AOV and Smoke Vent Testing for London Blocks: Frequency and Records

An automatic opening vent clears smoke from the common corridor, lobby or stair of a block of flats so that the escape route stays usable long enough for people to leave and for the fire service to get in. It is not a comfort ventilator. It exists for the twenty minutes that matter.

In a residential block the vent is normally a natural smoke and heat exhaust ventilator — an NSHEV, covered as a product by BS EN 12101-2 — driven open by an electric actuator when a smoke detector in the common part operates. Powered extract versions fall under BS EN 12101-3, the control panel under BS EN 12101-9 and its power supply under BS EN 12101-10.

Approved Document B's standard solution for a block of flats gives two routes. Either each common corridor or lobby gets a vent of at least 1.5m² free area sited as high as practicable, with a vent of at least 1m² free area at the head of the stair; or the corridors discharge into a smoke shaft with a minimum cross-sectional area of 1.5m² and a minimum internal dimension of 0.85m, vented from the corridor and at the head of the shaft. Engineered designs to BS 9991 depart from those figures deliberately, which is why the fire strategy document, not a rule of thumb, tells you what your building is supposed to achieve.

This matters on a test visit because you cannot say a system passed unless you know what it was designed to do. A shaft system where the fire-floor vent opens but the shaft head damper does not has failed, even though something visibly moved.

The legal duty is Article 17 of the Regulatory Reform (Fire Safety) Order 2005: fire safety equipment must be maintained in efficient working order and in good repair. The Order sets no interval. The interval comes from the fire risk assessment, the manufacturer's instructions and industry guidance, and those three together are what an enforcing officer will measure you against.

Weekly. Smoke Control Association guidance for apartment building escape routes expects a weekly functional test — usually a fireman's switch operation on one floor, rotated so every floor is covered over a cycle, with the panel checked for faults. This is the duty most managed blocks quietly skip.

Monthly. For high-rise residential buildings — broadly those at least 18m tall or of at least seven storeys — Regulation 7 of the Fire Safety (England) Regulations 2022 requires the responsible person to check firefighters' lifts and other key firefighting equipment monthly, and to report to the fire and rescue service where a fault is not put right within 24 hours. Smoke control serving the firefighting shaft is normally treated as falling inside that duty. Get written confirmation from your fire risk assessor either way rather than assuming.

Annually. A full functional test of every vent and every override switch, with cause-and-effect verified against the fire alarm panel, actuator current draw measured, and the system run once on battery with the mains supply isolated. Manufacturers commonly specify a service interval alongside this, and where they do, the manufacturer's interval wins if it is shorter.

One standard is often cited for this that should not be. BS 7346-8 is a code of practice for smoke control in covered car parks. It is a good document and it has nothing to say about the common corridor of a block of flats. If your maintenance contract quotes it as the basis for testing your residential smoke shaft, the contractor is reciting a standard they have not read.

Under the Fire Safety Order the responsible person for the common parts of a block of flats is whoever has control of those parts — normally the freeholder, the resident management company, or the managing agent acting under a management agreement. The Fire Safety Act 2021 put beyond argument that the structure, external walls and flat entrance doors sit inside that duty as well.

The practical failure mode in London is not ignorance of the duty but a split between the party that holds it and the party that holds the money. A resident management company instructs an agent; the agent instructs a contractor; the contractor tests what the purchase order says. Nobody in that chain owns whether the tested scope matches the fire strategy.

The test takes five minutes. Ask for the fire strategy or FRA action plan, then the last AOV test certificate, then count the vents on each. If the certificate covers fewer devices than the strategy describes, the difference is your open risk.

Delegation does not transfer the duty: an agent can do the work, the responsible person still answers for it.

A fire officer asking about smoke control wants to see, in one place: what was tested, on what date, by whom, what result, and what happened about the failures. Anything short of that reads as an untested system regardless of how well the vents actually work.

Per test entry, that means the date and time; which devices were operated, identified by location and reference rather than "AOVs tested"; the method used for each — alarm-triggered activation, fireman's switch, or panel test; the result including whether the vent achieved full travel and closed on reset; the measured actuator current draw where taken; the tester's name and the company; and the panel fault status before and after.

