Design error-inducing

Error-Inducing Conditions 1.7.1.3. Design and Culture Factors... 

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. 

At this stage of the technique, it is necessary for the analyst to make a general assessment of any error-inducing conditions due to poor PIFs in the situation under consideration, to determine if these are likely to give rise to any of the errors that will be considered at the next stage of the analysis. Typical error-inducing conditions such as poor procedures, time stress, inadequate interface design, have already been considered in Chapter 3. 

In classical potentiometric titration, soluble species produced by dissolution of the solid may contribute to the consumption of an acid or base and induce an error in the calculated Oq. This error is not corrected for in back titrations of an inert electrolyte (Figure 2.6). The back-titration method was designed to avoid the error induced by the dissolution of the solid phase, and it has been used for solids that show appreciable solubility. For solids that are practically insoluble, the... 

The first step is to design for minimum hazard. It includes the use of the safest possible energy sources and forms of energy and careful design of the hardware to ensure that the hardware itself will not fail at an unacceptable rate, that the failures that do occur are not catastrophic and do not produce unacceptable results, and that the hardware design tends to be human error reducing and tolerant rather than error inducing. 

Another form of design error can be poor material selection. A selection error may result from lack of knowledge or data about particular materials. Similar materials may have different properties that are critical. A selection error may result from lack of knowledge or from lack of field data or test data about a use environment. Selection of incompatible materials may induce or accelerate corrosion and fatigue, increase brittleness, or cause other effects that reduce the strength of the material. 

Process phenomena which are possible would be operator errors induced spiUs or overflows. Evaporator or condenser leaks could also occur. Since the ded iterization and HAM i ems are not designed to withstand a DBE, the probability of dther em rrieasing radionuclides is equal to the probability of the occurrence of a DBE, which equals 2.0x1 (Ref. 8-33). 

I lii.s case is an example of system-induced error." The poor design of the information display and poor steam valve icccssibility created the conditions for failure. 

The other main application area for predictive error analysis is in chemical process quantitative risk assessment (CPQRA) as a means of identifying human errors with significant risk consequences. In most cases, the generation of error modes in CPQRA is a somewhat unsystematic process, since it only considers errors that involve the failure to perform some pre-specified function, usually in an emergency (e.g., responding to an alarm within a time interval). The fact that errors of commission can arise as a result of diagnostic failures, or that poor interface design or procedures can also induce errors is rarely considered as part of CPQRA. However, this may be due to the fact that HEA techniques are not widely known in the chemical industry. The application of error analysis in CPQRA will be discussed further in Chapter 5. 

Management and Policy Influences on Error and Accident Causation As has been emphasized in Chapters 1,2, and 3, the system-induced error view states that it is insufficient to consider only the direct causes of errors. The underlying organizational influences also need to be taken into accoimt. However, most of the available techniques stop when an immediate cause has been identified, such as less than adequate procedures or poor equipment design. The questions of why the procedures were poor, or why the equipment was badly designed, are rarely addressed at the level of policy. Kletz (1994a)... 

Figure 5. Inhibitory effect of NO on Fe -induced lipid peroxidation. Shown is the decreased generation of an oxidative marker (thiobarbituric acid reactive substances, TBARS) as a result of 0.9 iM NO. HL-60 cells (5 x loVral) were placed in an O2 monitor and at the designated time points, butylated hydroxytoluene was added and samples were quick frozen for determination of TBARS. The values represent the mean and standard error of 3-5 independent determinations. Also shown for comparison is the residual concentration of O2 after exposure to the the same conditions. This shows a decrease in utilization of O2 in the presence of NO. We conclude that NO reduces TBARS, and the percent inhibition is similar to the poeent inhibition of O2 consumption. (Modified from our data in Kelley, E.E., Wagner, B.A., Buettner, G.R., and Bums, C.P., 1999, Arch. Biochem. Biophys. 370 97-104).

Poor operator interface design induces errors and inefficiency among even the best-trained operators, especially under conditions of stress, time constraints, and/or fatigue. Although labeling (e.g., user documentation) is extremely important for good performance, even well-written instructions are cumbersome to use in conjunction with actual operation. In addition, it is difficult to write coherent documentation that describes awkward operating procedures. 

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