Phoenix Journal · Extraction
A small fire at the range can stay in the kitchen or run through the whole building - and the difference is decided months earlier, inside your extraction ductwork. Here is how the first hour really unfolds.
Kitchen fire · the first hour
Two kitchens, the same flare-up on the range - and within sixty minutes, two completely different outcomes.
Picture a busy service. A pan of oil overheats, a burner flame licks up into the canopy, and a small fire takes hold at the cooking line. In those first seconds the two kitchens look identical. What separates them is not luck or bravery - it is what has been happening above and behind the cooking line for months, out of sight, inside the extraction system.
Grease is the fuel that decides how the next hour unfolds. Once a fire finds its way into a grease-lined duct, it stops being a contained cooking fire and becomes a structural fire that travels through the building, hidden from view and hard to reach. Fire and rescue services record a kitchen extract ductwork fire, on average, every nine days in the capital alone - so this is not a rare freak event, it is a recurring, predictable failure.
It helps to understand why the extract is the weak point. Every time you fry, grill or char-grill, warm droplets of fat and vapour are drawn up off the food and pulled through the filters into the ductwork. As that vapour cools on the metal it condenses into a sticky film, and layer by layer it hardens into a fuel that coats surfaces you never see and cannot easily reach. The cooking line can look immaculate while the hidden run above it is anything but.
Below we walk the same first hour through two systems side by side: one cleaned and maintained to the BESA TR19 Grease standard, the other left to accumulate. The contrast is the whole argument for planned extraction cleaning.
In this kitchen the ductwork is cleaned on a schedule matched to its usage, grease is kept below the TR19 Grease action level, and a fixed suppression system sits over the cooking range. Here is how the hour tends to go.
The heat detector or fusible link over the range trips and the wet chemical suppression system discharges across the appliances and into the canopy. Wet chemical works by saponification - it reacts with hot cooking oils to form a soapy, non-combustible crust that smothers the fuel and cools it below its ignition point. Gas and power to the cooking line are cut automatically. The fire is starved at source before it can climb into the duct.
Because the extract is not lined with combustible grease, there is little for a stray flame to feed on further up the system. Staff evacuate, the fire and rescue service attends a contained incident, and the building fabric is largely intact. Trading resumes in days rather than months, and the insurer sees a maintained system with cleaning certificates and a documented fire risk assessment.
None of this is accidental. Access panels have been fitted along the duct run so that every metre can be reached and cleaned, filters are swapped and degreased on a rota, and each visit ends with the grease measured and recorded, not just wiped away where it shows. That paper trail is what turns a good intention into a defensible position when the loss adjuster arrives.
Pros
Cons
This kitchen looks spotless at the cooking line, but the canopy, filters, plenum and vertical riser have not been properly cleaned in a long time. Deposits sit well beyond 200 microns, in places past 1,000 microns - a high fire-risk build-up. The same flare-up now behaves very differently.
If a suppression system is fitted at all, its nozzles may be caked and its coverage compromised. A flame reaches the greasy filters and canopy, and instead of being smothered it finds a continuous fuel path. Grease ignites at surprisingly modest temperatures once it is airborne as vapour and heat, and the fire begins to draw itself up into the extract.
This is where the two stories separate for good. Fire travels through the duct faster than crews can follow it, moving through voids, ceiling spaces and the riser toward the roof - often reaching those spaces before anyone realises the fire has left the kitchen. The extract system, built to move air quickly, now acts like a chimney feeding oxygen to the flames. A single-room incident becomes a whole-building fire, and the fire service is fighting something it cannot see. Many of these premises never reopen.
The bill that follows is rarely just the kitchen. Once fire has run the duct, the roof void, adjoining units and any flats above are all in play, and the reinstatement can dwarf the cost of the equipment that started it. Add lost trade over the months it takes to rebuild, the risk of losing staff who cannot wait, and the reputational hit, and the short-term saving on cleaning looks like the most expensive decision the business ever made.
Pros
Cons
Ignition does not only come from the range. Faulty appliances and worn leads add heat sources right where the grease is, which is why electrical safety and PAT testing in kitchens belong in the same conversation as extract cleaning.
The gap between Option A and Option B is not a matter of opinion - it is measured in microns and days. These are the figures a fire risk assessment turns on.
A heavy-use kitchen running 12 to 16 hours a day should have its extract system cleaned roughly every three months; moderate use every six months; light use every twelve. The right interval depends on what you cook and how hard the system works - but the goal is always the same: keep the fuel out of the duct so that hour one stays in the kitchen.
Questions
Faster than most people expect. Once flames reach grease-coated filters and canopy, the fire can draw itself up into the duct within the first minutes and then travel through hidden voids and the riser toward the roof, often reaching those spaces before anyone realises the fire has left the kitchen. The extract, built to move air quickly, effectively acts like a chimney feeding the flames. This is why keeping combustible grease out of the system matters far more than the size of the original flare-up.
No. A wet chemical suppression system protects the cooking range and canopy by smothering burning oil at source, but it does not clean grease from the ductwork above and behind it. If deposits have built up beyond the TR19 Grease thresholds, a fire can still find a fuel path further up the system where the suppression cannot reach. Suppression and planned TR19 cleaning are complementary controls, and a fire risk assessment expects both to be in place and maintained.
Possibly not. Many commercial policies require kitchen extraction to be cleaned and documented to a recognised standard such as TR19 Grease, and an insurer can decline or reduce a claim where that cleaning cannot be evidenced. The practical protection is a paper trail: dated cleaning reports, before-and-after grease measurements, and a current fire risk assessment. Without records, a maintained system and a neglected one can look identical to a loss adjuster - so the evidence is as important as the clean itself.
Phoenix Duct Clean · by the numbers
The right kit only helps if the system stays clean. Phoenix degreases canopies, filters and ductwork to TR19 Grease - UK-wide, overnight.