decision making were shown to be particularly applicable leading to a task analytic framework using hierarchical task analysis (HTA). In this way, human factors knowledge could be applied systematically to observed FPI processes. Visits were made to several engine repair facilities owned by major air carriers and engine manufac-... 

Pigure 4 Hierarchical Task Analysis for the Top Level of Fluorescent Penetrant Inspection. 

Hierarchical structure model (CIMS), 521-522 Hierarchical task analysis (HTA), 1028, 1029, 1909-1912... 

Household growth, 37 Housekeeping, industrial, 553, 559 HQL anthropometric database (Japan), 1114 HRA, see Human reUabUity analysis HRM, see Human resource management HTA, see Hierarchical task analysis HTML, see HyperText Markup Language HTTP, see Hypertext Transfer Protocol Hub-and-spoke model, 265 Human abilities limitations, 2196—2198 Human-centered automation, 962 Human-centered information systems, 962 Human-centered product plaitrring and design, 1297-1310... 

FIGURE 80.1 Diagram showing the concept of a hierarchical task analysis for physical tasks. 

Hierarchical task analysis The analysis of a task by breaking it down to its basic components, starting from an overall or gross description (e.g., Hfting a load manually) and moving down in a series of steps in sequence. 

Hierarchical Task Analysis (HTA) (Aimett, J., Duncan 1967) is a process for developing a description of tasks in terms of operations (things people do to reach goals) and plans (statements of conditions that tell when each operation is to be carried out). HTA has been mostly used for the design of training. Its merit is mainly the clear representation technique. HTA is cinrently supported by a software www.taskarchitect.com... 

Hierarchical Task Analysis (HTA) - a well-known human factors analysis approach the technique was followed as laid out by Shepherd and Stammers (2005). 

Hierarchical task analysis description Hierarchical task analysis starts its journey from the overall objective needed to be achieved. This objective is divided into a series of suboperations. The plan specifies the information source and when it is to be carried out. The question is do these suboperations need to be subdivided into finer elements This is totally dependent on the analyst, in case the analyst feels that there is scope for error. The analyst can then further divide the suboperations into the lowest level or elements to improve the quality of task analysis. This will be clear from the example of CCPS of isolating a one-level transmitter [13], as shown in Fig. II/3.7.1-1. It should be noted that in this example, one task has been further subdivided, so that the possibility of obtaining one side of a differential pressure transmitter is avoided, following instrumentation working convention. 

Hierarchical task analysis with example for isolation of drum-level transmitter. 

Hierarchical task analysis can be the starting point for further error analysis methods. 

When used as input to design functional safety, hierarchical task analysis can be placed at a higher level, which helps in allocating functions to the system and people concerned. 

Since hierarchical task analysis is developed in collaboration, the analyst is well aware of the perception of people and allocated tasks and plans. 

As hierarchical task analysis is developed with various levels of people a good amount of time is essential. 

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