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.

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| 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. |

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* **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).

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* **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.

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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).

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* **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.

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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).

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| 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. |