An AOV is an automatic opening ventilator which provides at least 1.0m2 of free area when open. In buildings of over 11 metres, there is a legal requirement to provide a means of protecting corridors and communal lobbies with access to the escape stairwell in order to control smoke. In these buildings AOVs are always installed at the highest point in an evacuation stairwell.
The AOV system is a critical component of a building’s overall fire safety strategy, particularly in multi-storey residential and commercial properties. Properly functioning AOVs not only aid in smoke ventilation but also assist the fire service by preventing smoke logging of escape routes. Under the 2022 amendments to Approved Document B, there is an increased focus on fire safety systems in residential buildings with a storey 11m or more in height, making the correct specification and maintenance of AOVs more important than ever. This vital system forms a core part of the passive and active fire protection measures businesses must have in place to ensure compliance and occupant safety.
An AOV is designed to remove any smoke from the stairwells of small buildings, enabling an easier and safer exit. More commonly, they are installed in large buildings to provide replacement air for a lobby smoke extract system.
When a fire breaks out, smoke accumulates in communal lobbies or corridors adjoining the escape stairwell. Ventilation is a means of removing smoke from these areas.
This ventilation is provided through installing an AOV or a natural/mechanical smoke shaft system.
These systems operate automatically, typically triggered by the building’s fire alarms or dedicated smoke detection devices, which can include sophisticated modern options like VESDA detection. Upon activation, the AOV automatically opens to create a clear path for smoke to escape the building, mitigating the risk of smoke inhalation, which remains the primary cause of fire-related deaths. For larger or more complex sites, like in the logistics sector, AOVs can be integrated into a wider intelligent building management system, forming part of a sophisticated smart fire system. Regular maintenance and testing, as outlined in our guide on predictive maintenance in fire safety systems, are crucial to ensure these automatic functions perform reliably when needed.
The horrific Grenfell tragedy in June 2017 sparked the requirement for a radical reform of building regulations. Dame Judith Hackett’s damning report ‘Building a Safer Future’, released in May 2018, looked at the regulatory framework around the construction, maintenance and ongoing use of buildings, focussing particularly on multiple occupancy, high-rise residential buildings. The report not only found that the existing regulations system was not fit for purpose, but that it also left room for short-cuts. The report set out 53 recommendations to establish a new regulatory framework and implement a culture change to create and maintain safe buildings. The government now aims to move from a passive system centred around compliance with building regulations to a proactive one – where developers and building owners take responsibility for ensuring that residents are safe.
This commitment to reform culminated in the introduction of the Building Safety Act 2022, which created the new Building Safety Regulator (BSR) and introduced the concept of the ‘Accountable Person’ for high-rise residential buildings. This legislation places clear, legal responsibilities on those who own or manage these buildings to assess and manage ‘building safety risks’ throughout the building’s entire lifecycle. The new regulatory environment demands a robust and demonstrable fire safety strategy. For example, while the overall number of fire incidents in England has fallen to a record low of 133,072, according to official government statistics, fires in purpose-built high-rise flats or maisonettes (ten or more storeys) actually saw a small increase compared to the previous year. This underlines the ongoing, critical need for effective smoke control measures like AOVs, particularly in the property management sector, where the safety stakes are highest.
Considering this imminent reform, high-rise building owners and developers are now reviewing their fire safety strategy to avoid another tragedy such as Grenfell.
Along with retrofitting AOV systems and testing and maintaining existing AOV systems, other fire safety measures include:
Proactive maintenance and inspection are no longer optional but a central pillar of compliance. A comprehensive fire safety strategy must also include robust security measures, as detailed in our analysis of integrating intruder alarms with fire safety systems. Businesses operating in high-risk environments, such as the factory sector, should also consult industry-specific standards to ensure all fire and security systems are fully aligned. This includes ensuring all personnel have adequate training, as we discuss in our post on creating fire safety champions.
The failure of the smoke-control system in Grenfell Tower has been identified by experts as a factor in the building’s escape route filling with thick smoke, which in turn prevented evacuation and rescue. The system was designed to extract smoke from lobbies outside flats and protect the staircase.
Dr Barbara Lane, appointed by the Grenfell Tower Inquiry, produced a report investigating the fire protection measures in place on the night of the fire. Her findings concluded that the fire safety provisions within the single escape stairs and lobbies were designed to operate on one floor only – based on the assumption that fire would be contained in one flat. The smoke-control system in place could not have protected the staircase from smoke on multiple floors.
Because of the cladding fire a whole-building fire occurred, meaning the stairs and lobbies became the most important life-safety feature. Lane stated that the smoke-ventilation system design did not follow guidance in Fire Safety: Approved Document B (ADB) 2013 because it was a bespoke system, with evidence that it did not perform as designed, with automatic opening vents not closing correctly.
However, even if the AOV system had been installed and maintained compliantly to current regulations, it’s unlikely to have had much positive effect in the evacuation of the building as current statutory guidance requires the system to be effective only in a localised fire incident, not a whole building fire.
This finding was a key driver for the monumental shift in UK building safety. The Grenfell Tower Inquiry Phase 1 report, released in October 2019, made a significant recommendation (Recommendation 33) that high-rise residential buildings should be required to have an M fire safety strategy in place that specifically addresses the evacuation of the building’s occupants. While the government initially faced legal challenges regarding the implementation of Personal Emergency Evacuation Plans (PEEPs), the focus on holistic fire safety design has intensified. The inquiry highlighted a critical gap: the standard ‘stay put’ policy failed due to the building’s construction flaws, and the single-zone AOV system was simply not designed for a total building fire event. This underscores the need for building managers in sectors like healthcare and education to consider a multi-layered approach to fire protection, which includes integrating AOV systems with a detailed business continuity plan.
In light of this, the proposed overhaul of current building regulations is vital in protecting lives of occupants in the future. An effective AOV system installed and maintained correctly, along with a holistic fire safety strategy will undoubtedly afford better fire protection to residents of high-rise buildings in the future.
The lessons learned from Grenfell continue to drive the evolution of fire safety standards, moving beyond minimum compliance to a culture of genuine safety and accountability. This affects all businesses, including those in the leisure sector, which often have high occupancy levels. Ensuring that all fire safety elements, including AOVs, are rigorously checked by accredited professionals is essential for fulfilling the new duties imposed by the Building Safety Act, as discussed in our article on legal responsibility in fire incidents at work. For an overview of best practices, see our guide on the top 7 mistakes businesses make when choosing a fire safety provider.
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