Cause Events

A common cause event causes two separate, supposedly independent systems to fail simultaneously. For example, solid materials in a liquid system may cause both a pressure controller instrument and the high-pressure shutdown system to be blocked at the same time. The normal control and the interlock are not independent of one another. 

Common cause events negate the value of an and gate in a fault tree (Chapter 15). 

A particularly noteworthy common cause scenario occurred at the Fukushima—Daiichi nuclear power complex in Japan. On March 11, 2011, north eastern Japan was devastated by the Tohoku subsea earthquake— the most powerful ever to have hit Japan since records have been kept. The earthquake was followed about 50 minutes later by a tsunami of 14 meters in height. It is estimated that the earthquake and tsunami together resulted in 15,883 deaths, with many others injured or missing. Up to 1 milhon buildings were destroyed or damaged. 

The earthquake caused extensive damage to the structures of the Fukushima—Daiichi power plant and knocked out the pump systems that supply cooling water to the reactors and the spent fuel pools. This is known as a Loss of Coolant Accident (LOCA) takes place. 

The tsunami then overwhelmed the facihty s inadequate 5.5 meter seawall and, most important from a process safety point of view, it knocked out the safety systems designed to keep the reactors cool. Consequently the cores of the reactors overheated leading to partial meltdowns and follow-on problems, such as the generation of hydrogen gas that exploded. A considerable amount of radioactive material leaked to the ground, the sea, and the air— and those leaks appear to be ongoing. 

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Fig. 2. Frequency of fatalities owing to human-caused events (—) and those caused by nucleai leactoi accidents (-) togethei with proposed nuclear...

WAMCOM Fault tree with susceptibilities 1 Uses modularizatton and SETS to more effectively identify cutsets that contain critical events, critical nindcmt events, and significant common cause events or to describe common cause sets for each failure Can identify etymon total or partial links between fault-tree components con handle very large fault trees CDC 7600, Available froni i I l Rl i V 1.-Cenler... 

Fatality Frequency for Man-Caused Events (from WASH-1400).9... 

Figure 4.10. At the top the raw data for dry residue for 63 successive batches is shown in a standard control chart format. The fact that as of batch 34 (arrow ) a different composition was manufactured can barely be discerned, see the horizontals that indicate the means DRi 33 resp. DR34 g3- A hypothesis that a change occurred as of batch 37 would find support, though. Cusum charts for base period 1. .. 63 resp. base period 1. .. 37 make the change fairly obvious, but the causative event cannot be pinpointed without further information. Starting with batch 55 (second arrow ), production switched back to the old composition.

In most situations, only a small fraction of events traversing the cell is causative. For instance, only one 1 of 6000 electrons traversing a cell nucleus will produce a lethal lesion [32]. A possibly more meaningful definition of low dose ( biological low dose) can be made in terms of these causative events (hits) by asking that the contribution of the quadratic term in dose be less than a certain fraction, say 10%, of the total effect. Let A be this limiting dose. By definition ... 

Although abundant evidence supports the existence of snch an antoimmnne phenomenon, the causative event that heralds this self-directed immune-mediated attack remains uncertain. A number of mechanisms have been proposed to afford a molecular-level explanation of autoimmunity. One such explanation is molecular mimicry. Molecular mimicry occurs when a protein associated with a foreign substance bears structural similarities to a protein found in the host. For example, if a person experiences an infection from bacteria, there is a possibility that a protein in the bacterium shares certain similar geometrical and conformational features with a protein already existing in the person. Thus, an immune response directed against the bacteria will cross-react with organs in the host organism. 

Di Lisa, F., Menabo, R., Canton, M., Barile, M., and Bernardi, P., 2001, Opening of the mitochondrial permeability transition pore causes depletion of mitochondrial and cytosolic NAD+ and is a causative event in the death of myocytes in postischemic reperfusion of the heart, J. Biol. Chem. 276, pp. 2571-2575... 

