Reliability models, system safety integration

As the lEC used reliability block diagrams for their calculations, and reliability block diagrams give results with more pessimistic hardware safety integrity values than Markov models (see part 6 of lEC 61508 in chapter B. 1) we can assume, that our model specifies the system correctly. 

In the past, safety engineering has been applied to build dependable systems out of less reliable components. A multitude of practical techniques such as fault masking, error detection, fault diagnosis, and recovery have evolved to improve the reliability of safety-critical system. Since the operations of these systems also depends on software and communicated information, malicious attacks to information security must be considered and appropriately addressed. Commonly, the focus of security can be described by the Confidentiality, Integrity, and Availability (CIA) model. A safety analysis needs to include security risks, determined by vulnerability, threat, and impact with respect to the CIA model. 

For analysing the safety integrity of safety-related systems many methods are possible. Reliability block diagrams and Markov models, however, belong to the most frequently applied. If correctly applied, both methods provide almost the same results. Nevertheless, the Markov models are still more exact (but more difficult) and provide accurate values, even for complex systems. 

There are a number of techniques to analyze the safety integrity of an E/E/PE safety-related systems. The two most used techniques are reliability block diagrams and Markov models. Both methods, if properly applied, give similar results however, for complex programmable electronic sub-systems (e g. when a logic... 

Efficient treatment of the disparate length and time scales will be the key to the further development of predictive computational models for both plasma and electrochemical engineering. This is not limited to the plasma or liquid-phase processes. It includes the solid materials produced or modified by these technologies from the atomic level, to the microstructure to the bulk material properties. Finally, integration of modeling/simulation with design, sensors, control, optimization, safety and reliability will result in an ultimate integrated system which is based on molecular principles and which extends all the way to the factory scale ... 

Under the AMM cluster a thematic network (FP-4 project IS ANEW) was set up in order to develop and compare different methods in order to study the interaction between human and technological systems. Attention was focused on methodologies based upon the integrated sequence analysis (ISA) of possible events, considering both the human system and the physical process. Sequences of events are simulated through modeling of the plant system and the actions of the operators. Input data used for the simulation come from different disciplines such as probabilistic safety assessments (PSA) and human reliability analysis studies. The... 

The reUabUity and safety analysis needs for complex safety critical systems development are not in contradiction with the current techniques used in SE. The effort consists in detailing new kinds of requirements and integrating the new type of analysis techniques and tools to the common SDE. Nevertheless, it imposes on the project management to define when the diverse phases of reliability and safety studies must be conducted. Indeed, it is impossible to quantify and to assess the dysfunctional behaviour of a system, only with a traditional functional model employed in classic SE. The study of the system must go through multiple phases, from the risks and failure mode identification... 

In any case, fault detection and isolation is a prerequisite for real-time system supervision. In order to ensure reliability and safety it is important to take into account detection and diagnosis of possible abnormal system behaviour and means for automatic correction already during an integrated, concurrent design of complex intelligent mechationic system by deliberately injecting faults into a system model and to study their effects on the system s dynamic behaviour. 

Johansson, J., Svegrup, L. Hassel, H. 2013. Societal consequences of critical infrastructure vulnerabilities integrating power system and regional inoperability input-output models. In Proceedings of European Safety and Reliability, ESREL 2013, Amsterdam. 

ABSTRACT Economical risks are directly connected with the technological risks. One major problem of a integrated technical and economic risk assessment is the identification of a suitable method, which can combine technological, safety and economical issues in one risk assessment. The Monte-Carlo-Simulation is used in both sciences (engineering economics) and can be adapted to perform a combine risk assessment. The paper explains the Monte-Carlo-Simulation integrated in a V-model process. Via a V-model the different issues can be partitioned, analysed on a low level (component reliability, safety and price) and later combined to a complete system risk assessment. 

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