Error category

For each subset of task steps that have been defined, the analyst first asks if any steps in the group involve any of the activities implied by the error categories, for example, action, checking, communication etc. If an activity does not occur within the task steps being considered, then this is not considered further at this stage. This enables groups of task steps to be eliminated at an early stage of the analysis, to reduce the number of questions that need to be asked later. 

This analysis is applied to each operation at the particular level of the HTA being evaluated. In most cases the analysis is performed at the level of a step, for example. Open valve 27B. For each operation, the analyst considers the likelihood that one or more of the error types set out in classification in Figure 5.7 could occur. This decision is made on the basis of the information supplied by the PIF analysis, and the analyst s knowledge concerning the types of error likely to arise given the nature of the mental and physical demands of the task and the particular configuration of PIFs that exist in the situation. The different error categories are described in more detail below ... 

The first stage of the operation error analysis is to determine if any of the error categories in Figure 5.7 apply to the task, subtask, or task step being analyzed. For example, at the level of individual task steps, operations would... 

Fraction of Results Probability-of-Error Category Interpretation... 

Therefore, in using the classification, the following fixed order is proposed (as indicated from top to bottom in figure 5,1.) to arrive at the best-fitting error category for causal factors of accidents and near misses first K-B errors, then R-B and finally S-B errors. In this way the above mentioned... 

The feedback loop in the basic NMMS framework should show whether a certain preferred action (according to the Classification/Action Matrix) had indeed an effect on the classification category it is linked with. This effect may be measured by looking at the relative occurrence of that specific error category in the near miss reports handed in during the period following the... 

The user-interface for the operators was based on the formalized ontology for the production process, as developed so far. The various tasks, interventions, error categories and error details and the available counter measures were all retrieved from this ontology. This allowed to record the user activities during production, and to store this data with its appropriate context to enable context-sensitive data-mining across all available data sources. To-... 

List at least five medication error categories. 

Gy s theory identifies, and proposes techniques for minimization of, seven major categories of sampling error, covering differences within samples. Other problems exist, including errors involving sampling over space (e.g., soil samples that provide a poor representation of a polluted site) and over time. The internal sample error categories are (Gy nomenclature) ... 

Procedural noncompliance is related to the complex error category that is known as violations (Reason, 1990), which are categorized as any behavior that deviates from accepted procedures, standards, and rules. Violations can be either deliberate or erroneous (Reason 1997). Deliberate violations occur when an actor deliberately deviates from set rules or procedures for example, a driver who is consciously exceeding the speed limit is committing a deliberate violation. Erroneous or unintentional violations, however, occur when an actor unintentionally deviates from a set of rules or procedures for example, a driver who unintentionally exceeds the speed limit, due to either not comprehending the speed of the vehicle or not being aware of the current speed limit, is committing an erroneous or unintentional violation. 

In addition to the simplistic slips, lapses, mistakes, and violations classification described above, further error types have been specified within each category for example. Reason (1990) proposed a taxonomy of nnsafe acts that identifies a number of different error types within each of these fom error categories. The taxonomy of unsafe acts is presented in Figme 14.1. 

In contrast, the errors of the polarization-resistance technique have been very thoroughly and quantitatively evaluated, and the reported errors are the smallest among the four techniques for all error categories. On the other hand, this technique has two more error possibilities (in linearization and Tafel-slope estimate) than the other techniques. Consequently, the overall error may be comparable to those of the three-point and curve-fitting techniques, and it has to be evaluated for each experimental situation. The systematic errors can be avoided by using the appropriately corrected polarization equations in the data evaluation however, that requires numerical values for the appropriate parameters, such as mass transport, double layer, solution resistance, equi-... 

The mental processes and related error mechanisms are different for various levels. Since one particular level applied in a given situation strongly depends upon the degree of training of the individual, it seems fairly obvious that error data collected from routine task situations are not applicable to unfamiliar, infrequent situations such as emergencies, irrespective of the effects of stress and similar factors. From a preliminary analysis of 200 U.S. Licencee Event Reports, Rasmussen (1982) proposed the error categories listed in Tab. 5.3. 

Density is generally measured at 15°C using a hydrometer in accordance with the NF T 60-101 method it is expressed in kg/1 with an error of 0.0002 to 0.0005 according to which category of hydrometer is utilized. However, in practice only three decimal places are usually retained. 

