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Hazardous Operated Safety Instrumented Systems

Introduction. Within a modern industrial society, automation technology is definitely a key factor for success. A long time very conservative environment, namely safe automation technology, has been strongly changing over the last two decades towards fully electronic control and automation systems..

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Hazardous Operated Safety Instrumented Systems

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    1. Hazardous Operated Safety Instrumented Systems

    2. Introduction Within a modern industrial society, automation technology is definitely a key factor for success. A long time very conservative environment, namely safe automation technology, has been strongly changing over the last two decades towards fully electronic control and automation systems.

    3. Introduction The requirements for safety-related automation system are as essential as the normative requirements.

    4. Agenda Basics of Functional Safety Fault Avoidance Basis and Measurement Hazard Analysis Project Approach

    5. Key Words SIS SIL HAZOP Redundancy Voting Device integrity Diagnostics

    6. Basics of Functional Safety History of development For nearly 20 years, great effort has been made in developing National, European und International standards for control engineering. In the early 1980s the International Electrotechnical Commission (IEC) and the German Institute of Standardization (DIN) investigated the fundamental requirements for protective systems using measurement and control techniques. In 1991, the IEC developed a holistic standard encapsulating full life cycle concepts and titled “Functional Safety of Electrical/Electronic/Programmable Electronic Safety-Related Systems” (IEC61508).

    7. Basics of Functional Safety Fundamental considerations . The most important contributor is the specification of how the system should operate, implemented by the engineer or the programmer. The next major factor is modifications after commissioning, operation and maintenance, as the end user often does not understand the intent of the original design and safety engineering. Measures must be taken to prevent or minimize such errors in a safety system’s development and/or design phase.

    8. Basics of Functional Safety Fundamental considerations For the original manufacturer of safety related systems, the standards DIN V VDE 0801 and IEC 61508 differentiate between measures for fault avoidance during the development stage and fault control of the final product. Fault avoidance procedures in designing electronics are implemented by the manufacturer and verified by a test organization such as the German test institute “Technischer Überwachungsverein” (TÜV). These measures are applied during planning, development and manufacturing such that errors can be detected and corrected. The measures for fault control are part of the system hardware and software functionality and result in an appropriate safety-related action

    9. Basics of Functional Safety Fault Avoidance Basis and Measurement The aim is to avoid errors from the very beginning using constructive and analytical processes along with testing and verification procedures throughout the overall safety life cycle. IEC 61508 describes the individual phases of the safety life cycle prescribing fundamental requirements for each phase.

    10. Basics of Functional Safety Fault Avoidance Basis and Measurement The safety-related reliability of complex safety systems can be only achieved by implementing rigorous and analytic processes which incorporate continual verification and testing procedures. . Required risk reduction may be achieved by combining technical and non technical methods, with the result that the remaining (residual) risk of the hazardous plant or equipment is reduced to an acceptable level

    11. Project Approach The project approach is an up-to-date international area of interest, using high-tech product and technologies constant evolving.

    12. Project Approach Protection Layers Layers of protection can be used to reduce unacceptable risk to an acceptable level. The amount of risk reduction for each layer is dependent on the specific nature of the safety risk and the impact of the layer on the risk. Economic analysis should be used to determine the appropriate combination of layers for mitigating safety risks.

    13. Project Approach SIS Factors The scope of an SIS is restricted to the instrumentation or controls that are responsible for bringing a process to a safe state in the event of a failure. The availability of an SIS is dependent upon: Failure rates and modes of components Installed instrumentation Redundancy Voting Diagnostic coverage Testing frequency

    14. Project Approach SIL Factors A SIL can be considered a statistical representation of the availability of an SIS at the time of a process demand. A SIL is the test of acceptable SIS design and includes the following factors: Device integrity Diagnostics Systematic and common cause failures Testing Operation Maintenance

    15. Project Approach Hazard Analysis Hazard and Operability Studies (HAZOP) is a technique (almost like brainstorming) whereby a group of well informed people aim to identify all the ways in which hazards may appear in a system. Its purpose is to:- Establish hazardous failure modes, and A measure of their effect by a systematic examination of the system and its components.

    16. Project Approach Hazard Analysis HAZOP is applicable at all stages of the system lifecycle although it is of limited use until a relatively detailed description of the system has been developed. Typically the selected members of the HAZOP team will have had previous experience of such systems, and complement one another (are from different backgrounds) so that the benefits of the team approach are apparent.

    17. Project Approach Hazard Analysis A disciplined and systematic approach is adopted to ensure there are no obvious omissions. Each component of the system and each hazard is considered in turn. The team employs a series of guidewords and variables to facilitate the process. Questions arise about the design and these act as the basis of the formulation of solutions to mitigate the hazards that are identified.

    18. Project Approach Hazard Analysis Example in use of guidelines: in analysing pipelines in a chemical plant, the guidewords:- NO LESS MORE could be applied to the variables FLOW PRESSURE TEMPERATURE to identify possible hazards.

    19. Project Approach Hazard Analysis The basis (paperwork or model of the system) of the activity must be accurate. The HAZOP process for a large system may take several months - each major component is typically considered in turn. A database of previous disasters can be used as a reminder of options to be looked at. It is possible for the team to get 'carried away' and install expensive equipment to compensate for possible hazards. Proposals for change should go through the HAZOP process.

    20. Project Approach Risk identification process-summary A summary of the risk identification process may be as follows:- use Preliminary Hazard Analysis techniques at the appropriate stage of development use the HAZOP process use Fault Tree Analysis for situations where control is involved or a service has to be provided Use carefully monitored design

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