Phoenix Journal · Ductwork
Post-clean verification is the measured evidence that your kitchen extract system was cleaned to standard - dated photographs and deposit readings, not just a certificate and a handshake.
Verification, explained
Post-clean verification is the evidence that your kitchen extract system was actually cleaned to standard - not just the promise that someone turned up with a brush and a van.
When a cleaning contractor packs up and hands you a certificate, that certificate should mean something. Under BESA TR19 Grease - the UK guidance that fire risk assessors, insurers and enforcing officers lean on for commercial kitchen extract - a clean is only complete once it has been measured, photographed and recorded. That measured record is what verification means. It is the difference between believing your ductwork is clean and being able to prove it.
For anyone responsible for a commercial kitchen, this matters because the parts of the system that catch fire are the parts you cannot see. Grease travels well beyond the canopy, up the riser and along horizontal duct runs. Verification is how you check the hidden lengths, not just the shiny surfaces at eye level.
Verification proves one specific thing - that the amount of grease left behind after cleaning is low enough to be considered safe, measured to an agreed standard rather than judged by eye. A duct can look clean under a torch and still hold a film of combustible residue that a fire would happily use as fuel. Verification replaces opinion with a number.
The number that matters is 50 microns. TR19 Grease sets an average post-clean deposit thickness of under 50µm - fifty thousandths of a millimetre - as the benchmark for a system to be regarded as clean. Readings are taken at representative points along the ductwork, so the figure reflects the whole run and not one convenient spot near an access panel.
Crucially, verification is about the concealed system, not the visible steel. This is exactly why a canopy can gleam while the extract behind it stays contaminated. If you have ever wondered why your canopy looks clean but the system still smells, the answer usually lives in the ductwork that never gets verified. A proper verification looks past the surfaces your team wipes down daily and into the lengths only a specialist reaches.
There are two recognised test methods, and a competent contractor chooses the right one for the deposit in front of them.
Both give a reading in microns, and both are taken before and after cleaning. The pre-clean measurement records how bad the contamination was on arrival; the post-clean measurement proves the work brought it down below the 50µm threshold. Two numbers, taken at the same points, tell the honest story of what the clean achieved.
Measurement is paired with visual inspection and photography. A verifier will open access panels along the run, photograph each section from a consistent position before and after, and log where each reading was taken. It is deliberately methodical. The whole point is that someone who was not on site - an insurer, a fire risk assessor, an incoming operator - can read the report and understand exactly what was cleaned and how clean it ended up.
Honest verification also records what could not be done. If a duct run has no access panels, or a section is genuinely inaccessible, that gets noted rather than quietly ignored. TR19 Grease expects contractors to flag where extra access hatches are needed so the concealed lengths can be reached, measured and cleaned on the next visit. A report that claims a perfect clean with no limitations, on an older system with no access provision, is a report worth questioning.
The document you are handed is a Post-Work Verification Report, and it should stand up on its own without anyone needing to explain it to you. At a minimum, expect to see the following.
That last point matters more than people expect. A heavy-use kitchen running long hours on grease-heavy cooking needs cleaning far more often than a light-use site. The report should tell you when to come back, so verification becomes part of a cycle rather than a one-off event. Many operators keep their reports uploaded to a national database run by BESA, so the record can be produced quickly if an insurer or enforcing authority asks for proof.
Verification is also the honest test of whether cleaning solved the problem you called about. If a kitchen still carries an odour after a thorough job, the report tells you whether the ductwork was genuinely brought below threshold - useful context if you are chasing down why a kitchen still smells after a full daily clean. Numbers and photographs turn a vague complaint into something you can actually act on.
Grease is fuel. Left in a warm extract system above a cooking line, it is one of the most common causes of serious kitchen fires - and one of the most preventable. Verification is how you demonstrate that the fuel has been removed to a recognised standard, which is why it sits at the heart of both fire safety and insurance conversations.
Under the Regulatory Reform (Fire Safety) Order 2005, the responsible person for a premises has a duty to manage fire risk, and a contaminated extract system is a recognised part of that risk. After an incident, an insurer will look for evidence that the duty was met. A verification report with dated photographs and sub-50-micron readings is exactly the kind of proof that stands up to scrutiny - a certificate with no measurements behind it often does not.
Put simply, verification protects you three ways at once - it lowers the real chance of a fire, it evidences your compliance, and it defends your insurance position if the worst ever happens.
Questions
No. A certificate simply states that a clean took place, while verification is the measured evidence behind it. Proper verification includes before and after deposit thickness readings, dated photographs from consistent positions, and a record of what was and was not reached. If your paperwork has no measurements or images, it is a certificate, not verification.
TR19 Grease treats an average post-clean deposit thickness of under 50 microns - fifty thousandths of a millimetre - as the benchmark for a clean system. Readings are taken at representative points along the ductwork using a Wet Film Thickness Test for soft grease or a Deposit Thickness Test for hard carbonised deposits. Both a pre-clean and a post-clean figure should appear in your report so you can see exactly what the clean achieved.
Phoenix Duct Clean · by the numbers
Phoenix surveys and cleans kitchen and building ductwork to the TR19 standard - measured, cleaned and certificated, UK-wide.