Fire Alarm Cause and Effect Matrix: How to Write and Verify One
The cause and effect matrix (sometimes called a cause-and-effect schedule or C&E matrix) is the document that defines exactly what the fire alarm system should do when each detection zone activates. It's the bridge between the system design intent and the panel configuration.
On most commercial projects, the cause and effect matrix is produced by the system designer or specifying engineer, handed to the installer, and should be verified as part of commissioning. In practice, it's often produced after the fact — written to describe what the system does rather than what it should do — which is where problems start.
Why It Matters
A fire alarm system does more than sound bells. On any system above a simple single-zone installation, activation of one zone will typically:
- Activate specific sounder circuits or sounder zones
- Release door holders or magnetic door locks
- Close fire dampers via interface modules
- Activate a pre-alarm or two-stage evacuation signal
- Trigger an output to a building management system (BMS)
- Send a signal to an alarm receiving centre (ARC)
- Potentially activate fire suppression (on specialist systems)
Without a documented cause and effect matrix, there is no clear record of what was intended, and no structured way to verify that the installed system actually does it. Engineers doing modifications years later have no reference point. If something goes wrong — a door fails to close, a suppression system doesn't activate — there is no document to audit against.
BS 5839-1:2017 Clause 12.2 requires that the system design documentation includes details of the system operation, including which zones trigger which outputs. The cause and effect matrix is the practical implementation of this requirement.
Structure of a Cause and Effect Matrix
The matrix has zones (or individual devices on fully-addressable systems) as rows, and outputs as columns. Each cell indicates whether that input causes that output — and in what way.
Typical outputs to include
Sounder outputs / sounder zones — which sounder circuits are activated, and at what stage (alert tone vs. evacuation tone for two-stage systems)
Door control outputs — door holders, electromagnetic locks, automatic door closers that release on alarm
Damper control outputs — fire and/or smoke damper interface modules
Lift control — lift recall outputs (recall to ground floor or designated floor on alarm)
Suppression interfaces — pre-action sounder delay, suppression abort, suppression release (for gaseous or sprinkler pre-action systems)
BMS interface — general alarm output, zone-by-zone outputs to BMS
Ancillary outputs — extract fan shutdown, HVAC isolation, stairwell pressurisation
ARC transmission — whether the zone triggers a confirmed alarm, a pre-alarm, or a non-transmit event
Example Matrix Format
| Zone | Zone label | Zone 01 sounder | Zone 02 sounder | All sounders | Door holders | BMS general alarm | ARC transmission | |---|---|---|---|---|---|---|---| | Zone 01 | Ground floor offices | ✓ | ✓ | ✓ | ✓ | ✓ | Confirmed alarm | | Zone 02 | Ground floor plant | ✓ | ✓ | ✓ | ✓ | ✓ | Confirmed alarm | | Zone 03 | Server room | ✓ | — | ✓ | ✓ | ✓ | Pre-alarm (first device), Confirmed alarm (second device) | | Zone 04 | Car park level 1 | — | — | ✓ | ✓ | ✓ | Confirmed alarm | | Zone 05 | Car park level 2 | — | — | ✓ | ✓ | ✓ | Confirmed alarm |
For two-stage evacuation systems, add columns for "Alert tone" and "Evacuation tone" separately, and note which zones trigger which stage.
For coincidence systems (two-detector confirmation required before alarm), note this in the zone row.
Verification
The cause and effect matrix should be verified during commissioning by testing each zone and confirming that every stated output activates correctly. This is often abbreviated in practice — but cutting it short is where expensive call-backs come from.
Commissioning verification checklist
For each zone:
- Activate the zone using the panel's test mode or by activating a device
- Confirm each stated sounder zone activates with the correct tone
- Confirm door holders release
- Confirm damper interfaces activate (where fitted) — this requires coordination with the mechanical contractor
- Confirm BMS output activates (where fitted) — requires a BMS engineer to confirm receipt
- Confirm ARC transmission occurs correctly — ring the ARC to confirm they received the right signal type from the right zone
- Confirm that zones marked as non-transmit do not generate a false ARC transmission
- Reset the zone and confirm all outputs reset
Document the test result against each zone in the commissioning certificate.
Common Gaps
Sounder zones not clearly defined. The matrix says "all sounders" but the building has sounder zones — a staged evacuation scheme where only some zones sound in the first stage. Without documenting exactly which sounder circuits activate at which stage, it's impossible to verify this on site.
Door holders not included. Door holders are frequently installed by a different contractor (the joinery or mechanical package) and their control wiring tied back to the fire alarm panel by an electrical sub-contractor. The fire alarm engineer may never have seen a complete schedule of which door holders are on which output. If the fire alarm C&E matrix doesn't list them, they may not be tested during commissioning.
Suppression interface not documented. On systems with gaseous suppression, the sequence is critical: pre-alarm sounder activates, abort delay starts, if not aborted the suppression releases. Each step has specific timing requirements. If the C&E matrix only says "suppression activate" with no timing detail, the installed configuration may not match the design.
Two-stage systems without clear trigger conditions. Two-stage evacuation (alert tone first, evacuation on second activation or after a time delay) requires the C&E to specify: what triggers the escalation from alert to evacuation? Is it a second device in the same zone? A device in any zone? After a fixed time? A staff operation at the keypad? All of these need to be documented.
Manual override not addressed. On zoned systems, a responsible person or fire warden may need to manually trigger a full evacuation. The C&E should note whether there is a manual override output and what it drives.
Updating the Matrix After Modifications
Every modification to the system — new zones, changed output configuration, new interfaces — requires the C&E matrix to be updated. The modification commissioning certificate should reference the updated C&E revision.
On older systems where no original C&E matrix exists, writing one based on the current as-installed configuration is a valuable service to the building owner. It forms part of bringing the documentation up to the standard required under the Regulatory Reform (Fire Safety) Order 2005.
Software Tools
Some fire alarm panel manufacturers provide configuration software that can export a cause-and-effect view of the programmed panel (Notifier, Gent/Honeywell, and Advanced MxPro 5 all have this capability to varying degrees). However, this shows what is programmed, not necessarily what was intended — which is why having a human-written C&E matrix as a reference document remains important.
For complex systems with BMS integration, the BMS contractor will typically require a fire alarm output schedule (listing every relay output, its label, and the conditions under which it activates) before they can integrate. The C&E matrix, properly formatted, serves as this document.