Contamination Source Control

Contamination control is fundamental to any indoor air quality (IAQ) strategy. Microbial contamination in the forms of mold and mildew is a major indoor pollutant. Particles and chemicals represent other forms of contamination which may come from building occupants and their activities as well as from furnishings and wall coverings. Particles and chemicals can also brought into the building with the intake of air from outdoors.

Indoor Sources

The most obvious indoor-generated contaminants are those created by the activities of the building occupants, such as cooking, smoking, photocopying, laser printing, and other processes. To address controlling these types of indoor contaminants, ASHRAE Standard 62-2001 states:

"Contaminants from stationary local sources within the space shall be controlled by collection and removal as close to the source as practical." (Section 5.6)

"Removal close to the source" usually requires one to provide a local exhaust. However, if the contaminant is due to volatile organic compounds (VOCs) emanating from furniture and building materials distributed throughout the building, providing a local exhaust is not always possible. VOCs are chemicals, such as formaldehyde, that outgas slowly from manufactured construction materials, furnishings, and cleaning products. In this situation, dilution with clean outdoor air is typically the most practical and cost-effective solution.

Microbial contamination (fungi and bacteria) can also be a major source of indoor contamination. Microbial colonies can grow in or on various building elements and furnishings, including carpets, ceilings, sheetrock walls, and within the HVAC system. When mold spores and other microbiological particles become airborne, some building occupants may experience allergic reactions and other health-related effects. Once the mold is established, the air-handling system can distribute the contaminants and offensive odors through the building. Because of the variety of potential indoor sources of microbial and fungal contamination, source control using local exhaust also can be difficult. ASHRAE Standard 62-2001 cites three specific air-handling equipment characteristics that significantly reduce the likelihood of the HVAC system becoming a source of microbial contamination: sloped drain pans, cleanable interior surfaces, and accessibility. It is critical that HVAC equipment be properly installed and drains properly. Also, even when equipment is operated properly, unexpected and unavoidable events, such as equipment malfunctions or power outages, can cause equipment and duct systems to become wet. Such occurrences demand that regular inspections of the air handler and duct system for signs of moisture or mold and fungi growth become part of the routine HVAC system maintenance. Finally, it is not possible to clean a system if the major components are not accessible. It is critical that accessibility be a major part of the HVAC's system design consideration.