# Fire Alarm Interfaces ## Overview Interfaces (also called I/O units or modules) provide the link between the fire alarm system and external equipment. They are essential for implementing cause & effect strategies, such as releasing doors, shutting down ventilation, or initiating smoke control. BS 5839-1:2025 (Clause 8) recognises that fire alarm systems can actuate other fire protection systems or safety facilities for **life safety, property protection, or both**, provided this interconnection does not prejudice system reliability. --- ## Types of Interfaces | Type | Function | Typical Examples | | ------------------------------ | ---------------------------------------------------------------- | -------------------------------------------------------------- | | **Input Modules** | Monitor a signal or contact from external equipment. | Sprinkler flow switch, plant shutdown feedback, door contact. | | **Output Modules** | Provide a relay or voltage output to trigger external equipment. | Releasing maglocks, fan start, damper closure. | | **I/O Modules** | Combined input and output in a single device. | Firefighter’s lift control, smoke vent with position feedback. | | **Sounder/Beacon Controllers** | Addressable control of notification appliances. | Localised evacuation, phased evacuation. | | **Protocol Gateways** | Convert fire panel signals into third-party protocols. | Modbus, BACnet, ONVIF, BMS integration. | --- ## Common Applications * **Access Control:** Release of electromagnetic locks, as required by BS 7273-4. * **HVAC & Plant:** Stopping fans, closing dampers, or isolating fuel valves. * **Smoke Control:** Starting AOVs, initiating mechanical extract, interfacing with smoke control panels. * **Lifts:** Recall/grounding of lifts or enabling firefighter’s override. * **Sprinkler Systems:** Monitoring flow and tamper switches, transmitting alarms. * **Suppression Systems:** Gas release or fire curtain deployment (with dual-signal safeguards). --- ## Technical Considerations (per BS 5839-1:2025) * **Compliance with BS 7273:** All relevant recommendations for door release, smoke control, and other safety functions must be met. * **Disablement during Test:** Where routine testing could actuate other systems (e.g. sprinklers, lifts), facilities must exist to disable outputs. This disablement (and its indication) must comply with BS EN 54-2. * **Power Supply:** Other systems should not normally draw power from the fire alarm. If unavoidable, demand must be calculated and supplied either by rated alarm PSU capacity or an ancillary PSU. * **Accessibility:** Interfaces must be installed in accessible locations for service. Housing them inside third-party enclosures (e.g. AHU panels) is discouraged unless service access is assured. * **Monitoring:** Connections between the fire alarm and external systems must be monitored for faults, in accordance with BS 7273 and BS 7346-8. * **Fail-Safe Design:** Outputs should default to a safe condition in the event of fault, loss of communication, or power failure. --- ## Documentation To meet BS 5839-1 requirements for system clarity and ongoing maintenance: * **Interface Schedules:** Document every I/O point, its location, and function. * **Cause & Effect Matrix:** Define logic clearly, ensuring outputs correspond with fire strategy. * **As-Fitted Drawings:** Show all interface wiring and modules. * **Certificates:** Modification or interface additions require appropriate certification (e.g. BS 5839-1 Annex G modification certificate). --- ## Relevant Standards * **BS 5839-1:2025 Clause 8 & Clause 11** - Actuation of other systems and monitoring of external circuits. * **BS 7273 series** - Operation of door release, smoke control, and suppression interfaces. * **BS EN 54-2** - Disablement facilities and indication requirements. * **BS 7346-8 / BS EN 12101** - Smoke and heat control systems. --- Perfect — here’s a table you can drop straight into the **Fire Alarms/Interfaces** page, showing the BS 7273 parts most relevant to interfacing, with a short description of each. This keeps it aligned with BS 5839-1:2025 (Clause 8 explicitly points to BS 7273 for actuation of other systems). --- ## BS 7273 Parts Relevant to Interfaces | Standard | Title | Application to Interfaces | | ------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------- | | **BS 7273-1** | Code of practice for operation of fire protection measures - Part 1: Electrical actuation of gaseous total flooding and local application extinguishing systems | Covers interface between fire alarm outputs and fixed gaseous suppression release equipment. | | **BS 7273-2** | Code of practice for operation of fire protection measures - Part 2: Electrical actuation of sprinkler systems, water spray and foam systems | Guidance for interfacing with sprinkler flow/pressure switches, water mist, foam systems. | | **BS 7273-3** | Specification for automatic release mechanisms for certain fire protection equipment | Focused on requirements for releasing devices (e.g. door holders, shutters) when actuated by fire alarm. | | **BS 7273-4** | Code of practice for operation of fire protection measures - Part 4: Actuation of release mechanisms for doors | Critical for maglock, door holder, and access control release. Sets out categories A, B, C of compliance. | | **BS 7273-5** | Code of practice for operation of fire protection measures - Part 5: Electrical actuation of fire dampers | Covers how fire alarm outputs should control motorised or fusible link dampers. | | **BS 7273-6** | Code of practice for operation of fire protection measures - Part 6: Electrical actuation of smoke control systems | Defines how smoke extract fans, AOVs, dampers and pressurisation systems should be controlled and monitored by the fire alarm system. |