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IEC 61508 & 61511
IEC 61511 has been developed as a Process Sector implementation of the international standard IEC 61508: “Functional safety of electrical / electronic / programmable electronic safety-related systems”.
IEC 61508 is a risk based standard for instrumented safety systems. It is erroneously thought that these standards are an electrical/control engineering issue alone. The standards require that a 'Functional Safety Assessment' (FSA) be carried out and the determination of an appropriate Safety Integrity Level (SIL) for the system. Fundamental to the FSA is the concept of Risk Assessment and techniques that have been in use in high hazard industry for many years.
The stages of a suitable FSA are:
- Setting a tolerable 'risk criteria'
- Risk assessment to determine the risk associated with failure of the equipment being controlled
- Assessing the risk reduction required to meet the 'risk criteria'.
- Setting the safety Integrity level (SIL) to achieve this risk reduction.