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IEC 61508 is an international standard published by the International Electrotechnical Commission of rules applied in industry. It is titled ''Functional Safety of Electrical/Electronic/Programmable Electronic Safety-related Systems'' (E/E/PE, or E/E/PES). IEC 61508 is intended to be a basic functional safety standard applicable to all kinds of industry. It defines functional safety as: “part of the overall safety relating to the EUC (Equipment Under Control) and the EUC control system which depends on the correct functioning of the E/E/PE safety-related systems, other technology safety-related systems and external risk reduction facilities.” The standard covers the complete safety life cycle, and may need interpretation to develop sector specific standards. It has its origins in the process control industry. The safety life cycle has 16 phases which roughly can be divided into three groups as follows: # Phases 1-5 address analysis # Phases 6-13 address realisation # Phases 14-16 address operation. All phases are concerned with the safety function of the system. The standard has seven parts: * Parts 1-3 contain the requirements of the standard (normative) * Parts 4-7 are guidelines and examples for development and thus informative. Central to the standard are the concepts of risk and safety function. The risk is a function of frequency (or likelihood) of the hazardous event and the event consequence severity. The risk is reduced to a tolerable level by applying safety functions which may consist of E/E/PES and/or other technologies. While other technologies may be employed in reducing the risk, only those safety functions relying on E/E/PES are covered by the detailed requirements of IEC 61508. IEC 61508 has the following views on risks: * Zero risk can never be reached * Safety must be considered from the beginning * Non-tolerable risks must be reduced (ALARP) ==Hazard and Risk Analysis== The standard requires that hazard and risk assessment should be carried out: 'The EUC (equipment under control) risk shall be evaluated, or estimated, for each determined hazardous event'. The standard advises that 'Either qualitative or quantitative hazard and risk analysis techniques may be used' and offers guidance on a number of approaches. One of these, for the qualitative analysis of hazards, is a framework based on 6 categories of likelihood of occurrence and 4 of consequence. Categories of likelihood of occurrence Consequence categories These are typically combined into a risk class matrix Where: * Class I: Unacceptable in any circumstance; * Class II: Undesirable: tolerable only if risk reduction is impracticable or if the costs are grossly disproportionate to the improvement gained; * Class III: Tolerable if the cost of risk reduction would exceed the improvement; * Class IV: Acceptable as it stands, though it may need to be monitored. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「IEC 61508」の詳細全文を読む スポンサード リンク
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