Errors perspectives

From a human error perspective, Guerrero et al. (2008) stated that an incident scenario is a composition of actors, objectives, instruments, action sequences, errors, error causes and error consequences, and context elements. 

At X-ray fluorescence analysis (XRF) of samples of the limited weight is perspective to prepare for specimens as polymeric films on a basis of methylcellulose [1]. By the example of definition of heavy metals in film specimens have studied dependence of intensity of X-ray radiation from their chemical compound, surface density (P ) and the size (D) particles of the powder introduced to polymer. Have theoretically established, that the basic source of an error of results XRF is dependence of intensity (F) analytical lines of determined elements from a specimen. Thus the best account of variations P provides a method of the internal standard at change P from 2 up to 6 mg/sm the coefficient of variation describing an error of definition Mo, Zn, Cu, Co, Fe and Mn in a method of the direct external standard, reaches 40 %, and at use of a method of the internal standard (an element of comparison Ga) value does not exceed 2,2 %. Experiment within the limits of a casual error (V changes from 2,9 up to 7,4 %) has confirmed theoretical conclusions. 

To put the errors in comparative models into perspective, we list the differences among strucmres of the same protein that have been detennined experimentally (Fig. 9). The 1 A accuracy of main chain atom positions corresponds to X-ray structures defined at a low resolution of about 2.5 A and with an / -factor of about 25% [192], as well as to medium resolution NMR structures determined from 10 interproton distance restraints per residue [193]. Similarly, differences between the highly refined X-ray and NMR structures of the same protein also tend to be about 1 A [193]. Changes in the environment... 

For the air quality manager to place model estimates in the proper perspective to aid in making decisions, it is becoming increasingly important to place error bounds about model estimates. In order to do this effectively, a history of model performance under circumstances similar to those of common model use must be established for the various models. It is anticipated that performance standards will eventually be set for models. 

From a human factors perspective, the chemistry of the process can be made inherently safer by selecting materials that can better tolerate human error in handling, mixing, and charging. If a concentrated reagent is used in a titration, precision in reading the burette is important. If a dilute reagent is used, less precision is needed. 

This section reflects on the limitations of the PSA process and draws extensively from NUREG-1050. These subjects are discussed as plant modeling and evaluation, data, human errors, accident processes, containment, fission product transport, consequence analysis, external events, and a perspective on the meaning of risk. 

Chapter 1, The Role of Human Error in Chemical Process Safety, discusses the importance of reducing human error to an effective process safety effort at the plant. The engineers, managers, and process plant personnel in the CPI need to replace a perspective that has a blame and punishment view of error with a systems viewpoint that sees error as a mismatch between human capabilities and demands. 

The structure of this book is based on a model of human error, its causes, and its role in accidents that is represented by Figures 1.4 and 1.5. This perspective is called the system-induced error approach. Up to now, only certain... 

The last area addressed by the systems approach is concerned with global issues involving the influence of organizational factors on human error. The major issues in this area are discussed in Chapter 2, Section 7. The two major perspectives that need to be considered as part of an error reduction program are the creation of an appropriate safety culture and the inclusion of human error reduction within safety management policies. 

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). 

From a reliability engineering perspective, error can be defined by analogy with hardware reliability as "The likelihood that the human fails to provide a required system function when called upon to provide that fimction, within a required time period" (Meister, 1966). This definition does not contain any references to why the error occurred, but instead focuses on the consequences of the error for the system (loss or unavailability of a required function). The disadvantage of such a definition is that it fails to consider the wide range of other actions that the human might make, which may have other safety implications for the system, as well as not achieving the required function. 

The four perspectives to be discussed in detail later in this chapter are contrasted in Table 2.1 in terms of the error control strategies that are usually employed, their main areas of application and the frequency that the approaches are applied in the CPI. 

The first perspective is the traditional safety engineering approach (Section 2.4). This stresses the individual factors that give rise to accidents and hence emphasizes selection, together with motivational and disciplinary approaches to accident and error reduction. The main emphasis here is on behavior modification, through persuasion (motivational campaigns) or pimishment. The main area of application of this approach has been to occupational safety, which focuses on hazards that affect the individual worker, rather than process safety, which emphasizes major systems failures that could cause major plant losses and impact to the environment as well as individual injury. 

The second perspective to be considered in this chapter is the human factors engineering (or ergonomics) approach (HFE/E). This approach, described in Section 2.5, emphasizes the mismatch between human capabilities and system demands as being the main source of human error. From this perspective, the primary remedy is to ensure that the design of the system takes into account the physical and mental characteristics of the human. This includes consideration of factors such as ... 

I Comparisons between Various Perspectives on Human Error... 

The sociotechnical systems perspective is essentially top-down, in that it addresses the question of how the implications of management policies at all levels in the organization will affect the likelihood of errors with significant consequences. The sociotechnical systems perspective is therefore concerned with the implications of management and policy on system safety, quality, and productivity. 

From the traditional HF/E perspective, error is seen as a consequence of a mismatch between the demands of a task and the physical and mental capabilities of an individual or an operating team. An extended version of this perspective was described in Chapter 1, Section 1.7. The basic approach of HF/E is to reduce the likelihood of error by the application of design principles and standards to match human capabilities and task demands. These encompass the physical environment (e.g., heat, lighting, vibration), and the design of the workplace together with display and control elements of the human-machine interface. Examples of the approach are given in Wilson and Corlett (1990) and Salvendy (1987). 

Decision making may involve calculations, reference to procedures and past experience, and other demands on long-term memory. This contributes further to the overall mental workload. From the HF/E perspective, many errors are likely to arise from information processing overload, essentially from the mismatch between demands and capabilities. Information-processing demands can be reduced by the provision of information in the form of job aids such as flow charts or decision trees. 

Explaining and Classifying Errors from the Cognitive Perspective... 

These explanations do not exhaust the possibilities with regard to underlying causes, but they do illustrate an important point the analysis of human error purely in terms of its external form is not sufficient. If the underlying causes of errors are to be addressed and suitable remedial strategies developed, then a much more comprehensive approach is required. This is also necessary from the predictive perspective. It is only by classifying errors on the basis of underlying causes that specific types of error can be predicted as a function of the specific conditions under review. 

Conclusions Regarding Application of the Cognitive Modeling Perspective to Errors in the CPI... 

The previous sections have presented an extensive description of some of the central concepts from the cognitive modeling perspective. These topics have been dealt with in some depth because they provide a comprehensive basis for the reduction of human error in the CPI. 

In the previous chapter, a comprehensive description was provided, from four complementary perspectives, of the process of how human errors arise during the tasks typically carried out in the chemical process industry (CPI). In other words, the primary concern was with the process of error causation. In this chapter the emphasis will be on the why of error causation. In terms of the system-induced error model presented in Chapter 1, errors can be seen as arising from the conjunction of an error inducing environment, the intrinsic error tendencies of the human and some initiating event which triggers the error sequence from this imstable situation (see Figure 1.5, Chapter 1). This error sequence may then go on to lead to an accident if no barrier or recovery process intervenes. Chapter 2 describes in detail the characteristics of the basic human error tendencies. Chapter 3 describes factors which combine with these tendencies to create the error-likely situation. These factors are called performance-influencing factors or PIFs. 

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