Risk analyse

Probit models have been found generally useful to describe the effects of incident outcome cases on people or property for more complex risk analyses. At the other end of the sc e, the estimation of a distance within which the population would be exposed to a concentration of ERPG-2 or higher may be sufficient to describe the impact of a simple risk analysis. 

Consequence Phase 1 Identify Consequence Types and Screening Thresholds. This activity is necessary to address Step 4 ( Is consequence potential great ) in Figure 5. Generally, consequence types for risk analyses are (1) employee safety, (2) public safety. 

It is unclear whether previously published fire risk analyses have adequately ircaicd dependent failures and systems interaetions. Examples of either experienced or postulated system interactions that have been missed include unrelated systems that share common locations and the attendant spatially related physical interactions arising from fire. Incomplete enumeration of causes of failure and cavalier assumptions of independence can lead to underestimation of accident l rci uencies by many orders of magnitude,... 

Having completed the risk analyses, computed the uncertainties, and identified critical systems by importance measures (which also identifies valuable systems improvements having low costs), the PSA results must be presented. An executive summary compares the risk of operations that were analyzed with the risks of similar operations. It identifies and explains the main contributors to the risk to people untrained in PSA and statistical methods. Figure 6.3-5 shows two pie-charts that show the risk contributions of various initiators for PWRs and BWRs. A chart similar to one of these would be an effective way of showing the risk contributions in simplified form. 

Bohn, M. P., and J. A. Lambright, Recommended Procedures for Simplified Pxiernj Event Risk Analyses, February 1988. 

Bernero, R.M. 1984, Probabilistic Risk Analyses NRC Programs and Perspectives, Risk Analysis 4, p 287, December. 

Vescly, V. E., 1977, Estimating Common Cause Failure Probability in Reliability and Risk Analyses Marshall-Olkin Specializations, Proc. Int. Conf. Nucl. Systems Rel. Eng. F ment, Gatlinburg, TN, June. 

As is true in PSM implementation in the United States, it is not practical to try to do everything at once you must establish priorities for PSM design, development, and installation. The priorities that were appropriate in your U.S. effort may not apply directly to international locations. For example, in some international locations, plants are required to submit risk analyses to the government before undertaking major capital projects. This existing practice may make the capital project review element of PSM a less uigent priority. 

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 ... 

Titles of potential resourees were obtained by eonducting a literature search and an industry survey. Simultaneous literature searches were condueted by CCPS and SAIC. CCPS eoneentrated on obtaining CPI data resources while SAIC used a literature search conducted for the nuclear power reliability eommunity. These literature searches used in-house eompany, engineering, and public libraries and recommendations from members of the user eommunity. At the same time, a questionnaire was sent to professionals who eonduct CPQRAs. The survey requested information on the data resourees used by the companies and whether they had plant-speeific data that could be used by CCPS. Members of the CCPS Equipment Reliability Data Subcommittee were also asked to eompile lists of data resources with which they were familiar and which they had used for reliability or risk analyses. As a result, an extensive but not necessarily eomplete list of data resource titles was assembled. Any resources uncovered after the publisher s eutoff date and not reviewed have been included in Appendix D. 

Section 4.5 Chemical Process Quantitative Risk Analyses (CPQRA)... 

Data resource A data base, report, technical paper, journal article, or conversation that contains reliability data subdivided into Data Bases, Data Sources, and Risk Analyses in this book. 

Quantitative risk analyses usually produces single-number estimates. Altliough tliere are sufficient uncertainties associated with tliese quantitative nmnerical values (see next Section) tliey seix e a valuable function. Tliese may be used to compare one risk witli anotlier in a quantitative sense or occasionally employed in an absolute sense. 

Another problem with risk estimates is that they are usually based on very conservati C assumptions. Thus, the aiuilyses may result in a calculation tliat presents too high a risk. Umicccsstiry equipment or procedures tnay have to be installcd/instituted at a facility to reduce tlie calculated risk. In an effort to better understand tlie significance of risk analyses, it is often helpful to place tlie estimated risks in perspective with otlicr risks. 

In making an effort to miderstand the significance of risk analyses, it is helpful to place tlie estimated risks in tlie same perspective as otlier everyday risks tliat have been determined by a similar inctliodology. Table 18.7.1 lists a nmnber of risks for comparison. These have been derived from actual statistics and reasonable estimates." " People often overestimate tlie frequency and seriousness of dramatic, sensational, dreaded, well-publicized causes of death and miderestimate the risks from more familiar, accepted causes tliat claim lives one by one. Indeed, risk estimates by "experts and lay people (or "the public ) on many key enviromiieiital problems differ significantly. This problem and the reasons for it are extremely important because in our society the public generally does not trust experts to make important risk decisions alone. 

In making an effort to understand the significance of risk analyses, it is helpful to place lire estimated risks in lire same perspective as other every day risks tliat liave been determined by a similar metJiodology. 

Adapted from Guidelines for Chemical Process Quantitative Risk Analyses , 2 ed., CCPS, AlCHE, New York City, 2000. 

A second reason is due to the absence of preliminary risk analyses in everyday activities involving chemical substances. Only sensitive activities are subjected to analyses (mainly because of what is at stake and for financial reasons). This is due to, on the one hand, the absence of literature on how to diagnose a priori risks and, on the other hand, the difficulty of such an analysis,(the chemistry being difficult). Finally, preliminary risk analyses are not part of managerial experience and work practice. 

