Phoenix Journal · Extraction
Most extraction failures are not sudden. The system gives you weeks of quiet warnings first - a louder fan, a warmer canopy, a smell that lingers - and every one of them is worth listening to.
Extraction cleaning
A kitchen extract system almost never fails without warning - it just fails quietly, in ways that are easy to explain away on a busy service.
Ask anyone who has dealt with a serious grease fire or a failed insurance claim and the story is usually the same. The signs were there for weeks. The fan sounded different. The canopy ran hotter. Nobody wrote it down, nobody acted, and the system kept working just well enough to be ignored. This piece is about learning to read those early signals - the small changes that tell you grease is winning - so you can act while it is still a cleaning job and not an emergency.
Grease does not announce itself. It builds a fraction of a millimetre at a time, so the change is gradual and the human eye adjusts. But the equipment cannot hide it. Long before a deposit becomes a fire risk, the way your system sounds, smells and performs starts to drift. Here is what to watch for.
Each of those warnings points back to the same root cause - grease accumulating where you cannot easily see it, deep in the ductwork and around the fan. That matters because the extract system is the single biggest fire pathway in a commercial kitchen. Industry figures put roughly 70% of commercial kitchen fires as originating in the extract ventilation, where a layer of fat sits directly above the one place in the building that produces open flame and intense heat. A fire that starts at the hob can run the length of contaminated ductwork in seconds, carrying itself through walls and floors that were supposed to contain it.
The UK benchmark for managing that risk is TR19® Grease, the specification published by the Building Engineering Services Association (BESA). It is the standard that insurers, fire risk assessors and enforcing authorities look to, and it turns those vague warning signs into something you can actually measure. Rather than guessing whether a system is dirty, a competent contractor takes readings at points along the ductwork using a deposit thickness test, checking the depth of grease in microns.
The headline number is 200 microns. TR19 Grease asks that grease is kept below a mean average of 200 microns across the system - a layer roughly half the thickness of a business card. Once the average passes that point, the full system should be cleaned. Any single reading above 500 microns calls for immediate localised attention, because that is a concentration serious enough to sustain a fire. A proper clean should bring deposits back down below 50 microns as an average, and the evidence for that - readings and photographs, before and after - is what belongs in your records.
There is no single answer, and that is the point people miss. TR19 Grease sets out indicative intervals based on how many hours a day you cook: heavy use of around 12 to 16 hours a day points to cleaning roughly every three months; moderate use of 6 to 12 hours a day around every six months; and light use of 2 to 6 hours a day around every twelve months. But these are starting points, not a licence to set a date and forget it. The specification is clear that the right frequency should be decided by a competent person through a cleanliness risk assessment - one that weighs the style of cooking, the volume, seasonal swings in trade and, crucially, the grease-depth readings the system is actually giving you. A kitchen that has quietly got busier since its interval was set is a kitchen cleaning to the wrong schedule.
This is not only good practice. Under the Regulatory Reform (Fire Safety) Order 2005, the responsible person for the premises has a legal duty to assess and reduce fire risk, and grease accumulation in the extract system is a hazard that falls squarely within that duty. Ignoring the warning signs is, in effect, leaving a known fire risk unmanaged.
The financial exposure is just as real. Insurers increasingly treat TR19 Grease compliance as a condition of cover, and some will only pay out where a recognised, competent contractor has carried out the work. If a fire spreads through neglected ductwork and you cannot produce dated evidence that the system was being cleaned to standard, a claim can be reduced or refused outright - at the exact moment you can least afford it. The certificate and photographic report from each clean are not paperwork for its own sake; they are the proof that protects both the building and the policy.
There is a quieter payoff to acting early, too. A system kept clean draws better, runs cooler and puts less strain on the fan motor, so it costs less to run and lasts longer. The warning signs you learn to catch are the same ones that, left alone, slowly push up your energy bills. It is worth understanding the quiet savings a well-maintained extraction system delivers - the case for staying ahead of the grease is a financial one as much as a safety one.
None of this asks you to become an expert in ductwork. It asks something simpler - that when the fan sounds wrong, the canopy runs hot, or the smell lingers where it used to clear, you treat it as information rather than noise. The systems that fail catastrophically are almost always the ones that spent months telling someone, in their own quiet way, that they needed help.
Questions
The first signs are usually subtle - a louder or vibrating extract fan, a canopy that feels warmer than usual, and airflow that seems weaker at the filters. You may also notice grease reappearing quickly after a wipe-down, cooking smells lingering in the kitchen, or filters clogging faster than your rota expects. These changes point to grease building up in the ductwork and fan where you cannot easily see it, and they are worth acting on before deposits reach a dangerous level.
TR19 Grease, the BESA specification, asks that grease is kept below a mean average of 200 microns across the system - roughly half the thickness of a business card. Once the average exceeds that, the full system should be cleaned, and any single reading above 500 microns needs immediate localised attention. A proper clean should return deposits to below 50 microns as an average, verified with readings and photographs.
TR19 Grease gives indicative intervals based on daily cooking hours: heavy use of 12 to 16 hours a day around every three months, moderate use of 6 to 12 hours around every six months, and light use of 2 to 6 hours around every twelve months. However, the correct frequency should be set by a competent person through a cleanliness risk assessment that considers your cooking style, volume and actual grease-depth readings, not just a fixed date in the diary.
Yes. Insurers increasingly treat TR19 Grease compliance as a condition of cover, and some will only pay out where a recognised, competent contractor has carried out the cleaning. If a fire spreads through neglected ductwork and you cannot produce dated evidence that the system was cleaned to standard, a claim can be reduced or refused. The certificate and photographic report from each clean are the proof that protects your policy.
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.