Risks measurement

Risk Estimation There are a number of risk measures which can be estimated. The specific risk measures chosen are generally related to the study objective and depth of study, and any preferences or requirements established by the decision makers. Generally, risk measures can be broken down into three categories risk indices, individual risk measures, and societal risk measures. 

A common form of societal risk measure is an F-N curve, which is normally presented as a cumulative distribution plot of frequency F... 

For all risk measures it is possible to estimate the risk level of the current process as well as the risk levels from incorporation of various risk reduction alternatives. Management can then use this information as an important input in the final risk decision-making process. 

Once frequency and consequence estimates are generated, the risk can be evaluated in many ways. It is essential that the large number of fre-quency/consequence estimates from a QRA be integrated into a presentation format that is easy to interpret and use. The presentation format you select will depend on the purpose of the QRA and the risk measure of interest. 

Ways of combining information on likelihood with the magnitude of loss or injury (e.g., risk indices, individual risk measures, and societal risk measures)... 

A risk equation for nuclear power may be derived by imagining a world with a very large nuclear power plant population. All plants are identical with the same demography and meteorology. The plants are separated such that one does not affect the other. Each year, n, plants fail in the ith failure mode, causing a population dose tf,. If the effects are additive, the population dose (other risk measures could be used) is linearly proportional to the number failing (Equation 1.4-4), where ( is... 

This step takes the information from Steps 6 and 8. The frequency of an accident multiplied by the consequences is the risk. The consequences need to be in common units to get a measure of the risk. Of course, multiple consequence measures may be used and give multiple risk measures frequency of fatalities, frequency of injuries, frequency of fishkill, frequency of monetary loss. Judgment must be used to rank there relative significance. 

Risk measurement. Few companies have undertaken the quantitative risk assessments necessary to indicate the level of risk they face for... 

Risk Indices - A risk index is a single-number measure of tlie risk associated with a facility. Some risk indices are qualitative or semi-quantitative, ranking risks in various general categories. Risk indices may also be quantitative averages or bencluiiarks based on otlier risk measures. 

Tlie total risk measured in terms of the average annual total number of people killed is obtained by multiplying tlie number of people in each impact zone by the sum of the probabilities of the events affecting the zone, and summing the results. Tlierefore,... 

Risk can be measured and expressed in a number of ways. CCPS s Guidelines for Chemical Process Quantitative Risk Analysis (Ref. 4) identifies three main categories of risk measure Risk Indices, Individual Risk, and Societal Risk. 

Individual Risk expresses the risk to a person exposed to a hazard. It is normally calculated as the frequency of serious or fatal injuries per year (fatalities/year). Three of the more common individual risk measurements are ... 

In using any risk measure, it should be remembered that risk measures, at best, are only estimates of possible event frequency and consequences All risk measurements have uncertainties. In some situations, the uncertainties can be highly significant. The fact that risk measurement is imprecise should be a consideration in any risk-based decision-making process. Chapter 5 of Reference 4 provides further discussion of uncertainty in risk decision making. 

Section 4.2.2 discussed the use of methods other than F-N curves for determining aggregate risk. An aggregate risk measure can be calculated for Example 10 by multiplying each incident frequency by the expected number of serious injuries or fatalities. This results in a parameter of "fatalities per year."... 

Population and individual risk can be determined in the same manner as discussed in Chapter 4. These risk measurements can then be compared with risk tolerance criteria, or decision methodologies can be used, to assist in making risk-reduction decisions about process plant buildings. 

The simplest and most appropriate way to evaluate uncertainty is by using sensitivity analysis on the risk assessments. Sensitivity to a parameter is defined as the change in risk measure per unit change in that parameter (Ref. 76). 

Average Individual Risk (total population), defined as the individual risk over a predetermined population, whether or not people are actually exposed to the risk. If the population used is large, this risk measure can be deceiving, as it might depict very low risks while limited portions of the population in fact are exposed to high risks. 

Societal Risk measures the potential for incidents to affect many people. It has historically been applied as a measure of risk to the general public exposed to the same event or events. Societal risk is often presented as a frequency distribution of multiple-casualty events, called an F-N curve, showing the frequency of events F) leading to N or more fatalities. 

As will be shown in Section 4.2, published data are available on the application of societal risk measures, including the development of risk tolerability limits for F-N curves. However, much of this guidance has been developed for characterizing risks to the general public and would not normally be considered as a basis for assessing risks to on-site personnel. It is appropriate, therefore, to suggest another risk measure, similar in concept to societal risk, for on-site applications to process plant buildings ... 

CNTs show sign of toxicity. Although biomolecules functionalized CNTs can be cleaned from blood circulation system by renal secretion, so far the course of CNTs metabolism in cells or environment, and the potential measurements to reduce CNTs toxicity, is still not clear. How to clarity those mechanisms and reduced risk measurements associated with CNTs toxicity is a great challenge. 

Risk indices are single numbers or a tabulation of numbers that are correlated to the magnitude of the risk to people. Some risk indices are relative values with no specific units. The limitations on the use of indices are that they may not be an absolute criteria for accepting or rejecting the risk. Risk indices also do not communicate the same information as individual or societal risk measures. An example of risk indices is a risk ranking matrix. Table 6-4 (modified from CCPS, 1992) shows how severity and likelihood are combined to obtain risk indices. An example risk matrix is shown in Figure 6-3 (RRS, 2002). 

Average individual risk (exposed population) is the individual risk averaged over the population that is exposed to risk from the facility (e.g., all of the operators in a building, or those people within the largest incident effect zone). This risk measure is only useful if the risk is relatively uniformly distributed over the population, and can be extremely misleading if risk is not evenly distributed. 

F-N curve—A plot of cumulative frequency verses consequences (often expressed as number of fatalities). A societal risk measure. 

Consideration of the expected value of profit alone as the objective function, which is characteristic of the classical stochastic linear programs introduced by Dantzig (1955) and Beale (1955), is obviously inappropriate for moderate and high-risk decisions under uncertainty since most decision makers are risk averse in facing important decisions. The expected value objective ignores both the risk attribute of the decision maker and the distribution of the objective values. Hence, variance of each of the random price coefficients can be adopted as a viable risk measure of the objective function, which is the second major component of the MV approach adopted in Risk Model I. 

It is noteworthy that from a modeling perspective, 0j is also a scaling factor, since the expectation operator and the variance are of different dimensions. If it is desirable to obtain a term that is dimensionally consistent with the expected value term, then the standard deviation of z0 may be considered, instead of the variance, as the risk measure (in which standard deviation is simply the square root of variance). Moreover, 0i represents the weight or weighting factor for the variance term in a multiobjective optimization setting that consists of the components mean and variance. 

Financial and Operational Risk (Measured hy Standard Deviation)... 

Ptofil Risk (Measured by Standard Deviation and Recourse Penally Costs Risk (Measured by Mean-Absolute Deviation... 

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