Home / Kitchen Extraction Cleaning / Guide
Kitchen extraction cleaning - fire dampers
A fire damper sits in the ductwork to close and stop fire spreading if a fire breaks out - a critical safety device. But the untold story of many dampers is that grease and neglect quietly seize them open, so when the moment comes, they don't close. Here is why fire dampers stick, what it means, and why cleaning and testing keep them working. This is general guidance, not fire-engineering advice.
The short answer
A fire damper is one of those safety devices you never see working - and that's the problem. It sits quietly in the ductwork, meant to spring into action only if there's a fire. But if grease and neglect have seized it, that moment of action never comes. Here's the true story behind a stuck fire damper, and why it matters. This is general guidance, not fire-engineering advice. What a fire damper does. A fire damper is fitted in ductwork where the duct passes through a fire-rated wall or floor - a boundary between fire compartments in the building. Its job is to close automatically if a fire breaks out, sealing the duct so that fire and smoke can't spread through the ductwork from one compartment to the next. It's typically held open in normal use and triggered to close by a fusible link (a heat-sensitive element that melts at a set high temperature, releasing the damper to shut) - so in a fire, the heat melts the link and the damper closes, containing the fire (as covered in the fusible-links and fire-damper pages). So the damper is a critical part of the building's passive fire protection - keeping fire from travelling through the ducts. Why dampers stick. The 'true story' behind many stuck dampers is that, over time, they can be seized by grease and neglect. Grease: in kitchen extract ductwork, grease is everywhere - and it accumulates in and around the damper mechanism, where it can gum up or clog the moving parts so the damper can't operate. Neglect and deterioration: corrosion, debris, dirt, and simple lack of maintenance can also jam or stiffen the mechanism over time. So a damper that was fine when installed can, years later, be effectively seized - stuck open, or unable to move freely. The silent failure. Here's the danger: a seized damper fails silently. It sits there looking perfectly normal - you can't tell a stuck damper from a working one just by looking at it (it's held open either way). But it's jammed, so when a fire actually breaks out, it doesn't close. And then the fire and smoke spread through the ductwork - exactly what the damper was installed to prevent - defeating the fire compartmentation and letting the fire travel through the building via the ducts. So the failure is hidden until the worst possible moment: you don't know the damper is stuck until it fails to save you. This is what makes a seized fire damper so dangerous - it's a safety device that's silently not working. Cleaning and testing: the answer. Because the failure is hidden, you can't rely on the damper looking fine - you have to actively keep it able to work, through cleaning and testing. Cleaning: keeping the ductwork and the damper area clean of grease means grease doesn't accumulate to seize the mechanism. In kitchen extract systems, where the ductwork is greasy, cleaning around fire dampers is part of proper extraction cleaning (and the point where duct cleaning and fire dampers meet - as covered in the fire-dampers-and-ductwork-cleaning page). Testing: fire dampers should be regularly tested - drop-tested (operated to check they actually close) at appropriate intervals - to verify they work, catching a seized one before a fire does (as covered in the fire-damper drop-testing and testing-frequency pages). Testing is the way to find a silently-stuck damper. So cleaning keeps dampers from seizing, and testing catches any that have. The takeaway. So the true story behind a stuck fire damper is grease and neglect seizing a critical safety device so it fails silently when a fire comes - and the answer is to keep dampers clean (so grease doesn't seize them) and regularly tested (so a seized one is caught before it matters). (Fire damper provision, testing regimes and fire-engineering matters are for fire-safety professionals - this is general guidance.) So don't let a fire damper become a stuck one: keep it clean and tested, so it works when it's needed. This is general guidance, not fire-engineering advice.
Key points
What a fire damper does
A fire damper is a safety device fitted in ductwork where the duct passes through a fire-rated wall or floor - a boundary between fire compartments in the building. Its job is to close automatically if a fire breaks out, sealing the duct so that fire and smoke can't spread through the ductwork from one compartment to the next. It's typically held open in normal use, and triggered to close by a fusible link - a heat-sensitive element that melts at a set high temperature, releasing the damper to shut (as covered in the fusible-links and fire-damper pages).
