Grease build-up and kitchen fire safety
Grease deposits inside extract ductwork are combustible, concealed and cumulative. That combination is why kitchen extract cleaning is a fire safety duty rather than a housekeeping task.
Grease build-up and kitchen fire safety
How the risk develops
Cooking produces grease-laden vapour. Canopy filters capture a proportion of it, but a significant share passes through and condenses on cooler internal surfaces further along the extract route — inside the plenum, along horizontal runs, at bends, on fan blades and within the discharge. Because it accumulates out of sight, the first visible symptom is often reduced extraction rather than the deposit itself.
The material is flammable. A flare-up at the cooking line that reaches the canopy can ignite deposits in the duct, and a fire inside ductwork travels quickly through a building along a route specifically designed to pass through fire compartments.
How deposits are measured
TR19 Grease sets out measurement of grease deposit thickness, typically expressed in microns, taken at representative points throughout the system. Measurement matters because it converts a subjective judgement into a number that can be trended, compared against a threshold and used to set a defensible cleaning frequency.
Readings should be taken before and after cleaning. A report showing a pre-clean average and a post-clean average across identified test points is far stronger evidence than photographs alone.
What the responsible person must do
- Include kitchen extract ductwork explicitly in the fire risk assessment
- Set a cleaning frequency based on cooking hours and measured deposit levels
- Ensure the whole system is cleaned, including the fan, plenum and discharge — not just the canopy and filters
- Install access panels where the system cannot be inspected or cleaned internally
- Retain reports with deposit readings and photographic evidence for the insurer
- Act on remedial recommendations, particularly missing access and damaged ductwork
The part most often missed
Filter cleaning and canopy wiping are frequently mistaken for extract cleaning. They are not the same thing, and a system with spotless filters can still hold heavy deposits throughout the duct run. When reviewing a quotation, check that it covers the full extract route from canopy to discharge, and that it prices any access panels needed to reach it.
Common questions
- How often should kitchen extract ductwork be cleaned?
- Frequency is risk-based. Heavy-use kitchens running long hours with high-fat cooking may need quarterly attention; light-use kitchens may be annual. Measured deposit thickness, not a default interval, should set it.
- Will my insurer accept photographs alone?
- Increasingly not. Most now expect deposit thickness readings, identified test points and a report referencing TR19 Grease.
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