Risk matrix semi-quantitative

Once the specific issues and scope of the analysis are defined, a semi-quantitative risk assessment may be conducted using either risk indexing or a risk ranking matrix. The risk indexing and risk matrix techniques should be built on the information from the earlier analyses. Each level of risk analysis should not be considered a separate effoit, but a continued understanding of the transportation issue. Additionally the information gained from these activities can be used to update the qualitative analysis, especially benchmarking comparisons. 

To complete this analysis a corporate risk management representative came to the facility to lead a local team through a semi-quantitative risk analysis methodology. The interdisciphnary team, which had received background information on the risk matrix and the semi-quantitative method that will be used, consists of... 

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 ... 

Once a set of recommendations has been developed, the options must be analyzed to determine the benefits, or essentially the level of risk reduction. The risk analysis method utilized to assess the baseline operational risks should be the same method used to analyze each of the potential risk mitigation options. Therefore, if a semi-quantitative technique was used to assess the baseline risk, then the same assumptions, techniques, and risk evaluation criteria (risk matrix, risk index, etc.) should be used to evaluate the effectiveness of the risk reduction options. 

Based on any unacceptable and unmitigated risk identified during hazard analysis, further risk assessment and risk mitigation techniques need to be applied. LORA and conceptual SIS designs based on Risk Matrix can be employed if a qualitative to semi-quantitative method is preferred. Fault tree and event tree analyses with a robust LOPA can be applied if a quantitative method is essential... 

The amoimt of detail and effort required increases from quahtative (Q) approach to semi-quantitative (SQ) one to quantified risk assessment (QRA). For the Q or SQ approaches, a risk matrix is a convenient method of ranking and presenting the results. It is important that the risk matrix used should be capable of... 

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. Oiganizations calculate a proposed inspection frequency by considering the consequences of failure and the likelihood of failure based upon specific factors, which affect internal corrosion rates. Practitioners of RBI look at the effects of operating temperature and pressure, metalluigy, and the aggressive (or passive) nature of the process, possible contaminants, and recent inspection results in this semi-quantitative assessment. The method employs a risk matrix. 

Semi-quantitative techniques, consisting of index and matrix methods. Examples are Dow Fire and Explosion Index, Mond Index, and Pipeline Index for risk ranking of different facilities of the same type, and the matrix method for risk ranking of potential hazardous events that a given facility or organization can face. 

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. 

Like the quaiitative approach, the semi-quantitative technique is essentiaiiy subjective and is based upon the risk assessor s personai interpretation of the ievei of risk, but with the added assistance of a risk matrix so that a risk factor can be caicuiated numericaiiy. 

An example of a semi-quantitative risk matrix, which incorporates the numerical scales discussed above, is shown in Figure 5.12. 

Figure 5.12 Example of a semi-quantitative risk matrix...

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