Fire Alarm Interface with Other Systems: Door Holders, Air Handling, Sprinklers, Lifts and Access Control

Summary

A modern fire alarm system is rarely a standalone system. In commercial, healthcare, and high-rise buildings, the fire alarm panel is the hub of a range of life-safety interfaces: it controls electromagnetic door holders that keep fire doors open during normal occupation, it shuts down air handling units to prevent smoke distribution, it receives signals from sprinkler flow switches, and it initiates lift recall to prevent occupants travelling into a fire floor.

These interfaces are not extras — they are often mandatory requirements under the relevant regulations and standards. Getting them wrong creates life-safety risk: a door holder that doesn't release allows the fire door to remain open; an AHU that continues running distributes smoke throughout the building; a lift that doesn't recall may carry occupants directly to the fire floor.

Every interface must be defined in the cause-and-effect schedule at design stage, physically installed and wired at installation, and verified at commissioning. The commissioning record must confirm that each interface was tested and functioned as designed.

Key Facts

• Cause-and-effect schedule — the document defining exactly which fire alarm inputs trigger which outputs; must be produced at design and verified at commissioning
• Dry contact output — volt-free relay contact on the fire alarm panel or interface module; no power output; requires external power source for the controlled device
• Interface module — panel accessory that provides additional relay outputs for interfacing with building services
• Electromagnetic door holders (EMDHs) — hold fire doors open during normal operation; release on fire alarm, allowing the door to self-close on its door closer; BS EN 1155:1997
• Fail-safe release — door holders must release (door closes) on power loss or fire alarm; a door holder that stays energised during a fire is a life-safety failure
• Air handling units (AHUs) — HVAC fan units that circulate air through ductwork; must be shut down on fire alarm activation to prevent smoke spread via the ductwork
• Smoke control systems — in some buildings, AHUs are configured to actively extract smoke (smoke control mode) on fire alarm — this is the opposite of shutdown and requires careful design
• Sprinkler flow switch — when a sprinkler head opens, water flows through the system; a flow switch detects this and sends a signal to the fire alarm panel; panel raises alarm
• Sprinkler tamper switch — monitors the position of sprinkler zone control valves; if a valve is closed (isolating the sprinkler zone), a tamper signal goes to the fire alarm panel
• Lift recall — lifts must travel to a designated floor (usually ground or the level of fire brigade vehicle access) and hold with doors open on fire alarm; required by BS EN 81-72 for firefighting lifts
• Lift evacuation — in buildings where lifts are provided for evacuation of mobility-impaired persons, separate controls and fire alarm interfaces are required under BS EN 81-70/76
• Access control release — access-controlled fire exits must release on fire alarm activation; fire alarm output connected to access controller input; see access control systems guide
• Voltage isolation — fire alarm panel outputs and building services equipment must be electrically isolated; never connect the fire alarm panel directly to mains-powered actuators without an appropriately rated relay and isolation
• BS EN 54-14:2004 — guidelines for system planning, design, installation, commissioning, and maintenance; covers interfacing principles

Quick Reference Table

Detailed Guidance

Electromagnetic Door Holders

EMDHs hold fire doors open during normal operation for convenience and pedestrian flow. On fire alarm, they release, allowing the door closer to shut the fire door and maintain compartmentation.

Installation requirements:

• The EMDH must be connected to the fire alarm panel via a monitored output
• The energise-to-hold principle means the EMDH is powered during normal operation (door held open) and de-energised on alarm (door releases)
• All EMDHs in a building should release on any zone alarm, not just the zone local to that door — compartmentation must be maintained throughout the building on any fire alarm, not just near the fire
• Exceptions to whole-building release may be designed where the cause-and-effect is specifically engineered for a building's evacuation strategy — but this requires careful design justification

Power supply:

• Most EMDHs operate at 24 V DC; some at 12 V DC or 24 V AC
• The panel or a dedicated interface PSU provides the 24 V supply
• The relay output from the panel switches the 24 V supply to the EMDH circuit
• Current draw: typically 0.1–0.5 A per EMDH; size the PSU and circuit accordingly

Testing at commissioning:

• Each EMDH must be verified to release when the zone associated with that floor/area alarms
• Verify that the door closer operates correctly when the EMDH releases — door must fully close and latch
• Check that the EMDH re-energises when the alarm is restored

Failure modes:

• EMDH fails energised (stays on during alarm) — usually a relay fault; door doesn't close; compartmentation lost
• Door closer insufficiently powerful — door opens against the closer force; EMDH release is ineffective; adjust or replace closer

Air Handling Unit Shutdown

AHUs must be shut down on fire alarm to prevent the ventilation system from distributing smoke throughout the building. Continuing to run an AHU during a fire pumps smoke-laden air through the ductwork to remote areas, extending the affected zone and complicating evacuation.

