Managing Microbial Contaminants

Molds, fungi and bacteria are grabbing the attention these days when it comes to indoor-air quality (IAQ). Volatile organic compounds (VOCs) are still of concern-with over 300 VOCs identified and more being created all the time through the development of new building materials-but the public, and much litigation, has focused of late on microbial contaminants.

02/01/2001


Molds, fungi and bacteria are grabbing the attention these days when it comes to indoor-air quality (IAQ). Volatile organic compounds ( VOCs ) are still of concern-with over 300 VOCs identified and more being created all the time through the development of new building materials-but the public, and much litigation, has focused of late on microbial contaminants. For example, most of the IAQ concerns in schools have to do with molds.

A major problem for engineers who are called upon to address these IAQ issues is that there are no exposure standards for molds and mycotoxins. Consequently, the designer needs to have a good working knowledge of potential microbial contamination and its causes, whether for new projects or retrofits and remediation work.

Legionella is a topic in itself. Outbreaks of legionellosis have been traced to condensers and cooling towers, among other sources. An outbreak last year began in a cooling tower at the Melbourne, Australia, municipal aquarium and resulted in the replacement of water-cooled air conditioning with an air-cooled system.

Good design and maintenance can help prevent the bioaerosol contamination that leads to legionellosis. An American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) position paper on legionellosis makes the following suggestion: avoid piping that is capped and has no flow; control domestic water temperature to below 25

In addition, air intakes must be placed away from cooling towers and evaporative condensers, effective drift eliminators on cooling towers and condensers should be maintained; and air filters for outside air must be kept dry.

Controlling dampness

With molds, in particular, moisture is always the culprit. Consequently, design and maintenance of HVAC systems is particularly important in controlling the moisture that breeds molds. One manufacturer offers a single-liquid desiccant technology, known as dry cooling. While its primary function is dehumidification, it is also said to supply clean, dry air.

Ultraviolet bulbs inside air-handling systems are used to saturate a space with ultraviolet light, eliminating microbial contaminants. Custom units accommodate the space requirements of the heating or air-conditioning system.

Filters often provide the perfect medium for growing molds, and because keeping filters clean and in proper working order is the responsible of a building operating staff, it is important for design professionals to stress this in training.

Insulation inside ducts is also a source of moisture, and hence, of microbial contaminant growth. In some remediation projects, insulation inside ducts is removed and replaced with external insulation.

Design professionals should anticipate a continuing public concern about microbial contaminants.





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