Volume 17, Number 2, June 2012
Bringing fresh air into offices is important to providing healthy and productive indoor conditions. As most office buildings rely on mechanical ventilation, fresh outdoor supply air must not be allowed to deteriorate in air handling systems, particularly through interaction with settled matter in air ducts.
Although outdoor supply air is filtered to some extent in air handling units, dust particles originating from outdoor and indoor sources may accumulate in the air ducts. Such particles may originate from many sources, including traffic or wild fires. They may also consist of biological matter such as mould spores, bacteria, pollen and allergens. Deposited bacteria and mould spores could even proliferate in these systems if a combination of poor system design, moisture control problems and improper maintenance of air handling systems are coming together.
To provide solutions, many companies are offering air duct cleaning services. These companies use a wide variety of cleaning procedures (see box). Their claims about the positive impact of duct cleaning (DC)—improved supply air quality, enhanced occupant health, better ventilation system performance, and even lower energy usage and maintenance costs—are often difficult to validate. Building operators should be in the position to evaluate the efficacy of the air duct cleaning, and to rule out potentially adverse health effects on the occupants of the building.
Air Duct Cleaning Techniques
Air duct cleaning techniques may include vacuuming, compressed air cleaning, mechanical brushing with vacuum collection, and water jet spraying, which are often combined with cleaning with chemicals. In some cases, potentially harmful biocides are used in an effort to inactivate accumulated biomass. Chemical sealants might be applied as well during the procedure to coat and encapsulate duct surfaces.
An NRC Construction research team, under the guidance of a multi-stakeholder committee, has developed a guide that will assist building operators in their work and enable them to:
- Interact in an informed way with companies offering air duct cleaning.
- Avoid excessive work by the cleaning company and negotiate a reasonable contract to address both adequate cleaning and cost-effectiveness.
- Minimize and assess, if applicable, potentially harmful effects on occupants resulting from improper cleaning procedures, thus avoiding complaints or even liability issues.
- Assess the potential adverse impacts of the use of chemical cleaning agents or biocides.
- Request the resolution of any problem by the service-providing company.
NRC Guide on Commercial Air Duct Cleaning
This publication was developed within the Canadian government’s Clean Air Agenda, with the ultimate objective to improve the health of Canadians through the establishment of guidelines and the creation or evaluation of technical solutions. NRC’s research team was guided by a Technical Advisory Committee, with members from industry associations, standard agencies, representatives from federal and provincial government departments, NGOs with an interest in IAQ, and consumer associations. Members were selected according to their expertise in IAQ technologies, IAQ characterization, and toxicology. The NRC Construction research team gratefully acknowledges the professional and constructive guidance provided by this Committee.
The guide is a diagnostic tool which will allow building operators or facility managers to assess whether duct cleaning work was successfully and appropriately performed in terms of cleanliness of the air ducts as well as meeting expectations concerning the quality of the resulting supply air. This is important as the quality of the supply air can deteriorate during and after air duct cleaning as settled particles, mould spores and bacteria may become airborne during the process and enter occupied spaces. As well, chemicals used in the process and biocides may be circulated in the building through the ventilation system.
The guide was validated in buildings in which commercial air duct cleaning was performed. The NRC research team is actively seeking feedback from building operators concerning the use of the guide, as well as from commercial services, which are interested in improving the quality of their work.