What is a Fire Door?

A fire door is a specially constructed door designed to resist the passage of fire and smoke for a specified period. Fire doors are critical life-safety features that compartmentalise buildings, protect escape routes, and buy time for people to evacuate safely.

What is a fire door?

A fire door is not just a standard door in a fire-resistant frame. It's a complete fire-resisting assembly that includes:

• Door leaf — the door itself, constructed with fire-resistant materials and core
• Frame and architrave — properly installed and fire-resistant
• Intumescent strips — expand when heated to seal gaps
• Smoke seals — prevent cold smoke passing through gaps
• Self-closing device — ensures the door closes fully after use
• Hinges — sufficient number (usually 3) of the correct type
• Latch — holds the door closed in the frame
• Hardware — appropriate letter plates, door viewers, etc. (if present)
• Glazing — fire-resistant glass if the door has a vision panel

All these components must work together as a system. If any part fails, the whole door may not perform as intended in a fire.

Fire door ratings: FD30 and FD60

Fire doors are rated by how long they can resist fire in a standard test:

FD30 (30-minute fire door)

• Provides 30 minutes of fire resistance
• The most common type in typical buildings
• Used for:
  • Internal doors in commercial buildings
  • Flat entrance doors in residential buildings
  • Doors to stairwells and corridors
  • Doors between different occupancies

FD60 (60-minute fire door)

• Provides 60 minutes of fire resistance
• Used where higher protection is needed:
  • Doors to protect means of escape in high-risk areas
  • Basement doors
  • Doors to plant rooms, storage areas with high fire load
  • Some doors in larger or complex buildings

What the rating means

The "FD" stands for "Fire Door." The number indicates minutes of fire resistance in test conditions. This includes:

• Integrity — preventing flames and hot gases passing through
• Insulation (sometimes) — limiting temperature rise on the non-fire side

An FD30 door may also be designated FD30s, where the "s" indicates it includes smoke seals for improved smoke control.

Essential fire door components

Each part of a fire door serves a critical function:

1. Intumescent strips

These strips contain a material that expands when exposed to heat (typically around 200°C). When activated:

• The material swells to many times its original size
• Seals gaps between the door and frame
• Prevents flames and hot gases passing through

Location: Fitted into grooves in the door edge or frame, on the hinge side, top, and closing edge (not usually on the bottom unless specified).

2. Smoke seals

Cold smoke can kill before fire reaches a person. Smoke seals:

• Consist of a flexible blade or brush strip
• Work at normal temperatures (unlike intumescent strips)
• Prevent smoke passing through gaps when the door is closed

Location: Often combined with intumescent strips in a single product, fitted around the door perimeter.

3. Self-closing device

A fire door must close fully and latch shut every time:

Overhead closers:

• Most reliable type
• Adjustable closing speed and latching force
• Regular adjustment needed as they wear

Concealed closers:

• Hidden in door or frame
• Neater appearance but harder to maintain

Rising butt hinges:

• Special hinges that cause the door to self-close
• Less reliable than overhead closers
• Not suitable for heavy doors

4. Hinges

Fire doors require:

• Minimum 3 hinges for standard doors (more for heavy or tall doors)
• Steel hinges (typically 100mm grade 13 or better)
• Correctly fitted with all screws in place

Inadequate hinges cause the door to drop and sag, creating gaps that compromise fire resistance.

5. Latch

The door must be held closed:

• Latching mechanism — mortice latch or lock
• Minimum 12mm engagement — the latch must enter the keep by at least 12mm
• No cylinder locks only — a cylinder lock without a latch won't hold the door closed

6. Glazing

If a fire door has a glass panel:

• Must be fire-resistant glazing (not standard glass)
• Usually restricted in size (often maximum 25% of door area)
• Must meet the same fire rating as the door
• Should have certification marks visible

Never replace glass in a fire door with standard glass — it will shatter in heat, allowing fire and smoke through.

