Events combining

Figure 14.17 A sequence of events combining the swinging cross-bridge model of actin and myosin filament sliding with structural data of myosin with and without bound nucleotides.

However, in the case of a root cause analysis system, a much more comprehensive evaluation of the structure of the accident is required. This is necessary to unravel the often complex chain of events and contributing causes that led to the accident occurring. A number of techniques are available to describe complex accidents. Some of these, such as STEP (Sequential Timed Event Plotting) involve the use of charting methods to track the ways in which process and human events combine to give rise to accidents. CCPS (1992d) describes many of these techniques. A case study involving a hydrocarbon leak is used to illustrate the STEP technique in Chapter 7 of this book. The STEP method and related techniques will be described in Section 6.8.3. 

Latent error An erroneous action or decision for which the consequences only become apparent after a period of time when other conditions or events combine with the original error to produce a negative consequence for the system. 

Data mining does not equal data dredging. It is a systematic screening for drug-event combinations that are being reported disproportionately. It is essentially a quantitative signal detection method. 

Awareness of the risk in the controlled process is a major component of safety-related decision making by controllers. The problem is that risk, when defined as the severity of a loss event combined with its likelihood, is not calculable or knowable. It can only be estimated from a set of variables, some of which may be unknown, or the information to evaluate hkelihood of these variables may be lacking or incorrect. But decisions need to be made based on this unknowable property. 

Certain rules help to calculate the probability of combinations of events. Combinations of events are common in the field of reliability evaluation. Often system failures occur only when certain combinations of events happen during certain times. 

Fault tree analysis is a complete procedure. If consistently applied it generates all event combinations leading to failure. Limitations do not derive from the procedure but from the knowledge and scrupulousness of the analyst. It goes without saying that phenomena not known at the time of analysis cannot be identified. 

The graphical structure of the fault tree makes it easy to see how primary causes and secondary events combine to produce hazards. Furthermore, by inserting the probabilities of occurrence of causes and events on the fault tree, one can compare the relative contributions of the different events to the probability of the hazardous outcome. 

Idempotent law AxA=A A+A=A An event combined (tbrougb either AND or OR) witb itself is simply the event itself... 

Internal events Equipment failures Human error Other internal events External events Combination of events... 

All four primary barriers PSB1-PSB4 are defined as two-outcome events, where in the first state the prevention measure exists and in the second it has failed. The occurrence of the initiating event combined with the failure of any of the primary barriers PSB1-PSB4 results to the center event, which is the contact with electricity or an electric arc. 

One reason for such a wide use of impact tests is the fact that materials ductile at slow strain rates exhibit brittle fracture under conditions of impact loading. The brittle nature of polymer fracture during an impact event, combined with the above notions of the dynamic effects during such an event, lead naturally to an... 

The SAR identifies events or transient, event sequences, and event combinations that can potentially challenge the safety or control functions of the NPP. These events or transients are further discussed in Sections 22.8.4.2 and 22.8.4.3. 

It should be pointed out here that corrosion processes often involve multiple conjoint effects. Rarely does a single mechanism or event drive corrosion rather, a number of events combine to produce severe effects. Thus, we must keep in mind that corrosion processes usually occur in the context of other factors (loads, wear, crevices, temporally and spatially varying environments, etc.). One such combination of factors can lead to mechanically assisted corrosion in total hip replacements ... 

In deriving the design basis flood for a nuclear power plant, combined events should be considered as well as single events. Combinations of events should be carefully analysed with account taken of the stochastic and nonlinear nature of the phenomena. Furthermore, the ambient conditions that are relevant for the important flood causing event or for each event of the selected combination should also be taken into account. 

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