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Extraction cleaning - building risk
A grease fire is easy to imagine as a kitchen problem - flames on the cookline, dealt with there. The real danger is that grease in the ductwork lets a fire leave the kitchen and travel the building.
The short answer
Kitchen grease is a building fire risk, not just a kitchen one, because the extract ductwork carrying the grease runs through the structure - across ceilings, up risers, between floors. A fire that starts on the cookline can follow the grease-lined ductwork through concealed voids into other parts of the building, defeating the fire compartmentation and threatening floors, occupiers and escape routes far beyond the kitchen itself.
The kitchen-only illusion
It is natural to think of a kitchen grease fire as contained to the kitchen - a flare-up on the cookline, serious but local. That picture is what makes people underestimate the risk, because it imagines the fire staying where it started. The danger of grease is precisely that it gives a fire a way out of the kitchen and into the rest of the building.
The route is the ductwork. Kitchen extract does not stay in the kitchen - it runs through the building, across ceiling voids, up vertical risers, between floors, to a discharge point often on the roof. That ductwork, lined with combustible grease, is a ready-made channel for fire to travel along, out of sight, into parts of the building far from where it began.
How it travels
When a fire reaches grease-laden ductwork, the grease is fuel and the duct is a conduit. The fire can run along the internal grease coating, spreading through the concealed run faster than anyone can see or reach it, carried through voids and risers that pass through the building's structure. A fire that would have been contained on the cookline instead follows the ductwork wherever it goes.
This is what turns a kitchen fire into a building fire. The ductwork breaches the compartments the building relies on to hold a fire in one place, and a grease-fuelled fire travelling that ductwork can emerge in another compartment entirely - a different floor, a void above a ceiling, a space occupied by someone else. The grease has taken the fire out of the kitchen and into the building.
Why it threatens the whole building
The consequences reach beyond the kitchen and its operator. In a multi-occupancy building - a kitchen beneath flats, a restaurant in a larger complex, a canteen within an office or care building - a fire travelling the ductwork threatens the people and spaces above and around it, who may have nothing to do with the kitchen at all. The grease-fire risk becomes everyone's risk in the building, not just the cook's.
It also threatens the things a building's fire safety depends on: escape routes that may be compromised if fire spreads into them, and the compartmentation that is supposed to give people time to get out. A fire that defeats compartmentation by travelling greasy ductwork undermines the whole fire strategy of the building - which is why grease in kitchen extract is treated as a serious building-level fire risk, not a kitchen housekeeping issue.
Fire dampers and their limits
Buildings try to control this with fire dampers - devices in the ductwork that close where it crosses a fire barrier, blocking the fire's path. But dampers only help if they actually close, and grease is one of the things that stops them - the same build-up that fuels the fire can clog the damper mechanism so it fails to shut. A grease-laden system can therefore be defeating its own fire barriers at the same time as fuelling the fire.
So grease attacks the building's fire defences twice: it provides the fuel and the path for the fire, and it can jam shut the very devices meant to stop that path. Keeping the ductwork clean and the dampers tested is what keeps those defences working - a grease-choked system leaves the building relying on barriers that may not close when the fire arrives.
Why cleaning matters at building scale
Understanding grease as a building fire risk reframes why extract cleaning matters. It is not only about protecting the kitchen or satisfying the operator's insurance - it is about keeping a fire that starts in the kitchen from spreading through the building and threatening everyone in it. Cleaning the grease out of the ductwork removes the fuel and the path that would let a local fire become a building-wide one.
That is why the responsible person's fire-safety duty, and the standards behind extract cleaning, take the whole system so seriously. Removing the grease from the concealed ductwork, keeping the fan and canopy clean, and keeping fire dampers working are what confine a kitchen fire to the kitchen - protecting not just the business but the building and the people in it. At building scale, extract cleaning is a fire-spread control, which is exactly what it should be understood as.
Questions
Because the extract ductwork carrying the grease runs through the building - across ceilings, up risers, between floors. A fire on the cookline can follow the grease-lined ductwork through concealed voids into other parts of the building, defeating its fire compartmentation.
Not necessarily - that is the dangerous assumption. Grease-lined ductwork gives a fire a path out of the kitchen and into the building, carried through voids and risers far from where it started.
The internal grease coating is fuel and the duct is a conduit, so the fire can run along the ductwork through concealed voids and risers faster than anyone can see or reach it - emerging in another compartment, floor or space entirely.
Everyone in the building. In multi-occupancy premises - a kitchen beneath flats, a restaurant in a complex - a fire travelling the ductwork threatens people and spaces above and around it who may have nothing to do with the kitchen.
They should, but only if they close - and grease is one of the things that clogs a damper mechanism so it fails to shut. A grease-laden system can fuel the fire and jam shut its own fire barriers at the same time.
Cleaning the grease from the ductwork removes the fuel and the path that would let a local kitchen fire become a building-wide one - confining the fire to the kitchen and protecting the whole building and everyone in it.
We clean the grease from the concealed extract system - the fuel and the path that would let a fire travel the building.
