SELECTING QRA TECHNIQUES

A multitude of analysis techniques and models have been developed to aid in performing these four steps (Figure 7). Many references exist for specific methods, and several recent publications give specific advice and how to details for the various techniques. You will not have to select specific techniques—your QRA team will do that. But you must appreciate the types of results available from each class of techniques. 

Once the decision has been made to use QRA, the next step is to execute it effectively. Chapter 3 describes the process of setting up an individual QRA. This chapter discusses the importance of defining the right problem for analysis and selecting the right analysis techniques it also provides an overview (not a how to) of the various classes of QRA techniques. Chapter 4 discusses ways to interpret and use QRA results. Conclusions about the future of QRA in the CPI are offered in Chapter 5. 

Some of these areas involve actions that primarily you, the ultimate user, must take (e.g., carefully defining written objectives for the QRA project team). Other areas involve decisions that you will influence, but that should be left to the team s discretion (e.g., selection of specific analytical techniques). Still other areas will require your careful interaction and negotiation with the QRA team to ensure that their final product meets your needs (e.g., defining analysis scope and available resources). 

The QRA project team can select the appropriate technical approach once you specify the study objectives, and together you can define the scope. A variety of modeling techniques and general data sources (discussed in Section 3.2) can be used to produce the desired results. Many computer programs are now available to aid in calculating risk estimates, and many automatically give more answers than you will need. The QRA team must take care to supply appropriate risk characteristics that satisfy your study objectives—and no more. 

Hazard analysis (HAZAN) is a quantitative way of assessing the likelihood of failure. Other names associated with this technique are risk analysis, quantitative risk assessment (QRA), and probability risk assessment (PRA). Keltz [44] expressed the view that HAZAN is a selective technique while HAZOP can be readily applied to new design and major modification. Some limitations of HAZOP are its inability to detect every weakness in design such as in plant layout, or miss hazards due to leaks on lines that pass through or close to a unit but cany material that is not used on that unit. In any case, hazards should... 

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