Risk-Ranking Approach

By taking into account the probability, frequency, and severity of a risk, a figure that is called the risk index can be derived. The formula for calculating a simple risk index is  

The consequences (outcome) are ranked on a scale—from catastrophe to minor interruption, for example. A catastrophe is where there are numerous fatalities and losses exceeding several million dollars damage. 

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Pillay A. and Wang J., (2003) A Risk Ranking Approach Incorporating Fuzzy Set Theory and Grey Theory , Engineering Reliability and System Safety, Vol. 79, No. 1, pp. 61-67. 

Each cell in tlie matrix (Table 18.4.2) is assigned a risk ranking as indicated by the letters. In this approach, an A level risk corresponds to a very severe consequence with a high likelihood of occurrence. Action must be taken, and it must be taken promptly. At tlie other end of the scale, a E level risk is of little or no consequence witli a low likelihood of occurrence, and no action is needed or justified. For example, a level C risk might warrant mitigation witli engineering and/or administrative controls or may represent risks tliat are acceptable with controls and procedures. 

A Ranking Approach to Multiple Stressor, Wide-Area Ecological Risk Assessment... 

Belfroid et al. [6] proposed a scheme to identify whether transformation products of pesticides are hkely to pose a lower, similar, or higher risk than their parent compound. Indicators used were presence and persistence in water and sediment and/or high toxicity/bioacciunulation potential. This approach allowed a relative risk ranking of metabohte mixtures, but only four out of 20 pesticides could be rehably ranked due to limited data availabihty. 

ABSTRACT The paper presents a decision support system (DSS) for evaluation of risk pipeline risk. The system is able to support risk assessment and risk ranking of sections of natural gas pipelines. The DSS uses an architecture based on a data base, a model base and user interface. The model base has been built based on Multi-Attribute Utility Theory. The multi-attribute approach analysis risks in three dimensions of impact. These dimensions are human, financial and environmental impact. The way in which the model translates decisionmakers preferences into risk management decisions is highlighted. The paper presents the DSS, including some dialogue modules of the system based on real appUcations. 

Risk matrices may use quantitative definitions of the frequency and consequence categories or some numerical indices of frequency and consequence (e.g., one to five) before adding the frequency and consequence pairs to rank the risks of each hazard or each box on the risk matrix. The strengths of the risk matrix approach are [10]... 

On analyzing the risk values under an intercriteria approach graphically (Fig. 1), we conclude that the first alternatives of the risk ranking show the human impact is major, while in the last-placed alternatives the human impact is nonexistent. The only major value of the impact of these last-placed alternatives is on the operational dimension. 

All the identitied hazards within the system under study can be evaluated using this method to produce a risk ranking based on the highest priority down to the lowest priority. A variation of this qualitative risk matrix approach will be presented in Chapter 5 with its application to the safety analysis of a ship. 

Once the hazards are identified with respect to each of above accident categories, compartments and operational phases, it is essential that they are screened so that they can be properly evaluated and the trivial ones to be excluded from further investigation. The Risk Matrix Approach (Loughran et al. (2002), MSA (1993), Wang et al. 1999)) can be used to combine frequency and severity rankings for the estimation of RRN values. 

Table 5.4 Fire Rankings Using Risk Matrix Approach - Expert Judgement...

The marine industry is recognising the need for powerful techniques that can be used to perform risk analysis of marine systems. One technique that has been applied in both national and international marine regulations and operations is Failure Mode and Effects Analysis (FMEA). This risk analysis tool assumes that a failure mode occurs in a system/component through some failure mechanism. The effect of this failure is then evaluated. A risk ranking is produced in order to prioritise the attention for each of the failure modes identified. The traditional method utilises the Risk Priority Number (RPN) ranking system. This method determines the RPN by finding the multiplication of factor scores. The three factors considered are probability of failure, severity and detectability. Traditional FMEA has been criticised to have several weaknesses. These weaknesses are addressed in this Chapter. A new approach, which utilises the fuzzy rules base and grey relation theory, is presented. 

The traditional FMEA, the fuzzy rule based method and the grey theory approach may complement each other to produce a risk ranking with confidence. 

The expansion of aquatic animal risk analysis into other areas is a distinct possibility in the future. For instance, the current European legislation (e.g. Directive 2006/88) is driving a risk-based approach for characterizing aquaculture farms through risk ranking exercises, with improved identification... 

The amount and type of hazards will determine the performance standard specified in site-specific control plans. This includes the content, detail, and formality of review. The approval of the plans is based on risk and hazard potential. Using the hazard-based approach, levels of risk or methods to rank risk (degree) are standardized. 

Significance of risk contribution may be done by ordering the risk contributors from most-to-least (rank order), but because of the arbitrariness of variation of the variables, this may be meaningless A more systematic approach is to calculate the fractional change in risk or reliability for a fractional change in a variable. 

The approach to developing metrics for process safety is analogous to those that might be used to assess Occupational Exposure risk. One can cite as well several indices that have been developed as metrics for estimating and ranking the safety of a given process or chemical reaction, such as the DOW fire and explosion index,the Stoessel index ° for hazard assessment and classification of chemical reactions, the Inherent Safety Index, the Prototype Index for Inherent Safety, amongst others. ... 

The expert panel can bridge the information gaps of concern for a given chemical and provide a qualitative ranking of those risk uncertainties which are to be clarified by testing. This case-by-case approach will be directed by the basic interests and... 

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