Risk matrices consequence matrix

Using a tool such as a qualitative risk ranking matrix can be very useful in identifying low-risk buildings. For those events that have potentially major or catastrophic consequences to buildings and their occupants, however, a qualitative risk matrix may not always be an appropriate final evaluation. For events that are potentially major or catastrophic, regardless... 

Hazard assessment is a consequence analysis for a range of potential hazardous chemical releases, including the history of such releases at the facility. The releases must include the worst-case scenario and the more likely but significant accident release scenarios. A risk matrix can be used to characterize the worst-case and more likely scenarios. 

These findings were obtained by discussing the different Sis with different experts from practice. Finally they are presented in the risk matrix at Figure 11 which shows the risk coverage area in terms of likelihood and consequences The data from this is used to construct pro-active Sis. Note that the results give an overview of the risk coverage area in qualitative terms in contrast to the risk coverage area of the events present in the accident trajectory described in the next Section. 

Some further explanation must be given here, because in practice some Sis encompass Tow consequence deviations. For the known risks type of predictive Sis it is obvious that they only cover high consequence deviations in the risk matrix. New risks type of predictive Si s are developed to encompass indirect safety related deviations (i.e. Tow consequence deviations). Though, in practice these deviations are often excluded from the predictive Sis tools as Bayutt (Bayutt, 2003) shows encompassing such indirect safety related deviations is perceived as a waste of resources and attention is distracted from more important scenarios. 

Finally, both the properties, likelihood and consequences, determine the risk. However, to prioritize between different risks, the risk has to be expressed as a onedimensional entity, as discussed in Chapter 1. To establish this one-dimensional risk, a standard risk matrix is used, as depicted on the left side in Figure 29, taken from the safety standard IEC 61508 (IEC 61508, 2000). From this standard risk matrix, the risk matrix used to prioritize the precursors is derived, as depicted on the right side in Figure 29. 

In Figure 29, the rows of both risk classification matrices show the established likelihood, while the columns show the perceived consequences. The result of both likelihood and perceived consequences is the perceived risk, which is indicated with a perceived risk class from 1 to 4 for the left risk matrix and from 1 to 3 for the right risk matrix. The interpretation of the different risk classes for the left matrix in Figure 29 is derived from the IEC 61508 (IEC 61508, 2000) and is stated as ... 

To establish the individual risks of all precursors the properties likelihood and perceived consequences are combined in the derived risk matrix, as shown in Figure 29. If there are several precursors of the same class of perceived risk the final choice of which precursor will be analysed further is made by the multi-disciplinary group of experts which established the perceived consequences. 

The second step, of sorting the selected precursors according to their perceived safety related consequences, is achieved by studying safety reports and confronting the precursors with multi-disciplinary experts, i.e. experts from production, maintenance and safety. The expert group provided the identified precursors with perceived safety related consequences, by formulating possible scenario s, from which the consequences could be obtained. From both the likelihood (see Table 17) and perceived consequences, the perceived risk class is obtained, as discussed in Chapter 5. Figure 42 shows the risk matrix for the precursors presented in Table 17. 

Some companies are now using Risk-Based Inspections (RBI), especially for the costly preparation efforts for internal inspections. RBI is a method that is gaining credibility and popularity. Organizations calculate a proposed inspection frequency by considering the consequences of failure (as described previously) and the likelihood of failure based on the anticipated internal corrosion rates. The method employs a risk matrix. 

The 4-by-4 risk matrix for this facilitated analysis is illustrated in Figure 4.5. The consequence, likelihood, and evaluation criteria definitions are detailed in Tables 4.9-4.11, respectively. 

Using the consequence and likelihood categories, risk matrix, and risk evaluation criteria, the team reviewed three release scenarios (small, medium, and large) for the segments identified for each of the chemical movements. The result of the semi-quantitative risk estimation for this facility s hazardous material transportation operation is detailed in Table 4.12. From this results table, the following are determined ... 

Analysis Guidelines—for consistency with other facilities, corporate provided the consequence, vulnerability (the likelihood of attack success), evaluation criteria, and risk matrix... 

An example of this process is illustrated in Figure 7.2. In this example, an operation was evaluated with a base case risk level of I, or a higher risk that required consideration of risk reduction options. Three risk mitigation options were developed and evaluated. As can be seen, one option reduced the consequence (Option 1), one option reduced the likelihood (Option 2), and one option reduced both consequence and likelihood (Option 3). Option 3 resulted in the greatest risk reduction benefit. While the options that reduce only consequence or likelihood did reduce risk (movement across or down the matrix), the resulting level of risk, as defined on the risk matrix, did not change from risk level I. Therefore, purely on a benefit basis, Option 3 provided the greatest risk reduction. 

