SIL
Right-size your safety instrumented functions — not over-engineered, not under-protected.
Safety Integrity Level determination and verification for instrumented protection functions per IEC 61511.
Request a ConsultationWhat is SIL?
Safety Integrity Level (SIL) Assessment is the process of determining the required risk reduction for a Safety Instrumented Function (SIF) and verifying that the designed instrumented system achieves that risk reduction, in accordance with IEC 61508/61511. SIL is expressed on a scale of 1 to 4, with SIL 4 representing the highest level of risk reduction.
Why It Matters
- ●Prevents both under-protection (unacceptable residual risk) and costly over-engineering
- ●Provides auditable, quantitative justification for instrumented protection layers identified in LOPA
- ●Required for compliance with IEC 61511 lifecycle management across owner-operators
- ●Forms the basis for proof-test intervals and SIF maintenance regimes
Our Methodology
- 1SIL determination workshop using LOPA or risk graph method per identified hazard scenario
- 2Safety Requirement Specification (SRS) development for each SIF
- 3SIL verification calculation — PFDavg, architecture constraints, common cause factors
- 4Independence and diversity review against other protection layers
- 5Proof test interval and maintenance recommendation
Deliverables
Industries We Serve
FAQ
SIL Frequently Asked Questions
What is SIL in process safety?
SIL (Safety Integrity Level) is a measure, on a scale of 1-4, of the probability that a safety instrumented function will perform its intended safety function under all stated conditions, as defined in IEC 61508/61511.
How is SIL determined?
SIL is typically determined using either a risk graph/matrix method or, more rigorously, through Layer of Protection Analysis (LOPA), which quantifies the required risk reduction the safety instrumented function must deliver.
What is the difference between SIL determination and SIL verification?
SIL determination establishes the target/required SIL for a safety function based on risk. SIL verification is the subsequent engineering calculation confirming that the as-designed instrumented system (sensor, logic solver, final element) actually achieves that target SIL.