IEC 61508
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IEC 61508 is titled "Functional safety of electrical/electronic/programmable electronic safety-related systems".
The international standard IEC 61508 “Functional safety of electrical / electronic / programmable electronic safety-related systems (E/E/PES)” is intended to be a basic functional safety standard applicable to all kinds of industry. IEC 61508 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 sector.
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 and 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), while 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 severity and probability. The risk can be reduced to a level that is tolerable by applying a safety function that consists of E/E/PES systems and other technologies. Only the E/E/PES risk reduction systems are considered in IEC 61508. The necessary risk reduction is the risk when no safety functions are applied minus the tolerable risk. The risk should be reduced to a level that is As Low As Reasonably Practicable (ALARP).
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)
