Risk scenario

Mangels G] Waterborne Environmental, Inc. 2001. The development of MUSCRAT (multiple scenario risk assessment tool) a software tool for conducting surface water exposure assessments, http //www.waterborne-env.com/modeling/model down-load muscrat.html (accessed January 2, 2007). 

The hazardous event is initiated by the failure of either of the BPCS control valves when the reactor is at high pressure (>5 Barg). The scenario will result in a loss of containment due to overpressure of equipment in the gas processing unit. Due to the scenario risk, an SIL 1 SIF is proposed to detect high pressure and isolate the vent line. 

SWITZERLAND Reg. Doc. R-21 (Revision underway) (since conq)leted - added) Individual dose <0.1mSv/a at any time for reasonably probable scenarios (risk limit also set-added) Sealing of the repository must be possible within a few years without the need for institutional control. 

Likelihood of n fatalities from a single scenario Risk tolerability ... 

Table 14.6 is one table of the results from the analysis. In this case, it is immediately apparent that scenario 1 of the valve 5 operator error risk is unacceptable and cannot stand as is. In fact, the risk is so important that the entire launch will be delayed until this risk is resolved. The other scenario risks are either undesirable (needs upper management approval) or are acceptable with review. 

The second pihar of risk assessment is the risk analysis (see Figure 21.1, point 3). It is the moment when ejq)erts from different backgrounds - operations, security department, technical departments and others, but also external stakeholders, especially police and law enforcement agencies - wiU analyze and assess the risks and risk scenarios. Risk analysis activities are divided into two main steps. 

The next part of the procedure involves risk assessment. This includes a deterrnination of the accident probabiUty and the consequence of the accident and is done for each of the scenarios identified in the previous step. The probabiUty is deterrnined using a number of statistical models generally used to represent failures. The consequence is deterrnined using mostiy fundamentally based models, called source models, to describe how material is ejected from process equipment. These source models are coupled with a suitable dispersion model and/or an explosion model to estimate the area affected and predict the damage. The consequence is thus determined. 

An important part of hazard analysis and risk assessment is the identification of the scenario, or design basis by which hazards result in accidents. Hazards are constandy present in any chemical faciUty. It is the scenario, or sequence of initiating and propagating events, which makes the hazard result in an accident. Many accidents have been the result of an improper identification of the scenario. 

Cause-Consequence Diagram These diagrams illustrate the causes and consequences of a particular scenario. They are not widely used because, even for simple systems, displaying all causes and outcomes leads to veiy complex diagrams. Again, this technique is employed by experienced risk analysts. 

QRA results can guide decision makers in their quest for continuous improvement in risk reduction, but zero risk is an unattainable goal. Any activity involves some risk. Even if it were hypothetically possible to eliminate the risk of every accident scenario in a QRA, some risk would still remain because no QRA examines every possible accident scenario. At best a QRA identifies the dominant contributors to risk from the system as it existed at the time of the analysis. Once those are eliminated, other minor risk contributors (including many that were left out of the original QRA because they were negligible contributors, as well as new risks introduced by changes to eliminate the original risks) remain as the new dominant risk contributors. 

Consequence Phase 3 Develop Detailed Quantitative Estimate of the impacts of the Accident Scenarios. Sometimes an accident scenario is not understood enough to make risk-based decisions without having a more quantitative estimation of the effects. Quantitative consequence analysis will vary according to the hazards of interest (e.g., toxic, flammable, or reactive materials), specific accident scenarios (e.g., releases, runaway reactions, fires, or explosions), and consequence type of interest (e.g., onsite impacts, offsite impacts, environmental releases). The general technique is to model release rates/quantities, dispersion of released materials, fires, and explosions, and then estimate the effects of these events on employees, the public, the facility, neighboring facilities, and the environment. 

A valuable QRA result is the importance of various components, human errors, and accident scenarios contributing to the total risk. The risk importance values highlight the major sources of risk and give the decision maker a clear target(s) for redesign or other loss prevention efforts. For example, two accident scenarios may contribute 90% of the total risk once you realize that, it is obvious that you should first focus... 

There are literally many thousands of chemical compounds that are potential air pollutants. It would be impossible to present all the pertinent data and information needed to evaluate each and every air pollution scenario. There are, however, a wealth of information and data bases that are available on the worldwide Web, along with a number of standard hard copy references to obtain information on the chemical and physical properties, and health risks of potential atmospheric contaminants. 

The process begins with initial system and accident definition for which accidem the probabilities and consequences must be determined to give the risk (Figure 6,3-1). Item 1, (he event tree is central to PSA because it diagrams the accident scenarios to connect accident imtiaiors to consequences. 

It can simulate a wide variety of release scenarios but is particularly well suited to assessing health consequence impacts and risk. 

The Modeling Engine in THERdbASE has the following model groups 1) Population Distributions, 2) Location/Activity Patterns, 3) Food Consumption Patterns, 4) Agent Releases Characteristics, 5) Microenvironment Agent Concentrations, 6) Macroenvironment Agent Concentrations, 7) Exposure Patterns and Scenarios, 8) Dose Patterns, and 9) Risk Assessment. 

Figure 1 shows part of a solvent phase polypropylene plant. The plant consists of three process lines, denoted A, B, and C. During a risk assessment review, a scenario was identified that involved a release of reactor contents from a location near the west end of the A line. Estimates are needed of the blast overpressures that would occur if the resulting cloud of vapor, mist, and power ignites. 

PROBLEM DEFINITION. This is achieved through plant visits and discussions with risk analysts. In the usual application of THERP, the scenarios of interest are defined by the hardware orientated risk analyst, who would specify critical tasks (such as performing emergency actions) in scenarios such as major fires or gas releases. Thus, the analysis is usually driven by the needs of the hardware assessment to consider specific human errors in predefined, potentially high-risk scenarios. This is in contrast to the qualitative error prediction methodology described in Section 5.5, where all interactions by the operator with critical systems are considered from the point of view of their risk potential. 

Section 13.2 Qualitative Risk Scenarios Section 13.3 Quantitative Risk Non-carcinogens Section 13.4 Quantitative Risk Carcinogens Section 13.5 Risk Uncertainties/Liinitations Section 13.6 Risk-Based Decision Making Section 13.7 Public Perception of Risk... 

---