Risk Ranking Tools

Tools are available to assist in comparing the risk associated with two or more different processes. For example, the first sheet of the Dow Fire and Explosion Index (FEI) (Dow, 1994b) ranks the safety characteristics of the process from a fire/explosion standpoint, without taking credit for protective and mitigation features. The Dow Chemical Exposure Index (CEI) (Dow, 1994a) and Id s Mond Index (ICI, 1985 Tyler, 1985) are other ranking tools. 

A number of vendors offer software based hazard assessment tools that help determine the magnitude of the hazards involved. With this software, calculations can be made to reflect the hazard for various failures. Some risk ranking software combines hazard assessment with probabilities of occurrence so that the relative risk levels can be assessed. 

There are a variety of ways of accomplishing a particular unit operation. Alternative types of process equipment have different inherently safer characteristics such as inventory, operating conditions, operating techniques, mechanical complexity, and forgiveness (i.e., the process/unit operation is inclined to move itself toward a safe region, rather than unsafe). For example, to complete a reaction step, the designer could select a continuous stirred tank reactor (CSTR), a small tubular reactor, or a distillation tower to process the reaction. 

Before studying alternative types of equipment, we need to understand the critical process requirements. Is a solvent necessary Must products or by-products be removed to complete the reaction What mixing and/or time requirements are necessary Once again, early work up front is needed before alternate reaction schemes can be evaluated. 

Similarly, different unit operations are available to accomplish the same processing objective. For example, a filter, a centrifuge, or a decanter could be used to separate a solid from a liquid. Crystallization or distillation could also be used for purification. 

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Several authors have provided comparative summaries of hazard and risk ranking tools. One publication organized examples of related hazard ranking tools according to a hierarchy based on the complexity of hazard and risk assessment decisions being supported. This relationship is shown in Figure 1. 

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... 

Qualitative findings of ecosystem risk assessments are of low utility for risk management. They cannot be compared with quantitative estimates of other risks this compromises the ability of risk ranking to provide insights to setting priorities. It is particularly difficult to convert them into a format applicable for cost-benefit analysis, which is a key tool that any proponent uses in decision-making on a proposed project. 

Figure 1 Hierarchy of hazard ranking tools in risk decision making. (Reproduced from Pittinger et al. (2003) Risk Analysis 23 529-535, with permission from Blackwell Publishing.)...

Eight case studies were selected for application of the Safe Place, Safe Person, Safe Systems framework and OHS management assessment tool. The risk ranking exercise was conducted as a two stage process firstly without taking into account interventions that were already in place so that areas of vulnerability could be identified should any of the current control measures fail (the raw hazard profile) secondly, an assessment... 

A number of qualitative hazard identification methods are available to the risk analyst. Some of the more popular ones are discussed here. Further detailed information can be found in CCPS (1992). These methods become more powerful tools if they are coupled with the matrix-based risk-ranking scheme previously described. 

Risk ranking is an important tool for risk management. It can readily offer the... 

The following example of a basic priority risk-ranking matrix system is provided to display one tool for determining whether the change or trigger event is simple - and able to use a short form PSSR - or more complex, thus in need of a long form PSSR. 

One tool used for risk ranking is the graphically organized matrix chart as shown below ... 

Not all near miss incidents have high potential to cause injury and loss, yet some do. The only way to prioritize the reported occurrences is to risk-rank th by means of a risk assessment. The best tool for this is the risk matrix. Rananber, it s not what happened, it s what could have happened. The risk matrix is a crystal ball to predict the future or possible outcome of an event. Use it to forecast the probability of the next loss. Near miss incidents that fall into the high-high areas on the risk matrix should receive priority for investigation and rectification. 

You don t need to be reminded of the most recent nuclear accidents, principally Fukushima Daiichi in Japan in 2011. After the Three Mile Island accident in the late 1970s, the U.S. Atomic Energy Commission developed WASH 1400, The Reactor Safety Study. The WASH 1400 report laid the foundation for the use of probabilistic risk assessments (called probabilistic safety assessments in Europe). According to Henley and Kumamoto (1991), probabilistic risk assessment involves studying accident scenarios and numerically rank[ing] them in order of their probability of occurrence, and then assess[ing] their potential consequence to the public. Event trees, fault trees, and other risk-consequence tools are applied in developing and studying these scenarios. These techniques are extremely useful for the engineer but very expensive. The nuclear industry has been the leader in probabilistic safety analyses. 

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. 

As Hendershot (1995) has pointed out, most process options will be inherently safer with respect to one type of hazard, but may be less safe from a different viewpoint. In some cases the overall balance is readily apparent and it is easy to get general agreement on which option offers the safest overall balance. In other cases that balance is less apparent, and more sophisticated tools including qualitative ranking schemes, quantitative risk analysis and formal decision making tools may be needed. 

These and other factors identified as being associated with early stroke risk (Gladstone et al. 2004 Hill et al. 2004) were used to derive the ABCD score, a predictive tool of stroke risk within seven days after TIA (Rothwell et al. 2005). Briefly, all clinical features that had previously been found to be independently predictive of stroke after TIA were tested in a derivation cohort of 209 patients recruited from the Oxfordshire Community Stroke Project (OCSP, Lovett et al. 2003). Any variable that was a univariate predictor of the seven-day risk of stroke with a significance ofp < 0.1 assessed with the log rank test was incorporated into the score. The score was then validated in three further independent cohorts. 

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