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Case study · Education · Kitchen extraction
A primary school ran a gas cooking line under a single island extraction canopy, serving hot meals every day. The canopy is the kitchen's local exhaust ventilation - and it passed, cleanly. Here is what a kitchen LEV examination checks, why the balance of air matters, and the one advisory we left behind.
The site
The school runs an on-site production kitchen, cooking fresh meals for its pupils every day on a gas cooking line beneath a single central island canopy. It is a working, in-use kitchen - exactly the kind of everyday setting where extraction is easy to take for granted.
The canopy here is a compensated design: it combines mechanical extraction - drawing the cooking plume up through a bank of grease baffle filters to a roof-mounted fan - with a tempered supply of make-up air delivered back into the kitchen through integral grilles. The two airflows are meant to be balanced against one another, so that for every cubic metre pulled out, fresh air is reintroduced to replace it.
The school had reported the kitchen running hot at times, and had recently had engineers working on the supply air handling unit. That made the balance between extract and make-up air a specific thing to check, not just a box to tick - overheating is often the first visible symptom of a canopy that cannot pull because its supply air is short.
The hazard and the law
It is tempting to think of a kitchen canopy as comfort ventilation - something to take away the heat and the smell. It is more than that. It captures grease aerosol, steam, heat and the products of gas combustion - carbon monoxide and nitrogen dioxide - and removes them from the breathing zone of the people cooking. That makes it local exhaust ventilation, and where it controls exposure to substances hazardous to health it sits under COSHH like any other LEV, with a thorough examination and test due at least every 14 months.
There is a second duty riding alongside the first. The grease the canopy captures loads its baffle filters and ductwork, and that grease is a fire risk - a separate obligation under fire-safety law to keep the system clean. A kitchen LEV examination and a grease-extract clean look at the same canopy from two angles: is it controlling exposure, and is it safe from fire. Both matter in a school.
What we tested
We measured the extract airflow at the canopy and confirmed the cooking plume was being captured cleanly rather than rolling out at the edges. We inspected the eight stainless baffle filters, the roof fan and the ductwork, and we checked the make-up air supply against the extract so we could judge whether the two were in balance - the point the recent AHU work made worth scrutinising.
A qualitative check confirmed that fume generated at the hob was drawn up into the canopy rather than spilling into the kitchen, and we noted the condition of the canopy lighting and the housekeeping around the filters. On a gas line, the question is not only "is it extracting" but "is it extracting enough, and is the replaced air keeping the capture steady under real cooking conditions".
What we found
| Check | Finding | Result |
|---|---|---|
| Extract airflow / plume capture | Cooking plume captured cleanly at the canopy | Pass |
| Extract / make-up air balance | Balanced after recent AHU works - no short supply | Pass |
| Grease baffle filters | Serviceable; cleaning cadence could be tightened | Advisory |
| Canopy lighting | Two of four integral lights not working | Advisory |
| Fan and ductwork | Running true, clean | Pass |
The result was effective control: the canopy captured the plume, the extract and make-up air were in balance after the AHU work, and combustion fume was being carried away as it should. The kitchen had been doing the important things right. What remained were advisories rather than failures - two canopy lights to replace and a baffle-filter cleaning routine to tighten - the kind of housekeeping that keeps a good system good.
The advisories
The outcome
The school left with a dated, quantified record showing effective control on its kitchen LEV, a short list of advisories to action, and a clear next-test date on the 14-month cycle. The recent AHU work had, if anything, put the system in good shape - the examination simply confirmed it and flagged the housekeeping.
The useful reminder is that a kitchen canopy is LEV, and the quiet failure mode is not a broken fan but a balance that has drifted - often after other works, when make-up air gets left short. A canopy that cannot pull runs hot and can draw combustion fume back into the room, and staff may notice only that the kitchen is uncomfortable. Testing on the 14-month cycle, ideally in a holiday and alongside the grease-extract clean, keeps both the health duty and the fire duty covered in a single, well-timed visit.
Sources and further reading
The duties, exposure limits and control standards described here come from the Health and Safety Executive. For your own process, always work from the current HSE guidance:
Questions
Yes. A commercial kitchen extraction canopy captures the cooking plume - grease aerosol, heat, steam and the products of gas combustion - and removes it from the room, which is exactly what local exhaust ventilation does. Where it is relied on to control exposure, it falls under COSHH and should be examined and tested on the same 14-month cycle as any other LEV.
We measure the extract airflow at the canopy and the capture of the cooking plume, inspect the baffle grease filters, fan and ductwork, and - importantly - check the balance between the extract and the make-up (supply) air. We confirm combustion fume is being drawn away rather than spilling into the room, and record it all with figures and photographs.
A kitchen canopy pulls a large volume of air out of the room, and that air has to be replaced. If the supply (make-up) air is short or out of balance with the extract, the canopy cannot pull properly, the kitchen goes hot and stuffy, and combustion fume can be drawn back down instead of up the flue. A balanced system is what keeps capture working and the room comfortable.
Burning gas produces carbon monoxide and nitrogen dioxide, along with heat, water vapour and - from the food - grease aerosol. In an enclosed kitchen these must be carried away reliably; that is one of the jobs the canopy does, alongside capturing grease before it loads the ductwork and becomes a fire risk.
A pass means control is effective on the day, but we still record advisories: here, two canopy lights were out and the baffle-filter cleaning routine needed tightening. Acting on advisories is what keeps a system from drifting into a fail at the next test - and clean baffles also matter for fire safety, which is a separate duty.
At least every 14 months under COSHH, and ideally during a school holiday so the examination and any remedial work happen while the kitchen is closed. Pairing it with the kitchen's grease-extract cleaning visit is efficient, since both look at the same canopy and ductwork.
Tell us your capture points and the process they control, and we will quote the thorough examination and test to COSHH and HSG258.
