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.
1 Executive summary
3 The status of TM26
3.1 With respect to health and safety regulations
3.2 TM26 in the context of other guidance
4 How to use this guidance
5 Ductwork hygiene indicators
5.2 Sampling methods
6 Air quality in buildings
6.1 Indoor pollutants
6.2 Microbial contaminants
6.3 Airborne microbial contaminants
6.4 Microbial contamination in buildings and air distribution systems
6.5 Health aspects of microbes in buildings
7 Cleaning air distribution ductwork systems
7.1 Mechanical cleaning methods
7.2 Use of biocides
7.3 Reducing the admission of micro-organisms
8 Protocol for sampling air in occupied spaces
9 Protocol for surface sampling
10 Interpretation of sampling results
10.1 Air sampling microbial limits
10.2 Surface sampling microbial limits
10.3 Actions following interpretation of the sampling results
Appendix 1: Glossary of microbiological terms
Appendix 2: Results of micobial sampling in indoor air and the
ventilation ductwork at a selection of UK buildings
Appendix 3: Air duct systems
Appendix 4: Expert Panel members