What is a fire door hinge?
A fire door hinge is a hinge rated for use on a fire door assembly. Hinges hold the leaf in the frame as it distorts under heat, and unrated hinges can let a door fall out of its opening.
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<img src="https://fireoptix.co.uk/glossary/hinge/diagram.svg" alt="fire door hinge — diagram from FireOptix" width="880" height="620" loading="lazy">
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<a href="https://fireoptix.co.uk/glossary/hinge">What is a fire door hinge?</a> — diagram by
<a href="https://fireoptix.co.uk">FireOptix</a>
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</figure>Under fire a door leaf moves. Hinges have to hold it in the frame while that happens, which is a different demand from an ordinary door and why fire door hinges are made and tested for it.
The number of hinges matters as much as their rating. A heavy leaf on too few hinges puts load on each one and pulls the leaf out of alignment, which opens the gap the seals are sized for.
Hinges are the component most quietly substituted. They are cheap, they look alike, and a maintenance visit that replaces a squeaking hinge with whatever is in the van has changed the assembly without anyone recording it.
In practice
A door with three hinges and four screws missing between them.
It hangs correctly and swings well. The missing screws were lost during an adjustment years ago.
Hinges carry a door's weight under heat, and a partially fixed hinge is the component most likely to let a door distort out of its frame.
It takes seconds to check and is almost never on a visual checklist.
What goes wrong in practice
- Unrated hinges fitted during routine maintenance because they fit and look the same.
- Screws replaced with shorter or non-ferrous equivalents that will not hold under heat.
- A hinge missing entirely, with the door still closing well enough that nobody reports it.