Phoenix Journal · Extraction
The most dangerous decisions in a commercial kitchen are made on the drawing, not the cook line. Here is how thoughtful layout designs fire risk out of an extract system from the start.
Kitchen design & fire safety
Picture the site meeting where the extract route gets decided in about ninety seconds - a designer points at a ceiling void, someone says the duct can simply turn there and drop behind the dry store, and everyone nods and moves on.
That single turn, agreed in passing, is often where a fire risk is quietly built into a kitchen for the next fifteen years. Nobody chose it on purpose. The canopy went where the chef wanted the range, the duct followed the path of least resistance through the building, and the awkward horizontal run behind a wall became the place grease settles, hardens and waits for an ignition source it will eventually find.
The reassuring part is that most of this is a design decision rather than an accident of fate. Fire risk in a commercial kitchen is not evenly spread - it concentrates in predictable places, and those places are set by the layout long before a single service is cooked. Get the routing, the access and the separation right on paper, and you spend the next decade cleaning a system that wants to be cleaned rather than fighting one that was built to defeat you.
Grease-laden vapour behaves in ways you can predict, which is exactly why layout matters so much. As hot, oily air leaves the canopy and travels through the ductwork, it cools against the duct walls and deposits a film of grease. The colder the metal and the slower the air, the faster that film builds. A well-designed run keeps the air moving briskly and gives grease few places to fall out of suspension. A poorly designed one does the opposite - and no amount of cleaning fully undoes a route that was wrong from the start.
The single most useful principle is that grease-bearing air wants to go up and out by the shortest sensible path. Long horizontal runs are where grease pools on the bottom of the duct under gravity, and every additional bend adds a spot where deposition accelerates and turbulence drops the velocity. BESA guidance in DW172 - the Specification for Kitchen Ventilation Systems, which environmental health officers and fire inspectors routinely expect you to follow - steers designers towards ductwork built from non-combustible material, typically stainless steel with continuously welded seams on grease-bearing sections so there are no laps or joints for grease to lodge in.
Air speed is part of the same conversation. Extract systems are generally designed to hold a transport velocity in the region of 8 to 12 metres per second so that grease stays airborne rather than settling out. Design the duct too large and slow to hit a noise target, and you trade a quieter kitchen for a greasier, more flammable one. When you sketch the route, keep these in mind:
A system is only as safe as it is cleanable, and cleanability is set at the drawing stage. TR19 Grease, the BESA code of practice introduced in 2019, sets the framework the UK now works to - it defines how kitchen extract systems should be cleaned, how often, and what evidence proves it was done, with cleans expected to bring grease deposits back down to an average below 50 microns across the system. None of that is achievable if a cleaning technician cannot physically reach the inside of the duct.
That is why access panels are a fire-safety feature, not an afterthought. They need to be numerous enough, and large enough, to let someone inspect and clean every internal surface. In practice that means access at regular intervals along the run - commonly around every two metres - and always at bends, junctions and either side of any in-line component such as a fan or a damper. A hidden metre of duct behind a fixed ceiling is a metre that never gets cleaned, and it only takes one such stretch to undermine an otherwise compliant system.
Fire needs heat, fuel and an ignition source in the same place at the same time. A kitchen layout is really an exercise in keeping those three apart - on the cook line, in the ceiling void, and around the outside of the building where the risk does not stop when service ends.
The area under and immediately around the canopy is the highest-risk zone in the building, so what you place there matters. Grease filters should sit at the correct angle - typically baffle filters set so drained grease runs to a collection point rather than back onto the appliances - and there should be a sensible vertical gap between the flame and the filter face so the filters are not sitting in direct heat. Combustible storage, packaging and cleaning chemicals have no place on or beside the range, however tempting the nearest shelf looks during a busy shift.
Layout also governs how well your safety systems can actually work. Fire suppression above the cook line needs the appliances positioned so the nozzles cover them; move a fryer six inches during a refit and the coverage can be lost. Gas interlocks matter here too - a system built to BS 6173 will shut the gas supply if the ventilation is not running, so ductwork, fan and gas train have to be laid out to make that interlock reliable rather than something an operator is tempted to bypass. Worth designing in from the outset:
Not every ignition source is a flame. A surprising share of kitchen fires start with the electrics - a failed appliance, a scorched flex trailing across a wet surface, an overloaded socket behind a hot line - and the layout decides how exposed those faults are. Positioning sockets away from splash and heat, giving each heavy appliance its own supply, and keeping a routine of PAT testing and managing electrical fire risk in kitchens turns a hidden hazard into a managed one. The best duct route in the world will not save you from an ignition source sitting quietly in the wall.
Risk also outlives the shift. External layout - where the bins live, how the yard is secured, what can be reached from outside after dark - shapes your exposure to fire when nobody is on site to catch it early. Bins pushed tight against the building, combustible waste left in an open yard and unsecured access points are all layout choices, and they feed directly into how you reduce arson and out-of-hours fire risk. Designing a kitchen for fire safety means thinking past the cook line to the whole footprint, because the Regulatory Reform (Fire Safety) Order 2005 holds the responsible person accountable for all of it, not just the parts on show to customers.
Questions
Design and cleaning work together, but the layout sets the ceiling on how safe the system can ever be. Short, rising, accessible duct runs at the right air velocity give grease fewer places to settle and make every clean more effective. A cleverly hidden or overly long run will keep collecting grease no matter how diligent your cleaning schedule is, so getting the routing and access right on paper is the highest-value fire-safety decision you make.
You need enough access panels, of sufficient size, to reach and clean every internal surface of the system. In practice that usually means panels at regular intervals along the run - commonly around every two metres - plus panels at each bend, junction and either side of in-line components such as fans and dampers. This is what makes cleaning to the TR19 Grease standard, bringing deposits back below an average of 50 microns, physically possible rather than just aspirational.
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.