What is a smoke compartment?
A smoke compartment is an enclosed part of a building intended as the maximum area over which smoke may spread. The point is that smoke from one room does not fill the whole building, so that escape routes remain usable.
Why smoke, not flame, is the criterion
In a building fire, smoke is more dangerous than flame. It spreads far faster than the fire itself, is hot, toxic and takes away visibility completely. Someone standing in a smoke-free route can walk out; someone standing in smoke is disorientated within a few breaths. That is why a fire compartment is subdivided: the fire compartment limits the spread of fire, the smoke compartment limits the spread of smoke.
How a smoke compartment is formed
- Smoke-tight walls and floors carried up to the structural soffit — not just to the suspended ceiling.
- Smoke control doors, self-closing and fitted with seals so that the closed leaf resists smoke passage. In the UK these are tested for ambient and medium-temperature smoke leakage (the Sa classification) as well as for fire resistance.
- Sealed service penetrations for pipes, cable trays and ducts.
- Smoke ventilation in larger buildings — natural smoke and heat exhaust vents, or mechanical smoke extract.
The permitted size of a smoke compartment and the exact requirements come from national building regulations and from guidance for the specific use — shops, assembly buildings, schools and hospitals each have their own limits. In the Netherlands the comparable term has been subbrandcompartiment since 2012; the older rookcompartiment, with a 30-minute smoke resistance requirement, still appears in old drawings.
Where it goes wrong in practice
- Penetrations. Every pipe, cable tray and duct crossing the separation punches a hole in it. Without a fire and smoke collar or seal, the requirement is met on paper only.
- Doors held open. A smoke control door only works closed. Wedged-open doors are the most common defect; the only acceptable solution is a hold-open device linked to the alarm so it releases on detection.
- Suspended ceilings. Smoke travels over the ceiling into the next room whenever the separating wall stops at the ceiling grid.
- Dwellings. A dwelling is normally a smoke compartment in its own right, with interlinked smoke alarms on every storey.
Related terms
- Fire compartment
- Fire resistance
- Escape route
- Smoke alarm
- Fire collar
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