Gap tolerances: the 3mm rule

For a fire door to work properly, the gaps around it must be controlled:

Standard gap tolerances

• Top and sides: Maximum 3mm (can use a £1 coin as a rough check — it should not slide into the gap)
• Bottom: Maximum 8mm (though often 3mm for improved smoke control)

Why gaps matter

Gaps too large:

• Fire, smoke, and hot gases pass through before intumescent strips activate
• Reduces the effective fire resistance time
• May allow smoke to spread even when strips have activated

Gaps too small:

• Door may bind and not close properly
• Can damage intumescent strips through friction
• Makes door hard to open and close

Where fire doors are required

Fire doors are typically required:

Residential buildings

• Flat entrance doors — doors into individual flats from common areas (FD30 minimum, FD30s preferred)
• Doors to stairways — protecting escape routes
• Cupboard doors — if housing meters, gas/electric services
• Room doors in HMOs (Houses in Multiple Occupation)

Commercial and public buildings

• Doors to protected stairways — maintaining fire-free escape routes
• Corridor and lobby doors — sub-dividing buildings into fire compartments
• Doors to high-risk areas — plant rooms, storage areas, kitchens
• Between different occupancies — separating different uses in mixed buildings

Care homes and hospitals

• Bedroom doors — often required to be FD30s
• Day room and lounge doors
• Doors to protected lobbies
• Doors to vertical escape routes

Specific requirements from your fire risk assessment

Your fire risk assessment will identify where fire doors are needed based on:

• Building design and layout
• Occupancy type and numbers
• Escape route protection
• Fire compartmentation requirements

Installation and certification

Certification labels

Fire doors should have a certification plug or label:

• Location: Usually on the top edge of the door
• Information: Manufacturer, fire rating, certificate number, installation requirements
• Purpose: Proves the door has been tested and certified

Never remove or paint over certification labels — they provide essential information for inspection and maintenance.

Installation requirements

A fire door is only as good as its installation:

1. Follow manufacturer's instructions — specific to that door model
2. Use compatible components — frame, ironmongery, seals must be appropriate for the rating
3. Correct gaps — maintain 3mm tolerance
4. Proper fixing — frames must be securely fixed, hinges properly screwed
5. No unauthorised modifications — additional holes, replaced glazing, etc. can invalidate certification

Third-party certification schemes

Look for doors certified under schemes such as:

• BWF-CERTIFIRE — UK's largest fire door certification scheme
• Warrington Certification — third-party testing and certification
• FIRAS — Fire Industry Association scheme

These schemes provide assurance that the door has been properly tested and, when correctly installed, will perform as rated.

Maintenance and inspection

Fire doors deteriorate through use and must be inspected regularly:

Visual inspection frequency

• Daily/weekly (high-traffic areas): Quick visual check by building users
• Monthly: More thorough checks by responsible person or facilities team
• Six-monthly to annually: Detailed inspection by competent person

Professional fire door survey

A competent person should survey fire doors periodically:

• Every 6-12 months for high-risk or heavily-used buildings
• After building work that may have affected fire doors
• Following any fire or near-miss in the building
• When defects are suspected

Common fire door deficiencies

During inspections, these are the most frequently found problems:

1. Doors wedged open

The problem: Fire doors propped open with door stops, fire extinguishers, or other objects.

Why it matters: An open fire door provides no protection. Fire and smoke spread freely.

The fix: Remove wedges. If doors need to be held open for operational reasons, fit automatic hold-open devices linked to the fire alarm.

2. Missing or damaged seals

The problem: Intumescent strips or smoke seals missing, damaged, painted over, or incorrectly fitted.

Why it matters: Seals are critical components. Without them, smoke and fire can pass through gaps even when the door is closed.

The fix: Replace seals. Ensure they're the correct type for the door rating and properly fitted in grooves.

3. Gaps too large

The problem: Gaps exceeding 3mm around the door edge, often due to dropped hinges or warped doors.

Why it matters: Large gaps allow smoke and fire to pass before seals can activate.

The fix: Adjust hinges, replace worn closers, or replace the door if warped beyond adjustment.

4. Faulty or missing self-closers

The problem: Closer missing, damaged, not adjusted correctly, or door doesn't close fully.

