Mishap risk analysis

See Hazard Risk Index (HRI) Matrix for additional related information. MISHAP RISK ANALYSIS... 

Risk is the safety measure of a potential future event, stated in terms of event likelihood and event severity. Likelihood can be characterized in terms of probability, frequency, or qualitative criteria, while severity can be characterized in terms of death, injury, dollar loss, and so on. Mishap risk analysis is the process of identifying and evaluating the risk presented by a system hazard. HA is an integral part of risk analysis since safety risk can only be determined via the identification of hazards and risk assessment of those identified hazards. See Hazard Risk and Mishap Risk for additional related information. 

Risk analysis of accidents serves a dual purpose. It estimates tlie probability tliat an accident will occur and also assesses the severity of the consequences of an accident. Consequences may include damage to tlie surrounding environment, financial loss, injury to life and/or deatli. This Part of the book (Part IV) is primarily concerned witli tlie inetliods used to identify liazards and causes and consequences of accidents. Issues dealing witli healtli risks have been explored in tlie previous Part (III). Risk assessment of accidents provides an effective way to help ensure eitlier tliat a mishap will not occur or reduces tlie likelihood of an accident. Tlie result of tlie risk assessment also allows concerned parties to take precautions to prevent an accident before it happens. 

System safety performs HAs and risk assessment on system architectures in order to identify hazards and potential mishap risk. A system hazard analysis (SHA) is essentially an HA of the overall system architecture, including its components and functions. System safety influences system architecture design by requiring the implementation of safety design features, such as redundancy, to reduce the overall mishap risk potential. 

System safety should be involved in the PDR, typically making a presentation summarizing the safety effort to date, the DSFs in the system design, and the current level of mishap risk which the design presents. System safety provides, as a minimum, a subsystem hazard analysis (SSHA), SHA, safety assessment report (SAR), and final safety requirements for this review. 

PHA analysis is both a system safety analysis type and technique for identifying for the early identihcation of hazards and potential mishap risk. The PHA provides a methodology for identifying and collating hazards in the system and estabhshing the initial SSRs for design from preliminary and limited design information. The intent of the PHA is to affect the DFS as early as possible in the development process. The PHA normally does not continue beyond the SSHA time frame. 

In a quantitative analysis, mathematical theories and models are used to calculate mishap risk factors. It is important to recognize that models are the analyst s viewpoint of a system and not the actual system itself. Do not ever confuse mathematical model results with reality. A probability guarantees nothing it is an estimate from a model that provides relative information for decision making. 

The concept and reality of risk has been around for some time. There are many different types of risk, such as safety risk, hazard risk, mishap risk, schedule risk, cost risk, investment risk, product risk, and sports risk. Risk also involves many contending factors, such as perceived risk, real risk, individual risk, group risk, societal risk, high risk takers, low risk takers, and risk aversion. On the surface, risk appears to be a very simple concept however, risk can easily become very complex due to all the types, factors, possibilities, and considerations involved. Risk and risk management are not just safety concepts. Risk analysis and risk management are used in many different fields, such as finance, project management, and health care, just to name a few. Risk is not about the present, it is about the future. Risk deals with uncertainty and outcomes. 

An SCI is a hardware or SI that has been determined, through system safety analysis, to potentially contribute to a catastrophic or critical hazard, or that may be implemented to mitigate a catastrophic or critical hazard. An SCI is essentially the same as a CSI except that systems required to identify CSIs have additional statutory and regulatory requirements that the contractor must meet in supplying those CSIs to the government. SCI and CSI lists are typically developed from HA and potential mishap risk assessment. 

The contract may require a wide range or types of system safety analyses to be performed for a variety of reasons during the life of the contract. For example, any time new equipment or hardware is introduced into the work environment, a series of system safety analyses should be performed. Likewise, when existing equipment is modified to the extent that critical functions of the equipment may be affected, a series of analyses should be conducted prior to the first operational use of the modified equipment. In addition, prudent system safety protocol will dictate that certain analyses be conducted under certain circumstances. For example, an accident investigation may utilize fault tree analysis, or the system safety technique known as MORT (Management Oversight and Risk Tree) to determine the exact cause(s) that lead to an accident/incident/mishap. 

There is no getting around these system laws they will happen, and they will shape the hazard risk presented by a system design. System safety must evaluate the potential impact of each of these system laws and determine if hazards will result, and if so, how the hazards can be eliminated or controlled to prevent mishaps. In other words, these system laws are hazard-shaping factors that must be dealt with during product/process/system design in order to develop a safe system. Since hazards are unique for each system design, safety compliance measures do not provide adequate safety coverage system hazard analysis is thus necessary. 

An IE is an event that commences a sequence of events that ultimately lead to the occurrence of a mishap or UE. Initiating event analysis (lEA) utilizes the concept of scenarios for identifying hazards, risk, and risk mitigations. In the scenario approach to mishap analysis, the scenario consists of a series of events that begins with the IE, which is then followed by one or more critical PEs until a final consequence has resulted. Typically, barriers are designed into the system to protect against lEs and the PEs are failure or success of these barriers. 

PHL analysis is both a system safety analysis Type and Technique for identifying and listing potential hazards and mishaps that may exist in a system. The PHL is performed during conceptual or preliminary design, and is the starting point for all subsequent HAs. Once a hazard is identified in the PHL, the hazard will be used to launch in-depth HAs and evaluations, as more system design details become available. The PHL is a means for management to focus on hazardous areas that may require more resources to eliminate the hazard or control risk to an acceptable level. Every hazard identified on the PHL will be analyzed with more detailed analysis techniques. The primary output from the PHL is a list of hazards and the hazard sources that spawn them. It is also... 

PRA is a comprehensive, structured, and logical analysis method for identifying and quantitatively evaluating risk in a complex technological system. The objective of a PRA is to obtain a quantitative risk assessment of a hazard or potential mishap scenario. FTA is one of the primary tools available for conducting a PRA. 

System safety typically applies the qualitative risk characterization method because for a large system with many hazards, it can become cost-prohibitive to quantitatively model, analyze, and predict the risk of each and every hazard. In addition, low risk hazards do not require the refinement provided by quantitative analysis. It may be necessary to conduct a quantitative analysis only on a select few high consequence hazards. Experience over the years has proven that qualitative methods are very effective, and in most cases provide decision-making capability comparable to quantitative analysis. Qualitative risk characterization provides a very practical and effective approach when cost and time are concerns, and/or when there is very little supporting data available. The key to developing a qualitative risk characterization approach is by carefully defining severity and mishap probability categories. 

Within process industries characterized by large production units and high levels of automation, risk and accident analysis is focused on the avoidance of low-probability events entailing serious consequences for the plant and its environment. Safety analysis is based here on causal or probabilistic models of the accidental chain of events that can serve to identify deficiencies in the design of the plant and its protective system as well as to predict the level of risk involved in an operation. Methods developed are fault tree analysis, MORT (Johnson 1975) and INRS (Leplat Rasmussen 1984). A detailed analysis of the actual, individual incident or failure is performed to identify these possible weak spots in the plant and its operation. It is a common experience that human acts play an important role in such industrial mishaps so, especially after the reactor incident at Three Miles Island in 1979, much effort has been spent on developing suitable predictive tools for the... 

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