Phoenix Journal · Extraction
A fire damper spends years doing nothing, then is asked to save a building in a single moment. In a grease-laden kitchen extract, that moment is exactly when it can fail.
Kitchen extraction
A fire damper is a quiet piece of engineering that spends years doing nothing at all - until the one moment it is asked to save a building.
The uncomfortable truth is that most stuck fire dampers are discovered on the day they are needed, which is the worst possible day to find out. In a busy commercial kitchen, the culprit is almost always the same: warm, sticky grease that has drifted up through the extract ductwork and quietly welded a moving part in place. The damper looks perfectly fine from the outside. It has simply lost the ability to do the single thing it exists to do - close.
This article is the real story of how that happens, why it matters so much in a kitchen extract, and what the current UK standards expect of you as the person responsible for the building.
A fire damper is a mechanical barrier built into ventilation ductwork where that duct passes through a fire-rated wall, floor or compartment line. In normal running it sits open, letting air move freely. When a fire takes hold, the damper is meant to snap shut and seal the opening, so that flames, heat and combustion gases such as smoke and CO₂ cannot travel along the duct and breach the compartment that was designed to hold them back.
Most spring-operated dampers are held open by a fusible link - a small metal fitting that melts at a set temperature, commonly around 72°C. Once the link releases, a spring pulls the blades or a folding curtain down until the duct is fully closed. It is deliberately simple, because simple things fail less often. The whole design assumes one thing, though: that the blades can actually move when the link lets go.
That assumption is tested with a drop test. A competent engineer releases the link or triggers the actuator, watches the damper travel fully to the closed position, confirms it has sealed, then resets it and records the result. Installation and maintenance sit under DW 145, and the wider fire strategy for the building sits under BS 9999. The drop test is not paperwork for its own sake - it is the only honest way to prove the damper still works, because a jammed damper and a healthy one look identical until the moment you ask them to close.
The numbers that matter
Fire damper testing is not optional. Under the Regulatory Reform (Fire Safety) Order 2005, the responsible person for a premises must keep all fire safety measures in effective working order, and fire dampers are squarely within that duty. BS 9999 sets the baseline of at least an annual drop test by a competent person - but it also makes clear that dampers in dust-laden or heavily contaminated settings need testing more often. For a commercial kitchen extract, industry guidance from bodies such as the BESA points to a six-monthly interval, precisely because grease accumulates so quickly.
Those three figures tell the whole story between them. A link that releases at 72°C is useless if grease has cemented the blades; a legal duty that dates from 2005 is not satisfied by a damper that was tested once and forgotten; and a six-monthly rhythm exists because kitchen grease does not wait twelve months to cause a problem. Read together, they explain why extract dampers demand far more attention than dampers in a clean office riser.
Here is where the true story usually goes wrong. Every service from a fryer or a range sends a fine aerosol of oil & grease into the extract stream. As that vapour cools along the duct, it condenses and settles as a soft film, then bakes into a hard, varnish-like crust under repeated heat. When that crust forms around a damper blade, its spindle or the fusible link itself, the moving parts stop being moving parts. The link may still melt on cue in a fire, but the blade never travels, because it is glued open by carbonised fat.
The scale of the risk is not theoretical. Around 70% of commercial kitchen fires are linked to grease and fat build-up in extraction systems, and a grease layer as thin as 0.1mm on a duct wall is already a meaningful fire load. This is why BS 9999 is cautious about placing conventional fire dampers in grease extract at all - a component that cannot be kept clean cannot be relied upon - and why the whole system has to be managed as a fire-safety asset, not just a ventilation one.
The measurable framework for that is TR19 Grease, the standalone specification the BESA introduced in 2019 for fire-risk management of grease in kitchen extraction. It defines cleanliness in numbers rather than opinions. Deposits below 200 microns are treated as an acceptable, lower-risk level; between 200 and 999 microns cleaning is required; and 1,000 microns or more is a high fire risk needing immediate attention. After a clean, verification should confirm grease has been reduced well below those thresholds, evidenced with matched before-and-after photographs and readings taken by a wet film thickness measurement behind the grease clean rather than a glance and a signature.
Keeping a damper reliable, then, is really two jobs done together. The extract has to be cleaned to a measured standard so grease never gets the chance to seize the mechanism, and the damper itself has to be drop-tested, freed, lubricated and reset on a sensible cycle. Skip the cleaning and the finest testing regime in the world is testing a component that is already compromised. If your last engineer noted a damper that would not travel, our guide on why a fire damper gets stuck walks through the usual causes and what a proper fix looks like.
Questions
BS 9999 sets a baseline of at least an annual drop test by a competent person. However, dampers in dust-laden or heavily contaminated settings such as kitchen grease extract need testing more frequently, and industry guidance points to a six-monthly interval. Grease accumulates quickly, so the shorter cycle exists to catch a seizing damper before it fails when it matters.
Yes. Under the Regulatory Reform (Fire Safety) Order 2005, the responsible person for a premises must keep all fire safety measures in effective working order, and fire dampers fall within that duty. In practice this means arranging drop tests by a competent person and keeping records of the results. Failing to maintain and prove your dampers can leave you in breach of the Order.
Cooking sends a fine aerosol of oil and grease into the extract, which condenses along the duct and bakes into a hard, varnish-like crust under repeated heat. When that crust forms around a damper blade, its spindle or the fusible link, the moving parts effectively become glued in place. The link may still melt in a fire, but the blade cannot travel, so the duct never seals.
A drop test is carried out to confirm the damper travels fully to the closed position, seals, and resets correctly. Alongside that, the surrounding extract is cleaned to the TR19 Grease specification and verified with deposit or wet film thickness readings against measured thresholds, supported by matched before-and-after photographs. Together this evidence shows the mechanism is free to move and the grease that would seize it has been removed.
Phoenix Duct Clean · by the numbers
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