The Safety Integrity Level (SIL) of a Safety Instrumented Function (SIF) depends on failures of the various components involved in performing the function. These failures depend on various factors and can be random hardware failures and /or systematic failures. Failures of a SIF need not necessarily result in a hazardous event when there are other Layers of Protection. Hence the residual risk probability that is left out after various layers of protection is of interest and it should be tolerable. In order to find the residual risk due to a hazard we need to know the demand rate of the hazard, the failure rates of various layers of protection and the factors, which influence these failures. So the failure rates are not static and are dynamic as various factors come into play during the lifecycle of the protection devices involved. In this paper the author proposes Bayesian Belief Networks to build the scenario based SIF model and use it in post design phase to track the residual risk probability. An example is used to illustrate the application.
This paper presents a method that will drastically reduce the calculation effort required to obtain quantitative safety and reliability assessments to determine safety integrity levels for applications in the process industry. The method described combines all benefits of Markov modeling with the practical benefits of Reliability Block Diagrams.
This paper is a summary of “Safety lifecycle management in the process industries : the development of a qualitative safety-related information analysis technique” / by Bert Knegtering. – Eindhoven : Technische Universiteit Eindhoven, 2002. – Proefschrift. - ISBN 90-386-1747-X NUGI 684
The new HIMA Quad (QMR) Architecture now available for Safety and Critical Control Applications is a major breakthrough in safety performance. The architecture provides four (4) processors, and remedies problems associated with dual processor architecture, as regards the dangerous undetected failure of one of the two (dual) processors.
This major technological enhancement allows the safety system to operate at the SIL 3 level (RC6) on either one or both channels for an unrestricted period of time, without the need for external devices of any kind. As such, it achieves a significant increase in both safety and availability which exceeds that provided by TMR architectures by a factor of three. In addition, it has significantly less susceptibility to common cause failure because of the absolute separation, isolation and operation of the redundant channels.
Given the safety performance and availability improvements, the most attractive advantage of this new architecture is a lower overall life cycle cost, which will enable it to be used effectively on both small and large safety projects.
This paper discusses the concepts of risk, safety lifecycle, and safety integrity for safety-related electrical/ electronic/ programmable electronic systems (E/E/PES) contained in the International Electrotechnical Commission (IEC) 61508 Standard: Functional safety of electrical/electronic/programmable electronic safety-related systems, Parts 1 through 7. This paper utilizes information from various parts of the IEC 61508 so the concepts and methodologies can be presented in an abridged form.
This paper also shows a number of PES architectures used in safety-related applications. Markov Models are used to calculate the PFDavg so the suitability of using the architectures in applications requiring different safety integrity levels can be determined. Markov Models are also used to compute MTTFspurious for all the PES architectures so the impact of spurious trips can be taken into account when selecting a PES architecture.
