Quantitative risk analysis

QRA is a method that identifies where operations, engineering, or management systems can be modified to reduce risk. The complexity of a QRA depends on the objectives of the study and the available information. Maximum benefits result when QRAs are used at the beginning 

5 CCPS, Guidelines for Chemical Process Quantitative Risk Analysis, 2d ed. (New York Center for Chemical Process Safety, AICHE, 2000). 

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. 

defining the potential event sequences and potential incidents, 

evaluating the incident consequences (the typical tools for this step include dispersion 

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Design procedures are developed with the intention of improving the safety of equipment. Tools used in this step are hazard and operability studies and quantitative risk analysis (ORA). The following scheme may be used ... 

Chemical Process Quantitative Risk Analysis Process Equipment Reliability Data, with Data Tables Technical Management of Chemical Process Safety (Plant)... 

FIGt 26-58 Nomograph to determine the downwind distance affected hy a release. Adapted from Guidelines for Chemical Process Quantitative Risk Analysis, 1989, p. 90. Used hy permission of the American Institute of Chemical Engineers.)... 

A complete analysis of dense gas dispersion is much beyond the scope of this treatise. More detailed references are available (Britter and McQuaid, Workbook on the Dispersion of Dense Gases, Health and Safety Executive Report No. 17/1988, England, 1988 Lees, 1986, pp. 455 61 Hanna and Drivas, 1987 Workbook of Test Cases for Vapor Cloud Source Dispersion Models, AlChE, 1989 Guidelines for Chemical Process Quantitative Risk Analysis, 1989, pp. 96-103). 

Quantitative risk analysis is subject to several theoretical limitations. Table 13 lists five of the most global limitations of QRA. Some of these may be relatively unimportant for a specific study, and others may be minimized through care in execution and by limiting one s expectations about the applicability of the results. However, you must respect these limitations when chartering a QRA study and when using the results for decision-making purposes. 

Quantitative risk analysis is a forecast concerning the degree of belief associated with the occurrence of future events. It normally focuses on those classes of events that are rarely expected to occur at a facility. However, because the potential consequences of such events may be so great, the possibility that the events could occur at all gives rise to concern. When a QRA generates results that reflect a very small likelihood of an event and confirm the suspicion that the event could have a severe impact, these questions inevitably arise What does it all mean What should I do about it ... 

Covernment and regulatoi y decisions. Sometimes these decisions are based on some type of quantitative risk analysis, and they provide some guidance on society s expectations with regard to risk management. In some cases these decisions will also include some kind of cost-benefit analysis. The current political climate in the United States may encourage more extensive use of risk analysis in the establishment of future regulations. 

CPQRA Chemical process quantitative risk analysis... 

The acronym for chemical process quantitative risk analysis. It is the process of hazard identification followed by numerical evaluation of incident consequences and frequencies, and their combination into an overall measure of risk when applied to the chemical process industry. It is particularly applied to episodic events. It differs from, but is related to, a probabilistic risk analysis (PRA), a quantitative tool used in the nuclear industry... 

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. 

The American Chemistry Council, formerly the Chemical Manufacturers Association (CMA), and the American Institute of Chemical Engineers Center for Chemical Process Safety (AIChE/CCPS) have jointly published Evaluating Process Safety in the Chemical Industry User s Guide to Quantitative Risk Analysis. This is a revised and updated edition of Evaluating Process Safety in the Chemical Industry A Manager s Guide to Quantitative Risk Analysis, published in 1989 by CMA. 

Qualitative answers to one or more of these questions are often sufficient for making good decisions about the allocation of resources for safety improvements. But, as managers seek quantitative cost/benefit information upon which to base their decisions, they increasingly turn their attention to the use of quantitative risk analysis (QRA). 

Inventory in transfer lines can be a major risk. For example, a quantitative risk analysis of a chlorine storage and supply system... 

Center for Chemical Process Safety (CCPS) (1989a). Guidelines for Ghemical Process Quantitative Risk Analysis. New York American Institute of Chemical Engineers. 

RISKMAN is an integrated Microsoft Windows , personal computer software system for [H. i forming quantitative risk analysis. Used for PSAs for aerospace, nuclear power, and chemical [iroccsses, it has five main modules Data Analysis, Systems Analysis, External Events Analysis, Event Tree Analysis, and Important Sequences. There are also modules for software system maintenance, backup, restoration, software updates, printer font, and page control. PEG has also integrated the fault tree programs CAFTA, SETS, NRCCUT, and IRRAS into RISKMAN. 

Hazards and Operability (HAZOP) Facility Risk Review Quantitative Risk Analysis... 

Oliveira, L. F. S., et al., 1994, Quantitative Risk Analysis of a Butane Storage Facility, PSAM-II, San Diego, CA, March 20-25. 

A program of research has been supported for several years by the United Kingdom Health Safety Executive (HSE) to address the effects of sociotechnical factors on risk in the CPI. The initial emphasis of this work was to develop a methodology so that chemical process quantitative risk analysis (CPQRA) would take into accotmt the effects of the quality of the management factors of plant being assessed. This work has been described in a series of publications (e.g., Bellamy et al., 1990 Hurst et al., 1991 Geyer et al., 1990 and Hurst et al., 1992). 

For application in chemical process quantitative risk analysis (CPQRA), the hierarchical format of HTA enables the analyst to choose the level of event breakdown for which data are likely to be available. This is useful for human reliability quantification (see the discussion in Chapter 5). 

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 ... 

GUIDELINES FOR CHEMICAL PROCESS QUANTITATIVE RISK ANALYSIS... 

Guidelines for Chemical Process Quantitative Risk Analysis (CPQRA Guidelines) builds on the earlier work to show the engineer how to make quantitative estimates of the risk of the hazards identified. The quantitative estimates can identify the major contributors to risk. They can also help to define the most effective ways to a safer process by indicating relative risk reduction from proposed alternate process safeguards and measures. 

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