Safety integrity level SIL

This is a discrete level (one of four) for specifying the safety integrity requirements of the safety-instrumented functions to be allocated to the safety-instrumented systems. SIL 4 has the highest level of safety integrity, and SIL 1 has the lowest. 

The target failure measures for the SIL are specified in Table 4.18 and Table 4.19. 

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Provide appropriate safety integrity level (SIL) level. 

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 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. 

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 )... 

The defining of the term Safety Integrity Level (SIL), a number from 1 to 4 representing the risk reduction required for the safe operation of a particular functional component. SILs are essentially an analogue for the extent of rigour required during the development process. 

The response to emergency situations is often controlled by the Safety Instrumentation System and its associated Safety Integrity Levels (SILs). 

Safety instrumented systems (SISs), with their associated Safety Integrity Levels (SILs), play an increasingly important part in assuring the safety of process plants. Referring to the standard example once more, a high-level interlock can be installed on LRC-101 such that when the level... 

Addition of layer of protection analysis (LOPA) in PHA to determine the safety integrity level (SIL) gap for safety instrumented systems (SIS)... 

Safety integrity level (SIL) Target average probability of failure on demand (PFDa, g) Target risk reduction Factor (RRF) Target frequency of dangerous failures to perform the SIF (per hour)... 

The consequence severity and the likelihood frequencies determine risk. In some cases, the risk of a hazard is within tolerable levels, and no risk reduction is needed. For these cases, no SIS is required. In other cases, risk reduction is required, and the quantity of risk reduction is specified by an order-of-magnitude level called the safety integrity level (SIL) as indicated in Figure 1-7. 

TR84.00.02-2002, Technical Report, Safety Instrumented System (SIS) - Safety Integrity Level (SIL) Evaluation Techniques, NC Research Triangle Park, ISA, 2002. 

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 ... 

Note that the example SIL levels provided in this chapter are only examples. They are not to be assumed recommended levels of protection. The selection of an appropriate Safety Integrity Level (SIL) is site-specific and the analysis requires selecting criteria for tolerable risk, and evaluating process conditions, specific chemicals, equipment design-limits, control schemes, process conditions, and unique hazards. Experts in process engineering, instrumentation, operations, and process safety should imdertake SIL selection. 

During the 1990s the concept of Safety Integrity Levels (SIL) was developed [1]. It serves to assess safety-related systems and concerns aU components and subsystems required to realize safety functions from the sensor to the final element. Apart from that it applies to application software, which was developed for systems with limited variability language (no branching) or programmable logic controllers (PLC). 

A basic concept of functional safety analysis related to a process of determining required safety integrity level (SIL) is described as below ... 

The risk graph method, proposed in lEC 61508 and lEC 61511, is useful in the process of determination of required risk reduction level associated with safety integrity level (SIL) of safety instrumented function (SIS). However, this normative document presents only an illustrative example which shows how the risk graph method can be used. 

Signoret, J-P. Dutuit, Y. Rauzy, A. 2007. High Integrity Protection Systems (TUPS) Methods and tools for efficient Safety Integrity Levels (SIL) analysis and calculations. 

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