Fig. 21.6. Frequency of property damage due to natural and human-caused events. (Notes (1) Property damage due to auto accidents not included. (2) Approximate uncertainties for nuclear events are estimated to be represented by factors of 1/5 and 2 on consequence magnitudes and by factors of 1/5 and 5 on probabilities. (3) For natural and human-caused occurrences the uncertainty in probability of the largest recorded consequence magnitude is estimated to be represented by factors of 1/20 and 5. Smaller magnitudes have less uncertainty.)...

In contrast, the impact of natural disasters on communities—lingering disruption, persisting long after the causative event itself and exceeding the communities ability to recover unaided—is determined as much or more by societal behavior and practice as by nature per se. The negative impacts of natural hazards can, at a minimum, be mitigated or, in some instances, prevented entirely. Natural disasters kill and inflict human suffering. In addition, they destroy property, economic productivity, and natural resources, and they harm the environment. Disaster response also diverts assets... 

Before proceeding with the discussion of these rules, we must define the terms events, favorable event, and events not favorable to another event. An event is an occurrence, or a happening. For example, consider Figure 1.3, which defines Z as Going from A to B. As shown, if the traveler goes through path E, he or she arrives at the destination point B. The arrival at B is an event. The travel through path E that causes event Z to occur is also an event. 

In evaluating relief scenarios, the design engineer should consider sequential events that result from the same root cause event, particularly when these can increase the relief load. For example, the loss of electric power in a plant that carries out a liquid phase exothermic reaction could have the following impacts ... 

Since these have a common cause, they should be considered as simultaneous events for that cause. If two events do not share a common cause, then the probability that they will occur simultaneously is remote and is not usually considered (API RP 521,3.2). Root cause events such as power loss, utility loss, and external fire will often cause multiple other events and hence large relief loads. 

The problem of human-caused events, how to control them, and how to discern the difference between high- and low-risk events continues to be studied in many industries (Reason, 1997 Hollnagel, 1998 lOM, 2000). 

After looking at thousands of processes, scientists have concluded that these two factors are the important driving forces that cause events to occur. That is, processes are favored if they involve energy spread and matter spread. 

Spontaneous case reports can reassure a company if a report describes a large accidental overdose with no serious adverse effects. They can also provide reassurance, when reviewed as a whole set, that no reports for drug x causing event y have been received. Clusters of similar spontaneous reports should be meaningfully analyzed for consistency in time to onset, pattern of presentation and dechallenge, to identify a signal and to get a feel for its significance. 

I think this line of defense falls short. I am not opposed to the idea that events can, in some way, be causes. However, I think Kim s criticism of Davidson is right when he says, the causal relation obtains between a pair of events because they are events of certain kinds, or have certain properties (Kim 1993c 22). Although it is events that are causes, I think it still makes sense to ask which properties had by an event are the causally relevant ones in the particular case of causation we are considering. Thus, for example, when one event A causes another event B, there are bound to be maiy properties that event A has. Some of these properties may be causal with respect to causing event B, while others might be epiphenomenal with respect to that particular case of causation. The fact that a property is a physical property or supervenes on a physical property does not mean that it is necessarily a causal property with respect to the particular case of causation in question. 

Thus, Davidson s claim that because mental properties supervene on physical properties and physical properties make a difference to what an event causes will not do. Events have lots of properties, and not even all of the events physical properties will always be causal with respect to each case of causation. In any case of causation we consider, we can and should ask, In virtue of which properties did event A cause event B Davidson is wrong to think that questions like this make no sense. 

Thus, Davidson s claim that supervenience saves mental causation falls short. Davidson is wrong to think that the question, hi virtue of which properties did event A cause event B makes no sense. To save AM fi om the epiphenomenalism of mental properties, we need a way to show how it is possible for causation to be in virtue of mental properties. The question is whether the anomalism of the mental will make it impossible for mental properties to be the one s in virtue of which events are causes. 

Conditions cause events, which lead to new conditions, which cause further events... 

In addition to subjectivity in selecting the events and the root cause event, the links between the events that are chosen to explain them are subjective and subject to bias. Leplat notes that the links are justified by knowledge or rules of different types, including physical and organizational knowledge. The same event can give rise to different types of links according to the mental representations the analyst has of... 

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