Safety concepts predictive system

Most of the current safety techniques and concepts we use today were bom at the end of the World War II. Operations research led the way, suggesting that the scientific method could be applied to the safety profession. In fact, operations research gave some legitimacy to the use of quantitative analysis in predicting accidents. One of the earliest concept definitions for systan safety (looking at safety from a system perspective) first appeared at the Fourteenth Annual Meeting of the Institute of Aeronautical Sciences in New York City in January 1946. The Organization of... 

Mishaps involve a set of causal factors that lead up to the final mishap event, and these factors are the actuated hazard conditions. Mishap causal factors can be identified prior to an actual mishap through the application of HA. Mishaps are an inevitable consequence of antecedent causes and, given the same causal factors, the same mishap is repeatable, with the frequency based on the component probabilities. Mishaps can be predicted via hazard identification, and they can be prevented or controlled via hazard elimination or hazard control methods. This safety concept demonstrates that we do have control over the potential mishaps in the systems we develop and operate. We are not destined to face an unknown suite of undesired mishaps, unless we allow it to be so (by not performing adequate system safety). In the safety sense, mishaps are preplanned events in that they are actually created through poor design and/or inadequate design foresight. 

Figure 7.4 Integrating Safety Concepts into the Reactive Proactive, and Predictive System. Based on and adapted from Safety Management System Basis, Federal Aviation Administration (FAA).

Naturally, the industry as a prime inventor has the opportunity to carry out seminal work with entirely unique concepts, even if many of them do not become therapies for humans. Human is a unique animal which can, and does, exhibit unique responses to a new chemical entity. No pre-clinical work can be entirely predictive of a successful response in the clinic, and there can, in the end, be no substitute for human testing. Some products fail because of safety problems specific to humans, and some because the early promise of efficacy in model systems is not realized in humans. 

Toward the end of the Second World War, systems techniques such as fault tree analysis were introduced in order to predict the reliability and performance of military airplanes and missiles. The use of such techniques led to the formalization of the concept of probabilistic risk assessment (PRA). The publication of the Reactor Safety Study (NRC, 1975)—often referred to as the Rasmussen Report after the name of principal author, or by its subtitle WASH 1400—demonstrated the use of such techniques in the fledgling nuclear power business. Although WASH 1400 has since been supplanted by more advanced analysis techniques, the report was groundbreaking in its approach to system safety. 

Those famiMar with the concepts of risk understand that attaining zero risk is impossible and that a predictive measurement system that can identify every possible risk on an anticipatory basis has not yet been developed. Furthermore, I believe we have to admit that we are not good yet at having developed measurement systems to determine whether cause-and-effect relationships exist for the safety interventions we propose. 

The Safety Lifecycle (SLC) is an engineering process that contains all the steps needed to achieve high levels of functional safety during conception, design, operation, and maintenance of instrumentation systems. Its objective is clear An automation system designed according to SLC requirements will predictably reduce risk in an industrial process. A simple version of the SLC is shown in Figure 1-3. 

Literature has many theories and concepts discussing human reliability and associated human error causal factors that always trigger incidents and accidents within safety-critical systems. The main - by definition - characteristics of such safety occurrences are their randonmess, rare predictability, sophisticated, yet vague sequence of propagation. Such characteristics can basically allow for the retrospective analysis of these occurrences and their causes at various sectors and levels within industry such that re-occurrence margins are reduced if not totally eliminated. The major drawback of such reactive treatment... 

The extreme action effects of structures are caused by service and chmate loads and may be modeled as intermittent rectangular renewal pulse processes. Therefore, it is e q)edient to treat the safety margin of particular members as a random sequence. The revised values of instantaneous survival probabihty of particular members may be analyzed by the concepts of truncated probabihty distribution and Bayes theorem. The presented new design methodology based on conventional resistances, rank sequences, correlation factors and transformed conditional probabihties may be successfully used in the prediction of long-term survival probabilities of members and their systems during residual service Ufe. 

The interpretation of performance assessment results as indicators of safety reflects the uncertainties associated with predictive modelling. The IAEA-TECDOC-767 recommends different indicators for different time frames (possibly in support of a safety case based on dose or risk). Some countries have introduced a fixed time cut-off for quantitative performance assessment to account also for the uncertainties. The concept of safety indicators may Aus render a time cut-off unnecessary. Predictions beyond about a million years, however, seem to be meaningless even as an indicator of the possible fiiture bdiaviour of the repository system (i.e. safety assessment). Releases possibly occurring after these long times may indicate a well chosen and designed repository system. 

Plant emergency is quite a large topic having variations with respect to specific plants. It is hardly possible to cover all these in the limited space of this book. As per the IPL concept, basically, plant emergency is mainly concerned with evacuation. In that sense, ESD is a predictive safety system. From an instrumentation point of view an ESD system is the main system deployed during an emergency and this will be discussed here. Here, only ESD philosophy and general requirements are discussed because specific details of ESD depend on the plant type/facility, for example, the ESD for offshore facilities will be different to that of other plants. 

Any autosystem is a highly correlated series system of particular elements and their durabihty parameters are related to reliability indices. However, the values of safety and durability indices may be objectively defined only by fully probability-based concepts and models because probabilistic approaches allow us explicitly predict uncertainties of analysis parameters and design models. 

The proposed approaches allow us to simplify the mathematical format, if the prediction of survival probabilities and reliability indices of sustainable series, parallel and series-parallel systems are based on the additional concepts of Transformed Conditional Probabilities (TCP) and Conventional Correlation Vectors (CCV). They help us avoid of complicated multidimensional integrations both in a safety analysis of general systems and their autosystem components. 

The incentives for considering the pool concept as an alternate design are its safety against primary pipe leaks and ruptures and its compact design, which may lead to lower overall capital costs. Potential advantages of the loop concept relate mainly to the ease of maintenance and access to primary system components, thus reflecting potential increases in overall plant availability. There also has been more experience behind this concept. It provides a relatively clear-cut separation of primary system components and places components in a more controllable and predictable environment. These considerations are discussed in more detail in the following section. 

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