The presence of the multiple arrangements make molecular scattering very challenging theoretically. After much trial and error, several teclmiques have been developed. These teclmiques generally fall into two broad categories ... 

Determinate errors may be divided into four categories sampling errors, method errors, measurement errors, and personal errors. 

Relative uncertainties for absorption spectrophotometry as a function of absorbance for the three categories of indeterminate instrumental errors (see Table 10.8 for equations). 

The potential for a wide range of human errors is greater in batch processes than in continuous processes. Some examples can be found in the categories of errors in Exhibit 6.2. 

The errors in comparative models can be divided into five categories [58] (Fig. 1) ... 

The measurement errors are divided into two categories systematic errors and random errors. ... 

The question may be asked. What is the reason in dividing the errors into two categories. I he answer is the totally different way of dealing with these different types. Systematic error can be eliminated to a sufficient degree, whereas random error cannot. The following section shows how to deal with these errors. 

Systematic error, as stated above, can be eliminated— not totally, but usually to a sufficient degree. This elimination process is called calibration. Calibration is simply a procedure where the result of measurement recorded by an instrument is compared with the measurement result of a standard. A standard is a measuring device intended to define, to represent physically, to conserve, or to reproduce the unit of measurement in order to transmit it to other measuring instruments by comparison. There are several categories of standards, but, simplifying a little, a standard is an instrument with a very high accuracy and can for that reason be... 

Insights into the human causes of accidents for a specific category of process plant installations are provided by the Oil Insurance Association report on boiler safety (Oil Insurance Association, 1971). This report provides a large number of case studies of human errors that have given rise to boiler explosions. 

This classification underscores the inadequacy of the approach common in reliability engineering of simply classifying errors into omission and commission categories. 

In the case of a latent human error the consequences of the error may only become apparent after a period of time when the condition caused by the error combines with other errors or particular operational conditions. Two types of latent error can be distinguished. One category originates at the operational level and leads to some required system function being degraded or unavailable. Maintenance and inspection operations are a frequent source of this type of latent failure. 

Because errors are frequently recoverable, it is also appropriate to define another category of errors, recovery failures. These are failures to recover a chain of events leading to a negative consequence (assuming that such a recovery was feasible) before the consequence occurs. This includes recovery from both active and latent failures. 

For the sake of completeness, it is also useful to define at this stage the category of errors known as violations. Violations occur when a worker carries out actions that are either prohibited or are different from those which are prescribed by the organization and carry some associated risks. Since violations are deliberate acts, they are not, strictly speaking, errors. However, the violations category is useful when classifying human caused failures. 

Violation Error/Failure A violation error occurs when an intended action is made which deliberately ignores known operational rules, restrictions, or procedures. However, this definition excludes actions that are deliberately intended to harm the system, which come within the category of sabotage. 

Motivational campaigns are one way of dealing with routine violations (see Section 2.5.1.1). They are not directly applicable to those human errors which are caused by design errors and mismatches between the human and the task. These categories of errors will be discussed in more detail in later sections. 

Performance-influencing factors are general conditions which increase or decrease the likelihood of specific forms of error. They can be broadly grouped into the following categories ... 

In the nex - section of this chapter, some application areas for PIF analyses will be described. This will be followed by a classification scheme for PIFs based on the demand-resource mismatch model of error described in Chapter 1, Section 1.6. Subsequent sections will describe each of the PIF categories in turn, followed by examples where appropriate. These sections are followed by a discussion of the effects of interactions between PIFs and the implications of high levels of stress in emergencies for human performance. 

The third category of methods addressed in this chapter are error analysis and reduction methodologies. Error analysis techniques can either be applied in a proactive or retrospective mode. In the proactive mode they are used to predict possible errors when tasks are being analyzed during chemical process quantitative risk assessment and design evaluations. When applied retrospectively, they are used to identify the underlying causes of errors giving rise to accidents. Very often the distinction between task analysis and error analysis is blurred, since the process of error analysis always has to proceed from a comprehensive description of a task, usually derived from a task analysis. 

Once certain categories of error have been ruled out, the analyst decides whether or not any of the errors in the remaining applicable categories could occur within the task, subtask, or task step being evaluated. 

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