Errors active

Minimal cut sets are then ranked. Two factors are considered in the ranking procedure. The first factor considers stmcture, ie, a one-event minimal cut set is more important than a two-event minimal cut set. The implication is that one event is more likely to occur than two events, two events are more likely than three events, and so on. The second factor considers ranking within equal-size minimal cut sets. The general ranking rules consider the probabihty of human error, active equipment failure, and passive equipment failure (73). 

The sampling of solution for activity measurement is carried out by filtration with 0.22 pm Millex filter (Millipore Co.) which is encapsuled and attached to a syringe for handy operation. The randomly selected filtrates are further passed through Amicon Centriflo membrane filter (CF-25) of 2 nm pore size. The activities measured for the filtrates from the two different pore sizes are observed to be identical within experimental error. Activities are measured by a liquid scintillation counter. For each sample solution, triplicate samplings and activity measurements are undertaken and the average of three values is used for calculation. Absorption spectra of experimental solutions are measured using a Beckman UV 5260 spectrophotometer for the analysis of oxidation states of dissolved Pu ions. 

The values of the apparent rate constants kj for each temperature and the activation enthalpies calculated using the Eyring equation (ref. 21) are summarized in Table 10. However, these values of activation enthalpies are only approximative ones because of the applied simplification and the great range of experimental errors. Activation entropies were not calculated in the lack of absolute rate constants. Presuming the likely first order with respect to 3-bromoflavanones, as well, approximative activation entropies would be between -24 and -30 e.u. for la -> Ih reaction, between -40 and - 45 e.u. for the Ih la reaction and between -33 and -38 e.u. for the elimination step. These activation parameters are in accordance with the mechanisms proposed above. 

In contrast to the dichotomy of reaction pathways observed for the debromination of 27, debromination of 1,2-dibromodecane (29) with either di-/i-hexyltelluride or tetra-/i-butylammonium iodide gave identical (within experimental error) activation parameters (Table The large negative values of ASt (—108 37 and... 

In contrast to the dichotomy of reaction pathways observed for the debromination of 27, debromination of 1,2-dibromodecane (29) with either di-n-hexyltelluride or tetra-M-butylammonium iodide gave identical (within experimental error) activation parameters (Table 3).44 The large negative values of (—108 37 and — 87 12 J K-1 mol-1, respectively) are consistent with a highly-ordered transition state, but the bromonium ion formed from this dibromide would not be particularly favored. The data suggest that both the telluride and the iodide proceed via the E2-like mechanism of Fig. 14 with anti-periplanar transition state 34. 

The procedure outlined above is fairly typical for a number of determinations of solubility products of metal selenites. Data from such investigations have been reevaluated by the review with the accepted protonation constants of the selenite ion, corrected for the hydrolysis of the metal ion when necessary, and the value of the solubility product extrapolated to standard state conditions. It has been observed that the initial and final pH values in cases are in conflict. This has been ignored and the calculations have been based solely on the data for the equilibrium solution. Complexation of the metal ion by the anions and temperature effects were neglected, which probably introduces a negligible error compared with other sources of error. Activity coefficients were calculated by the SIT expression with s = 0 kg-mol, which is a reasonable simplification due to the low ionic concentrations. The ionic strength was obtained by an iterative procedure from knowledge of the total metal concentration and the pH of the equilibrium solution. The results of the recalculations are entered in Chapter V. 

Specified Value Current Value Wt. Error Active Estimate Current ... 

Soedfied Value Current Value WL Error Active Estimate Cwrent ... 

In the U.S., Yao [184] marked the beginning of active control research when he proposed an error-activated structural system whose behaviour varies automatically in accordance with unpredictable variations in the loading, as well as environmental conditions. A remarkable number of different systems, mechanisms and devices has been proposed by researchers in the past 30 years. Although each of them introduces a certain novelty, all the presented systems can be classified in three groups ... 

The systems approach seeks to identify situations or factors likely to contribute to human error. James Reason s analysis of industrial accidents revealed that catastrophic safety failures almost never result from isolated errors conunitted by individuals. Most incidents result from smaller and multiple errors in components and environments with underlying system flaws. Reason s Swiss Cheese Model describes this phenomenon. Errors made by individuals can result in disastrous consequences due to flawed systans that are represented by the holes in the cheese. Reason believed human error would happen in complex systems. Striving for perfection or punishing individuals who make errors does not appreciably improve safety. A systems approach stresses efforts to catch or anticipate human errors before they occur. Reason used the terms active errors and latent errors to distinguish individual errors from system errors. Active errors almost always involve frontline personnel. They occur at the point of contact between a human and some element of a larger system. Latent errors occur due to failures of the organization or designs that allow inevitable active errors to cause harm. The terms sharp end and blunt end correspond to active error and latent error. The systems approach provides a framework for analysis of errors and efforts to improve safety. 

Example EN50128 declares design modularization as mandatory for all safety-critical software (SIL 1-4) to reduce effort for error-locating. If a system development aims at conformance to EN50128, Locate Error activity is added to the quality model (even if not mentioned in the case) and we impose a requirement that at least - —t- for the activity Locate Error has to be contributed from a design fact about the module structure or size. Now, an acceptable argument needs backing evidence (facts) whose effect evaluates to - — -. 

Unfortunately traditional approaches to human error in accident investigation often stop once a human error (active failure) has been identified. Such an approach is bound to fail, or at the most, ordy partially succeed. 

Establish working parties to address each latent failure and, where appropriate, individual errors/active failures. ... 

Human error active failures Some of the human error active failures identified during the first UK study are outlined below (see Simpson et al., 1994 for more detailed consideration). 

Latent failure Among the latent failures identified in this study, three were particularly important (in that they each influenced a significant number of the human error active failures identified). These are set out below. 

A total of 207 individual human errors/active failures were identified across the mines (several of which have been presented earlier as examples in Chapters 3-8). Tables 9.3 and 9.4 summarise the main areas where potential active failures were identified. 

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