AiVibeSafety Integrity Level (SIL)
A Safety Integrity Level is a discrete level, from SIL 1 to SIL 4 in IEC 61508, that specifies how much risk reduction a safety function must provide, with SIL 4 representing the highest integrity requirement.
A SIL is assigned to a safety function, not to an individual device, after hazard and risk analysis determines the risk reduction required. Methods include risk graphs, layer of protection analysis (LOPA) and risk matrices. For low-demand functions, each SIL corresponds to a range of average probability of dangerous failure on demand (PFDavg); for high-demand or continuous functions, it corresponds to a range of probability of dangerous failure per hour (PFH).
SILs are used throughout the process industries under IEC 61511, where safety instrumented functions protect against events such as overpressure or overfilling, and in machinery under IEC 62061, which uses SIL 1 to SIL 3. Device manufacturers state the maximum SIL for which a component is suitable, such as SIL 2 or SIL 3 capability, in a safety manual or certificate.
Achieving a SIL requires meeting three kinds of requirement: the quantitative failure measure, architectural constraints such as hardware fault tolerance, and systematic capability through appropriate development and management processes. A SIL-capable component does not by itself make a function meet that SIL; the whole loop of sensor, logic solver and final element must be assessed. Proof testing at defined intervals maintains the claimed integrity in operation.
Key points
- Four levels in IEC 61508, SIL 1 to SIL 4, with SIL 4 the most demanding
- Assigned to a safety function, not to an individual device
- Low-demand targets use PFDavg; high-demand targets use PFH
- Requires quantitative, architectural and systematic compliance
- Proof testing maintains the claimed integrity in service
Where AiVibe comes in
AiVibe designs and manufactures the AiAmbA AI Factory, whose edge devices and AI agents let people talk to PLC, CNC and robot controllers in plain language. Agents only propose changes, a trained operator confirms each one, and the AI Factory never replaces a machine's control or safety systems.