Fire Compartmentation Explained: What It Is and Where It Fails
By Sebastian Grabowski, DC Fire & Security, Luton. Updated October 2026.
What is fire compartmentation?
Fire compartmentation divides a building into sealed sections using fire-resisting walls, floors and doors, so a fire and its smoke stay in one section for a set time, usually 30, 60 or 120 minutes. It gives people time to leave and firefighters time to work. It only works if the barrier is unbroken, and in the two surveys we have written up, 371 of 407 locations (91%) had gaps that needed fire stopping.
Why buildings are divided into compartments
A fire is not stopped by good intentions. It is stopped by a barrier that has been tested to hold for a known time.
A compartment is a space bounded by walls, a floor and a ceiling that are rated to resist fire. If a fire starts in one flat, one hotel room or one shop unit, the compartment keeps heat and smoke in that space while the people next door get out, or while the fire service arrives.
This is the reason flats can use a stay-put approach. If the fire is in another flat, the walls, floor and front door between you and the fire are what keep you safe while you wait for instructions. If those barriers are broken, stay-put stops being safe, and nobody inside the building knows.
Compartmentation also protects the escape routes. A corridor or stair with fire-resisting walls and doors stays usable for longer, so people can leave through it.
Fire resistance periods in plain English
The number is minutes. The letters say what the barrier is tested for.
| Term | What it means | Where you see it |
|---|---|---|
| 30 minutes (FD30, EI 30) | The barrier holds back flames and heat for at least half an hour | Flat entrance doors, corridor walls in many blocks and offices |
| 60 minutes (EI 60) | One hour of resistance | Walls and floors between flats, stair enclosures, risers |
| 90 and 120 minutes (EI 90, EI 120) | Longer periods for taller or higher-risk buildings | Compartment floors, plant rooms, some stair cores |
| R | Load bearing: the structure keeps standing | Columns, beams, floors that carry weight |
| E | Integrity: no flames or hot gases get through | Walls, floors, doors, seals |
| I | Insulation: the far side does not get hot enough to ignite things | Walls, floors, doors, seals |
REI together means a wall or floor that carries load, holds back flames and limits heat. A fire door is normally rated on integrity and sometimes insulation. The period needed for each building comes from its fire strategy and the rules in force when it was built, set out for new work in Approved Document B. The rating applies to the whole assembly. A 60 minute wall with a hole through it is not a 60 minute wall.
What compartmentation is made of
Six parts. All of them have to be intact for the compartment to work.
| Part | Job | Usual weak point |
|---|---|---|
| Fire-resisting walls and floors | The main barrier | Holes cut for later cabling and pipes |
| Fire doors and frames | The openings in the barrier | Gaps, missing closers, damaged seals. See fire door inspections |
| Fire stopping | Seals round every pipe, cable and duct that passes through | Missing, wrong product, or removed during other work. See fire stopping |
| Cavity barriers | Stop fire travelling inside hidden voids and façades | Left out or cut short at corners |
| Fire and smoke dampers | Close ductwork when a fire starts | Seized, never tested, blocked access |
| Fire-resisting glazing and ceilings | Keep the barrier continuous | Wrong glass, damaged boards, missing sections above ceiling tiles |
One wall, and every place it can leak
Picture a single fire wall in a corridor, running from the floor slab to the slab above. Walk along it with a torch.
- 1The head of the wall. Above the suspended ceiling, the wall must go all the way up to the slab. Often it stops at the ceiling tile line. Nobody sees it, so nobody fixes it.
- 2The foot and the sides. Where the wall meets the floor, the external wall or a window mullion, there is a joint. If it is open or filled with the wrong material, fire gets round the end.
- 3Cables. A data or alarm cable pulled through after the building was finished. The hole is bigger than the cable and nothing seals it.
- 4Pipes. Plastic waste pipes melt in a fire and leave an open hole. They need a collar or wrap tested for that pipe size. Metal pipes need the gap packed correctly.
- 5Sockets and back boxes. Two sockets back to back in a plasterboard wall can leave a hole straight through the barrier.
- 6The door. A wall rated at 60 minutes with a door that does not shut properly is weak at the door, not at the wall.
None of these is visible from the corridor with the ceiling tiles in place. That is why a visual check by someone walking past is not a compartmentation check, and why a building can look fine and still fail.
Where compartmentation fails in real buildings
Rarely at the original build. Usually afterwards.
We have written up two compartmentation surveys: a 5-storey hotel and a restaurant. Across 407 locations checked, 371 needed fire stopping. That is 91%. The hotel was 305 of 327 and the restaurant 66 of 80. Two surveys is a small sample, so treat it as a guide and not a national figure. The detail is on what a compartmentation survey finds.
The pattern is consistent. A cable contractor, an electrician or a plumber makes a hole, the job finishes, and the seal is not put back. Over a few years a building collects dozens of these. Nobody did anything deliberate. The record just never existed.
How compartmentation links to stay-put and escape
Two different strategies depend on the same barriers.
| Strategy | How it works | What it needs from compartmentation |
|---|---|---|
| Stay-put | People in unaffected flats stay in their flat until told otherwise | Flat walls, floors and front doors that hold for the full rating |
| Simultaneous evacuation | Everyone leaves when the alarm sounds | Escape routes that stay clear of smoke, so corridors and stairs must be sealed from the rooms around them |
If you do not know whether the barriers are intact, you do not know whether your strategy is safe. A fire risk assessment should say how far compartmentation was checked. Where the assessor could not see above ceilings or inside risers, the report usually recommends a survey.
How to find out if yours is intact
Start with paper, then check the building.
- 1Find the fire strategy and plans. They show where the compartment lines are meant to be. If none exist, that is a finding in itself.
- 2Check the last fire risk assessment. Look for any line saying compartmentation could not be inspected.
- 3Ask for the work history. Cabling, new extraction, refits and conversions are where breaches come from. Ask whether anyone reinstated the fire stopping and kept a record.
- 4Get the doors inspected. A fire door inspection covers every door in the compartment line.
- 5Commission a survey. A fire stopping survey finds unsealed gaps. A compartmentation survey goes further, with opening-up and a drawing-referenced record for higher-risk buildings.
If you want the wider picture first, read what is passive fire protection. To decide when a survey is worth it, see when do you need a compartmentation survey. The full set of services is on our fire protection services page.
Sources
- Approved Document B: Fire safety (GOV.UK)
- Regulatory Reform (Fire Safety) Order 2005 (legislation.gov.uk)
- Building Safety Act 2022 (legislation.gov.uk)
Updated October 2026 by Sebastian Grabowski, DC Fire & Security, 2 Winsdon Court, Luton LU1 5LZ.
Sealing that can be shown to be right
Where we repair fire stopping, the work is done by our BM TRADA Q-Mark / FIRAS-certificated contractors using tested products fitted to the manufacturer's method. Each seal is photographed and recorded, and the certificate goes in your fire safety file.
Frequently Asked Questions
What is the difference between compartmentation and fire stopping?
How long does a compartment wall have to hold?
Can I check compartmentation myself?
Who is responsible for compartmentation in a building?
Do fire alarms replace compartmentation?
Does a fire risk assessment cover compartmentation?
Not sure if your compartments are intact?
Send us the fire risk assessment, floor plans or a few photos of your risers to info@dcsecurity.co.uk, or use the form. We usually come back with a fixed price the same day. Luton, Bedfordshire, Hertfordshire, Buckinghamshire and London.
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