Can I credit the control system alarm if the control system caused the event? No. A layer must be independent of the initiating cause.
How many control system layers can I credit in one scenario? Most company rules allow one at most, and only if it is independent of the cause.
The relief valve exists. Why should it not get credit? Only if it is sized for this scenario's relief case and discharges to a safe place. A valve sized for fire may be far too small for a runaway or gas blow-by.
What is the difference between an enabling condition and an IPL? An enabling condition describes when the hazard can occur (the plant state); an IPL is something that acts to stop the consequence.
The result is SIL 3. What now? Challenge the scenario, look for independent layers and inherent design changes first. See "When the target is SIL 3 or beyond".
The RRF is 9.5. Is that "no SIL"? Formally below SIL 1, but close to the boundary. Look at the uncertainty in the IEF and credits; many companies then still implement a SIL 1 function or a reliable alarm.
Should every HAZOP row go to LOPA? No. Rows with serious consequences or where a SIF or alarm is relied on should; minor ones can be closed in the HAZOP.
In First Out AI, what does a layer with value 1 mean? It is listed but not credited, so reviewers see that it was considered.
Written for First Out AI as engineering guidance. It supports engineering work and does not replace it; check every value against your standards, certificates and company rules with a competent functional safety engineer.