Qualitative Risk Evaluation

The QRA method is designed to provide managers with a tool to help them evaluate the overall risk of a process. QRAs are used to evaluate potential risks when qualitative methods cannot provide an adequate understanding of the risks. QRA is especially effective for evaluating alternative risk reduction strategies. 

With the focus on the actual quantities of wastes identified in the site inventory, appropriate field sampling and analysis must be undertaken to verify that the identified hazards actually exist. If a hazard has been identified and the potential for causing adverse effects confirmed, after considering both the qualitative and quantitative dimensions of the situation, the process requires proceeding to the next step - Risk Evaluation. 

Several methods relating to hazards analysis and risk assessment exist. They are generally divided into qualitative and quantitative (lEC 61508 lEC 61511). The choice of specific method depends on accident scenario being considered and available data. When a risk evaluated for scenario considered is high, it is necessary to reduce it to an acceptable level using protection layers, each of specified reliability, expressed often as the probability of failure on demand (PFD) (LOPA 2001). 

According to the ISO/IEC Guide 51 1999, risk evaluation is defined as a wide process of estimation and analysis. In its terminology risk analysis is defined as the systematic use of information to identify hazards and estimate risk, and the risk estimation is defined as a procedure to determine if the risks are tolerable or not. In this manner ISO/IEC Guide 51 1999 presents a iterative process model to evaluate and reduce risks that can be applied to qualitative and quantitative risk evaluations, as shown in Fig. 1. 

Risk evaluation The comparison of the estimated risk to given risk miteuia using a quantitative or qualitative scale to determine the significance of the risk. 

Qualitative risk evaluation and recommended control measures... 

An exhaustive list of hazards is important What is more important is a proper description of the hazard including details of sources and possible impacts. However, a list of causes should not dilute the main aim. There are various means to identify hazards (discussed later). Qualitative risk evaluation is done after analyzing the likelihood and consequence of each hazard and placing all these in a relative scale (specific for the project) to carry out risk ranking. 

Many hazards may be identified and controlled or eliminated through use of qualitative hazard analysis as defined in Guidelines for Hazard Evaluation Procedures, Second Edition (AICHE/CCPS, 1992). Qualitative studies typically identify potentially hazardous events and their causes. In some cases, where the risks are clearly excessive and the existing safeguards arc inadequate, corrective actions can be adequately identified with qualitative methods. CPQRA is used to help evaluate potential risks when qualitative methods cannot provide adequate understanding of the risks and more information is needed for risk management. It can also be used to evaluate alternative risk reduction strategies. 

Evaluating risks using qualitative and quantitative mechanisms... 

Qualitative analysis of risk is a subjective measure, based upon the risk assessor s judgement. As with all methods of risk evaluation, a qualitative assessment will need to allow consideration of the two aspects of risk, i.e. the likelihood of a particular occurrence and the severity of the consequences. 

Nine potential human interventions have been selected for further analysis. HOF risk is evaluated qualitatively by using the conventional risk matrix approach as indicated in Table 8 column 7. On the other hand, same interventions are also evaluated quantitatively using MEDIA approach as indicated in columns 10 and 11 of Table 8. 

IV Precautionary perspective Model is seen to describe a true underlying risk Direction of bias away from true risk is qualitatively evaluated. Judgment aiming at truth Risk is a property of the world. Based on hard evidence and judgment. Uncertainty related to impredsion of underlying true risk... 

We have illustrated in this paper the interest of considering safety and security aspects in a more integrated fashion in the risk evaluation process. Using the BDMP formalism we have modeled two examples a simple common example and a more elaborated industrial case study. Thanks to the qualitative and quantitative capacities of the formalism one can characterize different interdependencies between safety and security antagonism, conditional dependency and mutual reinforcement. 

Open File 7312 (Porter and Morgenstern 2013) examines landslide risk evaluation (ftp //ftp2.cits.mcan.gc.ca/pub/ geott/ess pubs/292/292234/of 7312.pdf). It assesses individual vs. societal risk, voluntary and involuntary risk, tolerable vs. acceptable risk, mortality rates, economic risks, qualitative and quantitative risk methods, partial risk and several other related topics. The authors include known regional examples of safety criteria for landslide and earthquake studies from across Canada. 

Risk Risk is usually defined as the combination of the severity and probability of an event. In other words, how often can it happen and how bad is it when it does Risk can be evaluated qualitatively or quantitatively ... 

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. 

In the past, qualitative approaches for hazard evaluation and risk analysis have been able to satisfy the majority of decision makers needs. In the future, there will be an increasing motivation to use QRA. For the special situations that appear to demand quantitative support for safety-related decisions, QRA can be effective in increasing the manager s understanding of the level of risk associated with a company activity. Whenever possible, decision makers should design QRA studies to produce relative results that support their information requirements. QRA studies used in this way are not subject to nearly as many of the numbers problems and limitations to which absolute risk studies are subject, and the results are less likely to be misused. 

Quantitative risk analysis (QRA) is a powerful analysis approach used to help manage risk and improve safety in many industries. When properly performed with appropriate respect for its theoretical and practical limitations, QRA provides a rational basis for evaluating process safety and comparing improvement alternatives. However, QRA is not a panacea that can solve all problems, make decisions for a manager, or substitute for existing safety assurance and loss prevention activities. Even when QRA is preferred, qualitative results, which always form the foundation for QRA, should be used to verify and support any conclusions drawn from QRA. 

Objective Provide a basis to judge the relative likelihood (probability) and severity of various possible events. Risks can be expressed in qualitative terms (high, medium, low) based on subjective, common-sense evaluations, or in quantitative terms (numerical and statistical calculations). 

The preparation of a matrix and the subsequent evaluation of the hazards identified can lead to a qualitative judgment of process risk and to the identification of available pathways to reduce that risk. Software is available to assist in making and maintaining interactionlike matrices. One example is a database shell called CHEMPAT (AIChE, 1995). When CHEMPAT is customized by the user, a compatibility chart is produced based on user-supplied chemical information. 

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. 

This application is similar to evaluation except that it may be performed as part of an overall qualitative or quantitative risk assessment. In the latter case, quantitative assessment techniques such as those described in Chapter 5 may be applied. 

The carcinogenic potential of the profiled substance is qualitatively evaluated, when appropriate, using existing toxicokinetic, genotoxic, and carcinogenic data. ATSDR does not currently assess cancer potency or perform cancer risk assessments. Minimal risk levels (MRLs) for noncancer end points (if derived) and the end points from which they were derived are indicated and discussed. 

In essence, the earlier components of this overall assessment process are mainly deterministic in character (albeit with some probabilistic elements), whereas the later stages are mainly probabilistic. Not all elements of the process are quantifiable (with any degree of confidence), however and the socicii-political-cultural context of any downstream decision-making process may be intensely uncertain. Such uncertainties make the process of risk communication and debate a complex and sometimes unpredictable undertaking. It is essential therefore that those elements of the risk management process that cein be objectively einalysed and evaluated (either qualitatively or quantitatively, as appropriate) are so assessed. 

The developed methodology is underlined, but this is not to underestimate the importance and interest of the prescribed (ie mandatory) approach. This methodology conforms to technical and scientific logic, and takes into account the quality of criteria, in the statistical sense of the term. The approach presented tends to evaluate the levels of risk, as defined, quantitatively rather than qualitatively, in progressive steps. 

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... 

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