Separately, the log book should hold the commissioning documentation and the cause-and-effect matrix, the manufacturer's O&M manual, the battery installation dates, and a defect register showing each fault raised, the date it was raised, the date it was rectified and by whom. An open defect with no rectification date is not automatically a breach. An open defect with no evidence anyone chased it is.

Keep it retrievable within the hour. For higher-risk buildings the same information belongs in the golden thread rather than a folder in a cupboard — in practice, a digital record with version history.

Three components account for most of what we find failed on annual visits, and each fails in a way that a visual check will not reveal.

Actuators. Chain and spindle actuators wear at the gearbox long before they stop working. The symptom is a rising current draw and a slower stroke, not a dead vent, which is why measuring current draw is worth more than watching the vent open. A vent that reaches full travel but pulls appreciably more current than the manufacturer's figure is on a countdown.

Control panels. A panel will happily pass a functional test on mains and fail the moment the mains is removed, because the fault is in the charger or the standby batteries and nothing in the everyday test path touches them. Sealed lead-acid standby batteries in these panels are typically on a three to five year replacement cycle, and a long building power cut that deep-discharges them will end their life early regardless of age. Testing on battery, with the supply isolated, is the only test that means anything.

Cause-and-effect drift. Someone replaces a detector head, adds a device, reconfigures a zone after a refurbishment, and the matrix that decides which vent opens for which detector no longer matches the drawing. The vents still open — just not the right ones. This is the failure that looks most like a working system and matters most.

Supply arrangements. Under BS 7671 the supply to a safety service is not an ordinary final circuit. Smoke control should be fed from a dedicated, clearly labelled supply that cannot be lost by an unrelated fault, using fire-resisting cabling of the grade the fire strategy calls for — standard grade to BS EN 50200 PH30, or enhanced to BS 8434-2 where the design requires it. AOV panels found on the landlord's general lighting circuit, sharing an RCD with a communal socket, are common in converted blocks and are a genuine finding, not a paperwork nicety.

Regulations 4(2) and 16 of the Electricity at Work Regulations 1989 sit behind all of this: the system must be maintained to prevent danger, and the person doing the work must be competent for it.

A higher-risk building is one at least 18m tall or of at least seven storeys that contains at least two residential units. If your block meets that test, smoke control stops being a line item on a maintenance schedule and becomes evidence in a safety case.

The principal accountable person has to be able to show the Building Safety Regulator how each safety measure is managed — what it is, how it is maintained, how failures are detected and how they are put right. For smoke control that means the design intent, the cause-and-effect matrix, the test regime, the actual test records and the defect history, all current and all traceable. That is the golden thread applied to a set of vents.

Mandatory occurrence reporting is the part most managing agents have not thought through. A smoke control system found inoperative in an occupied higher-risk building has to be considered against the reporting threshold, not added to a snagging list. The judgement is the accountable person's, but it has to be made and recorded.

The practical consequence is that a one-line annual certificate reading "AOV system tested — satisfactory" no longer does the job. It was always thin; in a higher-risk building it is the wrong shape of evidence entirely.

Part P of the Building Regulations covers electrical installations in dwellings and in the common parts of buildings serving one or more dwellings, excluding power supplies to lifts. Since 2013 the notifiable set is narrow: new circuits, consumer unit replacement, and work in special locations. Testing an existing AOV system is not notifiable. Installing a new AOV control panel on its own dedicated circuit usually is, and the certificate has to be notified accordingly.

Competence for the electrical work sits under BS 7671 and EAWR 1989. Competence for the smoke control system is a separate question — knowledge of the fire strategy, the cause-and-effect matrix and the commissioning data, not just the ability to test a circuit.

Ask for a sample certificate before you book. If it does not list devices individually, record how each was triggered, and state the mains-isolated battery result, you are buying a signature.

Our annual functional test is £179.99, covering up to two actuators and three fireman switches, with additional actuators at £35 each. Cause-and-effect verification against the fire alarm panel and the certificate are included, and the certificate is issued the same day.

The visit runs the manual fireman-switch open on every switch, the alarm-triggered open and the close-on-reset; measures actuator current draw; confirms battery back-up with the supply isolated; and includes a visual smoke shaft inspection. Failures are identified against their location and quoted separately.

For managed blocks we schedule AOV testing alongside the communal EICR, emergency lighting and fire alarm visits so the records share one date and one set of paperwork. If you do not yet know what the fire strategy requires, say so when you call.