What are stairwell AOVs?

A stairwell ventilator / stairwell AOV is an automatic opening ventilator (AOV) which provides at least 1.0m² of free area when open. The installation is always located at the highest point in an evacuation stairwell and can take a number of forms. The most common type of stairwell ventilators are louvred, hatch type, windows and roof windows.