Phoenix Journal · Extraction
A fire damper that will not close is one of the most common defects on a kitchen system - and grease is nearly always to blame. Here is what goes wrong and how to fix it for good.
Case postmortem
A routine fire damper drop test should take a fitter a couple of minutes per damper - so when yours refuses to close, it usually means something has been quietly going wrong for months.
Picture the scene. A busy commercial kitchen has its annual fire safety visit booked. The engineer works along the ductwork, releasing each fusible link in turn and watching the blades fall shut. Most behave. Then he reaches the damper sitting where the extract run passes through a fire-rated wall, trips the link, and nothing happens. The blades sit wide open, propped in place by a stiff, tacky film. He cleans the housing, tries again, and this time the curtain jerks halfway down and stops. On paper that damper was doing its job. In a real fire it would have held the barrier open and let flame and smoke travel straight through the compartment wall it was meant to protect.
If that sounds familiar, you are not dealing with a freak fault. A stuck fire damper is one of the most common defects found on kitchen and ventilation systems, and the cause is almost always the same handful of things. Here is what actually went wrong, and how to put it right for good.
A fire damper is a simple device with one job - to slam shut and seal a duct the moment a fire tries to spread through it. Most spring-operated dampers are held open by a fusible link, a small metal fitting that melts and splits apart at a set temperature, usually around 72°C. When the link fails, a spring or the weight of the blades drives the shutter closed. That is the whole mechanism. It only works if the blades are free to move.
In a kitchen extract environment, that freedom disappears fast. Warm, grease-laden air passes over the damper every service. As it cools, fats, oils and grease condense onto the blades, the runners and the housing. Layer by layer it builds into a sticky, then hard, deposit that glues the shutter in its open position. When the link finally releases, the blades have nothing left to fall against - they are cemented in place. Inspectors regularly find dampers jammed solid with grease, dust and debris, and a damper that cannot physically close is no barrier at all.
Grease is the headline cause, but it rarely acts alone. The other usual suspects are:
There is an important point specific to catering. Under BS 9999, fire dampers are not actually acceptable within a kitchen grease extract duct itself, precisely because grease will foul them - the clauses steer you towards fire-rated ductwork instead. Where you do legitimately find dampers is on the supply and make-up air side, on general ventilation branches, and where extract crosses a compartment wall in older or mixed installations. Wherever they sit, the same grease and dust that coats your extract will find them, so they need the same attention.
The numbers that matter
Those three figures frame the whole problem. The 72°C is how little it takes to arm the mechanism. The six months is how quickly a kitchen environment can foul it - standard buildings test annually under BS 9999, but dampers in dust-laden or heavily contaminated settings such as commercial kitchens need checking at intervals matched to the contamination, and six-monthly is the widely accepted benchmark. And 2005 is the year of the Regulatory Reform (Fire Safety) Order, which places a legal duty on the responsible person to keep fire safety provisions - dampers included - in efficient working order and good repair.
Freeing a stuck damper is not a case of forcing the blades and hoping. A proper remedial visit follows an order, because the aim is a damper that closes cleanly, seals fully and stays that way. This is roughly what a competent engineer will do:
The remedial fixes today's damper. Keeping it working is about attacking the cause, which in a kitchen means grease. A damper on or near an extract route can only stay free if the ductwork feeding it is clean, so the sensible move is to bring your dampers into the same regime as your extract cleaning. TR19 Grease, the BESA specification for fire risk management of grease within kitchen extraction, sets cleaning frequencies by how heavily the system is used - and a system cleaned to that standard simply does not deliver enough grease to glue a damper shut between visits.
Practically, that means three habits. First, test your dampers at an interval matched to how dirty the environment is - six-monthly is a safe default for catering. Second, clean the extract system to TR19 Grease so the dampers are not being re-fouled the week after they are freed. Third, keep the paperwork - your dampers, your grease cleaning and your test records should tell one consistent story. That last point matters more than people expect at inspection time; it is worth knowing what a fire risk assessor wants to see on arrival so your records answer the questions before they are asked.
Questions
BS 9999 sets a minimum of once a year for standard buildings, but dampers in dust-laden or grease-heavy environments such as commercial kitchens need checking more often. Six-monthly is the widely accepted benchmark for catering systems because grease fouls the mechanism far faster than in an ordinary office or corridor. The safest approach is to match the interval to how heavily the system is actually used.
Often it can be cleaned, freed and lubricated back to full working order, and a proper drop test afterwards will confirm the blades close and seal. Replacement is needed when there is real corrosion, a bent or seized blade, a damaged spring, or a fusible link that has already fired. A competent engineer assesses the condition first and records the outcome, so you know whether you are maintaining the damper or condemning it.
Under the Regulatory Reform (Fire Safety) Order 2005, the responsible person for the premises must keep all fire safety provisions, including fire dampers, in efficient working order and good repair. In practice that usually means the building owner, employer or managing agent arranging regular testing and keeping the records. Failing to maintain dampers is a common finding at fire risk assessment and can leave the responsible person exposed.
Phoenix Duct Clean · by the numbers
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