Phoenix Journal · Extraction
In a full kitchen at the height of service, most of what you are breathing is invisible. Here is what is really in that air - and what keeps the room breathable night after night.
By seven o'clock the pass is full, six burners are lit, the chargrill is throwing up a haze that catches the light, and the canopy is roaring away above it all as if nothing is happening.
It is a scene every busy kitchen knows. The heat, the noise, the blue shimmer coming off the flat-top - it feels like the natural weather of a room where good food gets made. And for the most part it is. But the air in a kitchen during service is doing a great deal of quiet work, and most of what it is carrying you cannot actually see. The visible smoke off a seared steak is only the loud part. Underneath it sits a fine, invisible load of particles, grease vapour and combustion gases that the extraction system is there to sweep away before your team breathes too much of it and before it settles cold inside the ductwork above the ceiling.
This is a column about that air - what is in it, why a full kitchen fills so quickly, and what keeps the room breathable night after night rather than gradually turning into a haze that stings the eyes by nine.
Ask anyone working a hot section what they are breathing and they will point at the smoke. Fair enough - it is the thing you can see. But the visible plume is a small fraction of the story, and understanding the rest is what separates a kitchen that merely feels smoky from one that is genuinely well ventilated.
When fat hits a hot surface it does not simply burn. It vaporises, and as that vapour cools it condenses back into a mist of extremely fine droplets and solid particles. Researchers measure these as fine particulate matter - PM2.5, meaning particles under two and a half microns across - and, smaller still, ultrafine particles. Frying and chargrilling are especially prolific sources. The University of Surrey's Global Centre for Clean Air Research, which has published practical guidance on kitchen pollution, notes that these are precisely the pollutants worth monitoring, and that a fine particle can sit suspended in the air far longer than any visible wisp of smoke.
The point that catches people out is this: the moment the visible haze clears, the room is not necessarily clean. The finest particles are the ones that travel deepest into the lungs, and they are invisible. Add the combustion gases from gas burners - carbon monoxide and carbon dioxide (CO₂) among them - and you have an air mix that a good canopy and a working extract fan are quietly diluting and removing all night. If you have ever wondered why smoke starts filling your kitchen during service when it behaved perfectly at the start of the week, the answer usually lies in how well that unseen load is being captured and carried away.
A kitchen at full tilt is a small room asking a lot of its air. Several things stack up at once, and each one adds to what the extraction has to shift:
Under the Control of Substances Hazardous to Health Regulations - COSHH - cooking fumes count as a substance hazardous to health, and an employer is expected to control your team's exposure to them. Long-term exposure to kitchen fume has been linked to respiratory problems including occupational asthma, which is exactly why local exhaust ventilation - the canopy and its ductwork - is treated as a control measure and not merely a comfort. It is there to protect people, and like any control measure it only counts while it is actually working.
Good air in a busy kitchen is not luck. It comes from a system designed to capture fumes at the source and move them away, and then from keeping every part of that system clean enough to do its job. Both halves matter, and the second one is the half that quietly falls behind.
The whole logic of a commercial kitchen canopy is to catch fumes where they are made - directly above the hot surface - before they can drift into the room and into people's breathing zone. The recognised design benchmark for this in the UK is DW172, the specification for kitchen ventilation systems that environmental health officers, insurers and consultants use as a yardstick. A well-designed system pulls a steady, generous volume of air through the filters, up the duct and out, while a matching supply of make-up air replaces what has left so the room is not fighting itself.
You can tell when this is working. The haze over the chargrill gets drawn up rather than rolling out across the pass, the far end of the kitchen stays breathable, and the room does not slowly fog over as the evening goes on. The kitchen behind a busy garden cafe is a good illustration of how much difference a properly sized, properly maintained extract makes to a small, hard-working space - the same volume of cooking feels entirely different in a room where the air keeps moving. Some operators now add a simple particulate or CO₂ monitor with a traffic-light display, an idea the Surrey guidance recommends, so the team gets an amber warning to check the extraction before the air turns bad rather than after.
Here is where the invisible load comes back to bite. Every night, some of that grease vapour that was not captured perfectly condenses and settles as a sticky film on the inside of the filters, the canopy plenum and the ductwork. It builds up slowly, out of sight, and it is flammable. Grease accumulation in extract systems is one of the leading causes of fire in commercial kitchens in the UK, and a duct fire behind a ceiling is about the worst place a fire can start. This is also why many insurers now make regular, evidenced cleaning a condition of cover - a neglected system can see a claim refused even where a contractor had been used.
The standard that governs this is TR19 Grease, published by the Building Engineering Services Association, and it is refreshingly concrete about what clean means:
That evidence trail is not box-ticking. It is what demonstrates to an insurer, an environmental health officer or your own fire risk assessment that the system carrying all that fume and grease is genuinely clean, and that the air your team breathes on a busy night is being handled the way it should be. Capture the fumes at the source, move them away cleanly, and prove the ducts behind them are clear - do those three things and a full, roaring kitchen stays a good place to breathe.
Questions
Not necessarily. The visible smoke is only the coarsest part of what cooking produces. Underneath it sits a load of fine and ultrafine particles - PM2.5 and smaller - along with combustion gases, and these are invisible yet can stay suspended in the air far longer than any wisp you can see. A room can look clear and still carry a significant particulate load, which is why a properly working canopy and extract fan matter even once the haze has gone.
There is no single interval that suits every kitchen, because the right frequency depends on how hard the system works. The TR19 Grease standard from the Building Engineering Services Association sets cleaning by measured grease deposits rather than the calendar - the mean should stay below 200 microns, and a heavy frying or chargrilling operation reaches that point far quicker than a light-use kitchen. A survey of your actual grease levels is the honest way to set an interval, and it is also what your insurer will expect to see evidenced.
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.