Whereas a sil is derived from an assessment of risk, it is not a measure of risk. Sc 65a functional safety of electricalelectronicprogrammable electronic safetyrelated systems part 1. It defines the requirements of safety systems in plant safety. These methods determine which safety integrity level sil needs to be. The sil table for demand mode is shown in figure 4. Audit of the return data and field failure experience feedback system for sil 3. Safety instrumented systems sis, safety integrity levels sil. The functional safety standards iec 61508, iec 61511 ansiisa 84. During the 1980s computer based systems generically referred to as. For railway applications, the en 501265012650129 iec 622786227962425 standards use the same type of approach. Iec 61511 cfse by french notified body ineris, iec 61508 experience. Sil performance of safety instrumented systems safetec. This application note is intended to provide a brief introduction to the iec 61508 standard, and to illustrate how it is applied.
Iec 61511 safety instrumented systems for process industry iec 61511 has been developed as a process sector implementation of the iec 61508. The standard iec61508 states the requirements for safety systems to. Introduction this manual is a practical aid for the analysis, installation and maintenance of safety instrumented systems and associated components and will hopefully serve as a guide for understanding and implementing procedures into practical applications. This standard should be read once part one and two are fully understood. Thus, iec 61508 is not a system development standard but a standard for.
The iec 61511 standard requires manufacturers and suppliers of devices for safety instrumented systems to conform to the iec 61508 standard. The safety lifecycle forms the central framework which links together most of the concepts in this standard, and evaluates process risks and sis performance requirements availability and risk reduction. The generic safety standard en iec 61508 is the main standard for the functional safety of control systems. Tm3safl5rg modicon tm3 safety module 2 function, cat 3. Hence the manufacturer of the logic solver should follow the iec 61508 standard. Iec 61508 3 pdf iec is an international standard published by the international electrotechnical commission consisting of methods on how to apply, design, deploy and. Sil methodology a methodology for sil verification in. Iec iec iec electronic functional safety systems package. The logic solver option of the sis sbould be suitable for implementing the sif requiring the highest sil. In safety circles, the draft standard iec 1508, published in 1995 by the. A full iec 61508 safety case was created using the exida safety case tool, which also was used as the primary audit tool. An sis is a distinct, reliable system used to safeguard a process to prevent a catastrophic release of toxic.