What TR19 Air covers
TR19 is the Building Engineering Services Association's guide to the internal cleanliness of ventilation systems. BESA first published TR19 Air in April 2024 as a separate document from TR19 Grease, which handles kitchen extract fire risk, and issued an updated edition on 3 March 2026 that makes post-clean reporting mandatory and formally recognises the Vent Hygiene Register. TR19 Air covers general ventilation: air handling units, supply and extract ductwork, grilles, diffusers, fans and the filters between them.
It incorporates the European standard BS EN 15780, Cleanliness of ventilation systems, which defines cleanliness classes by building use and sets acceptable dust levels for each. It also aligns with BS 40102-1:2023 on health and wellbeing in buildings. The BESA Vent Hygiene Register, which has covered kitchen extract cleaning for years, extended to TR19 Air work from March 2026.
Why the duty exists
There is no single law that says "clean your ducts". The duty is built from several.
- Regulation 6 of the Workplace (Health, Safety and Welfare) Regulations 1992 requires enclosed workplaces to be ventilated with a sufficient quantity of fresh or purified air, and the approved code of practice expects mechanical ventilation to be maintained and kept clean.
- Under the Health and Safety at Work etc. Act 1974 the employer carries a general duty for the health of employees and others.
- The Control of Substances Hazardous to Health Regulations 2002 apply where ductwork contamination could include biological agents.
Cleanliness classes
BS EN 15780 sorts buildings into three classes.
| Class | Typical spaces | Acceptable dust level |
|---|---|---|
| Low | Storage rooms, plant rooms, low occupancy areas | Least strict |
| Medium | Offices, hotels, restaurants, schools, general hospital areas | Set limit, tested by vacuum sample |
| High | Laboratories, hospital treatment areas, clean production | Strictest |
The class decides how much dust is acceptable before cleaning is required. Most London commercial property falls into the medium class. Specialist environments such as operating theatres, pharmaceutical suites and food production rooms sit in the high class and are tested to tighter limits.
How ductwork is tested
TR19 Air relies on measurement rather than opinion. Two test methods appear on reports.
Deposit thickness test (DTT). A calibrated gauge measures the depth of dust on the duct surface in microns at representative points. It is quick, gives a good picture of build-up across a system and is the usual pre-clean survey method.
Vacuum test. A measured area of duct surface is vacuumed onto a pre-weighed filter, which is weighed again to give a result in grams per square metre. This is the method behind the BS EN 15780 limits. It was previously called the preferred vacuum test (PVT) and is now generally called the European vacuum test (EVT). It is the standard way to prove a system is clean after work.
A competent survey also includes a visual inspection, often by camera through the access points, of the air handling unit, filters, coils, humidifiers and drain pans, since these are where biological growth starts.
When cleaning is due
TR19 Air asks for a baseline inspection at least every 12 months, with the cleaning decision driven by the test results and the building's class. Systems in the high class, in buildings with a history of contamination, or serving spaces where air quality complaints have been logged are inspected more often.
Some events bring cleaning forward regardless of the calendar:
- Building works or refurbishment where dust entered the system.
- Water ingress, flooding or a failed condensate drain.
- Visible mould or a persistent odour from the grilles.
- Pest activity found in the plant room or ductwork.
- A change of use, for example an office floor converted to a laboratory or clinic.
- Handover of a new or refurbished system where builders' debris was not removed.
What a compliant clean involves
- Pre-clean survey with photographs and test readings at named locations, plus a schematic of the system and its access points.
- Isolation of the system and protection of the occupied space. Cleaning is usually done out of hours.
- Mechanical cleaning of the duct interior using rotary brushes and compressed-air whips to loosen deposits, with negative-pressure HEPA-filtered extraction collecting the dust as it moves.
- Cleaning of the air handling unit, fan and coils, and replacement of filters where agreed.
- Sanitisation with an approved biocide where the survey found biological contamination, followed by rinsing or drying as the product requires.
- Post-clean photographs from the same positions and repeat testing to show the system meets its class limit.
- Refitting of access panels and reinstatement of the system.
Access is the first question at survey. Long runs without panels cannot be cleaned or tested properly. Where panels are missing the contractor should propose positions and fit them before the clean, with the client's agreement, rather than record the run as inaccessible afterwards.
What the report shows
The post-clean verification report is what you file for your health and safety records, your insurer and any tenant or auditor who asks. It should contain:
- Pre-clean and post-clean test results at each test location, with the method stated and the limit for the building class.
- Before and after photographs from matching positions, enough to represent the whole system.
- A drawing of the ductwork, air handling units and every access point used.
- Any section left uncleaned, where it is and why.
- Defects found, such as damaged insulation, corroded duct, failed dampers or blocked drains.
- The cleaning methods and any biocide used, with safety data sheets available.
- The date, the technician's name and a recommended date for the next inspection.
Who holds the duty
In a single-occupier building the employer is the duty holder. In multi-let property the landlord or managing agent usually holds the duty for the central plant and risers, and each tenant holds it for the ductwork inside its demise. Leases often blur this. Check the repairing and service charge clauses before assuming the other party is dealing with it, and ask the managing agent for the date and report of the last TR19 Air inspection on the landlord's plant.
How Commercial Cleaning London arranges it
Commercial Cleaning London surveys the system, confirms the building class, agrees a written specification that names TR19 Air and BS EN 15780 with the test points and access points listed, and appoints a TR19 Air specialist to do the work out of hours. You receive the specialist's report, laid out as described above, together with a date for the next inspection, so the annual baseline is booked before it lapses.