IEC61508 is a set of international norms for the functional safety of electrical/electronic/programmable electronic safety-related systems.
It introduces a deterministic approach to evaluate the robustness of a given Equipment Under Control or EUC. It also rules the documentation to be delivered with the safety system concerning the implementation and the validation flow of both HW and SW.

The table summarizes which Safety Integrity Level (SIL) can be claimed by a system based on its Safe Failure Fraction (SFF): the higher the HFT, the higher the availability. Annexes of IEC61508 deliver precise guidelines in terms of faults and failure modes to be considered for each system component (CPU, bus, internal/external communications, memories and so on) and include the recommended diagnostic techniques, graded according to their effectiveness with respect to the target SIL.

Notified bodies such as TÜV-SÜD assess the compliance of systems to IEC61508.

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• Automotive systems mainly concern the white boxes.
• SIL 2 is the minimum level: an example of systems requiring SIL2 is the Anti-Braking Systems or abs.
• SIL3 is the requirement for active safety systems such x-by-wire, active brake or stability control.
• SIL4 isn’t considered achievable for single chip solutions and in general it is not considered necessary
for automotive systems.