 |
 |
 |
|
 |
|
 |
IEC 61508 & 61511 - Safety Integrity Level (SIL)
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. This is sometimes called a "SIL Assessment". 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.