What is a fire door?
A fire door is a door assembly designed to hold back fire and smoke for a rated period, keeping escape routes usable. It performs as rated only when the whole assembly — leaf, frame, seals and hardware — is intact.
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<img src="https://fireoptix.co.uk/glossary/fire-door/diagram.svg" alt="fire door — diagram from FireOptix" width="880" height="620" loading="lazy">
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<a href="https://fireoptix.co.uk/glossary/fire-door">What is a fire door?</a> — diagram by
<a href="https://fireoptix.co.uk">FireOptix</a>
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</figure>The rating belongs to the assembly, not the door leaf. A correctly rated leaf hung in the wrong frame, or with the wrong hinges, or with a gap wider than its seal can bridge, does not deliver its rating — which is why inspection looks at the whole thing rather than reading the label.
Ratings are expressed as a period of fire resistance, commonly written as FD30 or FD60 for thirty and sixty minutes. Doors on escape routes often carry an additional requirement for smoke control.
Self-closing devices are what make a fire door a fire door in use. A door that would resist fire for an hour resists nothing while it is wedged open, which is the single most common defect found in service.
In practice
A door that passes every visual check and fails as a system.
The leaf is undamaged, the certification label is legible and the closer works. The smoke seal has been painted over four times and will do nothing at all.
A fire door is an assembly — leaf, frame, seals, ironmongery, glazing — and it fails at whichever component was neglected rather than at the one that looks important.
The paint is applied by decorators who have never been told, which makes it a communication failure rather than a maintenance one.
What goes wrong in practice
- Doors wedged or propped open, usually for a practical reason nobody recorded or addressed.
- Gaps around the leaf that have opened up as the building moved, taking the assembly outside the tolerance its rating depends on.
- Intumescent strips painted over during redecoration, or damaged and never replaced.
- Hardware swapped during maintenance for an unrated equivalent that fits and looks the same.