An automatic opening vent (AOV) works by detecting smoke, sending a signal through a dedicated control panel, and triggering motorised actuators to open vents — clearing escape routes and stairwells of smoke within seconds. The entire sequence is automatic, operates independently of the main electrical supply, and must comply with BS EN 12101.

Step 1: The Trigger — Smoke Detection

The sequence begins with a smoke detector. AOV systems are typically connected to optical smoke detectors positioned in common corridors, lobbies, and stairwell landings. When smoke enters the detector’s sensing chamber and scatters its infrared beam beyond a set threshold, the detector sends an alert signal initiating the AOV sequence.

In installations compliant with BS 9991, the smoke detectors may be part of, or interfaced with, the building’s main fire alarm system (L2 or L3 category).

Step 2: The Signal — AOV Control Panel

The alert is received by the AOV control panel — the brain of the system. On receiving the alarm signal, the panel: identifies which detection zone has activated; determines which vents should open; sends a power signal to the relevant actuators; logs the event with time and date; and triggers any connected alarms at manual override stations. AOV control panels must comply with BS EN 12101-9.

Step 3: The Action — Actuator Opens the Vent

The AOV actuator physically opens the vent. Two types are common: chain actuators (motorised chain drive pushing the vent open, common on roof lights and high-level windows) and rack-and-pinion actuators (gear mechanism for larger, heavier vent units). The actuator receives a low-voltage DC signal — typically 24V — and drives the vent to its fully open position. Performance must meet BS EN 12101-2.

Step 4: Battery Backup — Keeping the System Running During Mains Failure

A fire that triggers an AOV system may also compromise mains electrical supply. Battery backup is a mandatory requirement under BS EN 12101-10, which specifies AOV power supplies must maintain system operation for a minimum period — typically at least 72 hours in standby and 60 minutes under full operational load.

The battery backup switches to battery power automatically and instantaneously the moment mains is lost, with no interruption to system operation. It also monitors battery health, reporting fault conditions to the control panel.

View our range of AOV battery backup units — engineered for BS EN 12101-10 compliance.

Step 5: The Reset — Closing Vents After the Event

Once the emergency is over, the AOV system must be deliberately reset before vents close — a safety feature preventing inadvertent closure while smoke may still be present. The reset procedure involves: confirming with the fire service it is safe; silencing alarms; pressing the reset control at the main panel; confirming all detectors have cleared; actuators drive vents back to closed; and the panel returns to normal monitoring mode.

Step 6: Testing and Maintenance

Current fire safety law — including the Regulatory Reform (Fire Safety) Order 2005 and the Fire Safety (England) Regulations 2022 — requires the responsible person to ensure AOV systems are maintained in efficient working order:

  • Weekly: Visual inspection of the panel for fault indicators
  • Monthly: Functional tests to confirm vents open and close correctly
  • Annual: Full inspection by a competent person, including battery capacity testing and actuator force measurement
  • Records: All tests logged and retained

Battery backup units should be replaced proactively every three to five years rather than reactively.

People Also Ask

What triggers an automatic opening vent to open?

An AOV is triggered by a connected smoke detector. When smoke exceeds the detector’s threshold, it signals the AOV control panel, which activates actuators to open the vents. Manual override push buttons on each floor can also trigger opening independently of automatic detection.

Can an AOV system work without mains power?

Yes — and it must. BS EN 12101-10 requires AOV systems to include a battery backup capable of maintaining full system operation for at least 60 minutes under load and 72 hours in standby following mains failure.

Who is responsible for maintaining an AOV system?

The responsible person under the Regulatory Reform (Fire Safety) Order 2005 — typically the building owner, employer, or managing agent — is legally responsible. Day-to-day checks should be carried out by building management staff; annual inspections must be performed by a qualified fire safety engineer.

AOV Battery Backup Units — Specified for Reliability

AOV Direct supplies battery backup units engineered specifically for smoke ventilation control panel applications. Explore our AOV product range or speak to our technical team to discuss the right solution for your installation.