Physical factors favouring inflammability were analysed in paragraph 1.5.4, and the physical factors that apply to unstable compounds were also mentioned. Also underlined was that this classification method was aimed at carrying out quantitative risk analyses. It is precisely for the analysis of dangerous reactions that this method was suggested. It works as follows ... 

The belief that risks from reactor accident are small is based on the past safety record of nuclear reactors, results of on-going probabilistic risk analyses, indicators of improvement in reactor performance, and the prospect of still greater safety in a next generation of nuclear reactors. 

In many risk analyses standard dispersion models, available from the EPA for regulatory compliance purposes, are used to compute concentration patterns for prototypes of a class of sources, and the patterns are convolved with population patterns that are characteristic of the source sites (5, 6). A similar level of analysis detail that relies on measured pollutant (ozone) concentration in each county of the Northeast Corridor rather than on modeled concentrations was used by Johnson and Capel ( 7). 

In general, hazard identification criterion represents the deviation of one or more measured variables from specified values. This is the basis upon which a significant percentage of risk analyses are done. For a chemical process, a number of measurable variables, physical properties, and states or positions of various parts of the overall equipment, e.g., pumps, valves, and motors, can be specified for every time or phase of the process. Certain deviations from the "standard" recipe or settings can then be defined in advance as hazardous, and thus can be used for initiation of an alarm at the early stage of a runaway or upset condition. 

It is most important that the whole life cycle of a process plant can be evaluated on safety. Safety and risk analyses evaluate the probability of a risk to appear, and the decisions of necessary preventative actions are made after results of an analysis. The aim of the risk estimation is to support the decision making on plant localization, alternative processes and plant layout. Suokas and Kakko (1993) have introduced steps of a safety and risk analysis in Figure 2. The safety and risk analysis can be done on several levels. The level on which the analysis is stopped depends on the complexity of the object for analysis and the risk potential. 

An overview is provided of ongoing risk assessments on halogenated phosphate ester flame retardants in Europe. On the basis of the so-called second and fourth Priority lists on Existing Chemicals (Council Regulation No793/93) three chlorinated phosphate ester flame retardants are selected. The selection is based on their hazard profile, volume and use pattern. The three substances involved are TCPP, TDCP and TCEP (Antiblaze V6 from Albemarle is also involved but, due to confidentiality, is not discussed. An outline is provided from a European point of view on topics such as methodology of risk analyses, data-gaps and worst case approach, industry involvement, downstream participation and possible impact of final report on industry. 2 refs. 

Technical evaluation of options and consequence and risk analyses may be prepared. The analyses might include calculation of consequence severities for possible incidents. Subsequently, the basis for a mitigation system may be generated. This might involve, for example, a secondary containment structure, explosion suppression system, or scrubber. The rationale and technical design basis for such decisions should be documented and retained as part of the process knowledge. 

Contractors, contract manufacturers, transporters, warehouses, and end users of reactive chemicals should be informed not only of chemical reactivity hazards, but provided information or training on how to control them. This should be done as part of product life-cycle management and Responsible Care/Product Stewardship. Specific issues needing to be addressed may include but probably are not limited to those that are highlighted during the hazard/risk analyses (Section 4.5), including ... 

Risk analyses suggest that many of the chronic toxicants can be injurious to a small portion of the human population consuming waters or foods containing them. Chronic toxicants include a diversity of carcinogens, mutagens, and teratogens. 

In general, mycotoxin contamination of foods and feeds and the associated problems are primarily influenced by the location of production, storage, and marketing. The Aspergillus species that produce mycotoxins are more common in the warmer, subtropical and tropical areas than in the temperate areas of the world. However, stringent government regulations for mycotoxins and risk analyses are more common in temperate areas than in the warmer areas of the world, where it becomes both a health and a financial problem. 

The degree of meteorological data required for performing the analysis depends on the accuracy of the results desired. A single weather condition (combination of atmospheric stability and wind speed) can be used, however, it is usually impossible to isolate a single average condition that adequately represents all weather conditions. Many risk analyses use at least two weather conditions one stable (e.g., 2 m/s, stability F) and the other characteristic of average conditions (e.g., 5 m/s, stability D). 

A vital objective of future European chemicals policy is to avoid uncontrolled handling of hazardous substances. Assessment of each individual application on the basis of the individual substances involved (as provided for by the current regulatory system) is not an apt strategy, as the number of assessment and management cases that it produces is much too high. Quantitative risk analyses are only taken into account in the case of substances with clearly definable effect thresholds and controllable application conditions. For 90% of the market actors the particular product or application system must possess intrinsically safe properties, as most companies have neither closed systems nor the reqnired skills to deal with hazardons snbstances. 

Hattis D, Burmaster DE. 1994. Assessment of variability and uncertainty distributions for practical risk analyses. Risk Anal 14 713-730. 

In risk analyses, p-boxes serve as models of the total uncertainty about individual variables. There are several ways to obtain p-boxes from data and analytical judgment. But, before we consider where p-boxes come from, let s first review what we can do with them, in particular, how we can use p-boxes in risk calculations. 

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