The Safety Integrity Level (SIL) is a measure of performance required for a safety instrumented function or system (SIF or SIS).
F&G loops
F&G (Fire & Gas) systems are typically not SIL-rated because they are designed for asset protection, not life safety, which is what the SIL rating is primarily concerned with.
F&G systems aim to minimize damage to equipment and minimize downtime in the event of a fire or gas release, but they are not necessarily the primary means of ensuring human safety in these events.
While F&G systems can contribute to overall site safety, the primary responsibility of human safety lies with the SIS, which is SIL-rated.