Why it matters: A fire door that doesn't close is useless. Many fire deaths occur because smoke spread through open fire doors.

The fix: Fit or replace closers, adjust closing speed and latching force, repair or rehang door if it binds.

5. Incorrect or insufficient hinges

The problem: Fewer than 3 hinges, wrong type of hinges, or hinges with missing screws.

Why it matters: Inadequate hinges cause doors to sag, creating gaps and preventing proper closing.

The fix: Fit minimum 3 steel hinges, replace undersized hinges, ensure all screw holes filled.

6. Non-compliant glazing or panels

The problem: Standard glass fitted instead of fire-resistant glass, or glass panels too large for the rating.

Why it matters: Standard glass shatters in fire, creating a large opening for fire spread.

The fix: Replace with certified fire-resistant glazing of appropriate size and rating.

7. Unauthorised modifications

The problem: Holes drilled for cables, cat flaps fitted, door trimmed excessively, non-compliant letter plates.

Why it matters: Any modification can compromise the fire rating. The door is no longer tested and certified.

The fix: Replace door if significantly compromised, or make good with fire-stopping materials and certify the repair.

Flat entrance doors and the Fire Safety Act 2021

The Fire Safety Act 2021 made specific changes regarding flat entrance doors:

New requirements

• Explicit duty: Building owners/landlords must ensure flat entrance doors adequately resist fire
• Common areas covered: The Fire Safety Order now clearly applies to flat entrance doors as part of common areas
• Regular checks: Flat entrance doors must be included in fire risk assessments and inspection regimes

What this means for landlords

If you own or manage a block of flats:

1. Check existing flat entrance doors — Are they certified fire doors (FD30s minimum)?
2. Include in fire risk assessment — Doors must be assessed as part of building fire safety
3. Establish inspection regime — Periodic checks of condition and performance
4. Keep records — Document the type, rating, and condition of flat entrance doors
5. Consider remedial work — Budget for replacement if doors don't meet standards

Replacement and upgrading

When to replace a fire door

Replace a fire door when:

• Certification unknown — no label and cannot verify rating
• Significant damage — cracked, delaminated, holes beyond repair
• Warped beyond adjustment — gaps cannot be brought within tolerance
• Core exposed — edges damaged revealing core materials
• Repeated failures — door won't stay closed despite repairs
• Upgrade required — building changes mean higher rating needed

Upgrading existing doors

Can a normal door be upgraded to a fire door?

Generally, no. You cannot reliably upgrade a standard door to achieve fire resistance:

• Standard doors lack fire-resistant core materials
• Proper intumescent seals require routed grooves
• The door leaf itself must be tested and certified as a fire door

The only reliable option is to fit a certified fire door assembly.

Choosing replacement fire doors

When specifying replacement fire doors:

1. Confirm required rating — FD30, FD30s, FD60 based on fire risk assessment
2. Check compatibility — ensure frame, seals, and hardware are compatible
3. Use certified products — look for CERTIFIRE, FIRAS, or equivalent
4. Engage competent installers — incorrect installation invalidates certification
5. Keep certification — retain all certificates and installation records

Fire door signage

Fire doors should be clearly identified:

When signs are required

• Fire doors on escape routes — must have signage (Building Regulations requirement)
• Fire doors that need to be kept closed — "Fire door keep shut" signs
• Automatic release doors — "Automatic fire door keep clear" signs

Types of signs

"Fire door keep shut":

• Required on manually closing fire doors on escape routes
• Usually self-adhesive or screwed to door face
• Must be clearly visible

"Fire door keep locked shut":

• For fire doors that are normally locked
• Ensures doors not left open when unlocked for access

"Automatic fire door keep clear":

• For doors with hold-open devices
• Warns not to obstruct door's closing path

Frequently asked questions

Next steps

Fire doors are part of your overall fire safety strategy. Make sure you understand your broader responsibilities:

What is a fire risk assessment? →

Fire Safety Order explained →

Related articles:

• What is a fire risk assessment?
• Fire Safety Order explained
• Do I need a fire risk assessment?

Useful tools:

• Fire Safety Self-Check