So in a fire, the heat melts the link and the damper closes, containing the fire and stopping it travelling through the ducts. The fire damper is thus a critical part of the building's passive fire protection - it maintains the fire compartmentation (the division of the building into fire-resisting sections) at the points where ductwork passes through, which would otherwise be a gap fire could travel through. So what a fire damper does - closes to contain a fire - is a genuinely important safety function: keeping fire and smoke from spreading through the ductwork. The problem, covered next, is what happens when a damper can't do this because it's seized. So the damper is meant to shut and stop fire spreading through the ducts. This is general guidance, not fire-engineering advice.
Why dampers stick
The 'true story' behind many stuck dampers is that, over time, they can be seized by grease and neglect. Grease is the big one in kitchen extract ductwork: grease is everywhere in the ducts, and it accumulates in and around the damper mechanism, where it can gum up or clog the moving parts (the damper blade, the linkage, the fusible link) so the damper can't operate freely. A damper caked in grease may be physically unable to move. And neglect and deterioration add to it: corrosion, debris, dirt and simple lack of maintenance can jam or stiffen the mechanism over the years.
So a fire damper that was working perfectly when installed can, years later, be effectively seized - stuck open, or unable to move freely - through the gradual accumulation of grease and the effects of neglect. This is especially a risk in kitchen extract systems precisely because they're so greasy: the grease that the extraction cleaning exists to control is the same grease that can seize a fire damper in the ductwork. So the damper is a casualty of the same neglect that lets grease build up generally. So why dampers stick - grease and neglect seize the mechanism - is the cause: the moving parts gummed up or jammed by grease, corrosion and lack of maintenance. The consequence of that seizing, covered next, is the dangerous part. So grease and neglect can jam a damper over time. This is general guidance, not fire-engineering advice.
The silent failure
Here's what makes a stuck fire damper so dangerous: it fails silently. A seized damper sits there looking perfectly normal - you can't tell a stuck damper from a working one just by looking at it (it's held open in normal use either way, so a jammed-open damper looks identical to a healthy one). But it's seized, so when a fire actually breaks out and the fusible link melts, the damper doesn't close - it stays open.
And then the fire and smoke spread through the ductwork - exactly what the damper was installed to prevent - defeating the fire compartmentation and letting the fire travel through the building via the ducts. So the failure is hidden until the worst possible moment: you don't know the damper is stuck until it fails to close in a real fire, when it's too late. This is the crux of the problem - a fire damper is a safety device you rely on without ever seeing it work, so a silently-seized one gives a false sense of protection (you think you're protected; you're not). So the silent failure - it looks fine until a fire comes - is why a stuck damper is so serious: the failure is invisible in normal times and only revealed by the fire it was meant to contain. This is exactly why you can't just trust a damper to be fine - covered next. So a seized damper hides its failure until it's too late. This is general guidance, not fire-engineering advice.
Cleaning keeps them free
Because grease is a main cause of dampers seizing, keeping the ductwork and damper area clean of grease is a key part of keeping dampers able to work. In kitchen extract systems, where the ductwork is greasy, cleaning around fire dampers is part of proper extraction cleaning: removing the grease from the ductwork and the damper area so it doesn't accumulate to gum up or seize the mechanism. This is the point where duct cleaning and fire dampers meet (as covered in the fire-dampers-and-ductwork-cleaning page) - the cleaning that controls the grease also helps keep the dampers free.
So proper extraction cleaning, done where fire dampers are present, helps protect the dampers from grease-seizing: the same clean that removes the fire-risk grease from the ductwork keeps the damper area clear so the damper can still move. A neglected, grease-laden system, by contrast, is exactly where dampers seize (the grease that isn't being cleaned accumulates on the damper too). So keeping the system cleaned regularly helps keep the dampers working, as well as controlling the general fire risk. So cleaning keeps them free - grease-free dampers don't seize - is one half of the answer: don't let grease build up to seize the damper. But cleaning alone isn't the whole answer, because a damper can seize for other reasons (corrosion, age) - which is why testing is also essential, covered next. So cleaning helps stop grease seizing the dampers. This is general guidance, not fire-engineering advice.
