What are AOVs?

Posted by Conor Logan on 21/01/22 10:00

If you have become newly involved in the world of smoke control, you may hear or see the term ‘”AOV” quite frequently and be wondering what it means and what AOVs do. In this blog, we aim to give you a good understanding of what AOVs are and when they might be required in a building.

Simply put, “AOV” refers to “Automatic Opening Vent”. In the case of fire safety in buildings, this refers to a smoke or fire vent that will open and close automatically when triggered by a central control system. These can typically be activated by a smoke or heat detector, either directly or from a smoke detection system or possibly a fire alarm system, so they will open in the event of smoke and/or heat being detected.

When the AOVs open, they allow smoke which may otherwise have started gathering in various parts of a building to escape to the outside world. This has obvious benefits for anyone still in the building as reducing smoke concentrations not only improves visibility but also reduces the levels of harmful toxic air and increases their chances of a safe escape dramatically. As well as helping people get safely out of the building, the AOVs also assist firefighters with getting into the building and to the seat of the fire quickly. Not only do they have cleaner air to breathe, reducing their dependence on Breathing Apparatus, but visibility is also drastically improved. As firefighters will almost always be entering an unknown building, having the ability to see clearly will help them plan and move through the building much more quickly. As AOVs play such an important role in keeping people safe, they are typically roof mounted and installed in areas that protect stairwells, lobbies, corridors or other typical escape routes.

AOVs can come in the form of glazed or insulated casement, louvred or ‘flap’ ventilator with controls taking the form of:

  • A spring to open magnetic release (with manual reset)
  • Electric actuators or
  • Pneumatic controls and could look similar to the images below.

The design, manufacture, testing and certification of AOVs is covered by EN 12101-2 Smoke and Heat Control Systems – Specification for Natural Smoke and Heat Exhaust Ventilators. Under the existing Construction Products Regulation and the upcoming Building Safety Bill, compliance with this standard is mandatory.

To comply with this standard, AOVs must be tested as a complete unit for reliability, robustness, effectiveness and operation at elevated temperatures. A window, fitted by one company, opened by a motor fitted by another company, is unlikely to comply with this standard and cannot be considered as a smoke ventilator if it has not been tested in accordance with the standard.

To ensure constancy of performance, the standard also requires factory production control, to ensure that the product delivered to site has been manufactured in the same way as the original product that was tested and certified. This cannot happen if the unit is a kit of parts being delivered form multiple locations.

When do you need AOVs in your building?

There are regulations governing what types of buildings require smoke control. As AOVs form an integral part of almost all smoke control systems, building types that are outlined in these regulations will likely be required to install AOVs.

The most common types of buildings that need smoke control systems designed and installed are:

  • Large single storey buildings, such as factories and warehouses
  • Shopping centres
  • Multi-storey Residential buildings
  • Other multi-storey buildings, generally over 18m tall
  • Buildings with atria
  • Car parks where smoke, and fume extraction is required

Inevitably, due to differences in building layouts, heights, location etc. specialist advice should be sought to determine the exact requirements. However, for multi-storey residential buildings in England, the below image offers a simple overview of how an increase in height impacts on smoke control requirements. Similar, but not identical requirements exist in Wales, Scotland and Northern Ireland.

More information and guidance on how to design smoke control systems in England and the regulations surrounding them can also be found in the resources below:

  • The Building Regulations 2000
  • Approved Document B
  • Codes of practice: BS 9999, BS 9991
  • Specifications: EN 12101 Parts 1, 2, 3, 6, 7, 8 & 10
  • Design Guidance: BR 368 – Design Methodologies for Smoke and Heat Exhaust Ventilation
  • BS 7346- 4, 5 & 7, CEN TR 12101-5
  • BS 7974
  • Smoke Control Association Guides

If you are working on a project that needs a smoke control system designed, Colt’s experience and expertise can help you navigate the regulations to ensure you are installing the best system for your building’s requirements. Talk to our technical team for a free consultation today.


Conor Logan Conor Logan is Associate Technical Director of Colt UK, Smoke and Climate Control Division. Conor designs innovative smoke control and HVAC systems and was Chairman of the Smoke Control Association for over 9 years.

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Topics: Smoke Control, Smoke ventilation, HVAC, Controls