ATLANTA - As health and school officials deal with a second wave of the H1N1 virus, commonly referred to as swine flu, the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) has issued a position document on airborne infectious diseases and the implications on the design, installation, and operation of HVACR systems.

“While the long-standing public health view is that influenza transmission occurs through direct contact or large droplets, newer data suggests it also occurs through the airborne route, meaning HVACR systems may contribute far more to transmission of the disease and, potentially, to reduction of that same transmission risk,” said Gordon Holness, president of ASHRAE.

ASHRAE’s Airborne Infectious Diseases Position Document addresses the impact of ventilation on disease transmission, the diseases for which ventilation is important for either transmission or control, and the control strategies that are available for implementation in buildings. The paper can be read at

Since the first reported case in the spring of 2009, the H1N1 virus has spread to nearly 170 countries, resulting in 1,154 deaths and some 160,000 illnesses. With a better understanding of ventilation’s effect on the transmission of disease, future incidents of the H1N1 virus may now be easier to prevent, according to Holness. He said several technical solutions are available to assist in avoiding transmission. These include: dilution ventilation, airflow strategies, room pressurization, personalized ventilation, source control, filtration, and ultraviolet germicidal irradiation.

Airborne transmission through building ventilation systems can be significantly reduced by provision of adequate air filtration and pressurization, Holness said. ASHRAE’s other guidance of relevance includes Standard 170, Ventilation of Health Care Facilities, and Standard 611, Air Quality Within Commercial Aircraft.

Publication date:09/14/2009