Human errors individual

Individual Plant Examinations (IPE) (NUREG-1560) were performed by the U.S. utilities using their staff and utilities. Results from the IPEs indicate that human error can significantly increase or decrease the CDF. Certain human actions are consistently important for BWRs and PWRs. 

Human error has often been used as an excuse for deficiencies in the overall management of a plant. It may be convenient for an organization to attribute the blame for a major disaster to a single error made by a faUible process worker. As will be discussed in subsequent sections of this book, the individual who makes the final error leading to an accident may simply be the final straw that breaks a system already made vulnerable by poor management. 

The analysis of accidents and disasters in real systems makes it clear that it is not sufficient to consider error and its effects purely from the perspective of individual human failures. Major accidents are almost always the result of multiple errors or combinations of single errors with preexisting vulnerable conditions (Wagenaar et al., 1990). Another perspective from which to define errors is in terms of when in the system life cycle they occur. In the following discussion of the definitions of human error, the initial focus will be from the engineering and the accident analysis perspective. More detailed consideration of the definitions of error will be deferred to later sections in this chapter where the various error models will be described in detail (see Sections 5 and 6). 

The classification structure for PIFs used in this chapter is based on the model of human error as arising from a mismatch between demands and resources which was described in Chapter 1, Section 1.6 (Figure 1.6). In this model demands were seen as requirements for human performance which arise from the characteristics of the process environment (e.g., the need to monitor a panel or to be able to fix a seal in a flange) and the nature of the human capabilities to satisfy these demands (e.g., skills of perception, thinking, and physical action). These demands are met by the individual and group resources of personnel and the extent to which the design of the task allows these resources to be effectively deployed. Where demands exceeded resources, errors could be expected to occur. 

The various PIFs discussed so far provide a basis for the control of human error at the level of the individual. This section will consider various factors related to the performance of the team and the management practices related to safety. 

Many organizations that have evolved over a long period of time come to believe that the system of safety rules that they have developed is invulnerable to human error. The existence of a "rule book" culture can produce a complacent attitude which assumes that if the rules are followed then accidents are impossible. This is based on the belief that a rigid set of rules will cover every contingency and that interpretation by individuals to cover imanticipated situations will never be required. Of course, all rules will at some time require such interpretation, and the need for this should be accepted and built into the system. 

If the results of the qualitative analysis are to be used as a starting-point for quantification, they need to be represented in an appropriate form. The form of representation can be a fault tree, as shown in Figure 5.2, or an event tree (see Bellamy et al., 1986). The event tree has traditionally been used to model simple tasks at the level of individual task steps, for example in the THERP (Technique for Human Error Rate Prediction) method for human reliability... 

Project management also influences the likelihood that staffing levels wiU be adequate for the tasks required. This latter factor, together with the extent to which appropriate jobs are assigned to individuals, and the complexity of the jobs, all influence the level of time pressure likely to be felt by the operator. The detailed calculations, which show how the probability of human error is influenced by changes in the sociotechnical factors in the situation, are given in Appendix 5A. 

I.I. The Traditional Safety Engineering (TSE) View The traditional safety engineering view is the most commonly held of these models in the CPI (and most other industries). As discussed in Chapter 1, this view assumes that human error is primarily controllable by the individual, in that people can choose to behave safely or otherwise. Unsafe behavior is assumed to be due to carelessness, negligence, and to the deliberate breaking of operating rules and procedures designed to protect the individual and the system from known risks. 

Typically, the first phase of a comprehensive accident investigation process will involve describing the way in which the hardware, the chemical process, individual operators and operating teams are involved in the accident process. This is the domain of the structural analysis techniques and the technical analysis of the chemical process which gave rise to the accident. Analyses of human error will primarily address the interactions between hardware systems and individuals or operating teams (the first two layers... 

A human error or reliability analysis (HRA) can be performed to identify points that may contribute to an accidental loss. Human errors may occur in all facets of a the hydrocarbon industry. They are generally related to the complexity of the equipment, human-equipment interfaces, hardware for emergency actions, and procedures for operations, testing and training. The probabilities of certain types of errors occurring are normally predicted as indicated in Table 29. Individual tasks can be analyzed to determine the probability of an error occurring. From these probabilities, consequences can be identified which detemline the risk of a particular error. 

A slightly more structured approach uses AVhat-If Analysis,(i) which involves the team asking What if questions that usually concern equipment failures, human errors, or external occurrences. Some examples are What if the procedure was wrong What if the steps were performed out of order The questions can be generic in nature or highly specific to the process or activity where the incident occurred. Sometimes these questions are preprepared by one or two individuals, which may also potentially bias the discussion. 

Material failures can be caused by a number of factors, either individually, or in combination, including substandard materials, inappropriate materials selection, poor design, equipment abuse, unexpected stresses or environmental conditions, and poor maintenance practices and/or neglect. Many failures, in one way or another, involve human error to some extent. 

Occupational safety management concentrates on the safety of individual workers by promoting their safety-mindedness the prevailing view of human error is that of the traditional safety model where safety control is handled by motivation, and punishment, (for lack of attention). 

Detection of contamination levels (dust, food and drink, production materials) that can accumulate in equipment and lead to system malfunction Monitor hours worked by individuals and/or mundane nature of work that might result in loss of concentration and hence introduchon of human errors (data errors and user operahon errors)... 

Human errors, instrument errors, and random data scatter. Plant or laboratory personnel are responsible for setting and maintaining the process operating conditions, reading the feed and product stream flowmeters, and drawing samples of the product gas and analyzing them. Any error that any of these individuals makes could lead to errors in measured variable... 

The major advantages of this robotised approach are the limitation of human interventions, thus an increase in reproducibility and a decrease of the number of potential human errors. In our laboratory, this procedure currently yields a throughput of 400 fully analyzed spots per person and per week. The bottleneck is the validation step, because each individual protein identification has to be validated manually before being introduced into the SWISS-2DPAGE database. 

Accuracy and Precision. The accuracy and precision required of an atomic-emission spectroscopic method affect the approach used in the analysis as well as the time involved. A qualitative analysis requires a minimum of effort, but as better accuracy and precision are demanded, increasing care is needed. Even if a representative sample has been obtained, errors inherent in the method, human errors, and random errors contribute to inaccuracies. Spectrochemical equipment is largely responsible for the random errors that influence precision, and both method and individual laboratory errors influence the accuracy. In addition, relative precision and accuracy depend upon concentration levels. The standard deviation increases with increasing concentration, but the relative standard deviation decreases the latter may vary from a few percent to less than one percent using photographic detection, depending on the element and the concentration. 

SLIM-MAUD (Embrey 1984) implements a related approach in which expert ratings are used to estimate human error probabilities (HEPs) in various environments. The experts first rate a set of tasks in terms of performance-shaping factors (PSFs) that are present. Tasks with known HEPs are used as upper and lower anchor values. The experts also judge the importance of individual PSFs. A subjective likelihood index (SLI) is then calculated for each task in terms of the PSFs. A logarithmic relationship is assumed between the HEP and SLI, allowing calculation of the human error probability for task j (HEPj) from the subjective likelihood index assigned to task j (SLIj). More specifically ... 

In 1990 our understanding of the underlying causes of risk were challenged with the publication of Janies Reason s Human Error [8], For the first time the role of human factors in the incident causality chain were truly characterised. He eloquently made the case for adverse events being a function not of personal inadequacies but of the environment in which individuals operate. This paved the way for transforming a largely reactive approach to risk management in healthcare to one of hazard identification and proactive risk control. 

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