Safety integrity

Target Frequency of Dangerous Failures to Perform SIL the Safety-Instrumented Function (per Hour) 

These are systems composed of sensors, logic solvers, and final control elements for the purpose of taking the process to a safe state when predetermined conditions are violated. 

This is the average probability of a safety-instrumented system satisfactorily performing the required safety-instrumented fimctions imder all stated conditions within a stated period of time. 

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Provide appropriate safety integrity level (SIL) level. 

Clean up includes identifying, gathering, storing (when appropriate), and classifying materials associated with a specific toll. Decisions can then be made as to which raw materials, intermediates, and product will be shipped back to the client or kept by the toller. Some off-spec product, retained samples, or unused intermediates may be considered waste materials at this point. Equipment clean up can be extremely important to preserving quality and process safety integrity prior to the next production run of a new product. 

There are three safety integrity levels (SILs) that are generally accepted in the chemical process industry for emergency shutdown systems ... 

General References Guidelines for Hazard Evaluation Procedures, Second Edition with Worked Examples, American Institute of Chemical Engineers, New York, 1992 Layer of Protection Analysis A Simplified Risk Assessment Approach, American Institute of Chemical Engineers, New York, 2001 ISA TR84.00.02, Safety Instrumented Functions (SIF)—Safety Integrity Level (SIL) Evaluation Techniques, Instrumentation, Systems, and Automation Society, N.C., 2002. 

Safety instrumented function (SIF) A safety function allocated to the safety instrumented system with a safety integrity level necessary to achieve the desired risk reduction for an identified process hazard. 

Safety instrumented system (SIS) Any combination of separate and independent devices (sensors, logic solvers, final elements, and support systems) designed and managed to achieve a specified safety integrity level. An SIS may implement one or more safety instrumented functions. 

Safety integrity level (SIF) Discrete level (one out of a possible four SIL categories) used to specify the probability that a safety instrumented function will perform its required function under all operational states within a specified time. 

The different safety integrity levels normally applied within the petroleum and related industries are usually the following ... 

Safety Integrity Level (SIL) - The degree of redundancy and independence from the effects of inherent and operational failures and external conditions that may affect system performance. 

A safety integrity level 2 interlock is required to reduce the risks of the alternatives to comparable levels. 

Once the severity and the probability corresponding to a scenario are estimated, that is, the risk is assessed, a decision can be made on the nature of the protection system to be implemented. If a safety instrumented system (SIS) is to be used, consisting of one or more independent protection levels (IPL), the required reliability of the protection system, constituting a so-called Safety Integrated Level (SIL) can be determined by using this risk assessment, respective of the required risk reduction. 

Safety integrity levels (SILs) provide targets for risk reduction (Security EAL-Evaluation Assurance Level Correlation to SIL )... 

Jones, C., Bloomfield, R.E., Froome, PK.D., and Bishop, PG. (2001), Methods for Assessing the Safety Integrity of Safety-Related Software of Uncertain Pedigree (SOUP), U.K. Health and Safety Executive, Contract Research Report 337/2001. 

PLC-based systems are similar to solid-state systems. They nse the same field interface cards and have the same level of certification but the logic functions are performed by software. They are also easier to interface to other systems (via serial commnnications) in order to notify the system of a failnre. The PLC used is subject to rigorous source code (machine level) inspection and testing by an independent certification body (e.g., TUV in Europe) to examine the safety integrity of the code, inclnding all possible failure paths. The PLC system (application software and hardware) should be developed and tested using a formal, hfe-cycle methodology. ... 

An independent body (a review board or a committee, institutional, regional or national), constituted of medical professionals and non-medical members, whose responsibility is to verify that the safety, integrity and human rights of the subjects participating in a particular trial are protected and to consider the general ethics of the trial, thereby providing public reassurance. Ethics committees should be constituted and operated so that their tasks can be executed free from bias and from any influence of those who are conducting the trial. 

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