Phoenix Journal · Ductwork
The cheapest time to make a kitchen extract system cleanable and testable is before it is built. Design access in from the first drawing and every future clean, inspection and commissioning check becomes quicker, safer and far less disruptive.
Access · commissioning · maintenance
A technician arrives to clean a run of extract ductwork and finds it sealed from end to end - no panels, no reachable joints, a long horizontal run boxed into a bulkhead three metres up.
To reach the grease inside, the only options are to cut the duct open and patch it afterwards, or to sign a report noting the sections that could not be inspected at all. Neither is what anyone wanted. The system was designed to move air, and it does that well, but nobody drew in the doors, the ports or the standing room that a clean and a commissioning check actually need. This is the quiet failure that shows up years after handover - and the point of this piece is to help you avoid it while the design is still a set of lines on a screen. Access is not something you retrofit gracefully. It is a decision you make once, early, and live with for the life of the building.
Getting grease out of a commercial kitchen extract system is not optional maintenance - it is fire safety, and it is written into your insurance. TR/19® Grease, published by BESA, is the reference standard for cleanliness of kitchen extract, and it only works if a cleaner can physically reach the internal surfaces. That reachability is set by the ductwork designer, not the cleaner. So the first job is to treat access panels as primary components, drawn and specified alongside the fans and filters, never left as an afterthought for the installer to improvise on site.
DW/172, the BESA specification for kitchen ventilation systems, calls for access at every change of direction and at intervals along straight runs so the whole internal surface can be inspected and cleaned. TR/19® Grease tightens this in practice to access at roughly every 2 metres, and - crucially - positioned so that all of the ductwork can actually be reached. The distance is not arbitrary. It reflects how far a technician can pass a brush, a lance or a camera and still work the surface properly. Space panels too far apart and you create dead sections that never get cleaned, and those are precisely where a grease fire starts. A few points worth fixing on the drawing rather than discovering on site:
A panel every 2 metres is useless if it sits above a live fryer, behind a gas main, or in a ceiling void with no crawl space. Access is a three-dimensional problem, not a line on a plan. Think about the person and the ladder as well as the duct. Vertical risers need reachable openings at each floor level. Runs above suspended ceilings need removable tiles or hatches directly beneath the panels, and enough clearance to open a door and work. External roof runs need a safe way up and a place to stand. Coordinating this with the other services early - before the ceiling grid, the lighting and the sprinkler heads are fixed - is what separates a system that gets cleaned on schedule from one that gets a partial clean and a page of exclusions. This same forethought is what makes a genuine planned preventive maintenance programme possible rather than aspirational, because every visit can do its full scope instead of stopping at the first sealed section.
Access is not only for the years of cleaning ahead - it is what makes the system testable on day one. Commissioning a kitchen extract system means measuring what it actually does against what it was designed to do, and you cannot measure air you cannot reach. Test points, balancing dampers and safe standing positions all need to be designed in for the same reason the cleaning panels do. Get this right and the handover produces real evidence; get it wrong and you inherit a system nobody can honestly certify.
Commissioning is where the design meets reality. Airflows are measured against the design figures and the system is balanced so each canopy pulls its intended volume - duct transport velocities are typically held around 8 to 12 m/s to keep grease-laden air moving rather than settling. The gas interlock is proven to shut the gas supply if ventilation fails or airflow drops below the safe threshold, which is what lets a Gas Safe engineer sign the CP42 for the kitchen. Filter pressure drops are recorded as a clean baseline. None of these checks are possible without measurement access at the right places, so specify them alongside the cleaning panels:
The hardware is only half of a commissioning. The other half is paper - or, more usefully, a clean digital record you can find again. Building control and your insurer expect measured airflows, a commissioning certificate confirming compliance with DW/172, the gas safety certificate, and as-built drawings that show where every access panel and test point sits. That drawing set is what a cleaning contractor works from years later, and it is what lets a TR/19® Grease post-clean report mean something: wet film or deposit thickness readings, before-and-after photographs from matching positions, and confirmation that grease is held well below the 200-micron mean the standard sets between cleans. Keep the operating temperatures and design conditions on file too - extract handling air at 60°C behaves differently from ambient, and the next engineer should not have to guess. When all of this is in order, arranging future deep cleans stops being a crisis and becomes a plan, which is exactly what makes scheduling deep maintenance without closing the restaurant realistic. Access & documentation, designed together, are what turn a one-off installation into a system that stays compliant, cleanable and safe for its whole working life.
Questions
TR/19 Grease, the BESA standard for kitchen extract cleanliness, calls for access at roughly every 2 metres along the ductwork, with panels also at every change of direction such as bends and junctions. The key requirement is that all internal surfaces can actually be reached for inspection and cleaning. DW/172, the design specification, sets the same intent - access at direction changes and at intervals along straight runs. Anything left unreachable becomes a dead section where grease accumulates and fire risk builds.
Commissioning measures the built system against its design. Airflows are read and balanced against the design volumes at each canopy, the gas interlock is proven to shut off the gas if ventilation fails, and filter pressure drops are recorded as a baseline. The output is a commissioning certificate confirming compliance with DW/172, alongside the gas safety certificate and as-built drawings. Without measurement access designed into the ductwork, none of these readings can be taken, so the test points matter as much as the cleaning panels.
Phoenix Duct Clean · by the numbers
Phoenix surveys and cleans kitchen and building ductwork to the TR19 standard - measured, cleaned and certificated, UK-wide.