Theoretic Safety Analysis

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\subsection{Systems-Theoretic Safety Analysis} The nature of accident causation has, however, become more complex over time. Twenty years ago, accidents causation theory was developed further to capture this increased complexity and a new class of models emerged based on a holistic and systematic approach~\cite{Leveson04anew}. Furthermore, the prevailing chain-of-failure-events models provide the basis for almost all of today's hazard analysis techniques and the probabilistic risk assessment based on them. All of these analysis and design techniques focus on hardware component failures and thus reliability theory \cite{leveson2011engineering}. These methods inhere the assumptions that accidents are caused by component failures. However, they …show more content…

While STAMP acts as an underlying theory, the methods STPA (Systems-Theoretic Process Analysis) and \ac{CAST} (Causal Accident Analysis based on STAMP) are to be practically used for safety analysis. STPA is designed for safety analysis in the system development and operation stage; the goal here is to identify hazards existing in the system and providing so-called safety constraints to mitigate those hazards. CAST is designed for accident analysis, the goal here is to identify causal factors, which lead to the accident. The focus of this dissertation is set on the STPA safety analysis. STPA results in identifying a larger set of causes, many of them not involving failures or …show more content…

A control structure diagram is made up of basic feedback control loops. An example is shown in Figure \ref{fig:Figure2.2}. When put together, they can be used to model the high-level control structure of a particular system. Table \ref{tab:2.1} shows the STPA terminology. \begin{figure}[t] \centering \includegraphics[width=3.0in]{figures/figure8.png} \caption{The STPA process components} \label{fig:Figure2.1} \end{figure} Furthermore, STPA was developed also to address increasingly common component interaction accidents which can result from design flaws or unsafe interactions among non-failing (operational) component\cite{leveson2011engineering}. It accumulates information about how hazards can occur. This information can then be used to eliminate, reduce, and control hazards in system design, development, manufacturing and operations. The STPA safety analysis process is carried out in three major steps (shown in Figure \ref{fig:Figure2.3}): \begin{figure} % \missingfigure{} \centering \includegraphics[width=4.0in]{figures/Figure1.jpg} \caption{The main steps of the STPA approach} \label{fig:Figure2.3}

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