Provides information on the underlying concepts of risk, the relationship of risk to safety integrity, the determination of tolerable risk and a number of different methods that enable the safety integrity levels for the safety instru-mented functions to be determined. Experts in IEC Subcommittee 65A (System aspects) explain that this sector specific standard of IEC 61508 addresses the functional safety of safety instrumented systems (SIS) for the process sector. The purpose is to ensure that the safety integrity of safety instrumented systems is adequate taking into account the associated hazards &risks. It falls under the generic IEC 61508 standard and thus required adjustment to the requirements found in IEC 61508 (generic in content since it covers all sectors) to cover process sector needs. The standard will mainly be used by integrators and operators of chemical, petro-chemical and gas process plants. It also has applications in non-nuclear power generation. It will also be used as a benchmark by those responsible for assessing the adequacy of such plants including certification bodies and regulators. Part three is informative and provides outlines of several global approaches to hazard and risk analysis found in the process sector. It is not intended to define a single method as acceptable, but to list some of the acceptable methods in use today. In this way, it serves to enhance communication and understanding amongst global process sector safety decision-makers. IEC 61511-1 (2003-01) Ed. 1.0: Functional safety - Safety instrumented systems for the process industry sector - Part 1: Framework, definitions, system, hardware and software requirements was published in January 2003 IEC 61511-2 Ed. 1.0: Functional safety instrumented systems for the process industry - Part 2: Guidelines in the application of Part 1 is scheduled to be published in June 2003.