A Devil's Advocate on SIL 4

This presentation discusses Safety Integrity Level (SIL) 4, which is the most dependable level of the European functional safety standards based on the IEC 61508 standard. SIL 4 is the highest level of risk reduction that can be obtained through a safety instrumented system. However, in the process industry, this is not a realistic level, and currently there are few, if any, products/systems that support it. SIL 4 systems are typically so complex and costly that they are not economically beneficial to implement. Additionally, if a process includes so much risk that a SIL 4 system is required to bring it to a safe state, then fundamentally there is a problem in the process design, which needs to be addressed by a process change or other non-instrumented method.