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2.2.1.1 Expressing Risk
ОглавлениеThe answer to the first question in Definition 2.1 gives a set of accident scenarios . The answer to the second question gives the likelihood (i.e. usually the frequency) of accident scenario for each . If accident scenario occurs, it may harm several assets in different ways and with different probabilities. The answer to the third question is therefore a set of possible harms with associated probabilities. This set is called the consequence spectrum associated with accident scenario , for . The consequence spectrum may be expressed as a multidimensional vector that includes various types of harm or damage to all relevant assets (e.g. people, property, and the environment). may sometimes be time dependent if the magnitude of damage varies with time. This means that the answers to the three questions in Definition 2.1 can be answered by the triplet for each , where
provides a name, a precise definition, and a description of potential accident scenario
is an estimate of the likelihood (e.g. frequency) of accident scenario
is a multidimensional vector of the potential types of harm/damage to all relevant assets caused by accident scenario , with associated probabilities, that is, the consequence spectrum for
The risk related to the study object can now, according to Kaplan and Garrick (1981), be expressed by the set of triplets
If all relevant accident scenarios are included, the set of triplets is considered to be complete and hence to represent the risk.
The risk – defined by answers to the three questions – may be presented as in Table 2.2 , where the first column lists the accident scenarios that may give harm. The second column lists the frequency of , and the last column lists the consequence spectrum associated with . The frequency and the consequence spectrum depend on the capability and reliability of the barriers that are available in the study object. A more thorough discussion of accident scenarios can be found in Section 2.3 .
Table 2.2 Risk related to a system (example).
Accident scenario | Frequency | Consequence | |
1 | Gas leak in area 1 | 0.01 | Consequence spectrum 1 |
2 | Falling load from crane 2 | 0.03 | Consequence spectrum 2 |