The importance of any engineering subject is calculated by two factors risk and cost. While risky is an unscientific way of addressing an issue that is potentially dangerous, risk has a clear engineering definition risk is the product of likelihood and consequences. These factors are expressed in a risk assessment matrix Figure 1.2 shows an example of a risk matrix. 

Once the hazards have been identified, and their causes, consequences, and frequencies discussed, the team should risk rank each identified hazard scenario. If a risk matrix is used then the estimated risk values for the two scenarios are B and C, respectively. 

Determine the consequence and likelihood of the hazard scenario. This evaluation should include an examination of safety, environmental, and economic losses (including the requirements associated with safety and environmental regulations). Based on an assessment of the overall risk associated with the identified hazard, decide if additional safeguards or Layers of Protection/lndependent Protection Layers (IPL) are required. The criterion for acceptable risk could be single numerical value, or it could be determined through use of a risk matrix. 

Establish numerical rankings for the consequences and also likelihood of the effect. For example, use risk matrix classification as per Table 3.2... 

Not all of the initial 14 unwanted events are placed in the risk matrix for safety, because some of them are regarded as not relevant for this consequence category. 

In this example, the different types of assets were further placed into a risk matrix (illustrated in Figure 3), according to the estimated safety risk using the BN model. Probabdity and consequence levels for the assets plotted in the risk matrix were estimated based on the same assumptions used in the BN model. 

For simphfication, the asset age does not come into the picture in this risk matrix, but it wiU be considered in further analyses. Tables 2 and 3 show the probability and consequence scales used in the risk matrix. 

Typical example of risk matrix are defined by the popular safety codes MIL-STD-882D (DOD 2000) and lEC 61508 (CEI 2002). The frequency is categorized into 5 categories (6 in IEC61508) and severity of the consequences into 4 categories. This is the basis to constitute a plane matrix of 20 (24 in IEC61508) cells, with an associated risk level. 

A rating of a risk from lowest to highest or vice versa. A rating is usually derived from a risk matrix assessing the risk from frequency or probability (high to low) against its consequences (minor to severe), whereby the function of the two provide a relative ranking of the risk compared to other risks, and the result will indicate the level of action that is required to resolve the risk. See also Risk Matrix. 

Discussions and results of qualitative ride analyses of possible aeddent scenarios in the area by comprehensivdy identi potential events and thdr initiators, estimating thdrfinequendes and consequences, and displaying the results in a risk matrix... 

The result of an SLRA is a list of potential hazardous events that could occur at that facility, aU ranked using a risk matrix (made up of frequency and consequence components), based on the experience and knowledge of the analysts undertaking the assessment. The ranking process involves assigning each hazardous event to an appropriate frequency and consequence elass. 

Requirement PHA, identification of human/process error existing additional protection factors for PHA hazard identification and consequence risk analysis, estimate from risk matrix presentation of result systematic selection of various processes. 

Consequence details such as likelihood of occurrence, severity, etc. to assess risk level or risk matrix (discussed in Chapter II in details). 

The impact of all mitigating actions and sources of assurance are considered before calculating the residual risk. Reduction of each of likelihood and consequence depends on underlying subject issue and specific control considered. When the actual control plan is not correctly implemented, then the concerned person of the risk team and manager risk team need to think of improvement for action plan implementation and/or modify the framework for control action as warranted for the project. After completion of risk register, all risk should be populated in a consolidated risk matrix (or heat map) with risk IDs. Based on this, a report summary is put before management for consideration major points here are ... 

There are several standard guidelines and published risk matrices, but at the beginning one has to decide the intent for which it is to be developed. Table 1/3.3.2-1 is an example of a risk matrix available from CCPS. Tables 1/3.3.2-2—1/3.3.2-4 show the explanation of risk levels, likelihood, and consequence range criteria for the risk matrix in Table 1/3.1.4-1 (based on technical review by MS. D. Aptikar). 

Here, risk levels also can be defined as discussed previously, but in the reverse manner. Here, the top left part of the matrix is the highest risk area, whereas the bottom right part is lowest risk. There is no upper and lower limit. Too much increase/ decrease of in the categories of risk frequency or consequence, has no practical value really. So, in practice, these are restricted to 3 x3 or 5 x5 matrix, which need not be a square matrix as is evident from the above (6x4). Table 1/3.3.2-6 is an example of 4x4 semi-quantitative risk matrix. 

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