Risk assessment process qualitative analysis

Figure 4.1 illustrates the risk assessment process for qualitative and semi-quantitative techniques that can be apphed to transportation safety scenarios. Typically, these will be a scenario and issues developed and escalated for more detailed analysis during the identification and prioritization process described in Chapter 3. 

The four steps of the risk-assessment process are hazard identification, analysis of exposure, analysis of effect, and risk characterization. In the hazard identification step, the risk assessor identifies chemicals of concern, environmental pathways of exposure, and populations and subpopulations at risk. The exposure analysis develops exposure scenarios and estimates the chronic daily intake of each chemical of concern. In the analysis of effect, the risk assessor combines the chronic daily intake calculated in the exposure analysis with toxicity data from animal studies (and/or human epidemiological studies, if available) to estimate the risk of toxic effects in exposed populations, whereby risks to public health are divided into two broad categories noncancer health effects and cancer. The final step of the risk-assessment process, risk characterization, is a narrative that marshals all the evidence of risk to public health, including quantitative risk assessments and qualitative evidence of risk. The risk assessor weighs all the evidence and uses professional judgment to draw conclusions about risks. 

Performance-influencing factors analysis is an important part of the human reliability aspects of risk assessment. It can be applied in two areas. The first of these is the qualitative prediction of possible errors that could have a major impact on plant or personnel safety. The second is the evaluation of the operational conditions under which tasks are performed. These conditions will have a major impact in determining the probability that a particular error will be committed, and hence need to be systematically assessed as part of the quantification process. This application of PIFs will be described in Chapters 4 and 5. 

In addition, the chapter will provide an overview of htunan reliability quantification techniques, and the relationship between these techniques and qualitative modeling. The chapter will also describe how human reliability is integrated into chemical process quantitative risk assessment (CPQRA). Both qualitative and quantitative techniques will be integrated within a framework called SPEAR (System for Predictive Error Analysis and Reduction). 

The Chemical Process Industry (CPI) uses various quantitative and qualitative techniques to assess the reliability and risk of process equipment, process systems, and chemical manufacturing operations. These techniques identify the interactions of equipment, systems, and persons that have potentially undesirable consequences. In the case of reliability analyses, the undesirable consequences (e.g., plant shutdown, excessive downtime, or production of off-specification product) are those incidents which reduce system profitability through loss of production and increased maintenance costs. In the case of risk analyses, the primary concerns are human injuries, environmental impacts, and system damage caused by occurrence of fires, explosions, toxic material releases, and related hazards. Quantification of risk in terms of the severity of the consequences and the likelihood of occurrence provides the manager of the system with an important decisionmaking tool. By using the results of a quantitative risk analysis, we are better able to answer such questions as, Which of several candidate systems poses the least risk Are risk reduction modifications necessary and What modifications would be most effective in reducing risk ... 

This chapter provides general information for performing qualitative or quantitative risk assessments on buildings in process plants. For detailed guidance on risk assessment techniques, the user is referred to other CCPS books on this subject, including Reference 3, Guidelines for Hazard Evaluation Procedures, Second Edition, and Reference 4, Guidelines for Chemical Process Quantitative Risk Analysis. 

Risk assessment—The process by which the results of a risk analysis are used to make decisions either through a relative ranking of risk reduction strategies or through comparison with risk targets. Risk assessment is often defined as the qualitative estimation of probability and consequence of an incident or incidents. 

Process Hazard Analysis— An organized effort to identify and evaluate hazards associated with chemical processes and operations to enable their control. This review normally involves the use of qualitative techniques to identify and assess the significance of hazards. Conclusions and appropriate recommendations are developed. Occasionally, quantitative methods are used to help prioritize risk reduction measures. 

The deviation scenarios found in the previous step of the risk analysis must be assessed in terms of risk, which consists of assigning a level of severity and probability of occurrence to each scenario. This assessment is qualitative or semi-quantitative, but rarely quantitative, since a quantitative assessment requires a statistical database on failure frequency, which is difficult to obtain for the fine chemicals industry with such a huge diversity of processes. The severity is clearly linked to the consequences of the scenario or to the extent of possible damage. It may be assessed using different points of view, such as the impact on humans, the environment, property, the business continuity, or the company s reputation. Table 1.4 gives an example of such a set of criteria. In order to allow for a correct assessment, it is essential to describe the scenarios with all their consequences. This is often a demanding task for the team, which must interpret the available data in order to work out the consequences of a scenario, together with its chain of events. 

The quantitative risk analysis process uses the prioritized list of risks produced by qualitative risk analysis to analyze the effect of the listed risks and assign a numerical rating to those risks. These ratings help in assessing the probability and impact of the identified risks. Quantitative risk analysis also creates an overall risk score that is applicable to the situation. 

The decision regarding outsourcing is related to speculative risk. The decision-making process should be supported by risk assessment, both before and during cooperation. At this point, companies use qualitative (28%) and quantitative analyses (25%), which are indisputably methods used for risk analysis. What is alarming is that the assessment of the... 

E.D. van Breukelen, R.J. Hatnarm, E.G. Overbosch, Qualitative Fault Tree Analysis Applied as a Design Tool in a Low Cost Satellite Design Method and Lessons Learned, May 2006. CCPS, Layer of Protection Analysis Simplified Process Risk Assessment, Wiley Publications. 

There are several levels of risk analysis within most methodologies for assessing risk quantitative, semi-quantitative, and qualitative. For PSSR concerns we deal almost exclusively with qualitative assessments, that is, just a determination of high or low risk. Generally any truly quantitative risk analysis (QRA) indicated for a trigger event would be performed to enhance the process hazard analysis. The associated PSSR for such a trigger event would simply follow action item progress related to the quantitative risk assessment s action items. In this case the PSSR helps assure that any action items from a QRA are appropriately followed. 

Risk is the safety measure of a potential future event, stated in terms of event likelihood and event severity. Likelihood can be characterized in terms of probability, frequency, or qualitative criteria, while severity can be characterized in terms of death, injury, dollar loss, and so on. Mishap risk analysis is the process of identifying and evaluating the risk presented by a system hazard. HA is an integral part of risk analysis since safety risk can only be determined via the identification of hazards and risk assessment of those identified hazards. See Hazard Risk and Mishap Risk for additional related information. 

The process of risk assessment is initially performed qualitatively and later extended quantitatively to include data when it becomes available, l e interactions and outcomes of both these methods are seen in Figure 3.3. Using the quantified method, risk evaluation can be carried out to determine the major risk contributors and the analysis can be attenuated to include cost beneftt assessment of the risk control options. 

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