A cause and effect matrix maps every initiating cause (rows) to every action (columns). It is the most compact logic specification for shutdown systems and the basis for the logic test.
Layout
- Cause rows: tag, description, trip setpoint with units, voting (2oo3), and often the SIF number and SIL.
- Effect columns: tag, action (close, open, stop, start), and the final element's fail-safe state.
- Cells: X for "acts", with additional marks for time delays (D), latching or permissive conditions; define every mark in a legend.
Details often missing
- Time delays and their values.
- Whether the cause latches until manual reset.
- Overrides and which causes they inhibit.
- Alarms, first-out groups and annunciation.
- Notes for actions that depend on other conditions ("only if pump running").
Using it for testing
The logic test walks every row: activate the cause, check every effect in the row and that no other effect acts. A matrix with clear tags turns directly into the test record.
In First Out AI
Cause & effect tab: "Build from SIFs" creates rows from sensor groups and columns from final elements, with X at each SIF's actions; then add manual trips, alarms and delays. X / D cycles by clicking. Export to Excel.
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.