Safety integrity level methods

The required safety integrity level of the instrumented function shall be derived by taking into account the required risk reduction that is to be provided by that function. For those SILs, the target PFDj,yg on demand and the target frequencies of dangerous failure are hsted in Table 3.8 [ANSI/ISA-84.00.01(2004) Part 3] for each SIF. Several risk analysis methods ranging from qualitative to fully quantitative can be deployed based on the severity and complexity of the scope, as listed in Table 3.9. 

Marszal, E. M. and E. W. Scharpf. Safety Integrity Level Selection Systematic Methods Including Layer of Protection Analysis. ISA, 2003. 

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. 

CEI 2002 Functional safety of electrical/ electronic/ programmable electronic scfety related systems lEC 61508 Part 5 Examples of methods for the determination of safety integrity levels annex B pp. 31 35 (Italian edition authorized by CENELEC) Comitato Elettrotecnico Ttaliano. Milano. 

The risk reduction strategy is outlined in ISO 12100 and IS014121 and a number of different methods for determining safety integrity level requirements are shown in these standards and in the already mentioned ISO 13849, lEC 62061 and lEC 61508 standards, they are all shown as informative annex in these standards. 

The preliminary risk assessment is made by a risk graph qualitative method described in lEC 61508-5 Annex E according Figure E.l (Figure 3) and Table E.l. This method has been used extensively within the machinery sector, see ISO 14121-2 and Annex A of ISO 13849-1, and enables the safety integrity level to be determined from knowledge of risk factors associated with the hoist machinery and it control system. 

Methods of Determining Safety Integrity Level (SIL) Requirements - Pros and Cons... 

Examples of methods for the determination of safety integrity levels Guidelines on the appUcation of parts 2 and 3... 

From earlier discussions we can gather knowledge about various methods for hazard analysis systems, and implication of these methods from international standards. Also details about safety instrumentation system (SIS) and safety integrity level (SIL) have been covered. From previous discussions it is quite clear that the essence of a safety system can be described by Ref. [2] ... 

Part 3 gives more detailed guidance on targeting the Safety Integrity Levels and has a number of Appendixes covering both quantitative and qualitative methods. 

In Seetion 2.1.2 the LOPA (Levels of Proteetion Analysis) method was described. In this example, a Safety Integrity Level (SIL) assessment is conducted for a hydro-electric dam plant for the requirements of a Flood Gate Control System (FGCS). The required SIL is... 

Marszal EM, Scharph EW. Safety integrity level selection systematic methods including layer of protection analysis. ISA 2002. 

SIL-based approach uses obtained time-dependent PFH functions for a monosystem and for a system with applied redundancy architecture to calculate the corresponded safety integrity level at any period of time. This approach can be implemented in an intelligent system that will periodically recalculate PFH value of a system and related SIL. An intelligent system will notify an operator about a close border between SILs. In addition, based on introduced method, it can be suggested two modes of maintenance for a braking system of moving walks full and economical. In a full maintenance mode the system has to be completely recovered till the initial value of reliability. In an economical mode SIL will be kept on the required level, but the system will be recovered partially by means of replacement/repair of the elements with the worst reliability characteristics. Time of periodical maintenance t is different in these two modes. In case of full mode is constant. In case of economical mode, this time is reduced every maintenance period. 

The purpose of the HARA is to find all foreseeable hazards of an item by applying a systematic search method, and to rate the hazards on a scale of Automotive Safety Integrity Levels (ASILs) from A (lowest) to D (highest), or to rate them as not specifically safety-critical (QM = normal Quality Management is considered sufficient to cope with them). 

Since the 1970s, TOTAL has developed and implemented a very poweifiil range of methods and tools based on traditional approaches. They ate nsed on a daily basis to perform onr lehability analysis. However, in recent years international standards such as the lEC 61508 [lEC 00] and lEC 61511 [lEC 03] have proposed a new concept of safety integrity level (SIL) required to achieve a level of acceptable risk. They are progressively imposed on the design of SlSs and as their scope naturally concern HIPS, their implementation carmot be ignored. Much work was necessary to establish hnks between these two approaches and identify their similarities and differences. 

Relevance Chapter 2. The quantitative method for determining target safety integrity levels ... 

An example of a risk situation is used in this exercise. We are asked to use layers of protection analysis to arrive at a risk reduction model for the situation. The quantitative analysis method is then used to define the safety integrity level (SIL) required for the safety instrumented system. This model can also be used to check the practical application of qualitative methods for determining SILs. 

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