SIL Verification

SIL Verification

Safety Integrated Systems & Safety Life-cycle Management

Risk Management Professionals provides assistance to facilities throughout the safety life-cycle associated with managing Safety Instrumented Systems (SIS) in accordance with the following standards:

  • IEC 61508 – Functional Safety of Electrical/Electronic/Programmable Electronic, Safety-related Systems
  • IEC 61511 – Functional Safety – Safety Instrumented Systems for the Process Industry Sector
  • ANSI/ISA 84.00.01-2004 (IEC61511-Mod) – Application of Safety Instrumented Systems (SIS) for Process Industries

In addition to the Hazard and Operability (HAZOP) Studies and Layer of Protection Analyses (LOPA) that provide direct input into the Risk Assessment phase of the safety life-cycle and definition of Safety Integrity Level (SIL) targets, Risk Management Professionals also offers SIL Verification services. Risk Management Professionals recognizes that higher SIL ratings require that the function be that much more reliable and available at all times (see table below). The SIL Verification calculations demonstrate that the design of the Safety Instrumented Function (SIF) meets the specified integrity requirement.

The SIL Verification calculations are performed using fault tree analysis or Markov modeling in order to calculate the following:

  • Mean Time to Fail Spuriously (MTTFS) – False Trip Rate
  • Probability of Failure on Demand (PFD)
  • Risk Reduction Factor (1/PFD)
  • Safe Failure Fraction (SFF)


The SIL Verification can be an iterative process, and if the required SIL cannot be achieved with the initial design, some design options are:

  • Increase proof testing frequency
  • Add redundancy (i.e., initiating device, control, system, final element)
  • Install “smarter” device (i.e., HART smart transmitter or transmitter vs. switch or relay, smart control valve with diagnostics and feedback, and position indication vs. basic control valve)
  • Add protection layers (independent), including the following: BPCS (control system), alarms and operator response, physical devices (PSV’s, dikes, flares, deluges, etc.) and other human mitigation (emergency response)