SIL

Safety Integrity Level Analysis

  • Standard IEC 61508 “Functional Safety of Electrical/Electronic/Programmable Electronic Safety-related Systems”
  • Standard IEC 61511 “Safety instrumented systems for the process industry sector”

The Safety Integrity Level (SIL) is a discrete level number (one out of four) allocated to the a system composed of servers, logic servers, and final control elements (Safety Instrumented System – SIS) for the purpose of taking the process to a safe state when predetermined conditions are violated A SIS may implement one or more Safety Instrumented Functions (SIFs).

SIL Analysis can be split in two parts SIL Allocation in design phase and SIL Verification in the completion phase.

An important concept in the standard is that of the Safety Instrumented Function (SIF), which is a function to be implemented by a Safety Instrumented System (SIS) composed mainly by sensors (e.g. transmitters), logic solvers (E/E/PE) and final elements (e.g. solenoids), which is intended to achieve or maintain a safe state for the process, with respect to a specific hazardous event.