Interface method:

• Fire alarm panel relay output connects to the AHU BMS (Building Management System) control panel or directly to the AHU safety stop circuit
• The relay is normally energised (AHU permitted to run); on fire alarm, the relay drops out, cutting the AHU's run signal
• Some AHUs have a dedicated fire safety stop input — use this where available
• For large buildings with BMS, the BMS typically receives the fire alarm signal and manages AHU shutdown; a direct interface from fire panel to BMS override input is required

Smoke control exception: In buildings designed with active smoke control, the fire alarm does not simply shut down all AHUs. Instead, it initiates a specific smoke control sequence:

• Supply air fans stop (prevent pressurising the fire compartment)
• Smoke extract fans start (extract smoke from the fire compartment and maintain clear escape routes)
• Dampers open/close in a specific sequence

This is entirely different from standard AHU shutdown and must be designed by a smoke control engineer as part of the building's fire safety strategy (typically using BS EN 12101 standards). The fire alarm installer does not design the smoke control sequence — they interface the fire alarm panel to the smoke control system's activation inputs.

Commissioning test:

• Activate the relevant fire alarm zone and confirm the AHU stops within a defined period (typically < 10 seconds)
• Confirm the AHU does not restart while the fire alarm is active
• Restore the alarm and confirm the AHU can be restarted (manually or automatically depending on the BMS configuration)
• For smoke control systems: test the sequence with the smoke control system designer present

Sprinkler System Interface

Sprinkler systems and fire alarm systems are complementary — the fire alarm detects and warns; sprinklers suppress. Their interface ensures each system knows what the other is doing.

Flow switch input to fire alarm panel: When a sprinkler head opens (activated by heat), water flows through the wet-side pipe. A flow switch detects this flow and sends a signal to the fire alarm panel. The panel:

• Generates an alarm for the zone corresponding to the sprinkler zone
• Alerts the ARC and fire brigade
• Does not suppress or fight the fire — it alerts; the sprinklers fight

The flow switch signal is treated the same as a detector activation for alarm purposes.

Tamper switch (valve supervisory) input to fire alarm panel: The sprinkler zone control valve's position is monitored by a tamper switch. If the valve is closed (isolating a sprinkler zone for maintenance), the tamper switch sends a supervisory fault to the fire alarm panel. This alerts building management that a sprinkler zone is out of service — without this monitoring, a valve accidentally left closed after maintenance would leave the building unprotected without warning.

LPC Rules (Loss Prevention Council): Sprinkler systems in commercial premises are often specified to LPC Rules (published by the Fire Protection Association on behalf of insurers). LPC Rules require that sprinkler flow switches and tamper switches are connected to a listed fire alarm panel with ARC monitoring. The fire alarm installer must confirm with the sprinkler design engineer exactly what signals are required and what the LPC specification demands.

Zoning alignment: The sprinkler zone boundaries should align with the fire alarm zone boundaries. Misalignment (a sprinkler zone covering parts of two fire alarm zones) complicates the cause-and-effect and makes it harder to identify the specific location of activation. Discuss zone alignment with both the fire alarm and sprinkler designers at design stage.

Lift Recall

BS EN 81-72:2020 — the European standard for firefighters' lifts — requires that lifts recall to a designated floor (the "fire service recall floor," typically the principal exit level or ground floor) on receipt of a fire alarm signal.

On alarm:

1. Lift immediately travels to the recall floor without stopping at intermediate floors
2. Lift doors open and remain open on arrival
3. The lift is locked out from normal passenger use
4. Only the fire brigade key switch can take the lift out of recall mode

Evacuation lifts (BS EN 81-76): Lifts specifically provided for evacuation of mobility-impaired persons (required in tall buildings under Building Regulations Part M and BS EN 81-70/76) have a separate phase — evacuation mode — that allows lifts to be used under fire brigade control for controlled evacuation. This is distinct from firefighters' lift recall and has different interface requirements.

Interface wiring:

• The fire alarm panel provides a normally-open dry contact that closes on any fire alarm
• This contact connects to the lift panel's fire recall input
• The lift panel interprets the closed contact as a fire alarm signal and initiates recall
• Cable to the lift panel must use fire-resistant cable (FP200 or equivalent) for circuits requiring integrity

Testing:

• Activate the fire alarm and verify each lift recalls to the correct floor
• Confirm doors open and remain open
• Confirm the lift does not respond to landing calls during recall
• Restore the alarm; confirm the lift controller requires the fire brigade key switch to exit recall mode before normal service resumes

Access Control Release

Access-controlled fire exits must release on fire alarm. This is a mandatory requirement under the Regulatory Reform (Fire Safety) Order 2005 and BS 9999:2017 — fire exits must be openable without keys or special knowledge during an emergency.

Interface method:

• Fire alarm panel provides a dry contact output (normally closed; opens on alarm)
• Access controller has an input that, when the contact opens, triggers all controlled fire exits to release
• All fail-safe locks (magnetic locks, fail-safe electric strikes) release when this input activates

Documentation: The fire alarm cause-and-effect must document which fire alarm zone outputs trigger which access control inputs. In buildings where staged evacuation is used (evacuate fire floor first, adjacent floors second), the access control release may be zone-specific — only the access-controlled exits on the alarming floor release immediately.

For further detail on access control integration, see access control systems guide.

