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Though sick-building syndrome is typically blamed on poor indoor air quality, it’s difficult to trace the precise causes of a person’s symptoms. Nonetheless, HVAC systems—those large-scale Petri-dish-cum-microbial Habitrails— figure prominently in efforts to deal with this workplace scourge. Recently, a team of Canadian and U.S. scientists may have spotted a light at the end of the duct: ultraviolet germicidal irradiation (UVGI).

A study led by McGill University of Montreal suggests that mounting UVGI lamps in air ducts can improve the health of a building’s occupants. While it’s been known for some time that zapping cooling coils and drip pans with UV rays can cut down microbial action, this study is considered to be the first significant demonstration of the technique’s health benefits. Researchers surveyed 771 workers in several Montreal office buildings over a nearly one-year period. They installed UVGI lamps in the ducts of the buildings, turned them off for 12 weeks, then on for 4 weeks—a cycle repeated three times.

The researchers noted a 20 percent drop in “building- related” symptoms (e.g., headaches, fatigue, skin irritation, and respiratory problems) among study subjects when the lamps were on. Allergy symptoms in some subjects dropped by as much as 40 percent. “I would recommend that if people have a problem with microbial contamination in their ventilation system, they use UVGI [instead of] germicidal chemicals,” says epidemiologist Dick Menzies, the lead researcher on the study. The researchers noted a 20 percent drop in “building- related” symptoms (e.g., headaches, fatigue, skin irritation, and respiratory problems) among study subjects when the lamps were on. Allergy symptoms in some subjects dropped by as much as 40 percent. “I would recommend that if people have a problem with microbial contamination in their ventilation system, they use UVGI [instead of] germicidal chemicals,” says epidemiologist Dick Menzies, the lead researcher on the study. Researchers also reported that UVGI was 99 percent effective at destroying microbes on duct surfaces, and about 25 to 30 percent effective in killing airborne bacteria.

UV treatment has advantages over alternatives like chemical disinfectants and ionization, according to experts. Disinfectants have a limited range and can pose chemical dangers of their own; ionization can cause particles to settle on the walls and floors of a building, where they can be stirred up again. The study concluded it would cost $52,000 to equip a roughly 118,000-square-foot office building with UV lamps, which would add $14,000 in operating costs per year. This is a modest investment, they suggest, compared to productivity losses tied to sick-building syndrome.

A longtime fixture in hospitals and factory clean rooms, UVGI technology has attracted renewed interest from scientists and public health officials, who suggest it may be effective in treating drug-resistant tuberculosis and SARS and could figure in bioterrorism-preparedness scenarios. Experts say the results of this study, while promising, must be replicated to be validated, and that neither UVGI nor other treatment techniques can correct design flaws that introduce airborne pathogens in the first place. “UV shouldn’t be used as a band-aid,” said J. Patrick Carpenter, senior engineering principal at Kling, a Philadelphia-based A/E firm. “You want to eliminate contamination at the source.”