Error precursor analysis

Error precursor analysis identifies the specific error precursors that were in existence at the time of or prior to the accident. Error precursors are unfavorable factors or conditions embedded in the job environment that increase the chances of error during the performance of a specific task by a particular individual or group of individuals. Error precursors create an error-likely situation that typically exists when the demands of the task exceed the capabilities of the individual or when work conditions aggravate the limitations of human nature. 

The use of a model of human error allows a systematic approach to be adopted to the prediction of human failures in CPI operations. Although there are difficulties associated with predicting the precise forms of mistakes, as opposed to slips, the cognitive approach provides a framework which can be used as part of a comprehensive qualitative assessment of failure modes. This can be used during design to eliminate potential error inducing conditions. It also has applications in the context of CPQRA methods, where a comprehensive qualitative analysis is an essential precursor of quantification. The links between these approaches and CPQRA will be discussed in Chapter 5. 

A hallmark of Class II and Class III charges is that they are derived from analysis of computed wave functions and physical observables, respectively. Thus, to the extent that an employed level of theory is in error for die particular quantity computed, the partial charges will faithfully reflect that error. A Class IV charge, on die other hand, is one that is derived by a semiempirical mapping of a precursor charge (eidier from a Class II or Class III model), in order to reproduce an experimentally determined observable. 

Furthermore, quantitative structural phase analysis, for instance, is important for investigations of solid catalysts, because one frequently has to deal with more than one phase in the active or precursor state of the catalyst. Principal component analysis (PCA) permits a quantitative determination of the number of primary components in a set of experimental XANES or EXAFS spectra. Primary components are those that are sufficient to reconstruct each experimental spectrum by suitable linear combination. Secondary components are those that contain only the noise. The objective of a PCA of a set of experimental spectra is to determine how many "components" (i.e., reference spectra) are required to reconstruct the spectra within the experimental error. Provided that, first, the number of "references" and, second, potential references have been identified, a linear combination fit can be attempted to quantify the amount of each reference in each experimental spectrum. If a PCA is performed prior to XANES data fitting, no assumptions have to be made as to the number of references and the type of reference compounds used, and the fits can be performed with considerably less ambiguity than otherwise. Details of PCA are available in the literature (Malinowski and Flowery, 1980 Ressler et al., 2000). Recently, this approach has been successfully extended to the analysis of EXAFS data measured for mixtures containing various phases (Frenkel et al., 2002). 

From a safety management perspective a specific goal within this broader purpose is then to identify likely factors or system elements in the sequence of events leading to near misses which in turn may be considered as precursors to actual future accidents. From such a qualitative analysis two ways emerge to reduce the likelihood of such actual accidents error-inducing factors can be eliminated (or their potential impact weakened), and recovery-promoting factors can be strengthened (or even introduced) in the system. 

The first two goals would have the effect of evaluating the accuracy of emission inventories, while the third goal would evaluate the accuracy of photochemical production rates. Model applications that met these criteria would be very likely to predict the relation between ozone and precursor emissions correctly. Conversely, major errors in photochemistry or in emission inventories would be quickly apparent in this type of analysis. Analyses of these species should also facihtate the identification of long-term trends in both ozone and its precursors. 

Electroanalytical methods have been used repeatedly in HTSC studies for the quantitative determination of the chemical composition of ceramics and films, their precursors, and also the degradation products. To analyze a multicomponent non-stoichiometric oxide it is necessary to determine independently with sufficient accuracy, the content of individual components that are simultaneously present in the samples [282]. The independent quantitative determination of oxygen is most essential (difference analysis introduces noticeable errors in the values of the important parameter 6). Also important is the determination of the valence of copper. Certain theories of superconductivity of cuprate systems consider Cu " as the principal essential component of HTSCs [9,10], which attracts special attention to this problem. 

Calculated on the basis of chlorine content of the activated polymer precursors. Values obtained by analysis are, within experimental error, indistinguishable from the calculated data... 

To test this hypothesis, Wilhams et al. synthesized the hypothetical Diels-Alder cycloadduct in racemic form bearing a C label at the tryptophyl methylene carbon [19]. Biosynthetic feeding of this potential precursor suspended in DMSO to cultures of PeniciUium hrevicompoctHmyieldedbothbrevianamides A and B but, within the limits of experimental error, there was no evidence for the incorporation of the labeled precursor into either metabolite by NMR and/or mass spectral analysis (see Scheme 9). In addition, culture filtrates and myceUa from PeniciUium brevicompactum were extracted and examined for the presence of the hypothetical Diels-Alder cycloaddition product, yet evidence for the existence of this substance was not obtained. 

Prior to the mid-1980 s, catalysts formed using achiral CpaMCb precursors were found to produce only atactic polypropylene (which, incidentally cannot be obtained in the pure form directly from heterogeneous catalysts). In 1984, Ewen reported the use of metallocene-based catalysts for the isospecific polymerization of propylene.38 The polymerization of propylene at -45°C using a Cp2TiPh2 (I,Fig.4) / MAO catalyst system produced a partially isotactic polymer with an mmmm pentad content of 52% (versus 6.25% for a purely atactic polymer). NMR analysis of the polymer revealed the stereochemical errors mmmr and mmrm in the ratio of 1 1, which is indicative of a stereoblock microstructure (Fig.5). Such a structure is consistent with a chain-end control mechanism,39 where the stereocenter of the last inserted monomer unit provides... 

At the same time, the fact that the homogeneous catalyst precursors are structurally well-defined has provided an extraordinary opportunity to investigate the origin of stereospecificity in olefin polymerization at a level of detail that was difficult if not impossible with the conventional heterogeneous catalysts. For example, NMR analysis of the isotactic polymer produced with HI revealed the stereochemical errors mmmr, mmrr, and mrrm in the ratios of 2 2 1 (Fig.5). This observation is consistent with an enantiomorphic site control mechanism, where the geometry of the catalyst framework controls the stereochemistry of olefin insertion.6 30,31 These results established unambiguously a clear experimental correlation between the chirality of the active site, which could be established by x-ray crystallography of the metallocene catalyst precursor, and the isotacticity of the polymer produced. 

Had an ICAM analysis occurred before the incident, could the precursors to error and the deficiencies in the safety system been identified, and thus prevented the accident The precursors to error need to be identified and resolved, thereby breaking the chain of latent conditions and its effects. To conduct a complete ICAM analysis of a particular incident, a full investigation would need to be conducted by the investigation team as soon as possible after the incident had occurred. 

My approach in studying tryptophan synthetase was greatly influenced by the rigorous training in enzymology I had at Yale in tutorial and laboratory courses with the biochemist Joseph Fruton. Because of this experience, I was determined to purify the protein and characterize it further before I attempted an analysis of the available mutant strains. This was a wise decision, I feel, because there was much to learn about the enzyme. From my studies I concluded that the previously reported activation of a possible tryptophan synthetase precursor was in error. The initial investigators also failed to repeat the activation. ... 

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