(archived) TM26 Hygienic maintenance of office ventilation ductwork (2000) (pdf)

This publication has been archived, and should not be used on current projects. For up-to-date guidance on the maintenance of ductwork, see CIBSE Guide M Maintenance engineering and management.

This publication aims to demonstrate to building managers the importance of ductwork maintenance and to provide practical guidance on the proper procedures for maintaining ductwork systems in a safe and effective state.

Recent publications from the Heating and Ventilation Contractors Association (HVCA) and Building Services Research and Information Association (BSRIA) have provided a general review of the issues of ventilation system hygiene and ductwork cleaning. BSRIA has also produced a standard form of contract for ductwork cleaning, with associated guidance. These documents give specific guidance on good cleaning and maintenance practices for ductwork systems in terms of particulate (dust) contamination only.

The guidance contained in this publication is intended to add to that good practice by providing guidance for managers of buildings that are air conditioned, or otherwise mechanically ventilated, on the issues of assessment and maintenance of the microbiological cleanliness of ductwork systems. For those who are unfamiliar with current practice in air duct systems, a separate section reviews this subject.

This publication gives guidance on the methods to use when obtaining microbial samples from the air in occupied spaces and from the inside surfaces of the ducts. It also indicates the levels of microbial contamination that are likely to be found on uncleaned and cleaned duct surfaces, and draws on a body of expert opinion to help the building manager to interpret the results of sampling. The procedure may also be used to assess the residual microbial contamination following a commercial cleaning process, or following disinfection, and as a remote means of assessing the performance of filtration of ventilation air.