Fire Door AnatomyOpen the 3D explorer

Component 05 of 10 · Ironmongery

Hinges

Single axis hinges. The load path.

Three hinges typically carry a full-size leaf, through years of daily traffic and then through a fire. The hinges are part of what the fire door's evidence covers: single axis hinges within the scope of BS EN 1935 are conformity marked, and other types are permitted where the evidence covers them. Every screw is structural.

Key facts

Function
Carries the leaf and keeps it aligned in the frame under fire
Specification
Per the manufacturer's evidence. Typically three per full-size leaf, selected for the leaf's size and mass, the number and position of hinges, the duty the door sees, any closer fitted, and the manufacturer's instructions
Materials
Most commonly steel or stainless steel. Brass is also used. Load-bearing parts must not melt below 800 °C unless evidence proves otherwise
Critical tolerances
Per the manufacturer's evidence. All screws present; in timber commonly at least No. 8 gauge (3.8 mm) and 30 mm long; hinges recessed flush
Standards
BS EN 1935 for single axis hinges, with the fire door digit classified 1. Pivots and other hinge types sit outside it and need evidence of their own
Role in fire
Holds the burning leaf in the rebate so the seals can do their work
Where it sits
Hinge jamb: positions per the evidence, commonly top, bottom and centre

Compliance

Hinges are part of the fire door's tested specification. Replacing them with hinges the evidence does not cover, or leaving screws out, changes the load path the evidence was earned with. Rising butt and spring hinges are discouraged on fire doors and are no substitute for a closing device: a rising butt needs the top edge easing to clear the frame, which opens the head gap at the very point where hot gases push hardest. Fit either only where the evidence specifically covers it.

Did you know

A single missing screw matters: in a fire the leaf can bow toward the heat, and hinge fixings take loads far beyond anything everyday use applies.

On the model

Knuckle & pin
The pivot under full load
Leaf plate
Recessed flush into the edge
Fixing screws
Every one is structural
CE/UKCA mark
BS EN 1935 classification

What inspectors check

Work through the checklist with the door closed, then in motion. Every line here is a recordable outcome for a Fire Door Inspector.

  1. Count the hinges and check their number and positions against the evidence: three is typical on a full leaf, more on a heavy one
  2. Check every screw is present, tight, the right length and the right material
  3. Check hinge positions against the door's data sheet, not against habit
  4. Look for oil weeping from the knuckles; it warrants investigation, though it may be excess lubricant, dirt or dust rather than wear
  5. Look for a CE or UKCA mark on single axis hinges, but do not condemn an unmarked hinge on sight
  6. Check whether the evidence calls for intumescent protection behind the blade
  7. Check any rising butt or spring hinge is covered by the evidence
  8. Watch the leaf swing for drop or misalignment
  9. Check recesses are cut neat and flush

Common defects

Go deeper

Types of hinge

The model here is a steel butt hinge, which is what most timber fire doors hang on. It is not the only option: some fire doors hang on concealed hinges, and some turn on floor pivots rather than hinges at all.

Butt hinge, plain
Two blades and a knuckle, recessed into leaf and frame. The most common type. Typically used for lighter leaves and lower traffic.
Butt hinge, washered or ball bearing
Washers or a bearing race in the knuckle carry the load and cut friction. Typically what heavier leaves and busy doors need, and what a closer effectively demands, because a closer adds load every time the door cycles.
Floor pivots
The leaf turns on a spindle in a floor spring below and a top centre above, rather than hanging off the jamb. The floor carries the weight, so very heavy leaves become practical, and pivots are often used for double-action doors. The floor unit sits in a box in the floor, largely out of the fire's reach, but the top centre is in one of the most exposed positions on the door. Pivots sit outside BS EN 1935 and need evidence of their own.
Concealed hinges
Hidden in the joint when the door is closed, and usually adjustable in three planes. They remove more timber than a butt hinge, so the fire evidence and any intumescent protection matter more, not less. They are not single axis hinges in the BS EN 1935 sense, so their evidence is their own.
Rising butt and spring hinges
Both are discouraged on fire doors. A rising butt needs the top edge easing to clear the frame, opening the head gap where gas pressure is highest, and neither is a reliable substitute for a closing device. Where either is found, the question is whether the door's evidence covers it.

Reading the classification

BS EN 1935 classifies a single axis hinge in eight digits. One of them decides whether it belongs on a fire door at all, and the last is the grade.

The fire door digit
The fourth digit says whether the hinge is suitable for use on fire and smoke doors: 0 for no, 1 for yes. On a fire door it has to read 1.
The hinge grade
The final digit is the hinge grade, 1 to 14. Not every grade is meant for doors, and none of them maps onto FD30 or FD60. The right grade follows the door's evidence, the leaf's size and mass, the number and position of hinges, the duty and frequency of use, any closer fitted, and the manufacturer's instructions.
Allow for the closer
Hinges have to be specified for the load they actually carry. A closer adds to it every time the door cycles, and a backcheck closer adds more, so manufacturers' selection guidance allows for the closer on top of the leaf's own mass. A hinge chosen on the bare weight of the leaf may be under-specified once the closer is on it.
Melting point
Unless test evidence proves otherwise, the parts of a hinge that carry the leaf must be non-combustible and must not melt below 800 °C. Steel and stainless are comfortably above it. Brass alloys are above it too, though a brass-look hinge may be plated steel, which is a different thing to record.
Three hinges, and when three is not enough
Three is typical on a full-size fire door, not a rule that overrides the evidence. Heavier, taller and wider leaves may need more, and on heavy doors there is a practice of fitting two hinges high and one low, because the top of the door takes the most. Beyond what the hinge manufacturer's guidance covers, ask the hinge or door manufacturer rather than guessing.

Marking, and when not to condemn

This is where inspections go wrong most often, and it costs building owners real money for no gain in safety.

What the mark is
Single axis hinges within the scope of BS EN 1935 carry a CE or UKCA mark and a classification, and the standard sets out how they should be marked. Other hinge types, and hinges permitted under the door's evidence without a third-party scheme, may carry no such mark. Looking for it is a reasonable first step, not the last.
No visible mark is not a condemnation
A mark can be tiny, on a face you cannot see with the door hung, or buried under decades of paint. The performance evidence may live on the Declaration of Performance and the door's data sheet rather than stamped on the blade. Older doors may predate the marking regime entirely and still be perfectly serviceable.Replacing every hinge that has no visible mark is common and usually unjustified. Establish what the hinge is from the door's data sheet, the Declaration of Performance or the manufacturer. If unsure, refer to a competent fire door inspector or risk assessor to evaluate the hinge in context, before anyone rips out working hardware.
Intumescent protection behind the blade
Some fire doors were tested with intumescent material between the hinge blade and the timber, protecting the recess from charring early and taking the hinge with it. Where the test used it, the same material has to be there for the evidence to hold. Whether yours needs it is a question for the manufacturer and the evidence, not a judgement to make on site.
Oil at the knuckle
Weeping oil warrants investigation. It may be a bearing past its best, and dark oil can be metal worn off the bearing surfaces and suspended in the lubricant, but it may also be excess applied lubricant, dirt or atmospheric dust. Establish which before recording wear. A hinge genuinely shedding its own material is on its way to letting the leaf drop, which puts the door out of the frame and off the seal line.

Fire Door Anatomy is an introduction to fire doors, not the whole subject. Always defer to the fire door’s certification, its test evidence and a competent inspection.