What Is Fire Alarm Cause and Effect? (And Why It Matters)
By the DC Fire & Security engineering team — installing and maintaining fire and security systems since 2010. Updated June 2026.
Quick answer
Cause and effect is the programmed logic linking fire alarm inputs to building responses: which detector activations release which door holders, open which smoke vents, ground the lifts, shut down which plant, and sound which alarms in which order. It's documented in a cause-and-effect matrix, programmed into the panel, and must be tested end-to-end at commissioning and service.
What does cause and effect control?
- Magnetic door holders release so fire doors close on the alarm
- AOVs and smoke control: corridor detection opens vents to clear escape routes
- Lifts return to ground and park open (so no one rides into a fire floor)
- Access control unlocks escape-route doors
- HVAC and plant shutdowns stop air systems spreading smoke
- Phased or staged evacuation: alert tones on some floors, evacuate on others, in sequence
- Kitchen suppression interlocks, roller shutters, gas solenoid shut-off
- ARC signalling: what gets transmitted, and when
Why it's where fire systems go wrong
Devices rarely fail individually — integrations fail silently. The AOV contractor changed a relay; the lift was modernised; access control was replaced and nobody re-linked the fire interface. Each system passes its own service, while the chain between them is broken. That's why BS 5839-1 commissioning requires proving the documented matrix end to end — actually triggering detection and watching doors close, vents open and lifts behave — and why a current cause-and-effect document should live with the zone plan and log book.
Who needs a documented matrix?
Any building where the alarm does more than make noise: schools (door holders, kitchen interlocks), care homes (phased evacuation, door management), blocks of flats (AOVs), warehouses (shutters, plant), multi-tenant offices (phasing, lifts, BMS). For a small shop with sounders only, cause and effect is trivially simple — but the moment interfaces exist, an undocumented system is unverifiable. We produce or reverse-engineer matrices during takeovers; it's often the first time the building has one.
Frequently Asked Questions
Is a cause-and-effect document required by BS 5839?
How often should cause and effect be tested?
What is phased evacuation?
Our alarm sounds but doors don't release — who fixes that?
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