Phoenix Journal · Ductwork
Remote monitoring can tell you a fan is running, not what is baked inside the ductwork above it. This is where technology stops and compliance really begins.
On compliance · Kitchen extract
A dashboard can tell you a fan is running. It cannot tell you what is baked onto the inside of the bend three metres above the canopy.
Picture the scene. It is Monday morning and the facilities inbox is calm. The monitoring portal glows a reassuring green, the airflow readings sit where they should, and a sensor somewhere in the plant room has not raised an alarm in weeks. By every digital measure the extract system is behaving. And yet, in a horizontal run you cannot see from the floor, a film of grease has been quietly thickening since the last visit - past the point where the guidance says it should have been dealt with. The technology did its job perfectly. It just was not asked the right question.
This is the awkward truth about compliance in commercial kitchens. We have never had more clever kit pointed at the problem, and the problem has not gone anywhere. Understanding where the software stops and the survey begins is what keeps a building genuinely safe rather than merely well documented.
Remote monitoring has earned its place. Airflow sensors, pressure differentials, run-hour counters and fan telemetry all give you something the old paper regime never could - a live sense of whether the system is moving air the way it was designed to. That is genuinely useful, and it flags real faults early. But it is worth being honest about what these tools actually measure, because the gap between that and full compliance is exactly where fires start.
The single most common misreading is to treat a healthy airflow figure as proof of a clean duct. It is not. A system can pull perfectly adequate air while carrying a substantial grease burden along its walls, particularly in the long horizontal sections and behind fire dampers where deposits collect out of sight. TR19® Grease, the BESA specification that underpins kitchen extract fire risk management in the UK, is not written around airflow at all. It is written around grease thickness. The benchmark is a mean average deposit that should not exceed 200 microns between cleans, with any reading of 500 microns or more treated as needing immediate attention. No airflow sensor on the market reports in microns of grease. It reports in air.
Around 70% of fires in commercial kitchens are linked to the build-up of grease in extract ventilation, so the thing your monitoring cannot see is precisely the thing most likely to hurt you. That is not an argument against sensors. It is an argument for knowing their blind spots.
Even the best-instrumented system only measures where you put the instrument. Grease does not distribute itself evenly or politely. It gathers at changes of direction, at transitions, around dampers, and in the dead legs that a fixed sensor was never positioned to watch. Verifying those areas means physically getting to them - opening access panels, or cutting new ones where none exist - and putting a calibrated measurement onto the metal itself.
The measurement itself is deliberately physical. A Wet Film Thickness Test or Deposit Thickness Test uses a comb pressed against the surface, read by a competent technician. Even that has limits worth naming - a wet film comb typically only reads down to around 25 microns, so a genuine zero is a figure no honest report should claim. Knowing that boundary is part of doing the job properly.
If sensors answer "is it moving air?", the human survey answers "is it safe, and can you prove it?" Those are different questions, and the law that sits behind them - the Regulatory Reform (Fire Safety) Order 2005 in England and Wales, with its equivalents in Scotland and Northern Ireland - asks for the second one. It puts a duty on the responsible person to carry out a suitable and sufficient fire risk assessment, and TR19® Grease is the best-practice benchmark that assessment is expected to draw on. None of that is satisfied by a green light on a screen.
One of the quieter but more important shifts in recent guidance is that it names who is allowed to do the work. TR19® Grease sets minimum competency levels for kitchen extract cleaning, and technicians are expected to hold the BESA Grease Hygiene Technician qualification so that measurement, cleaning and verification are all carried out to a known standard. The parallel discipline of Local Exhaust Ventilation testing goes further still - under COSHH, an LEV system serving a kitchen should be given a thorough examination and test at least every 14 months, carried out by a suitably competent engineer, typically P601-qualified. A monitoring platform can schedule that visit. It cannot be that visit.
This matters because judgement is not automatable. Deciding whether a deposit warrants a spot clean, whether an access hatch is in the right place, whether a damper has been compromised, whether the frequency of cleaning still suits how hard the kitchen is now working - these are readings of a situation, not readings off a gauge. The guidance itself flexes with use, expecting heavy-use kitchens running long hours to be cleaned far more often than a light-use site. Someone has to look at the actual kitchen to make that call.
Here is the part that quietly separates a compliant building from an exposed one - the record. Technology is superb at logging that a task happened; it is far weaker at proving the task was adequate. If there is ever a fire, an insurer or an investigator will not ask to see your dashboard’s uptime. They will ask for the post-clean verification, and it needs to stand up on its own. A report that earns its keep will include:
Notice how much of that depends on candour - the note about the section you could not reach, the drawing that admits a blind spot. Automated systems are built to report success. A survey done well is willing to report a limit, and that honesty is exactly what makes the document defensible later. Keeping these records in good order is its own discipline, and it is worth understanding which compliance documents every FM should keep so nothing load-bearing goes missing before you need it.
The sensible position, then, is not to choose between technology and inspection. It is to let each do what it is good at. Let the monitoring watch airflow and flag faults between visits; let a competent survey measure the grease, reach the hidden runs, exercise judgement and produce evidence that holds. The screen tells you the system is alive. The survey tells you it is safe. Compliance lives in the second sentence, and no amount of clever kit has yet learned to write it for you.
Questions
No. Airflow sensors and telemetry confirm a system is moving air, but TR19 Grease is measured in grease thickness, not airflow, with a mean benchmark of 200 microns between cleans. Deposits gather in bends, risers and behind dampers that no fixed sensor can read. Only a physical Wet Film or Deposit Thickness Test by a competent technician verifies the surface itself.
It should include before-and-after photographs from matching positions, Wet Film or Deposit Thickness Test readings confirming grease is below the required threshold, a written summary of the works, and honest notes on any areas of restricted or no access. It should also carry system drawings of what was cleaned and a hygiene certificate naming the date, site and qualified technician. That evidence is what stands up to an insurer or fire investigator later.
Phoenix Duct Clean · by the numbers
Phoenix surveys and cleans kitchen and building ductwork to the TR19 standard - measured, cleaned and certificated, UK-wide.