Testing catches the stuck ones
Because a seized damper fails silently and can seize for reasons beyond grease (corrosion, debris, age), the essential way to catch a stuck damper is testing - actively checking that the damper operates. Fire dampers should be regularly tested, typically by drop-testing - operating the damper to check it actually closes (drops shut) as it should - at appropriate intervals (as covered in the fire-damper drop-testing and testing-frequency pages). Testing is how you find a silently-stuck damper: you make it operate, and if it doesn't close, you've found the problem before a fire did.
So testing is the safeguard that catches what looking can't: a damper that appears fine but is actually seized. A regular drop-testing regime means each damper is proven to work (or found faulty and fixed) periodically, rather than being trusted blindly for years until a fire reveals a failure. So the two measures work together: cleaning keeps dampers from seizing (removing the grease that gums them up), and testing catches any that have seized anyway (for whatever reason) - so a stuck damper is found and rectified before it matters. Fire damper provision, testing intervals and the fire-engineering specifics are matters for fire-safety professionals (this is general guidance) - but the principle is clear. So testing catches the stuck ones - drop-test to prove they work - is the other half of the answer: don't trust a damper is working, test it. So test dampers regularly so a seized one is caught early. This is general guidance, not fire-engineering advice.
Questions
It closes automatically if a fire breaks out - usually triggered by a fusible link melting - sealing the ductwork where it passes through a fire-rated wall or floor, so fire and smoke can't spread through the ducts between fire compartments. A fire damper is a safety device fitted in ductwork where the duct passes through a fire-rated wall or floor - a boundary between fire compartments in the building. Its job is to close automatically if a fire breaks out, sealing the duct so fire and smoke can't spread through the ductwork from one compartment to the next. It's typically held open in normal use and triggered to close by a fusible link - a heat-sensitive element that melts at a set high temperature, releasing the damper to shut. So in a fire, the heat melts the link and the damper closes, containing the fire and stopping it travelling through the ducts. It's a critical part of the building's passive fire protection, maintaining the fire compartmentation where ductwork passes through. So it closes to contain a fire and stop it spreading through the ducts. So it shuts to stop fire spreading through the ductwork. This is general guidance, not fire-engineering advice.
Grease and neglect seize them over time - grease accumulating in and around the mechanism (everywhere in kitchen extract ducts) gums it up, and corrosion, debris and lack of maintenance jam or stiffen it, so the damper can't move. Fire dampers get stuck over time through grease and neglect seizing the mechanism. Grease is the big cause in kitchen extract ductwork: grease is everywhere in the ducts, and it accumulates in and around the damper mechanism (the blade, linkage, fusible link), gumming up or clogging the moving parts so the damper can't operate freely - a damper caked in grease may be physically unable to move. And neglect and deterioration add to it: corrosion, debris, dirt and simple lack of maintenance can jam or stiffen the mechanism over the years. So a fire damper that worked perfectly when installed can, years later, be effectively seized (stuck open or unable to move). This is especially a risk in kitchen extract systems because they're so greasy - the grease the extraction cleaning controls is the same grease that can seize the damper. So because grease and neglect gum up and jam the mechanism. So grease, corrosion and neglect seize them. This is general guidance, not fire-engineering advice.
