Safety-instrumented function SIF

1) Safety function with a specified safety integrity level, which is necessary to achieve functional safety (ANSI/ISA-84.00.01-2004-1 Clause 3.2.71). 

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ANSI/ISA-84.01-1996 does not use the term safety instrumented function.  

ANSI/ISA-84.00.01-2004-1 introduced the concept that safety functions are identified during the hazard and risk analysis and allocated to protection layers. When the safety function is allocated to the safety instrumented system, the function becomes a safety instrumented function. The SIF is designed to mitigate a specified safety-related process risk using sensor(s), logic solver(s), and final element(s). At this time, SIF is a process industry sector specific term. 

This is a safety function with a specified integrity level which is necessary to achieve functional safety and which can be either a safety-instrumented protection function or a safety-instrumented control function. 

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

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The concept of PFD is also used when designing emergency shutdown systems called safety instrumented functions (SIFs). A SIF achieves low PFD figures by... 

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. 

The development of the SIS safety requirements specification is one of the more important activities of the whole safety lifecycle. It is through this specification that the user is able to define how he wants the Safety Instrumented Functions (SIF) to be designed and integrated into a SIS. 

Each safety instrumented function (SIF) in a safety instrumented system must perform its protection function, must not falsely shut down the process, and must perform ancillary functions such as communications and diagnostics. However, all these functions are not necessarily included in all analyses. Diagnostic functions or communications functions may or may not be counted as a failure depending on the purpose of the analysis. 

The determination of Safety Integrity Level (SIL) for safety instrumented functions (SIF) is a basic concept of performance based safety standards. The safety integrity or performance of a SIF must increase with higher SIL levels. There are a number of factors that influence the performance of any safety instrumented function. Some of the key factors are ... 

In this chapter a Safety Instrumented Function (SIF) for gas wells encountered in gas fields will be reviewed. For the SIF identified, a detailed review of the function will be done and a calculation of possible PFDavg values achieved will be done so that the SIL verification for the SIF can be accomplished in part. 

Prior to carrying out SIL verification calculations for Safety Instrumented Functions (SIF) it is essential and very important that each function and its associated input and output signals be weU defined. The identification of the SIF is part of the analysis phase and the detail requirements for each function are documented in the Safety Requirements Specifications (SRS). 

High Line Pressure Safety Instrumented Function (SIF)... 

It is therefore essential that the inputs and outputs associated with all Safety Instrumented Functions (SIF) be properly defined to address the specific hazardous event being prevented or mitigated by the SIF. Failing to do so will result in erroneous SIL verification results. 

ISA 2002, Safety Instrumented Functions (SIF) - Safety Integrity Levels (SIL) Evaluation Techniques Parts 1 to 5 , ISA TR84.00.02-2002 (Parts 1 to 5), Research Triangle Park, NC. 

A safety instrumented function (SIF), however, is a function that is implemented by a SIS. A SIS may consist of several SIFs. Each SIF has to fulfill a requirement which is called safety instrumented level (SIL). Safety integrity is in IEC61511 (2003) defined as... 

Phases 1 to 5 deal with concept and analysis—risk assessments to discover the Safety Instrumented Functions (SIF) and assign an appropriate Safety Integrity Level (SIL) rating. 

The level of overall availability for a system component is calculated as 1 minus the sum of the average probability of dangerous failure on demand. SIL-1 availability of 90-99 percent SIL-2 availability of 99-99.9 percent SIL-3 availability of 99.9-99.99 percent. See also Layers of Protection Analysis (LOPA) Safety Instrumented Function (SIF) Safety Instrumented System (SIS). 

Safety function Safety instrumented function (SIF) lEC 61508 safety function implemented by E/E/PES, other technology safety related system, or external risk reduction facilities. lEC 61511 ANSI/ISA-84.00.01-2004 flEC 61511 Mod) SIF is imolemented solely by SIS... 

Decommissioning To ensure proper review, sector organization, and ensure Safety Instrumented Function (SIF) remain appropriate. 18 Apply appropriate safety lifecycle phase during project execution... 

Confirm that a hazard and risk analysis has been done to determine qualitatively or quantitatively the level of risk reduction needed for each Safety Instrumented Function (SIF) in the SIS. 

Perhaps, the most significant new term is Safety Instrumented Function (SIF). In ANSI/ISA-84.01-1996, there was very little differentiation between an SIS and SIF. ANSI/ISA-84.00.01-2004-1 spells out the difference between the SIF (e.g., hardware software used to mitigate a specific process risk) and the SIS (i.e., the hardware and software used to implement multiple SIFs). For example, consider a process furnace. If the main fuel gas pressure to the burner is too high, the flame may blow out, allowing uncombusted gases to be introduced into the furnace with the potential for a fire within the furnace. To prevent this hazard, an SIF is implemented in which block valves are used to isolate the main fuel gas from the process furnace when high fuel gas pressure is detected. These same main fuel gas valves may also be closed in response to low pilot gas pressure (i.e., a different process hazard). The SIS is the implementation of these two SIFs in the same logic solver. 

When safety functions are allocated to the safety instrumented system layer, they are known as Safety Instrumented Functions (SIF). The differences and/or relationships between safety functions, safety instrumented functions, safety instrumented systems, interlocks, and permissives are important. Annex H provides a discussion including important historical references to assist in the understanding of the new terms. 

Safety instrumented functions (SIF) are assigned a safety integrity level (SIL) and a mode of operation (continuous or demand) during the H RA. These are recent requirements and application guidance is limited at best. 

ISA-TR84.00.03, Guidance for Testing of Process Sector Safety Instrumented Functions (SIF) Implemented as or Within Safety Instrumented Systems (SIS), International Society of Automation (ISA), www.isa.orq. ISBN 978 1 55617 801-6. 

SIF stands for safety instrumented function. SIF consists of sensors, logic solver, and final control element combination. SIF takes the system or process in to safe zone in the event of hazardous situation/event, which is determined by predefined conditions for the process (see Clause 8.1 also, for definition as per various standards). 

It is interesting to note the heading of the chapter It is named like this to indicate that safety instrumented functions (SIFs—in plural) constitute a safety instrumented system (SIS). From the discussions in previous chapters, readers have come across varieties of definitions of accidents, hazards, and risks from different perspectives. Also there were a few things common such as the accidents are not always negative, and there are always aim to avoid accidents so that there is not loss to the system, personnel, and environment. At the back of the mind, we always try to develop and incorporate some things to reduce risks and to maintain work safety. Therefore, safety work involves some activities, measures, and techniques, which can contribute or help to reductions in losses in different forms, and human injury or fatality. There are quite a good number of elements involved in work safety these include, but are not limited to the following ... 

According to lEC 61511, safety instrumented control function stands for safety instrumented function with a specifled SIL operating in continuous mode which is necessary to prevent a hazardous condition from arising and/or to mitigate its consequences. Safety instrumented control system is instrumented system used to implement one or more safety instrumented control functions. Also safety instrumented system (SIS) is instrumented system used to implement one or more safety instrumented functions (SIF). An SIS is composed of any combination of sensor(s), logic solvers, and final element(s). 

Safety instrumented function SIF stands for safety instmmented function. A set of control equipment intended to reduce the risk due to a specific hazard. SIF is designed to control, prevent, or mitigate a specific hazard and takes the process to... 

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