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Should we clean our ductwork?

01 June 2015

Facilities managers, property managers and employers often ask health and safety professionals whether they should clean their ductwork. Craig Booth, technical sales manager and founding chairman of the UK Ventilation Hygiene branch of the Building and Engineering Services Association, describes the legislative and standards background to cleaning ductwork.

Why should kitchen extract ductwork be kept clean, and why must heating, ventilation and air conditioning (HVAC) ductwork be kept in good condition? What other health and safety considerations surround air conditioning and ventilation ductwork maintenance? The prime driver for kitchen extract ductwork is fire safety, and it falls within the Regulatory Reform Order (2005) and insurers’ requirements.

The grease that inevitably accumulates within the duct system forms a hidden combustion load. There are ready sources of ignition in a kitchen and the duct system perfectly funnels oxygen. One of the big problems is that the ductwork that connects the kitchen canopy to the fan for discharging heat, smells and fumes to atmosphere is typically hard to access and easy to ignore. When grease and oil is ignited, the ductwork can spread flame and heat through the building like a fuse.

Super-heated ductwork may ignite nearby combustible materials - hot or burning oil can spread fire from small leaks and flame at the discharge can light up a roof. Sometimes, the path of the fire is difficult to predict and firefighters can lose valuable minutes tracing out the implications of fire discovered in a building.

There are standards available, such as the Building and Engineering Services (B&ES) Guide to Good Practice TR19: Cleanliness of Ventilation Systems. This advocates cleaning 'when necessary' and describes measurement techniques, such as the wet film thickness test, to define when a system should be cleaned. In the absence of such measurement, the advice defaults to time based maintenance, as suggested in this Table.

Air Ductwork

For HVAC ductwork, the prime drivers are health, comfort and wellbeing, and this is underlined in the Workplace (Health Safety & Welfare) Regulations, as updated in 2014. The Regulation 6 ACOP 51 states: "Mechanical ventilation systems (including air-conditioning systems) should be regularly and adequately cleaned. They should also be properly tested and maintained to ensure that they are kept clean and free from anything which may contaminate the air.”

British Standard EN15780: Ventilation for buildings — Ductwork — Cleanliness of ventilation systems describes the various cleanliness quality classes of building and the appropriate frequency of inspection and cleanliness standards to be achieved.

Table A.1 — Typical applications of cleanliness quality classes

Quality Class
Typical examples
Rooms with only intermittent occupancy, e.g. storage rooms, technical rooms

Offices, hotels, restaurants, schools, theatres, residential homes, shopping areas, exhibition buildings, sport buildings, general areas in hospitals and general working areas in industries


laboratories, treatment areas in hospitals, high quality offices

Again, B&ES TR19 provides further detail on how to measure cleanliness/dirtiness and suggests good practice techniques for remedial works.

Often, the relatively complex procedures for inspection, monitoring and measurement of cleanliness or dirtiness serve to support common sense assessments, which are carried out by simply viewing the duct interior. However, the measured standards are useful in cases of uncertainty as to whether a system needs cleaning.

Increasing interest from employers, developers and academics is focused on the productivity gains from relatively small expenditures on improving the working environment. The World Green Building Council’s recent report on health, wellbeing and productivity, supported by heavyweights, such as Jones Lang LaSalle, Skanska and Lend Lease, makes the point that there is overwhelming evidence that demonstrates that the design and maintenance of an office impacts the health, wellbeing and productivity of its occupants. It goes on to describe the costs of proper maintenance as trivial compared to staff costs.

Fire Damper Testing

Fire damper testing is another aspect of heating, ventilation and air conditioning maintenance that health and safety professionals need to deal with. Fire dampers are essential life safety components that shut in the event of fire to prevent the spread of fire from one compartment to another via ductwork. British Standard 9999 (2008) Annex W1 mandates regular testing of these systems to ensure that they operate properly. This is crucial in a fire situation, and experience shows that a significant number of dampers may fail in practice.

Editor’s note: 

System Hygienics is a member of the Hotchkiss Group, which provides specialist services in ductwork contracting, fire resistant duct systems, ventilation products and accessories, and fire resistant and acoustic ductwork coating.

For further information, visit  HYPERLINK "http://www.systemhygienics.co.uk" www.systemhygienics.co.uk

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