CROSS-UK has today issued a critical safety alert about the risks associated with preventing the operation of smoke vents by construction work on existing buildings.

CROSS-UK, which stands for Collaborative Reporting for Safer Structures, is the unique safety reporting scheme supported by the Institution of Structural Engineers (IStructE), the Institution of Civil Engineers (ICE) and the Institution of Fire Engineers (IFE).

Today’s alert – particularly relevant for buildings undergoing removal work of combustible cladding – draws attention to the safety risks associated with preventing the operation of Automatic Opening Vents (AOVs).

AOVs are provided as part of a fire safety smoke control system. In the event of a fire, an inoperable smoke vent poses a significant hazard. If smoke cannot be released from the building, it could hamper the escape of occupants and the ability of the fire and rescue service to fight a fire.

In many cases, AOVs can be indistinguishable from standard windows. This may lead to their inadvertent obstruction.

As part of its confidential reporting system, CROSS-UK has received several reports of AOVs being made inoperable by building work, including when façade materials are being replaced.

An AOV might easily be rendered inoperable by a scaffold pole, temporary masking, the storage of materials, or adjustments to cladding.

CROSS-UK has issued a Red Safety Alert – the highest rating possible on the CROSS traffic light system. It is particularly relevant for buildings undergoing removal work of combustible cladding.

CROSS-UK has published a Q&A alongside the alert providing more information:

What is an AOV?
AOV stands for Automatic Opening Vent. AOVs are usually triggered by smoke detection in the common parts of a building, for example a lobby or corridor. AOVs form part of the building’s smoke control system. They may be an inlet in a staircase to enable fresh, replacement air so another vent or system can extract/vent smoke from the fire floor.

What is the consequence of obstructing AOVs?
Obstructing either type of Automatic Opening Vent (AOV) can reduce the effectiveness of the building’s smoke control strategy. This could allow smoke and heat from a fire in a flat to spread into corridors, lobbies, and up staircases, potentially compromising residents’ ability to escape safely. Firefighters also rely on effective smoke and heat control in corridors and lobbies to open the front door of the fire-affected flat without facing extreme conditions or compromising their own exit routes.

How does this impact fire risk assessments?
Because the potential consequences of obstructing an AOV are serious, these vents must be tested regularly by the Responsible Person. If any vent is found to be faulty, obstructed, or temporarily decommissioned, the Responsible Person must immediately review their fire risk assessment. This assessment will likely recommend significant interim control measures, which may include changing the escape strategy from “stay put” to “simultaneous evacuation” (everyone exiting the building at once). In such cases, 24/7 fire marshals or a “waking watch” may be required to manage the evacuation effectively.