Operant task performance

After the incident, an investigation team determined that the first operator had not added the initiator when required earlier in the process. When the relief operator added the initiator, the entire monomer mass was in the reactor and the reaction was too energetic for the cooling system to handle. Errors by both operators contributed to the runaway. Both operators were performing many tasks. The initiator should have been added much earlier in the process when much smaller quantities of monomer were present. There was also no procedure to require supervision review if residual monomers were detected. The lesson learned was that operators need thorough training and need to be made aware of significant hazardous scenarios that could develop. 

In any given situation, there may be different levels of dependence between an operator s performance on one task and on another because of the characteristics of the tasks theraseb e.s. or because of the manner in which the operator was cued to perform the tasks. Dependence levels between the performances of two (or more) operators also may differ. The analyses should account for dependency in human-error probabilities. In addition, each sequence may have a set of human recovery actions that if successfully performed will terminate or reduce the consequences of the sequence. This information, coupled with a knowledge of the system success criteria leads to the development of human success and failure probabilities which are input to the quantification of the fault iices or event trees. With this last step, the HRA is integrated into the PSA, and Pl. ise 4 is complete. 

The practical implications of this experiment are that when evaluating the effects of shift work due to circadian effects, the type of task being carried out by the worker must be taken into account. For example, skill-based tasks would be expected to exhibit the performance changes characteristic of low memory load tasks, whereas performance variations in knowledge-based tasks would be expected to follow the pattern of high memory load tasks. Performance on rule-based tasks may depend on the degree of frequency of use of the rules, which in turn may determine the memory load. If these results were confirmed by further process plant studies, it would have implications for when different types of operation (involving different levels of memory load) should be scheduled to reduce circadian rhythm effects and minimize errors. 

Discussions and interviews with the task experts can be supplemented with observations of their actual performance, for example, taking notes on certain aspects of the task or taking video or audio recordings. Observational techniques can reveal information that may be difficult to acquire in any other way. Detailed physical task performance data can be recorded, and major environmental influences (e.g., noise, light, interruptions) can all be faithfully represented. Observations can also provide an insight into the way that the team members communicate, allocate job responsibilities, and make use of operating procedures and other resources. 

Modify the basic data according to guidelines provided in the handbook, to reflect differences in the assumed "nominal" conditions and the specific conditions for the task being evaluated. The major factor that is taken in to account is the level of stress perceived by the operator when performing the task. 

Task Analysis and Error Analysis of the Blowdown Operation Task analysis was carried out in order to organize all the performance data about the way that workers process information, the nature of the emergency and the way that decisions are made. Figure 7.20 shows a tabular task analysis of the workers response to a significant unignited gas leak in MSM. The analysis was a combination of a tabular HTA and a CADET analysis (see Chapter 4). Human error analysis identified the major human failure modes which could affect time to blowdown (see Table 7.2). 

Some of the tasks performed by the menu selections invoke utility programs that are supplied with the computer s operating system, while other tasks are FORTRAN programs written specifically for our application. 

We have identified five functional areas in which our QA unit should operate. These areas include inspection, reporting, record-keeping, custodial and advisory. The main tasks performed in each functional area can be summarized as follows ... 

Institute of Medicine (U.S.). Committee on Military Nutrition. Caffeine for the Sustainment of Mental Task Performance Formulations for Military Operations. Washington, DC National Academy Press, 2001. 

Human (operator) Error cannot be separated entirely from the Technical and Organisational context of task performance (see figure 2.1). At the very least one should know the importance of Human Behaviour relative to that of the Technical and Organisational factors in understanding the causes of accidents and near misses. On the basis of our own pilot CCR studies (Van der Schaaf, 1989) the following extensions arc suggested ... 

We tried to arrive at a representative picture of CCR task performance by having a series of extensive, confidential interviews (based on Flanagan s (1954) CIT) with CCR operators before implementation of the first NMMS modules had started. In each interview a different operator was asked to report on a CCR near miss during the last year and of his own choice, which had not been previously reported. The near miss was then described (as if it were a forced near miss report) in the form of an Incident Production Tree, after which all its root causes were classified according to the RAP model described earlier. After each set of five subsequent interviews the overall pattern of classification results was checked for stability it turned out that the results (i.e. the relative frequencies of classified root causes) after 30 interviews did not differ overall from those of the first 25 therefore the series of interviews was stopped after 35 operators (about two thirds of the available CCR population at the time) had participated. 

A prime example of such an approach in the chemical industry is DuPont The American giant has established a powerful target-setting process that starts with so-called critical operating tasks (COTs). These are derived from financial origins at the business unit level, and cascade down through the plant to the production line. The system creates transparency for each production line employee about his or her targets and about how the individual s performance is linked to that of the whole unit (Fig. 12.4). 

There are several operant tasks that offer the opportunity to separate an animal s learning from its performance of a known task. Repeated acquisition is such a task and requires the animal to learn a new sequence of lever presses each session. The learning baseline may be more sensitive to disruption by a toxicant than the performance of an already acquired sequence. 

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