A Safety Integrity Level is determined via a procedure called Risk/Process Hazard Analysis (PHA).
It identifies all the hazards of a process and estimates the risks inherently involved and determines if that risk is tolerable/acceptable.
This safety procedure must verify that each instrument utilized in the system (SIS) as well as each instrument’s parts such as sensors, logic solvers and integral components will work safely to achieve the Safety Instrumented Functions (SIF) in compliance with the confines required by SIL.
IEC 61508 is the international standard used by safety equipment manufacturers to verify and document that their products are suitable for use in SIL rated systems.
IEC 61508 concern "Functional safety of electrical, electronic, programmable electronic safety-related systems...."
This calculation has never been done for MV circuit breakers and contactors and our product are not certified (SIL2,3…)
SIL notion applies to a system performed a function not for a product than a circuit breaker.
If the circuit breaker is a component of a chain of safety function, a study could be done by a project safety leader from REC (study not free).