Accident worst-case scenario

This aids ia tlie analysis of a worst-case scenario tliat could result from a simple accident. 

The objective of emergency planning is to reduce die probability of serious loss due to a particular liazardous accident. The probability of an occurrence of a hazardous accident is first evaluated. It is tlien it is assumed tliat, if the accident occurs, tlie worst consequences will follow (tlie so-called worst-case scenario). Procedures for liandling a particular accident are tlien dex eloped and practiced, both to minimize tlie exposure of persoiuiel and to prevent escalation of the original incident. 

Hazard assessment is a consequence analysis for a range of potential hazardous chemical releases, including the history of such releases at the facility. The releases must include the worst-case scenario and the more likely but significant accident release scenarios. A risk matrix can be used to characterize the worst-case and more likely scenarios. 

Hazard assessment. A hazard assessment is required to assess the potential effects of an accidental (or intentional) release of a covered chemical/material. This RMP element generally includes performing an off-site consequence analysis (OCA) and the compilation of a five-year accident history. The OCA must include analysis of a least one worst-case scenario. It must also include one alternative release scenario for the flammables class as a whole also each covered toxic substance must have an alternative release scenario. USEPA has summarized some simplified consequence modeling... 

Examine the chemical processes in detail while looking for possible uncontrolled conditions that might occur, including modes of failure, worst case scenarios and other ways of potentially having a reactive chemicals accident. 

Bartnicki J, Salbu B, Saltbones J, Foss A, Lind OC (2005) Atmospheric transport and deposition of radioactive particles from potential accidents at Kola nuclear power plant. Re-analysis of worst case scenarios. Norwegian Meteorological Institute, Oslo, Norway. Met.no research report No. 10/2005. ISSN-1503-8025... 

We must emphasize, however, that many of the unit operations encountered in the analytical laboratory are timeless. These tried and true operations have gradually evolved over the past two centuries. From time to time, the directions given in this chapter may seem somewhat didactic. Although we attempt to explain why unit operations are carried out in the way that we describe, you may be tempted to modify a procedure or skip a step here or there to save time and effort. We must caution you against modifying techniques and procedures unless you have discussed your proposed modification with your instructor and have considered its consequences carefully. Such modifications may cause unanticipated results, including unacceptable levels of accuracy or precision in a worst-case scenario, a serious accident could result. Today, the time required to prepare a carefully standardized solution of sodium hydroxide is about the same as it was 100 years ago. 

Emergency and first aid procedures. This section usually includes recommendations for firefighting procedures, first aid treatment, and steps to be taken if the material is released or spilled. Again, the measures outlined here are chosen to encompass worst-case scenarios, including accidents on a larger scale than could conceivably occur in a laboratory. 

Across the United States, approximately 15,000 chemical plants, manufacturers, water utilities, and other facilities store and use extremely hazardous substances that would injure or kill employees and residents in nearby communities if suddenly released. Approximately 125 of these facilities each put at least 1 million people at risk 700 facilities each put at least 100,000 people at risk and 3000 facilities each put at least 10,000 people at risk, cumulatively placing the well-being of more than 200 million American people at risk, in many cases unnecessarily. The threat of terrorism has brought new scrutiny to the potential for terrorists to deliberately trigger accidents that until recently the chemical industry characterized as unlikely worst-case scenarios. Such an act could have even more severe consequences than the thousands of accidental releases that occur each year as a result of ongoing use of hazardous chemicals. 

One of the justifications for the use of Safety Cases is that if, in the worst case scenario, the facility does have a serious accident, then it is likely that litigation will follow. A well-constructed and maintained Safety Case provides the basis of an excellent defense. Even though an accident has occurred, the Safety Case can demonstrate that management had given serious consideration to understanding the risk that their system posed and that an appropriate Safety Management System was in place. 

Another important point is to find the worst case scenario. Worst case scenario must include all foreseeable factors that could exacerbate the severity of an accident. It was mentioned earlier that there shall be a defined scope and boundary naturally, this will focus attention on the accident of interest. Here, effort has been made to classify these hazard scenarios or risks into three basic categories, namely, people, environment, and property, based on their impact (combination of likelihood and severity). Matrix size and category divisions are purely specific for the project s and analysts prerogative. Table III/1.6-1 gives an idea of such scenario classifications. Impacts are in decreasing order from the top in five categories. 

