Phoenix Journal · Ductwork
The hob usually gets the blame, but a kitchen fire investigation almost always leads up into the extract ductwork. Here is what investigators find, and how to make sure it is never your system.
After the fire
When a commercial kitchen goes up, the story the fire tells is rarely the one people expect - the hob or the fryer usually gets the blame, but the investigation almost always leads somewhere higher up and out of sight.
A fire investigator works backwards. They look for the point of origin, the path the fire took and the fuel that let it grow, and in a catering premises that trail very often runs straight into the extract canopy and up through the ductwork. It is an uncomfortable pattern, but a consistent one - industry estimates put roughly 70% of commercial kitchen fires as originating in, or being made far worse by, the extract ventilation system, where a lining of cooking grease sits waiting for a spark.
The reason is simple physics. Every service, grease-laden vapour is drawn off the cooking line, and a share of it condenses and coats the inside of the canopy, filters, plenum and duct. Cooking oil autoignites at around 360°C, and a flare-up on a chargrill or a fryer boil-over reaches that easily. Once the grease film catches, the duct becomes a chimney - the fire runs the length of the run, breaches ceiling voids and roof spaces, and reaches parts of the building nobody thought were connected to the kitchen at all. That is why the extract system is one of the first things a serious investigation examines.
When the ductwork is opened up and swabbed after a fire, the findings tend to fall into a few familiar categories. None of them are exotic, and almost all of them are preventable.
The through-line in every one of these findings is the same - the fire did not start because a kitchen is dangerous by nature. It grew because a maintainable system was left un-maintained, and the evidence of that neglect is written all over the inside of the duct.
Physical evidence is only half of it. The other half is documentary, and this is where a kitchen fire investigation crosses over into your insurance claim and your legal position. Under the Regulatory Reform (Fire Safety) Order 2005, the Responsible Person for the premises has a legal duty to identify, assess and control foreseeable fire hazards - and grease-contaminated ductwork is about as foreseeable a hazard as commercial catering has. Investigators, insurers and enforcing authorities all want to see that the duty was taken seriously.
In practice, they ask for a specific paper trail:
The stakes here are not abstract. Around 1,275 fires were recorded in UK food and drink premises in 2024/25, and by the end of 2025 insurers had become markedly stricter about catering claims. Where a fire has spread through neglected ductwork and there is no valid TR19 Grease record to produce, cover can be delayed, reduced or refused outright. The documentation an assessor or investigator wants is the same documentation that protects your claim - our guide to what a fire risk assessor wants to see on arrival sets out exactly how to have it ready.
The good news buried in all of this is that the failures investigators find are the failures you can design out in advance. You cannot guarantee a flare-up never happens on the line - kitchens are busy, hot places - but you can guarantee that a flare-up has nothing to feed on once it reaches the duct, and that your paperwork stands up the moment it is asked for.
Three things do the heavy lifting. First, clean the whole system to TR19 Grease, not just the visible canopy - the deposits that matter are the ones you cannot see. Second, fit access panels along the full run so the interior can genuinely be reached and verified. Third, keep a dated, photographed record of every clean, with grease-thickness readings, so the evidence exists before you ever need it. Do those three, and a fire investigation moves quickly from your extract system to somewhere else, because there is nothing there to find.
Questions
Both, in effect. Grease rarely provides the first spark - that usually comes from a flare-up on the line - but a heavy grease lining is the fuel that turns a small, containable flame into a fast-moving duct fire. Investigators consistently find that the difference between a contained incident and a serious structural fire is how much grease had been allowed to build up inside the run.
It happens, and it has become more common. By the end of 2025 UK insurers were routinely requesting proof of TR19 Grease compliant cleaning after a catering fire, and where a fire spread through neglected ductwork with no valid record to produce, cover has been delayed, reduced or declined. Keeping dated, photographed verification of every clean is the simplest way to keep your claim intact.
Phoenix Duct Clean · by the numbers
Phoenix surveys and cleans kitchen and building ductwork to the TR19 standard - measured, cleaned and certificated, UK-wide.