Every fire door closing mechanism has to do two things: bring the leaf fully to the frame, and drive the latch home so the door stays there. Mechanisms differ in how they store and release energy and in how they behave during normal use, and the choice is usually driven by the traffic through the opening rather than by the fire requirement.
Spring mechanisms
Overhead closers and floor springs store energy in a spring as the door opens and release it on closing, with hydraulic damping controlling the speed. They are the default because they need no power, no wiring and no maintenance beyond adjustment, and because they fail in the closed direction. Their weakness is that the force needed to open them is the force they will use to close.
Free swing devices
An electromechanical closer that decouples the spring during normal use so the door behaves like an ordinary door, and re-engages on alarm activation or power loss so that it closes. These suit care settings and other buildings where doors need to be movable and stay where they are put, and they remove the incentive to wedge without leaving the door permanently open.
Hold open devices
An electromagnet or an electromechanical arm that holds the door fully open and releases it on alarm activation and on power loss, letting a conventional closer shut it. These are the standard answer on busy routes. They come as wired devices on the alarm system and as acoustically triggered units that listen for the sounder, the latter being used where wiring is impractical.
Powered operators
A motorised operator opens the door for users and closes it under control, with a fail safe behaviour on alarm. They are the accessibility answer on heavy doors and they are the most expensive and the most maintenance dependent, because a failed operator on a fire door is a door that may not close at all unless the fail safe behaviour is correct and tested.
Questions people ask about fire door closing mechanism
Which mechanism is best for a busy corridor?
A hold open device released by the alarm, with a conventional closer behind it. It removes the reason people wedge and keeps the fire function intact.
Do free swing closers need a power supply?
Yes, and they must close the door on power failure as well as on alarm. That fail safe behaviour is what makes them acceptable on a fire door.
Are acoustic hold open devices as good as wired ones?
They are accepted where wiring is impractical and they depend on hearing the alarm at the door, so their siting and their commissioning matter more. They are tested with the alarm like any other release.