The assessment should cover the proposed normal use of the product and treated material if applicable. In addition, the realistic worst-case scenarios should include reasonably foreseeable misuse, such as ingestion by a child, but not accidents or attempted suicides). It should also include relevant production and disposal issues for both the product and treated material. Therefore, the risk assessment should cover the entire the lifecycle of the product. 

But how far do you go in preventing an accident When do you stop You can t protect against everything, can you What is a reasonable design limit Do you need to worry about worst-case scenarios or just an average accident scenario What about black swan events These are critical questions that you have to answer before you start anything. 

Another measure of risk is to imagine the worst possible consequence of an operation. Such a study is called a worst-case scenario study, and it is required by some government agencies. These studies have some drawbacks, but they can be very useful in identifying ways to avoid serious accidents. A related strategy that is routinely used throughout the industry for identifying potential hazards is called HAZOP and is discussed in Section 24.4. 

The development of worst-case scenarios is certainly subjective, but government agencies and organizations develop guidelines for this task. For example, there is certainly a chance that an asteroid will inpact Earth direcdy in the middle of the chemical plant. Should this be the worst-case scenario Most people would argue that this takes the worst-case scenario study beyond reason, but there are no clear-cut rules. The subjective rules that have been developed contain definitions such as the worst accident that might reasonably be assumed possible over the life of the facility. Different people would define possible (or probable ) in different ways. Is sabotage by an enployee possible Is the simultaneous failure of three independent safety systems probable Certainly the events of September 11, 2001, have indicated that a terrorist-attack scenario is not inpossible. Sometimes probabilities of occurrence can be estimated, but often they cannot. 

All this is to say that worst-case scenario analyses can be extremely helpful, but they are difficult to perform and potentially difficult to understand. They are most useful when specific guidelines are followed and when they are used to enhance safety by developing safeguards against the accident scenarios developed. For the risk management plan described in Section 24.2.2. worst-case scenario analyses are required by regulation. 

This is why the systematic and complete identification of meaningful accident scenarios for Critical Infrastructure is still one of the major challenges to achieve higher resilience performance. At European/National level it is a part of the Cl identification process, since the EC Directive 2008/114/ EC requires to develop worst case scenarios , to simulate the failure of a potential ECI, in order to assess the transboundary impacts on other Member States. At infrastructure level, vulnerabiUty... 

To motivate the consequence deviation potential part of the extended uncertainty assessment (cf. Section 4.2.2), consider as an example the event Bus Accident . The expected consequences of such an event could perhaps be a few injuries however, the consequences could also be a large number of fataUties. If the risk analysis only reports the probabiUty and expected consequence of this event, its consequence potential is not reflected. On the other hand, if the probability of the rather broadly defined event Bus Accident is linked to some sort of worst case scenario, there will be a mismatch between probability and consequence. One solution could be to split the single event into two events, for example Bus Accident and Bus accident with multiple fatalities . This is still a simplification, as the consequences of a bus accident could be one injury, two injuries. 

The OASIS code has been used for the thermal hydraulics analyses. A large number of events were analysed. The objective of these studies was to identify the worst-case scenario. Therefore, rupture position, rupture time, and break size spectra must be analysed. Currently, the detailed thermal hydraulics analysis for the primary coolant pipe break accident as a function of the break position is being performed. This study is based on conservative assumptions, as required for Category 4 DBE analyses. The main results of this analysis are the core inlet and outlet temperatures, the break flow rate, the IHX inlet and outlet temperatures, as well as the and clad temperature distribution. The results of the calculations show that the hotspot temperatures for the cladding and for the coolant are below the design safety limits (DSL). These temperatures are lower than the sodium boiling temperature. The regulator accepted the methods applied, as well as the results of the analysis. 

Alternative release scenario. Alternative release scenarios must be more likely to occur than the worst-case scenario, and must reach an off-site endpoint. The EPA says owners should also consider these factors in selecting alternative release scenarios five-year accident history and failure scenarios identified by a process hazard analysis (PHA) or Program Level 2 hazard review. The alternative release scenario analyses may be performed using somewhat more flexible modeling approaches and parameters than specified for worst-case scenario analyses. For example, active mitigation credit can be given. 

The subsequent step is to identify the various scenarios which could cause loss of control of the hazard and result in an accident. This is perhaps the most difficult step in the procedure. Many accidents have been the result of improper characterization of the accident scenarios. For a reasonably complex chemical process, there might exist dozens, or even hundreds, of scenarios for each hazard. The essential part of the analysis is to select the scenarios which are deemed credible and worst case. 

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