Gas Suppression System Interface

In server rooms, data centres, and specialist risk areas, gaseous suppression systems (FM200/HFC-227ea, Novec 1230, CO2, Inergen) require fire alarm confirmation before discharge. Premature discharge is hazardous — CO2 suppression in particular can be fatal to anyone in the room.

Typical activation sequence:

1. First detector in protected room activates — pre-alarm (audible warning in room only)
2. Second detector in protected room activates within a defined time — full alarm + countdown timer starts
3. Countdown (typically 30–60 seconds) allows occupants to evacuate
4. At countdown end: suppression panel initiates discharge
5. Discharge solenoid activates; gas is released

Fire alarm interface:

• The fire alarm panel provides inputs to the suppression panel (first detector, second detector for coincidence)
• The suppression panel provides outputs to the fire alarm panel (system fault, discharge in progress, room empty signal if door position monitoring is fitted)
• A manual abort button allows discharge cancellation during the countdown if the fire is confirmed as false

IMPORTANT: Never connect a fire alarm output directly to a gas suppression discharge solenoid without the suppression panel as an intermediate. The suppression panel handles the confirmation logic, countdown, and discharge sequencing with safety interlocks. Direct connection bypasses these safety measures.

Frequently Asked Questions

Who is responsible for designing the cause-and-effect schedule?

The fire alarm designer is responsible for the cause-and-effect schedule. For complex buildings with multiple systems (smoke control, suppression, access control, lift recall), the fire alarm designer must coordinate with the designers of each interfacing system. The fire safety engineer (if involved in the project) should review and approve the cause-and-effect schedule. The cause-and-effect should be reviewed by building control or the fire safety officer as part of the commissioning process.

Can a BMS replace the fire alarm for AHU control?

No. The fire alarm system and the BMS are separate systems with separate functions. The fire alarm must have a direct interface to the AHU shutdown circuit — it should not rely on the BMS to interpret the fire alarm signal and then shut down AHUs. BMS failure could break this chain. The fire alarm-to-AHU interface should be a direct relay connection, with BMS integration as supplementary monitoring only.

What voltage isolation is required between the fire alarm panel and interfacing systems?

All interfaces from the fire alarm panel to external systems must use volt-free (dry contact) relay outputs from the panel. The external system's power supply is entirely separate from the fire alarm panel's supply. This prevents a fault in the external system from affecting the fire alarm. Where the external system requires an active signal (not a contact closure), an interface relay module rated for both voltages must be used.

Do all door holders in the building need to release on every fire alarm?

Generally yes — on any zone alarm, all EMDHs throughout the building should release so that fire compartmentation is maintained everywhere. There are engineered exceptions in large buildings with sophisticated staged evacuation strategies, where door holders on unaffected floors may be released in stages. These exceptions require fire engineer input and careful cause-and-effect documentation — they are not appropriate for standard installations.

What happens if the connection between the fire alarm panel and the lift recall input fails?

Lift recall circuit integrity must be maintained using FP-rated cable. If the cable breaks or develops a fault, the lift should fail safe — either the lift controller goes into recall mode (preferred) or the fault is detected and alarmed. Most lift panels are designed to trigger recall on a "loss of signal" from the fire alarm (normally-closed circuit that goes open on fire alarm — the same open condition occurs if the cable breaks). This fail-safe design ensures the lift recalls even if the cable is destroyed by fire.

Regulations & Standards

• BS 5839-1:2017 — Clauses 29–33 cover output devices and ancillary functions; interfacing principles

• BS EN 1155:1997 — Electromagnetic door holders; performance and testing

• BS EN 81-72:2020 — Safety rules for construction of lifts; firefighters' lifts; fire recall requirements

• BS EN 81-70:2021 — Safety rules for construction of lifts; accessibility to lifts; evacuation lift interface

• BS EN 12101-6:2005 — Smoke and heat control systems; pressure differential systems

• BS 9999:2017 — Code of practice for fire safety in the design of buildings; door holder and lift recall requirements

• LPC Rules for Automatic Sprinkler Installations — Loss Prevention Council rules; alarm and monitoring interface requirements

• Regulatory Reform (Fire Safety) Order 2005 — requires means of escape to be free; governs access control release

• BS EN 54-14:2004 — Guidelines for planning, design, installation, commissioning and maintenance; interfacing principles

• FIA Interface Guidance — Fire Industry Association guidance on fire alarm interfaces with building services

• BS EN 81-72:2020 — BSI standard for firefighters' lifts; recall interface requirements

• FPA LPC Sprinkler Rules — Fire Protection Association; LPC Rules for sprinkler system alarm interfaces

• Hochiki Interface Module Documentation — Example interface module specifications for fire alarm outputs

• Advanced Electronics Application Guide — Outputs — Relay output and interface module application notes

• bs 5839 1 fire alarm standard — Standard covering interface requirements for non-domestic systems

• fire alarm commissioning procedure — Interface testing as part of commissioning cause-and-effect verification

• fire alarm zoning design — Zone design affects which alarm zones trigger which interfaces

• access control systems guide — Access control system design for integration with fire alarm

• door entry systems installation — Electric locking hardware and fire safety requirements