Because it fails silently - it looks normal (held open like a working one), so you can't tell it's seized, but when a fire comes it doesn't close, and the fire and smoke spread through the ductwork exactly as the damper was meant to prevent. A stuck fire damper is dangerous because it fails silently. A seized damper sits there looking perfectly normal - you can't tell a stuck one from a working one by looking (both are held open in normal use), so a jammed-open damper looks identical to a healthy one. But it's seized, so when a fire actually breaks out and the fusible link melts, the damper doesn't close - it stays open. And then the fire and smoke spread through the ductwork, defeating the fire compartmentation and letting the fire travel through the building via the ducts - exactly what the damper was installed to prevent. So the failure is hidden until the worst possible moment (a real fire), giving a false sense of protection until then. That's what makes it so serious - a safety device that's silently not working, discovered only when it fails to save you. So because it fails silently, at the one moment it's needed. So it hides its failure until a fire. This is general guidance, not fire-engineering advice.
By removing the grease that seizes them - keeping the ductwork and damper area clean of grease means it doesn't accumulate to gum up the mechanism; cleaning around dampers is part of proper extraction cleaning in greasy kitchen extract systems. Cleaning helps keep fire dampers working by removing the grease that seizes them. Grease is a main cause of dampers seizing (accumulating in and around the mechanism and gumming it up), so keeping the ductwork and the damper area clean of grease means it doesn't build up to jam the damper. In kitchen extract systems, where the ductwork is greasy, cleaning around fire dampers is part of proper extraction cleaning - the same clean that removes the fire-risk grease from the ductwork keeps the damper area clear so the damper can still move. So proper extraction cleaning helps protect the dampers from grease-seizing. A neglected, grease-laden system is exactly where dampers seize. But cleaning alone isn't the whole answer - a damper can seize for other reasons (corrosion, age) - so testing is also essential to catch any that have seized. So cleaning stops grease seizing them; testing catches the rest. So by keeping grease from gumming up the mechanism. This is general guidance, not fire-engineering advice.
You can't tell by looking - a seized damper looks normal; the only reliable way is testing (drop-testing), operating the damper to check it actually closes, which catches a silently-stuck one before a fire does. You can't tell a stuck fire damper by looking at it - a seized damper looks perfectly normal (held open like a working one), so visual inspection alone won't reveal it. The reliable way to know is testing: fire dampers should be regularly tested, typically by drop-testing - operating the damper to check it actually closes (drops shut) as it should, at appropriate intervals. Testing is how you find a silently-stuck damper: you make it operate, and if it doesn't close, you've found the problem before a fire did. So a regular drop-testing regime means each damper is proven to work (or found faulty and fixed) periodically, rather than being trusted blindly until a fire reveals a failure. Testing catches what looking can't. The testing intervals and regime are matters for fire-safety professionals. So by testing (drop-testing) it, not by looking. So you test it - you can't tell by sight. This is general guidance, not fire-engineering advice.
Cleaning the grease from the ductwork and damper area is part of extraction cleaning; fire damper testing (drop-testing) and the fire-safety regime are matters for fire-safety professionals and the responsible person - the two work together to keep dampers functioning. Keeping fire dampers working involves two things with different responsibilities. Cleaning the grease from the ductwork and the damper area is part of proper extraction cleaning - your extraction cleaner cleans around the dampers as part of cleaning the whole greasy system, helping keep grease from seizing them. Testing the dampers (drop-testing to check they operate) and the overall fire-safety regime are matters for fire-safety professionals and the building's responsible person (under fire-safety duties) - the testing intervals, the fire-engineering, and the maintenance of the dampers as fire-safety devices sit within fire safety, not general cleaning. So the two work together: extraction cleaning keeps the dampers free of grease, and fire-safety testing verifies they work. Coordinate both to keep the dampers functioning. This page is general guidance, not fire-engineering advice - so involve the appropriate fire-safety professional for the testing and provision. So cleaning is extraction's part; testing is fire safety's. So cleaning by your cleaner, testing by fire-safety professionals. This is general guidance, not fire-engineering advice.
Grease in the ductwork can seize a fire damper open; our extraction cleaning removes the grease from the ductwork and around the dampers - helping keep them free to close - as part of cleaning the whole system to TR19 Grease. Ask us to clean your system; arrange damper testing with your fire-safety provider. This is general guidance, not fire-engineering advice.
